National Academy of Sciences National Research Council NUCLEAR SCIENCE SERIES The Radiochemistry of Protactinium 4BV LT /' Commission 9 COMMITTEE ON NUCLEAR SCIENCE L. F. CURTISS, Chairman National Bureau of Standards ROBLEY D. EVANS, Vice Chairman Massachusetts Institute of Technology J. A. DeJUREN, Secretary Westinghouse Electric Corporation C. J. BORKOWSKI Oak Ridge National Laboratory ROBERT G. COCHRAN Texas Agricultural and Mechanical College SAMUEL EPSTEIN California Institute of Technology U. FANO National Bureau of Standards HERBERT GOLDSTEIN Nuclear Development Corporation of America J. W. IRVINE, JR. Massachusetts Institute of Technology E. D. KLEMA Northwestern University W. WAYNE MEINKE University of Michigan J. J. NICKSON Memorial Hospital, New York ROBERT L. PLATZMAN Laboratoire de Chimie Physique D. M. VAN PATTER Bartol Research Foundation LIAISON MEMBERS PAUL C. AEBERSOLD Atomic Energy Commission J. HOWARD McMILLEN National Science Foundation CHARLES K. REED U. 8. Air Force WILLIAM E, WRIGHT Office of Naval Research SUBCOMMITTEE ON RADIOCHEMISTRY W. WAYNE MEINKE, Chairman University of Michigan GREGORY R. CHOPPIN Florida State University GEORGE A. COWAN Los Alamos Scientific Laboratory ARTHUR W. FAIRHALL University of Washington JEROME HUDIS Brookhaven National Laboratory EARL HYDE University of California (Berkeley) HAROLD KIRBY Mound Laboratory GEORGE LEDDICOTTE Ozk Ridge National Laboratory JULIAN NIELSEN Hanford Laboratories ELLIS P. STEINBERG Argonne National Laboratory PETER C. STEVENSON University of California (Livermore) LEO YAFFE McGill University CONSULTANTS NATHAN BALLCU Centre d’Etude de I’Energie Nucleaire Mol~Donk, Belgium JAMES DeVOE University of Michigan WILLIAM MARLOW National Bureau of Standards CHEMISTRY-—RADIATION AND RADIOCHEMISTRY The Radiochemistry of Protactinium By H. W. KIRBY Mound Laboratory Operated by Monsanto Chemical Company Miamisburg, Ohio December 1959 Subcommittee on Radiochemistry National Academy of Sciences —National Research Council Printed in USA. Price $1.00. Available from the Office of Technical SBervicea, Department of Commerce, Washington 25, D. C. FOREWORD The Subcommittee on Radlochemistry is one of a number of subcommittees working under the Committee on Nuclear Science within the National Academy of Sciences - Natlonal Research Council. Its members represent government, industrial, and ‘university laboratories in the areas of nuclear chemistry and analytical chemistry. The Subcommittee has concerned itself with those areas of nuclear science which involve the chemist, such as the col- lection and distribution of radiochemical procedures, the egtablishment of specificatlons for radiochemically pure reagents, the problems of stockpiling uncontaminated materials, the availability of cyclotron time for service irradiations, the place of radiochemistry in the undergraduate college program, etc. This serles of monographs has grown out of the need for up- to-date compilatlons of radiochemical information and pro- cedures.. e Subcommittee has endeavored to present a series which will be of maximum use to the working sclentist and which contains the latest avallable information. Each monograph collects in one volume the pertinent information required for radiochemlcal work with an individual element or a group of closely related elements. An expert in the radiochemlstry of the particular element has written the monograph, following a standard format developed by the Subcommittee. The Atomlc Energy Commis- sion has sponsored the printing of the seriles. The Subcommittee is confident these publications will be useful not only to the radiochemist but also to the research worker in other fields such as physics, biochemlstry or medicine who wlshes to use radiochemical techniques to solve a specific problem. W. Wayne Melnke, Chairman Subcommittee. on Radiochemistry 111 INTRODUCTION This volume which deals with the radiochemistry of grot- actinium is one of a series of monographs on radiochemistry of the elements. There is included a review of the nuclear and chemical features of particular interest to the radio- chemist; a dlscussion of problems of dissolution of a sample and counting techniques, and finally, a collectlon of radio- chemical procedures for the element as found in the literature. The series of monographs will cover all elements for which radiochemical procedures are pertinent. Plans include revislon of the monograph perlodically as new techniques and procedures warrant. The reader is therefore encouraged to call to the attention of the author any published or unpub- lished material on the radiochemistry of protactinium which might be included in a revised version of the monograph. Any new review on protactinium at this time has been rendered largely superfluous by the recent§publication of the critical article by Haissinsky and Bouissieres!. This excellent comprehensive monograph covers the published (and much of the unpublished)literature through November 1, 1957. Except for translation from the French, 1t can hardly be ilmproved upon. Such a translation has been made;, and it is hoped that per- mission for its general distribution will be granted by the publisher in the near future. : ' The present regort has the limited objective of acquainting the reader with the brecad outllines of protactinium chemistry, especially in relation to methods of preparation, separation, and analysis. The literature survey gas been limiteg to materlal reported since about 1950; for the older literature, the author fias relled heavily on the Hailssinsky-Boulissieres review. Critical comments, however, are those of this writer. Patents, as such,; have been largely ignored, as in the oplnion of the author, thelr significance is more legal than sclentific. . iv I. II. I1I. Iv. CONTENTS GENERAL REVIEWS OF THE CHEMISTRY OF PRDTACTINIUM S0 wd o doee oot o tdygdode bt B IReben ISOTOPES OF PROTACTINIUM ccevscvevvscncancas CmSTRY OF PROTACTINIUM [ B BB B BN B B BN BN B BN BN BN BN BN BN BN 1. General 2. Metallic Protactinium 3. Soluble Salts of Protactinium ., Inasoluble Salts Useful in Separation and Analysls 5. Coprecipication and Carrying of Protactinium 6. Solvent Extraction of Protactinium 7. Ion Exchange Behavior of Protactinium - 8. Miscellany Paper Chromatography Electrochemistry Spectrophotometry Dry Chemistry DISSOLUTION OF PROTACTINIUM SAMPLES ........ COWTIHG TECmIQUES o 9 8 & P & ® 09 3 8 P AaAOC S S ORI E " ES l. Protactinium-233 2. Protactinium-231 10 12 13 7 23 23 26 26 28 - 28 30 30 32 VI. VII.. DETAILED RADIOCHEMICAL PROCEDURES FOR PRDTACTINIIJM # 5 8 8 8 O F S0P P OF O ET SR A TS A e A. E. Preparation of Carrler-Free Prot- zgtinium-ij (Procedure 1 through Determination of Protactinium (Procedures 5 through 10) Speclal Preparations of Protactinium (Procedures 11 through 13) Separations of Protactinium (Procedures 14 through 15) Urinalysis of Protactinium (Procedures 16 through 17) APPENDIK .......‘.II.I.'I.II...IO..II.lI.lIl. Summary of the Protactinium Project at Mound Laboratory vi 37 37 41 54 57 59 65 The Radiochemistry of Protactinium* By H. W. Kirby Mound Isaboratory Operated by Moneanto Chemical Company Miamisburg, Ohlo December 1959 I. GENERAL REVIEWS OF THE CHEMISTRY OF PROTACTINIUM Hfizssinsky,'u. and Bouissffires, G., Protactinium, Nouveau Traite de Chimie Mifiérale, XII, pp. 617-680, ed. by P. Pascal; Masson ‘et Cie., Paris (1953). (This should be required read- ing for anyone working with'protactinium. The bibliography, containing 165 references, is complete to November 1, 1957.) Salutsky, M. L., Protactinium, Comprehensive Analytical Chem- istry, Vol. I, Chapter IV, Section 44, 11 pp.,-ed. by Cecil L. Wilson; Elsevier Publishing Co., Amsterdam (Ifi'Press). (Primarily devoted to analytical aspects. References, 49.) * ' : - Permission for the use of copyrighted material has been kindly granted by Pergamon Press, publishers of the Journal of Inorganic and Nuclear Chemistry, and by the editor of the Journal of the American Chemical Society. Katzin, L. I., editor, Production and Separatlon of U233° Collected Papers, U. S. Atomic Energy Comm., TID-5223, 728 pp. in 2 vols. (1952). Avallable at $3.25 from Office of Tech- nical Services, Dept. of Commerce, Washington 25, D. C. (79 papers devoted to thorium, protactinium, and uranium chemistry, radlochemistry, separations, and nuclear charact- eristics. Not a true review, but a valuable collection of | research papers and data.) Gmelins Handbuch der anorganischen Chemie, Protactinium und Isotope, System Number 51, 99 pp., Verlag Chemle, G.m.b.H., Berlin (1942). (Reviews the literature to 1940.) Elson, R. E., The Chemistry of Protactinium, The Actinide . Elements, Chapter 5, pp. 103-129, National Nuclear'Energy Series, Division IV, Plutonium Project Record, Vol. 1A, ed. by G. T. Seaborg and J. J. Katz, MchEw,HiLl Book Co., New York (1954). (Referefices, 69, the latest original reference being dated 1951.) Hyde, E. K., Radiochemical Separations of thé Actinide Elements, Ibid., Chapter 15, pp. 542-95. Literature Survey on: 1. The Chemistry of Actinium and Prota- actinlum -- Especlally in Aqueous Solutions. 2. Determinatiom of Actinium and Protactinium. 3. Technical Information on Radium Industry Residues. Anon., Atomic Energy Commission, Tel-Aviv, Israel, LS-6, 34 pp. (Sept., 1958). IT. TABLE I ISOTOPES OF PROTACTINIUMS Mass Mode of Decay Half-Life Source 225 a 2.0 sec Th + d 226 a 1.8 min Th + a 227 a ~ 85% 38.3 min Th + d, U + a, daughter Np231 EC w 15% 228 EC ~ 98% 22 hrs Th + d, daughter Y228 aw 2% 229 EC - 99+% 1.5 days Th?30 4 4 a = 0.25% 230 EC ~ 85% 17.7 days Th + d, Pa23l 4+ 4, Th230 4 g B~ ~15% ' ' a?, pt? 231 (Ppa) Q 32,500 yrs h230 . n, Th + n, descendigg | | U 232 B" 1.31 days Th + d pa23l 4 n, Th + o 233 - 27.0 days Th +d, Th+n 234™(UXy) B~ - 99+% 1.175 min Descendant U238 (metastable) IT - 0.63% - - | 234M 234 (UZ) B 6.66 hrs Daughter Pa 235 8™ 23.7 min U+ p, U+ d, daughter ThZ>> 237 g~ 11 min U+ d EC - electron capture P - proton IT -~ 1iscmeric transitior n - neutron d - deuteron III. CHEMISTRY OF PROTACTINIUM 1. General The only naturally occurring protactinium isotopes are prot- actinium-231 and protactinium-234. Because of their short half-11ives, 1.2-minute protactinium-234 (UXp) and its 6.7-hour isomer (UZ) fire of relatively little interest to radiochemists. The 27-day protactinium-233 is readily produced by neutron | irradiation of thorium and is of considerable value both as a tracer and as the parent of fissile uranium-233. Signifi- cantly, the v-p branching ratio of UXp was determined with the aid of protactinium-233 as a tracer.9 Al though the natural sbundance of protactinium is almost as great as that of radium, the known world supply of the iso- lated element and its compounds did not exceed one or two grams until the late 1950's. Interest in thorium breeder reactors gave necessary lmpetus to the recovery of gram quantities of protactinium for study of its macrochemistry. . Abundant source material was avallable as a result of the accelerated prodfiction of uranium for nuclear reactors. Chemical technology (solvent extraction) and Instrumentation (scintillation spectrometers) had advanced to a point where éeparations and analyses which were previously difficult or impossible could be made with relative ease and rapidity. Almost 100 grams of protactinium-231 was recently isolated from uranium fefinery wastes In Great Britain, and groups at Cambridge, Harwell, and elsewhere are actively engaged'in studying the chemistry (as distinct from the radiochemistry) of protactinium. Dr. A. G. Maddock has kindly supplied this reviewer with an unpublished report on the 1958 activities of the Cambridge protaétinium grouplo, in which he describes the preparation, in centigram quantities, of the penta- and tetrahalides of protactinium and polarographlc studies of its oxalate, chloride, fluoride, and sulfate solutions. These data will be published shortly. It is safe to predict that the 1960's will see much of the mystery and wlitchcraft elimingted from protactinium chemistry. Nevertheless, the greatest amount of information published to date has come from work done with protactinium-233 on tracer levels. These data have not been consistently applicable to the macrochemlstry of protactinium-231. To some extent, the discrepancles are due to the origins of the isotopes. Prot- actinium-233 1s likely to be contaminated 6n1y by thorlium. Protactinium-231, on the other hand, may be contaminated with any or all of the elements in groups IVa and Va of the Period;c Table, as well as with phOSphate ion, which tends to make its chemistry somewhat erratic. Furthermore, radiochemical analysls of protactinium-231 is complicated by thé presence of its own a-, B-, and y-active descendants (Table I1) and those of uranium-238. Protactinium-231 can also be produced by the neutron irradia- tion of thorium-230 (ionium), in which case it will usually also be dontaminated by thorium-232 and protactinium-233. Too much has been made of the apparently capricious chemlcal behavior of protactinium, In the pentévalent state, its 5 TABLE II. URANIUM-ACTINIUM SERIES {(4n + 3) . 1sotope Synonym Mode of Decay Energles, Mev. Half Life y235 AcU a 204 4.6 ' 8 . . 8.8 x 10°Y 1 80% 4.4 Th231 1) p- 0.2 25.65 H | oo 25% 4.9 pa23l . a 3% 4.8 92,500 Y Lz 13% 4.7 Ac22777 [; - 0.02 - ' 22.0 Y | 248 6.1 m227 | 2 o i RdAe a 7% 5.9 18.6 D ! 25% 5.8 ! 22% 5.7 Fre23e aox B- 1.2 21 M (555 2 Ra 223 AcK o 22 5:3 11.2 D 7% 5. e Rn21? An a 124 6.4 3.92 8 1 | 4% 6.2 a 7.4 Po?lo._ AcA [; 0.00183 S 1 ' 0.,0005% B~) (?) | 20% 0.5 b2ll | AcB B- . 36.1 M ' 80% 1.4 1 At ¢ ... @ 8.0 10-¥ s { B4 6.6 a B121l__ acc 16% 6.3 2,16 M 1 ; (0.32% B-) (?) 1 71207 | AcCn B" 1.5 4,76 M . i P°211 < AcCt ) a 7.4 0.52 8 PbH207 AcD Stable ——— — chemletry is similar to that of its homologues in graup'Va of the Periodic Table. Like niobium and tantalum, prot- actinium is almost completely insoluble in all the common aqueous media except sulfuric and hydrofluoric acids. I* 18 readily precipitated by hydroxides and phosphates; and, 1n.trace quantities,.ia carried more or less quantitatively by precipitates of a wide varlety of elements. The well-publiclzed tendency of protactinium to deposlt on the walls of glass vessels 1s primarily due to its insolubility; this tendency 1s not apparent in appropriate concentrations of gulfuric and hydrofluoric acids. 2, Metallic Protactinium Metallic protactinium has been prepared by thermal decom- position of 1ts halldes on a tungsten fllament and by electron bombardment of the oxidell, by reduction of.the tetrafluoride with barlum at 1400012. and by electrodeposi-. tion on various metal cathodes from very dilute, slighflv acid, fluoride solutionulB. The metal is grey in color, malleable, and approximately as hard as uranium. On exposure to air, it acquires a thin pkin of PaO, 3. 8Soluble Salts of Protactinium Nowhere 1s the literature of protactinium more confused or ambiguous than in the refsrences to its solubility in common mineral acids. The only asystematic study in this area is the L4 with solution volumes of the preliminary work of Thompson order of 0,05 ml;_(Table I11). The avallablility of gram quantities of protactinium makes this a potentially fertile field for investlgation. 'The bast solvent for protactinium is hydrofluoric acid, which rdndtly digsolves the ignited pentoxide and nearly all pre- cipitates, forming the stable complex ion PaF7’. Protactinium pentoxide disaolves slowly in hot concentrated sulfuric acld, but the solubllity 1s low. Prolonged diges- tion convarts the oxide to a sulfate, which dissolves on dilution of the acid. | A solution containing 17 mg./ml. of protactinium-231 in approximately 7.7 N stou has been stable for over a year15, and one contalning 36 mg./ml. in approximately 3 N D,S0, has been stable for six monthslfi. In the author's experience, only hydrofluoric and sulfurilec acids permanently dissolve ‘appreciable quantities of prot- actintuq. With all other mineral acilds, solutions are unstable, resulting in precipitates or colloidal suspensions’ after periods ranging from a few hours to several weeks. Solutiena containing 10~3 to 10'4 M protactinium in 6 M I-NOJ (0.2 - 0.02 mg./ml.) hydrolyzed slowly, but, at concentra- tions between 10-% and 10-7 M protactinium, the solutions were sufficiently stable for 24 hours to ylald reproducible extraction and ion exchange datal?. Although the literature is prolific of. references to the solvent extraction and ion exchange of protactinium from TABLE III. SOLUBILITY OF Pa IN COMMON ACIDSlu* Solubility Starting Acids Normallity {g./1liter) Material HC10,, 11.1 0.030 Hydroxide 7.1 0.0027 Dilution HC1l 9.61 0.30 Hydroxide 4,90 0.01 Dilution 3.33 0.0085 Dilution 0.99 0.0015 Dilution HNO, 15.3 4.2 Hydroxide 13.8 6.6 Evaporation Q HNO3 9.44 5.5 Dilution 5.66 0.043 Dilution 1.88 0.0056 Hydroxide 1.17 0.0037 Hydroxide H2304 32.5 0.093 Evaporation 21.9 1.8 Dilutlion 9.93 3.3 Dilution 0.92 0.78 Dilutlion HF 0.05 3.9 1N HN03 ¥ Reviewer'a Note: the only one of its kind avallable. recent experlence, however, the values, which were based on volumes of the order of 0.05 ml., are highly questionable. This table is included because it is In the light of HC1 solutions, no data other than Thompson's are given to indicate the limits of solubllity. The insoiubility of prot- actinium in 6-8fl HCl is useful as a method of separation from decay products: When the lodate preclpitate of protactinium 1s digested with concentrated HCl, the protactinium dissolves temporarily, then reprecipitates quantitatively. After digestion on a hot water bath and'centrifugation,;the'Sufier- nate contains no detectable protactinium15° Where an occaglonal reference occurs to solubllities of the order of 1 mg./fil. of profactinium in 6 N HCllB, it must be regarded as questionable. When elaborate precautions are taken to eliminate organic complexlng agents and fluoride ion, the subsequefit HC1l solutlons are unstable. A solution containing 2 mg./ml. of protactinium, in 8 M HCLl was prepared from a peroxlde precipitate, but, over a period of three weeks, about 80 per cent of the protactinlum precipitfitedl9. 4. Insoluble Salts Useful in Separation and Analysis The normal oxldation state of protactinlum is + 5, but prot- actinium (V) probably does not exist in solution as a simple cation. On reduction to protactinium (IV) [e.g., with zinc amalgaml, the fluoride can be preclpitated and is insoluble 1n water and most acids. Tetravalent protactinium is slowly oxidized 1n air to the pentavalent state, and the fluoride redissolveszo. Protactinium (V) can be precipitated from fluoride solution by the addition of a stoichiometric amount of KF, which forms an lnscluble double fluoride, KzPaF7. A double fluoride with barium has also been reportele. Alkall hydroxides and carbonates precipitate firotactinium in both oxlidatlon states, and the precipltate 1ls not soluble in excess 6f the reagent. Depending on the concentrations, NH,0H mav fall to precipitate protactinium quantitatively from fluoride solutionzz. 10 The phoéph#fie'and hypophosphate of profiactinium cant be pre- cipitated from acid solutions. It has been reported that the preclpitate will not redissclve even in strong mineral aclds. However,:the author has regularly redissolved protactinium precipitated by phosphate, whether in trace amounts carried by titanium or niobium, or in carrier-free milligram quantities, The precipitate, upon dilgestion with a sufficlent quantity of warm 18 N H;504 either dissolves or becomes soluble on dilu- tion with HCl to which some H,0, has been added. The phosphate can alsc be precipitated from fluoride solution, depending upon the relative concentratione of the anions. If excess phosphate is separated by f£iltration or centrifugation, the protactinium is soluble in dilute HF. Iodates precipitate both protactinium (IV) and protactinium (V) from moderately acid solution {e.g., 5 N H,S0y). The precip- ltate 1is gelatinous and velumlnous, but becomes more dense on standing, especially if it is warmed on a water bath. Iodate precipitation from acid solution provides excellent separation from phosphate. Sodium phenylarsenate precipitates protectinium in either oxldation state; the gelatinous precipitate 1s readlly soluble in dilute HFZO. Dilution of a sulfuric acid solution of protactinium(V) produces a preclpitate which redissolves in ammonium sul- fate. Potasslum sulfate, however, ylelds a crystalline pre- clpitate, probably a double sulfate. Tartaric and citric aclds dissolye the hydroxides of both protactinium(V) and protactinium(IV), and the solution 1s 11 stable on the addition of NHuoH. Sodium hydroxide precipl- tates protactinium from a citrate, but not from a tartrate _solution. With Hy,0, in large excess, protactinium(V) fo:ms a precip}tate which is insoluble in NH OH and NaOH. The precipitate is Iy soluble in dilute stou only after decomposition of the per- oxide on a water bath. Freshly precipitated protactinium hydroxide dissolved rdpidly in warm aqueous oxallc acidza. Addition of NHQOH to 3 M H2C204 containing 0.15 mg./ml. of protactinlum resulted in peféistent turbldity at pH 5-6, but precipitation fias not éomplete until pH 8-9 was reached. Addition of an equal volume of 1 N HC1 to the original oxalate solution had no effect in the cold, but a white crystalline precipitate contalning approximately 90 per cent of the protactinium was formed in warm solutions. This precipitate dissolved completely in 8 N HCl. In general, protactinium(V) follows the chemistry of niobium, while protactinium(IV) follows that of thorium. 5. Coprecipitation and Carrying of Protactinlum Most methods for the recoverf of either protactinium-231 or protactinium-233 rely, for an initial concentration step, on the entrainment of protactinium by an insoluble carrier of another element. From the foregoing discussion of insoluble compounds of protacfinium, it follows that hydroxidé, carbon- ate, or phosphate precipitateé of tantalum, zirconium, niobium, hafnium, and titanium will carry protactinium quantitatively, or nearly so. In addition, protactinlium is carried by most other flocculent hydroxides (e.g., calcium and iron), probably by adsorption rather than by isomorphous replacement. Protactinium is carried by.MnOZ produced by the additlon of KMnO, to a dilute HNO, solution containing Mn(NOB) In 3 2° solutions of high lonlc strength the entrainment is not com- pletely quantitative, but it becomes more so as the precipi- tate 1s repeatedly redissolved and fractlionally precipitated. Since titanium and zirconium are also carried, these impurities, 1f present, can serve as carriers for the sep- aration from manganeaezu. 6. Solvent Extractlon of Protactinium At tracer levels (10'5 - 10'10 M) protactinium 1s extracted, to some extent, from hydrochloric, nltric, sulfuric and even perchloric acid solutions by a wide variety of unrelated organic solvents. At the macro level (ca. 1 mg./ml.) the roater of effective extractants is more exclusive. In gefleral, protactinium is extracted readily by long-chain alcohols and certain ketones, but poorly by the lower ethers. Extractions from aqueous chloride media give better ylelds and more reproducible results than those made from nitrate solutions?®?. This would follow from the relative rates of hydrolysis previously noted. Maddock and his co-workers (18: 19, 21,.26, 27, 28) p,,e studied the extraction of protactinium from hydrochloric acid by various organic solvents (Figure 1l). For extraction of macro amounts, they found diisopropyl ketone most satisfactory, 13 HT % Extraction, 100 60 1—." ’ @ Tributyl phosphate o :;(),r"‘ O ff-dichlorodiethyl ether : / ® nitrobenzene @ 5% tributylamine in benzene / / (not pre-equilibrated) © di-isopropy! carbinol ° / © acetophenone ® chlorobenzene @ benzonitrile / ; s e . / /) | e ° —‘“//1 1°0 2:0 30 4:0 50 60 7:0 80 90 Normality HCL Fige 1o Percentage of protactinium extracted by an equal volume of the sclvent from an aqueous hydrochloric acid sclution as a function of the acidity of the aqueous phase. Initial concentration of protactimum~233 in the aqueous phase 4 to 6 x 10~10y, (Goble, A. and Maddock, Ae Ge, Jo Inorg. Nucl. Chem. 7, 84 (1958).) 100 but diisobutyl ketone was used because 1t was commercially available. Regardless of the organic solvent used, protactinium (V) exhibits its highest distribution coefficients from strongly acid aqueous media, consistent with its existence in aqueous golution as a complex anion. In this respect, it resembles most of the elements of groups IVa and Va of the Periodic Table. Thorium and uranium, which can be extracted from solutions of low acidity with the ald of s<ing agents, can, therefore, be easily separafed. In this laboratory, solvent extraction of protactinium has been largely confined to diisobutyi carbinol diluted with kerosene or benzene, primarily hecause of the extremely high distribution coefflcients, capacity, and decontamina- tion attainable wlth this solvent. The author does not subscribe to the hypothesls of a soluble but inéxtractable specles of protactiniung. In numerous extractions of solutions containing both traces and milli- grams of protactinium per milliliter, no such phenomenon has been observed so long as the protacfiniufi was in true solution and fluoride ion was absent. A transient specles, preliminary to hydrolysis, remains a possibility. The following conditions have ylelded apparently inextract- able protactinium: (a) the "protactinium™ was actually actinium-227 and its decay products; (b) £luoride ion was present; (c) the solution was colloidal; (d) interfering elements (e.g., nlobium and iron),were present in large amounts and were preferentially extracted; (e) the organic 15 solvent was excesslvely soluble in the aqueous phase (usua- lly due to insufficient diluent); and (f) there was insuf- ficlent sulfuric acid or hydrochlorlc acid to ccmplex both protactinium and the impurities. It has been suggested that a polymer of protactinium alone 26,30 renders the protactinium or of protactinium with niobium inextractable or :educes the distribution coefficlent. Such a suggestion is unténable unless the polymer is regarded as the precursor of a colloid or a preclpitate. As has been stated previously, aqueous solutions (other than sulfate or fluoride solutions) contalning macro amounts of protactinium invariably yleld precipltates after a period of time varying from a few hours to several weeksl7! 19.- It 1s significant to note that, whenever protactinium 1s extracted from an acid phase containing only hydrochloric or nitric acid, investlgators report that the exfiractions are carried out soon after dissolution of the protactinium [or after addition of fluoride-complexing catlons such as aluminum (III) or boron (III)]. Aging of these solutions increases the percentage of the "inextractable species", a behavior consistent with slow hydrolysis and formation of a colloid. The addition of sulfuric ficid, originally recommeénded by Moore30 to break a "nonextractable complex of niobium- protactinium oxalate"”, has been found to be necessary for the complete extraction of protactinium by dlisobutyl carbinol even in the abserce of niobium!?, The precise conditions required have not yet been fully determined, 16 but an aqueous phase containing 9 N #5530, - 6 N HC1 has been useful for all protactinium concentrations and degrees of purity. Solutions containing up to 20 mg./ml. of prot- actinium in dilsobutyl carbifiol have been prepared. The extraction of protactinium-233 from niltric acid by dilsobutyl carbinol has been examinéd, and high decon- tamination factors for uranium, thorium, zirconium, nio- bium, and rare earths are reported33. Tributyl phosphate extraction of protactinlum from hydro- chloric_acid29 and from nitric.acidl7 has been studied. Dibutyl phosphate dlluted with dibutyl ether extracted protactinium-233 quantitatively from an équal volume of 1M }INO3 contalning 2% H,C50y 34, Long-chain amines extract protactinium from strong HCl solutions-l, The effect of HF on the extraction of protactinium from HC1 by diisopropyl cafbinol 1s shown in Figure-zzg. Since the extraction of niobium is not inhibited by HF, asepara- tion of protactinium is obtaimed if the niobium is extracted. from 6 M H,50, containing 0.5 M WF. Protactinium remalns in the aqueous phasejz. 7. Ion Exchange Behavior of Protactinium A series of anion exchange studies by Kraus and Moore, using protactinium-233 and Dowex-l1 resin, has provided distribution coefficientsja, a separation from zirconlum, nioblum, and tantal , a separation from iron36, and a separation from thorium and uranium’’ . (Figures 3,4,5.) 17 100 g 6o 2 540 d N 20 o -4.4 LOG.HF NORMALITY Fig. 2. Effect of HF on solvent extraotion of Pa from " hydrochloric acld (shown for di-isopropylcarbinol and 5.79 ¥ K1), (Nairn, J. S., Collins, D. A., McKay, He Ae Co; and Maddock, A. G., Second U. N. Intl. Conf,. on Peaceful Uses of Atcmlc Energy, A/CONF.15/P/1158). Typlcally, the feed solution is 9 M in HC1l, from which Pa(V) is strongly adsorbed by Dowex-1, along with Fe, Ta, Nb, Zr, and U(IV or VI). Thorium 1s only weakly adsorbed and afipears in the feed effluent, The elutriant is a mixture of HCl and HF, the concentrations of each depending upon the separation required. Zirconium (IV) and Pa(V) are eluted with 9 M HC1-0.004 M HF, with the Zr preceding the Pa. Niobium(V) is eluted with 9 M HC1-0.18 M HF., Tantalum(V) is eluted with 1 M HF-4 M NH,Cl. TIron(fII), U(IV), and U(VI) remain adsorbed when Pa(V) 1s eluted with 9 M HCl-0,LMHF. They are subse- quently eluted in dilute HC1, 18 10 T T rr——mrr-r- T Tr T T Tr(l) . 5 s - = =3 I 4 1 '-:‘J Ta(X) Lo | i b \C_Ef f 4 | 1 B i = > | i _u-l o 9 il P | < M KC1- +BIHCI 0.18 N HMF -I"HNF- 0.004 N HF 4 NNHCI ] uum J ] O . 0 40 80 120 160. 200 Volume (ml.) of eluent. Fig. 3. Separation of zirconium(IV), protactiniwm(V), nicbium(V) and tantalum(V) by anion exchange: 6-cm. Dowex-1 columm, 0.32-8q.-cm. crfas-a_gtional area, average flow rate 0.2 ml. min.™t cnm. (Eraus, K. '_.A.- and Ioore, G‘. E., J. Am. Chem. Soc. 73 2900-2 (1951).) Zirconlum and protactinium can be separated by elution with HC1 alone38'39;-'Both elements are feebly adsorbed.from HC1 solutions below 5M, but strongly adsorbed above 9 M HCL. From Amberlite IRA-400 resin, at least 95 per cent of the Zr(IV) 15 eluted with 6-7 M HC1l.in about six-column volumes - with not.moré than 0.1 per cent of the Pa(V). The latter is eluted in small volume with HCl below 3 M. (Figure 6) Relatively few elements are adsorbed on anion exchange resins from strong HCl solufions, or if adsorbed, eluted by strong HCl contalning small amounts of fluoride. Prot- 19 COUNTS/ mins/ml. 07— T T Y T — T T T ™7 T rrri i1 1. 141]) Pa T A % = E A 5 - 10°= | = - . 5 a . 0 — S - = N - L : | - 103 — — F . | . P _RVERAGE BAGKGROUND ™\ =9 M HCl—=fe——9 M HCI - 0.1 4 HF ——o}.0.5 # HCle |02 ' 1 I 1 1 1 1 1 1 ] 1 1 - O 15 30 45 60 75 90 105 120 135 150 165 180 Volume, ml. | : Fig. 4. Separation of Pa(V) and Fe(IIT) with HC1-EF mixtures. (5-cm. colum, flow rate 2.5 cm./min.). (Erens, K. A., and - Moore, G. E., J. Am, Chem. Soc. 77, 1383 (1955).) 20 2 - CONCENTRATION (arbitrary units) 1 T T 1 l IOMHCI 9MHGI, IMHF O4 MHCI _ A\ Th(m) (i Po@ | fl_U(m 1!) LJ_x_S?mLJ—J___&-x-_x__I__J_J__—_ ————— T 2 3 4 5 6 - NUMBER OF COLUMN VOLUMES. Fig. 35. Separ&tion of Th(IV) PB(V)’ and U(V-I . (K:I."ID.B, Ko Ao, Hoore, G. '.E., and Nelson, F., J. Am, Chem. Soc.’@, 2692=5 (1956;.) log Kq — ® Pa2?33powex 1X%10 200-230 3 days (Ref.2). 0 Pa®®Dowex 2 _ | ~ .200-250 2 days (Ref.1) 2 .' . : - 0 Pa?3¥Amberiite 400 - 2days (Ref.1) o Pa® Dowex 1x10 200-400 2hr | | ® Zr°SAmberiite 400 J ‘ .. 2 days (Ref.1) 1 — . i A Zr9pDowex 2 60-100-4 hr (Ref.3) @ Zr®3Dowex 1X10 200~400 T L 0 2 4 6 8 10 12 ’ Normality of HCl =— Flg. 6+ Relation between distribution coefficient K. and 'nol'ari{:y of hydrochloric acid for Pa23l and 2r92 on different on~exchange resins. (Kahn, S, and Hawkinson, D. E., J. Inorg. Nucl. Chem. 3, 155-6 (1956).) actinium(V) in trace amounts can, therefore, be purified to a considerable extent by this method. The protactinium eluted in solutions containing HF can be resorbed if HBO'3' of AlCl, 1s added to complex the fluoride'’. Hardy and c.:a-v»;vt:u'.'l~7.e1.'|3]'7 have studied the ion exchange of 10'5 M protactinium from HNOB solutions in batch experi- ments with ZeoKarb 225 cation resin and DeAcidi_te'FF anion resin in the H' and NO,- forms, respectively (Figures 7 22 and 8). Equilibrium between the cation resin and 6 M HNO4 was reachea within 15 minutes, about ?3'per cent of the protactinium being adsorbed. About 95 per cent of the protactinifim was adsorbed on the anion resin after one to two hours. The samé investigators found that, from a 105 M protactinium solution in 0.0l M HF-6 M HNO3 16 per cent of the protactinium was adsorbed on ZeoKarb 225 cation resin and 75 per cent on DeAcidite FF anion resin. On the other hand, the au_thor15 has found tfiat 10'5 M protactinium-231 in 0.05 M HF-1 l.\_'ll-HNO3 or in 0.004 M HF- 0.04 M HNO3 passes freely thrfiugh a column of Dowex-50 cation'resin._ Whereas the decay products, actinium-227, thorium-227, and radium-223; are qgantitativeiy adsorbed, more than 99.5 per cent of thé protactinium-231 appears in the effluept. 8. Miscellany Paper Chromatography: The R value of protactinium(V) inc:eases with increasing HCl concentration when the chro- matogram 1s developed with a mixture'consisting of 90 parts acetone and 10 parts HCl + H,0 41. Evidence for a soluble form of'protactinium-23j in alkaline solution is based on its movement on filter paper developed with 1 N KOH and ite slow migration toward the anode in paper electrophoresis with 1 N ROH as the electrolyteuz. Paper chromatographic aeparations of protaétinium-from tantalum, niobium, titan- ium, bismuth, 1ron, and polonium have been mdde by varying the elution mixture, butanol-HF-HC1-H,0 with respect to the HCl or HF concentrationuj. 23 10 [ o Protactinium 231 o Thorium 230 +232}ref. A Urqnium 233 | T (29) N /1 \ W > 4 6 ' Aqueous HNO3 _concentration > M Fig. 7. Adsorption of thorim(IV), protactinium(V), and uranium (VI), on DeAcidite FF resin. (Hardy, C. J., Scarglll, D., and Fletcher, Jo Mo, Jo Inorg. Nucl. Chem, 7, 257-75 (1958).) ol 8. .103 ' : | I T I o Thorium 230 + 232 ° Protactinium 231(forward) a Protactinium 231(strip) * Uranium 233 10 T A NL L o 2 4 & 8 10 12 Aqueous HNO; concentration, M Fig. 8. Adsorption of thorium(IV), prntactinifin(v) s and uranium (VI), on ZeoKarb 225 resin. (Hardy, C. J., Scargill, '.D..s and Fletcher, J. M., J. Inorge Nucl. Chem. 7, 257-75 (1958). 25 Electrochemistry: The spontaneous electrodeposition of protactinium from HF and HZSOh'solutions on various metals has been studieduu’ 45, 46. The critical potential for cathodic deposition of protactinium by electrolysis of neutral fluoride solutions is -1.20 volts with respect to the hydrogen e1ectrodel3’u7. Spectrophotometry: The absorption spectra of solutions 'containing 0.006 mg./ml, protactinium in varying concen- trations of HCl have been examined by Maddock and his | l. 1.ON HC! IMMEDIATELY AFTER PREPN. 7 2 I.ON HCI I5HRS. AFTER PREPN, 6\ 3 5ONHCI - 4 7-ON HCI 5 '5.8.5N HClI 6. 9-5N HCI O.2} 7 10-2N HCIi o OPTICAL DENSITY ke 200 - 240 280 320 360 400 WAVELENGTH - IN ‘m . Pig. 9. Absorption Spectra of protactinium in hydro-— . chlorio aclid solutlons. (Naim, Je S., 'Co].'l.ins, D. A., “cKay’ He A, G._, and l[addock, A. G., Second U. N. Intl. Conf. on Peaceful Uses of Atcmic Energy, A/CONF.15/P/1158). 26 MOLAR EXTINCTION COEFFIGIENT. 7000 ~—— Pa(IV)-[Pa] = 1.1 X 103 M 6000 }— 5000 — 4000 3000 1600 1400 1200 1000 - 800 600 400 200 ~ - Pa(V)~[Pa] = 43 X 10 M -+« Ce{III) Fig. 10, Lo’ | 1 | 3400 3200 3000 2800 2600 2400 2200 X\ (4). / i I i | l | I | l ! 1 Absorption spectrum of Pa(IV) in 1 M HC1, (Fried, S. and Hindman, J. Ce, J« Ame Chem. Scoc. 15, 4863~k (195L).) 19’280 They report that the onset of hydrolysis co-workers and disappearance of the solvent extractability of prot- actinium coincide with the appeavance of an absorption band with its maximum at 260 mu. (Figure 9}. In 2.4 - 11.8 M HC10y; containing about 10-2 M protactinium(V), a weak peak at 210 mu. disappeared in eight to ten days“’ga A pesk at 213 mu. was observed for 0.7 - & M H2304 containing L ox 1075 M protactinium(V); in 6.5 M HéSOQ the peak was displaced to 217.5 mu, and, in 9 - 18 M acid, it was resclved into two components at about 212.5 and 220 mu. The absorption spectrum of protactinium(IV) in 1 M HCL is shown in Figure 10 %9 (Also see reference 50.) Dry Chemistry: Protactinium metal, Pa0, Pal,, Pag@59 Pal4, PaFa, PaCly,, and Pa0S have been prepared on a 50 - 100 micro- gram scale and the compounds identified by X~Yay analysislze Most of the compounds were found to be isostructural with the analogous compounds of uranium. The extraction of protactinium tracer from solid Th¥, by fluorine and other gases was investigated under a variety of conditionssl. 1V. DISSOLUTION OF PROTACTINIUM SAMPLES Protactinium-233 or protactinium-231 made by neutron irrad- iation of Th-232 or Th-230 offers no special problem other than that of dissclving the thorium. Concentrated HNO3 containing 0.01 M HF will dissolve thorium without render- ing it passive520 The HF also insures the solubllity of protactinium. 28 In the case of'Pa231 from natural sources; the.variety of these sburces defies any attempt to offer a general dissolu- tion procedure. Typically, residues from processes for recovering uranium and/or radium contain oxldes of Si, Fe, Pb, Al, Mn, Ca, Mg, TL, and Zr, afid a random selgction of trace elements which are usually more abundant than prot- actinium. Virgln pitchblende or other uranium ores will contain other elements as well, usually in a refractory condition. Hahn and Meitner53 mixed a siliceous residue with Ta205 and fused the mixture with NaHS30, . After washing the cooled melt with water, they dissolved the Pa and Ta in HF. Pitchblende was digested with a mixture of HNO, and H,S0,, - and the digestion liquor was treated with Nazcgjsun The protactinium in the carbonate precipitate'remained lnsoluble when the carbonates were dissolved in excess HNO3° When the washed residue from the HNOj ;reatment was digested with a mixture of HF and H,50, at an elevated temperature, over 90% of the protactinium went into solution, while tne bulk of the residue remalned insoluble. A slliceous material consistingimainly of lead, barium, and calcium sulfatea was digested wi;h 60% oleum, and the sul- fates dissolved. The siliceous fesidue, containing the protactinlum, was separated and dissolved in HF. Alterna- tively, the original materlial was attacked with 404 HF, dissolving the Pa and leaving the heavy-metal sulfates as residueZI. Depending upon the amount of material to be processed, alkaline fusions are sometimes useful in separating large amounts of silica, etc., while leaving the Pa insoluble. 29 In géneral, the followlng treatments can be recommended, in the order given: 1. Digest the materlal wlth strong HCl to remove - Fe. 2. Digest the residue from the HCl treatment with hot, concentrated stou. 3. Digest the residue from the H,S0, treatment with 25-48% HF or a mixture of HF and H,S50,. 4. Digest the residue with a hot mixture of HNO3 5. Digest the residue with hot 40-50% NaOH. 6. Fuse the residue with NaZCOJ, NaOH, XOH, or KHSO4. Throughout the dissolution, the fragtipns should be examined by gamma-ray spectrometry, as the 27 kev peak of protactinium- 231 is unique and diastinctive (Figure 11). While Pa233 has sometimes beén used as a tracer to follow ' the course of the Pa23l dissolutionZI, it is doubtful that isotopic exchange takes place to a great extent between a reffactory solid and a tracer-contalning dolufiion. V. COUNTING TECHNIQUES 1. Protactinium-233 Protactinium-233 decays by beta emission, with a half-life of 27.0 days, to uranium-233, an alpha emitter with a half- 30 INTENSITY (ARBITRARY UNITS) 1 1| ] 100 130 200 250 300 350 400 450 500 KEV Fig. 11. Gamma spectrum of protactinium-231. (Kitby, He W., unpublished.) - ME] 4 c/mEC Fig., 12. Camma spectrmm of protactinium-233. (Heath, R. L., U. Se Atomic Energy Comm. Repgrt IDO-16408, July 1, 1957) 31 life of 1.62 x 107 yearsu7. The princlpal beta energies in mev are: 0.15 (37 per cent), 0.257 (58 per cent), and 0.568 (five per cent)®5, The gamma spectrum is shown in Figure_1256. In most work, only relativé values of protactinium-233 are needed, hence the counting problems are essentially'the game as with other relatively weak beta-emitters; sélf- absorption, geometry, an& backscattering must be carefully controlled:. For the absolute determination of pure prot- actinium-233, a method based on 1fis growth from neptunium- 23? has been suggested57. Here, é highly purified sample of néptunium-ZB? 1s .electrodeposited and allowed to decay. The beta-counting rate of protactinium-233 is compared with the alpha-counting rate of neptunium—Zj?Iand the counting efficiency calculated from the tfieoretical growth curve. Altefnatively, the neptunium-237 may be permitted to decay to secular equilibrium, when the disintegration rateé of the two lsotopes are equal. A simpler and more versatile method58 consists of standard- 1zing a scintillation gamma counter with-é solution of purified protactinium-233 whose disintegration rate has been determined in a 4T beta counter. A scintillation spectro- meter is useful for identifying and determining protactinium- 233 in the presence of other activities. Correction for interference by Compton conversion electrons must be made if more energetic gamma rays are present.- 2. Protactinium-231 Protactinium-231 decays by alpha emlssion to actinium-227, also an alpha emitter (Table 1I). The half-life has been 32 reported fo be 34,300 years59, and 32,000 yeafszz. A Tecent calorimetric measurement on approximately 0.5 gram of prot- actinium pentoxide15 yielded a value of 32,480 * 260 years. Protactinium-231 has ten groups of élphfi particles, of which 43 per cent have energles below 5.0 mev. Thié_fact, combined "with its low specific activity (about 56 mc/g);.makes prot- actinium-231 alpha counting especially susceptlble to self- absorptidn. Care must-be taken to keep the radioactive deposit as thin as possible. A higher degree of counting precision is attainable with a proportional alpha counter than with either a parallel-plate alr-ionization counter or a zinc sulfide scintillation counter. . Ideally, the alpha plateau should be determined 1ndividually for each samplé, but this is a tedious and time-consuming procedure. The following mounting and counting techniqge has been found to give high alpha-counting'precision15: Trfinsfer one ml. or less of a fluoride solution of protactinium-231 to a platifium or gold plate, or to a stainless steel disk coated-with a thin plastic film (a clear plaétic spray coatlng or a ~ dilute collodion solution is convenient for this lpurpose). Evaporate the solution to dryness under an infrared lamp, tilting the plate as necessary to retain the solution in the center of the plate. Cool the plfite and cover the resi- due with one ml. of 0,1 N HNOB. Add one drop of concentrated NHuoH and again gvaporate;the solu- tion to dryness. Lower the lamp sufficiently to drive off all the NHuNOB, and-ignite the plate 33 over a flame until the organic coating has burned off (or, 1f gold or platinum was used, ignite to just below red heat). . Determine the alpha platéau-of the proportional counter by counting a standard alpha source (Pu239, radium D-E-F, or Po210) at 50-volt inter- vals. At the high-voltage end of the alpha plateau, count a sample of Sr90/Y90 at 25-volt iniervals,-and find the voltage below which only 0.01 per cent of the betas are counted. The protactinium-231 sample can be counted at this point with goo& precision and no significent interference from beta emitters. A gamm#-ray scintillation spectrometer is virtually a necegssity in modern work with protactinium-zjl. The 27, | 95, and 300 kev photopeaks (Figure 11) are characteristic, and the 27 kev peak in particular is unique in the gamma spectra of the naturally occurring radioisotopes. (Compare Figures 13 through 16.) The sensitivity of this method of detectlon 1s shown in Figure 17, where 0.2 ppm of protactinium-231 is positively .1dentified in a uranium refinery residue by the presence of the distinctlve pho;opeak at 27-kev. The high susceptibility of the 27 kev peék to absorption precludes its use for the quantitative determination of protactinium-231, but it 1s particularly valuable in the preliminary dissolutién of a raw materlal. The 300 kev peak js useful for quantitative work if cofrgétion i1s made for the contribution of decay products and other gamma-active materials. - 1 b | o 1 INTENSITY (ARBITRARY UNITS) ~n T ] I | L L1 ] I ] 50 100 150 200 250 300 350 400 450 500 KEV Fig. 13, CGamma spectrum of actinium-—227 in equilibrium, (Xirby, H. W., unpublished.) ;9' INTENSITY (ARBITRARY UNITS) 5C 100 150 200 250 300 350 400 430 300 KEV Tige. 1. Gazma spectrmm of thoriwm-230 (lonium). (Xirby, He W., unpublished.) 35 INTENSITY (ARBITRARY UNITS) l l l l l ] | | 50 100 (50 200 250 300 350 450 450 500 KEV Fige 15, Camma spectrum of radium=-226 in equilibrium. (Kirby, H, W., unp'l]blishedo) INTENSITY (ARBITRARY UNITS) 9 I I I I | | | | I 50 100 150 200 250 300 350 400 450 500 KEV . f‘:l.g. 16. Gamma spectrum of uraniuwm-235/238, (Kirby, He W., unpublished.) 36 INTENSITY (ARBITRARY UNITS) ] | | | l | | L S0 100 150 200 250 300 350 400 450 500 KEV ¥ig. 17. OCamag spectrum of raw material (ursanium refinery residuoe.) (Eirby, H. W., unpublished.) VI. DETAILED RADIOCHEMICAL PROCEDURES FOR PRDTACIINIUfi Procedure 1 "Preparation of carrler-free protactinium-233", according to J. Golden and A. G. Maddock, J. Inorg. Nucl. Chem. 2, 46 (1956) Protactinium-233 was prepared by the neutron irradiation of samples of acid-insoluble thorlum carbonate. Thls material, of uncertain composltion, ls reasonably thermally stable, but completely soluble in dilute HND, and HCl. After irradiationm the material was dissolved in 8 N HCl and extracted wlth diiso- propyl ketone (DIPK), The extract was treated with 2 HCL when the Pa passed back to the aquecus layer. The aqueous 37T Procedure 1 (Continued) extract was then made 8 N again and the extraction repeatéd. The protactinium was kept in solution in 8 N HCL in a poly- ethylene vessel, It was observed that losses by adsorption quickly took place on the walls of glass containers even with golutions of the chloride complex in DIPK. Better recoveries were obtained if the irradiated carbonate was dissolved in 8 N HF, Thié solution was nearly saturated with A1C13 before the first solvent extraction. -The subsequent separation followed the first procedure. Neither product con- tained detectable amounts of thorium. (Reviewer's Note: - Irradiation of one gram of Th232 at 1013n/cm2-sec. for one day willl produce 0,25 curie of P3233.) Procedure 2 Preparation of carrier-free protactinium-233, accerding to F. Hagemann, M., H. Studier, and A. Ghiorso, U. S. Atomic Energy Comm. Report CF-3796 (1947), as quoted by Hyde (&) The bombarded Th metal was dissolved in concentrated HNOg, using a small amount of F~ as a catalyst. The aqueous solu- tion was salted with Ca(NO3), to give solutions of 2.5 M Ca(NO 1 M HNO The bulk of the U233 3)2’ 3 4° was removed by ether extraction, following which Pa233 yas iso- » and 0.42 M Th(NO,) lated by dilsopropyl ketone extraction. Further purification wag obtained by three Mn0, cycles in which 1 mg/ml of MnO, was successively precipitated from HNO3 solution and redissolved in HNO5 in the presence of NaNOz. After the third cycle the 38 Procedure 2 (Continued}) solution was made 3.5 M Ca(NO3), and 1 M HNO; and was extracted with ethyl ether again to effect complete removal of uranium. The protactinium was again coprecipitated on MnO;, dissolved in concentrated HCl, and diluted to an acidity of 0.05 M; the protactinium was extracted into é 0.15 M solution of thenoyl- trifluorocacetone in benzene. Procedure 3 -Prepafation of carrier-free protactinium-233, according to W. W. Meinke, U. S. Atomic Energy Comm. Reports AECD-2738 and AECD-2750 (1949) as quoted by Hyde (6) The bombarded thorium-metal target is dissolved in concentrated HNO;, using 0.01 M (NH4)231F6 as a catalyst. The solution is diluted to approximstely 4 N HNO; and a thorium concentration less than 0.65 M. Then Mo'' in excess and KMnO; are added to precipitate 1.5 mg/ml MnO, to carry the protactinium. The Mn02 is dissolved in a small amount of 4 M NH,OH, The MnO, is reprecipltated and redissolved three times to reduce the final solution volume to a few milliliters. After it is made 6 M HC1 or HNO,, it 1s extracted with two to three volumes of diiso- propyl ketone. The ketone phase is washed three times with 1 M HNOy and 3 M NH,NO; wash solution. The protaétinium is finally stripped out into 0.1 M HNOj. The protactinium left behind is recovered by using fresh ketome to repeat the extraction cycle, All 0.1 M HNOj re-extraction solutions are combined, made 6 M HNO3, and contacted with an equal volume of 0.4 M thenoyltri- fluoroacetone (TTA) in benzene. The benzene solution of prot- actinium-TTA complex is washed with 6 M HNO4 once. 39 Procedure 4 Preparation of carrier-free protactinium-233, according to Max. W. Hill (Thesis), U. S. Atomic Energy Comm. Report UCRL-8423 (August, 1958) The targets were either Th metal or ThCl, powder, some of which was converted to ThO, during the bombardments. Concentrated HC1-0.01 M HF was used for dissolving relatively small amounts of powder. Thorium metal was dissolved in con- centrated HC1 - 0.2 M HF., The flfioride was complexed by the addition of borax (Na,B,07-10 H,0) or AlCly béfore the solu- tion was passed through the columm. The colum was 3 mm. in diameter and was filled to a.height of 55 mm. with Dowex-1 anion-exchange resin. The colum volume, defined as the number of drops required for a band to traverse the length of the resin column, was 5-6 drops. In 10 M HC1l solutions, Pa(V), Zr(IV), and Nb(V) stick to the resin, while Th(IV) passes through with the other alpha emltters below Pa in the periodic table. With 6 M HCl as the eluting agent, Zr(IV) is rapidly stripped off in a few column volumes, without loss of Pa(V) or Nb(V). The Pa is then eluted in 9.0 M HC1-0.1 M HF. The Nb(V) is eluted in 1-4 M HCL. The 9.0 M HC1 - 0.1 M HF solution containing the Pa was con- tacted with an equal volume of diisopropyl ketone (DIPK). Under these conditions, such species as Fe(1II) and Po(1V) extract quantitatively into the DIPK along with appreclable 40 Procedure 4 (Continued) amounts of Sn(IV), Nb(V), and others. Protactinium(V) ex- tracts to the extent of less than 0.4%. The solvent phase was discarded, and borax or anhydrous AlCl3 was added to the aqueous phase. (Although AlCl, seemed-to have . 6lightly better complexing characteristics, it appeared to be appreciably soluble in DIPK, and excess quantities in solution gave voluminous precipitates.) The aqueous phase was then contacted with an equal volume of fresh DIPK, Under these conditions, Pa(V) is extracted quantitatively by the solvent phase, sefiarating it from Th(IV), Ti(1v), v(V), Zr(IV), U(VI), and other species. The Pa was then re-extracted from the solvent phase into an equal volume of 2.0 M HCI. To remove all extraneous mass and reduce the volume to a very few drops, the golution containing the Pa was then made apprpxi- mately 10 M in HCl1l and p&ssed through a small anion resin colum (3 mm. in diameter, 12 mm. in height). After being washed with 10 M HCl, the Pa was eluted with 2.7 M HCl. The third through sixth drops contained more than 90 fier cent of the protactinium, Procedure 5 Determination of protactinium-233, according to F. L. Moore and S. A. Reynolds Anal. Chem. 29, 1956 (1957) 1. The sample drawn from the process should immediately be adjusted to 6 M HCl or greater. Add an aliquot of suitable L1 Procedure 5 (Continued) counting rate to a separatory funnel or 50-ml. Lusteroid tube, Adjust the aqueous phase to 6 M HCl-47% HpCp04. (If the original sample contains Th, omit the H,C,0, in the original aqueous phase and perform.tfie extraction from 6 M HCl. Wash the di=- isobutyl carbinol (DIBC) phase (see next step) for 1 to 2 minutes with an equal volume of 6 I{ HC1l before beginning the three scrubé of 6 M HCl-4% H,C,0,). 2. Extract for 5 minutes with an equal volume of DIBC (previously treated for 5 minutes with an equal volume of 6 M HC1). | | 3. After the phases havé disengaged, draw off and discard the aqueous phase. Scrub the organic phase for 5 minutes with- an equal volume of wash solution (6 Y HCl - 4% HoC90s). Repeat with two additional scrubs of the organic phase. Draw the organic phase into a 50-ml, Lusteroid tube,-centrifuge for 1 minute, and draw off an aqueous phase which appéérs in the bottom of the tube, being careful.not tollose any of the organic phase. (In many samples, an aiiquot of the organic phase may be taken at this stage for counting. Only if a substantial activity of Nb, Sb, or free I, is present is it necessary to-strip the organic phasé.) 4. Strip the organic éhase by extracting for 3 minutes with an equal volume of 6 M H,S0, -6 If HF. Allow the phases to disengage, centrifuge for 1l minute, and draw off most of the organic phase, being careful not to lose any of the aqueous ho Procedure 5 (Continued) ~ phase. Add an equal volume of DIBC and extract for 3 minutes. Centrifuge ffir 1l minute and draw off most of the organic phase, being careful not to lose any of the aqueous phase. Centrifuge for 1 minute. 5. Pipet suitable aliquots of the aqueous phase for 233 Pa counting. The expected yield is 97-98%. The follofiing table is given by the authors: Per Cent Extracted by DIBC from 6 M HCl-47% 1-120204 2 g mdie 2 gos gt 99.5 0.4 0.07 0.003 0.01 9.2 <0.04 99.6 0.5 0.13 0.003 0.04 0.3 <0.04 0.3 0.12 0.005 0.0L 0.1 <0.01 0.3 0.1l 0.003 0.02 0.2 0.06 * Oxallc acid omitted from original aqueous phase, values given for Th represent lower limit of detection of analytical " method used. (Reviewer's Comment: - The procedure is basically sound; but the degree of separation is affected by the concentrations of Pa and Nb, A DIBC solution containing 2.5 mg. Pa23l and 20 mg. Nb per ml. plus a stoichiometric amount of phosphate was scrubbed with an equal volume of 6 M HC1-5% H,C,0,. The aqueous phase contained 1.5% of the Pa and 75.3% of the Nb, When the organic phaee was scrubbed a second time with fresh L3 Procedure 5 (Continued) aqueous, the aqueous phase contained 92.1% of the residual Nb and 2.3% of the Pa. The presence of iron also interferes significantly, presumably because of the formation of a strong oxalate complex. .The concentration of oxalic acid is probably less important than the total amount relative to the amount of nicbium and other oxalate-complexing cations.) Procedure 6 Determination of protactinium in uranium residues, according to J. Golden and A. G. Maddock, J. Inorg. Nucl. Chem. 2, 48-59 (1956) The siliceous material consisted mainly of the sulfates of Pb, Ba, and Ca. Two methods of opening up were used. In the first, one-gram samples were treated with 10 ml. of 60% 6leum, and a known 233 ,dded to the mixture. The Pb, Ba, and €a amount of Pa sulfates were dissolved, and the siliceous residue, containing the Pa, was separated and dissclved in 5 ml, of 40% HF, | Alternatively, it was found that the original material could be attacked with 40% HF containing the pa233 tracer, leaving the heavy-metal sulfates as residue and dissolving both Pa231 and Pa233. (Reviewer's Comment: - It is highly questionable that isotopic exchange was complete.) Either solution was diluted to 100 ml., and an excess of BaCi2 was added. The Ban precipitéte was washed until no bl Procedure 6 (Continued) obvious decrease in bulk took place. The remaining precipitate consisted presumably of fluosilicates and was dissolved in 1M AL(NO4)4-6 N Hfl03.. The Pa was then carried down on a MnO, precipitate, sufficient MnCl, and KMnO, solutions being added to produce about 10 mg. of precipitate per ml. of original solution. The mixtfire was digested at 100°C. for half an hour. The resulting precipitate was separated, washed, and dissolved in 20 ml. of 7 N HCl with a trace of NaNOz. Alternatively, the precipitate was leached with 10 ml. of 1 N HF, In some analyses, the MnO2 stage was omitted entirely, and the fluosilicate precipitate was dissolved in 7 N HCl-1 M AlCly. The HCl solution from either of these three variations was extracted with an equal volume of diisopropyl ketone. Separation from most of the polonium can be effected by re- extraction from the solvent into 7-8 N HCl-0.5 N HF.- Procedure 7 Determination of protactinium in uranyl solutiom, according to J. Golden and A. G. Maddock, J. Inorg. Nucl. Chem. 2, 46-59 {(1956) The solution was made 8 N in HCl and 0.5 N in HF and the tracer protactinium=-233 added. Direct extraction with diisopropyl ketone removed many impuri- ties, e.g., iron and polonium. Extraction after adding AlCl3 to complex the fluoride present brought the protactinium into L5 Procedure 7 (Continued) the solvent layer. Washing this layer with 8 N HCl removed those elements whose extraction had been enhanced by the presence of AlCl;, e.g., uranium and zirconium. Finally, the protactinium was back-extracted with 6-8 N HCI - 0.5 N HF, The next solvent cycle avoided the use of AlCl,, repeated NH,OH precipitation and HCl solution, or continued evaporation with HCl, being used to remove fluoride. ln either case, the efficiency of a cycle was 98% or more, without repetition of any step. At the most two of these cycles were found to be sufficient to achleve radiochemical purity. Procedure 8 Determination of protactinium by gamma spectrometry, according to M. L. Salutsky, M. L. Curtis, K. Shaver, A, Elmlinger, and R, A. Miller, Anal, Chem. 29, 373 (1957) l. Welgh about 5 g. of uranium residue into a vial suitable for counting in a well-type gamma scintillation spectrometer. Determine the counting rate at 300 kev. 2. Transfer the sample to # beaker with a small amount of HZO’ add 100 ml. of 9 N HCl and 1-2 ml. of 48% HF. Heat until the sample dilissolves. Add more HF, if fiecessary. 3. Cool to room temperature. Add slowly, with stirring, 10 ml. 1 N HCl containing 10 mg. Th. Allow the mixture to 46 Procedure 8 (Continued) stand 5 minutes. Add a second 10 mg. of Th, stir, and allow the mixture to stand 5 minutes. Filter the ThF,. 4. Trafisfer the filter baper and precipitate to the vilal used for the original sample. Determine-the gamma counting rate at 300 kev. Make a blank determinatlion for the activity- of the Th carrier used. 5. Obtain the fa gamna counting rate by difference. Compare this counting rate wlth that of a standard profactinium gample at 300 kev, and calculate the concentration of Fa in the uranium residue. (Reviewer's Comment: - This procedure contains a number of fundamental errors, but, with appropriate modifications, may be useful for obtalining a rough estimate of the Pa concentra- tlon in certain types of samples. The basic assumption of this procedure is that, under the conditions given, all of the protactinium will remain in solution, while all other radioisotopes which contribute to the 300 kev gamma-counting rate will be carried on ThF,. The first part of this assumption is subject to considerablé doubt; Moore and Reynolds (cited in Procedure 1) found wide variations in the behavior of protéctinium in the presénce of fluoride precipitates. The second part of the assumption lgnores the substantial contribution of radium-223 and other radium isotopes to the 300 kev counting rate. It 1s unlikely that a large percentage of the radium would be carried on ThF, under the conditions recommended. 47 Procedure 8 (Continued) Finally, no correction was made for the contribution to the 300 kev gamma-counting'rate by.decay products in the "“standard -gample", The following modifications seem indicated:. 1. Determine the yield by adding protactinium-233 to a separate sample at Step 2. (The yield determination must be:fiade separately because of the 310 ke§ gamma ray of protactinium-233.) 2. Add barium carrier after Step 4,.and precipiltate barium chloride by the addition of diethyl ether. (Moore and Reynolds found that both BaCl2 and BaS0, carried sub- stantial afiounts of protéctinium-233 in the absence of fluoride, bgt did not test them in fluoride solutions. The yield correction allows for_thé-possibility that some protactinium is carried by the barium precipitate.) 3. Correct the gamma-count rate of the standard sample for growth of decay products, or prepare a fresh standard sample free of decay products (See Procedure 9). ) Procedure 9 Determination of protactinium by differential gamma spectrometry, according to H. W, Kirby and P. E. Figgins. Unpublished. (Reviewer's Note: - This procedure is limited to analysis of samples containing only protactinium-231 and the actinifim-227 chain.) 1. Procedure 9 (Continued) Obtain a sample of actinium-227 in equilibrium with its decay products (AEM). The actinium should preferably have been prepared by neutron irradiation of radium-226 to avoid possible Pa 2. 231 contamination. 231 Prepare a radibchemically pure Pa standard by one of two methods. 8. If the protactinium is in a dry state; dissolve it in hot concentrated H2504 and dilute the solution to 18 N H,50,. Add an equal volume of 12 N HC1 to the cooled solution and one or two drops of 30% Hy0,. (If the prétactinium is in aqueous solution, adjust the concentration to 9 N H,S0, -6 N HCl. Fluoride must be absent or complexed with Al+3 or HSBO3. It may also be removed by evaporation to fumes with H SDA.) 2 Extract the aqueous solution with 2 ml. of diisobutyl carbinol (DIBC) diluted to 50% with benzene, Amsco'kerosene, or other inert diluent, Scrub the organic phase with fresh 9 N HZSO4’ 6 N HCl. The organic phase will contain radio- chemically pure Pa231. " 1f the PaZ3l ig in DIBC or other organic solution, scrub the organic solution with two or three volumes of 9 N H2504-6 N HC1 to remove decay products. The Pa should be repurified at least once a week. L9 Procedure 9 (Continued) 3. Determine the location of the peaks of the unknown sample in the regilons of 90 and 300 kev. Count the AEM, the unknown, and standard Pa in that order at the peak of the unknown in the 90 kev ‘region. Repeat the procedure in the 300 kev region. (Background in each region should be de- termined before and after each series of three counts, and weighted if there is significafit variation with time.) 4, Calculate the ratio of the 90 kev count to the 300 kev count in each sample. 6. Determine the alpha counting rates of Fhe Pa and AEM standard samples either by transferring them to alpha- counting plates or by counting aliquots of the same solutions. 6. Bj simultaneous equations, calculate the contribu- tion of protactinium and.of AEM to the gamma-counting rate of the unknown at its peak in the 300 kev region. Correlate these gamma counts of AEM and protactinium. Example - Determination of Pa by differential gamma spectrometry. Gamma Cts/Min at Base AEM std. 3001.5 343.4 8.741 127,367 Pa + AEM 2395.4 1044.9 2,292 332,112 Pa?3l gea. 1233.5 885.2 1.393 267,124 2395.4 = 8.741 AEM + 1,393 Pa Simultaneous equations: 1044.9 = AEM + Pa Procedure 9 (Continued) 127.9 cts/min; Pa = 917.0 cts/min (Gamma cts/min at B.L. - 295) Solution: AEM 47,438 cts/min; Pa = 276,723 cts/min AEM - (Alpha in unknown) Total alpha calculated: 324,161 cts/min (97.6%) (Reviewer's Comment: - The results are invalid 1f the actinium-227 chain (thorium-227, radium-223) has been recently broken. Both the AEM standard and the Pa unknown should be at least six months old. 'The procedure needs to be evaluated with synthetic mixtures of Pa and AEM;.but it appears to work well with samples of ‘known age, in which the decay product growth can be calculated.) Procedure 10 Determination of.protactinium in uranium residues, according to H. W. Kirby (Unpublished) 1. To five gramé of the residue in' a 50-ml. centrifuge tube add 25 ml. of 12 N HCl, mix thoroughly, and warm gently until the initial evolution of_gés subsides. Bring the temperature of the water bath to 85-90°C. and heat the mi#ture in the bath for one hdur,'stirring occasionally. | | 2. Without waiting for thé mixture to cool,.centrifuge and decant to a second centrifuge tube. 3. To the residue in the first tuBe, cautiously add 3 mi. concentratéd H,50,, and digest on the water bath 15 minutes with occasional stirring. Cool to room temperature, o1 Procedurs 10 (Continued) o and cautiously add 3 ml. H,0. Mix. Add 6.ml. 12 N HCl and 3-4 drops of 30% H,0,. Extract the slurry. three times with two ml. diisobutyl carbinol (DIBC) diluted to 50 per cent with benzene. Separare the.phases (ceqtrifuging if necessary) and retain the organic. Centrifuge the elurry and discard. the aqueous supernate. Repeat the'digestion of ‘the residue “with fresh HZSD , adjust with HC], and H2 2. and extract as ° before. Dlscard the aqueous phase. 4. Transfer the resldue as a slurry in 10 ml. H20 to a test tube of a size suitable for use in a well-type gamma acintillation_epectremeter; Centrifuge the residue:tp'fhe bottoe of rhe test tube and pour or draw off the'sepernate. To the residue add 10 ml. of a saturated solution of the tetraaodium salt of ethylene dismine tetraacetic acid (Na4EDTA) adJueted to pH 12. Digeat the mixture on the hot water bath for 15 minutes, stirring occasionally. Cool, centrifuge, and discard the aqueous supernate.. Examine.the gamma spectrum of the residue’ in the region of 27 kev If there is no _peak | at 27 kev diacard the resldue. If there 1s a poasibility that a 27 kev peak exists, but it :Le obacured by excessive gamma " radiation in. the 90 kev region, repeat the digestion with the’ NasEDTA., If a definite 27 kev peak is found, proceed to : Step-S. - | 5. Digest the residue with 10 ml. 40%Z NaOH for 15 minutes on the hot water bath, stirring occasionally. Centrifuge and ' discard the supernate. . Wash the_reeidue with 10 ml. H,0, centrifuge, and transfer the wash to the HCl solution from. 52 . Procedure 10 (Continued) Step 2. Treat the residue as in Steps 3 and 4. Retain the organic extracts and discard the aqueous phase and the residue. (We have not found it necessary to go beyond this - point to recover protactinium from the HCl insoluble residue.) = (1f the fesidue-should.prove more refractory than those withl which we have had experienée, a repetition of Sfiep 5 is- | . Tecommended. If that should fail, the use of HCl would be consideredf).- 6.. To the.HCI solution in the second centrifuge tube (Step 2). add 10 mg. Ti as TiCly and mix thoroughly. Add 0.5 ml, of 85% HaPO, and two or three drops_of concentfgted HN03. Mix and heaf on the water bath at 85-90°C for one hour, stirring occasionally. Cool, centrifuge and decant the sfiperfiate to a third centriffige tube, | 7. Treat the precipitate as in Step 3. (The Ti preci- pitate usually dissolves completely after the addition of | HCl and H,0,. However, any insoluble residue may be treated as in Steps 4 and 5, if necessary.) 8. To the HCl golution in the tfiird cenfirifuge tube (Step 6), add 10 mg. Ti, two or three drops of concentrated HN03, and enough 12 N HC1l to restore the volume to 30;35 ml. Treat this solution as in Steps 6 and 7. 9, Combine all the organic extracts in a single 50-m1. centrifuge'tube §r a separatory funnel and add two ml. of 1 H'HNO3-r0.05 N HF. Mix the phaseé thoroughly for ten minutes, and draw off the aqueous phase with a transfer pipet. 53 _ Procedurs 10 (Cfintiuuadi) '_ Rape#t the strip of the organic.phaae with fresh HNO,-HF. Discard the organic phase, combine the aqueous phases and evaporate the solution to two ml. in a vial or test tube sultable for ulé_in the well of the gamma scintiila;ifin. counter, _ 10. . Compare the 'gma. count at l300 kev with that of a standard sample of protacfiinium—231 (See Procedure 9). | Procedure 1l Preparatlion of tetravalent protactinium, according to M. Halssinsky and G. Bouissiéres, Bull. Soc. Chim. France 1931, 146-8, No, 37, (From the translation _ by Mae Sitney, AEC-tr-1878) ' A 1-3 E,HZSO4_or'Hc1 golution of pure protactinium or prot- actinium mixed with its carriers 1s placed in contact with solid zin¢ amalgam in a plexiglas-colufin. The column is joine& to a Buchner funnel, also of plexiglas. The latter 1s closed at the bottom by clamped rubber tubing, 80 that the liquid does not run out through the filter paper. Hydrogen gas ls constantly circulated through.the various parts of the apparatus, and at the game time, the solution of protactlnium_is rfip throfigh the Buchner. It slowly forms a.precipitate congisting either of the fluoride sait of reduted protactinium or of a mixturé with'LaF3 if a lanfhanum halt 1a used as a carriér. When the precipitate is collected, it 1s separated rapidly by flltration, accomplished by increasing the pressure of o4 Procedure 1i (Continued} hydrogen and opening the clamp on the Buchner. Eventually, it can be washed with Hy0 which is passed over the amalgam, 'The reduction can also be carried out in the Buchner, in ‘which the amalgam is placéd in contact with the HF solution of protactinium. The precipitation of the fluoride profiuced in this case is proportional to the reduction. The procedure may be advantageous for separating protactinium from tantalum, zirconium and titanium, which can.be dissoived much more easily in HF than in other mineral acids. If the precipitate (6f PaFQ) is collected on filter paper, it can be stored for 12 to 15 hours without being combletely reoxldized. Procedure 12 Preparation of solutions of prOtEQtiniufi(V) in alkali according te Z. Jakovac and M. Lederer, J. Chromatography 2, 411-17 (1959) Protactinium=233 tracer in- 6 N HCl was evaporated in a micro- beaker, a few pelletg of NaOH or KOH were added and fused - over a naked flame for a few minutes, cooled and diluted with HZO to yield a solution SIE with respect to alkali. Such solutions usually contain a soluble fraction but also an in- goluble activity. 1f the solution in HCl ig taken to dryness and moistened with concentrated HCl and again evaporated,-and this process - repeated three times, the insoluble compound does not form. 55 Procedure 12 (Continued) It seems that during evaporation with 6 N HCl some radio- colloid is formed which does not - react readily with NaOH, When evaporated repeatedly with concentrated HCl this seems to he inhibited and presumably the protactinium(v) is left in the beaker as a very thin layer'on ‘the surface, which then reacts readily.with fused NaOH. When solutione which have been evaporated three timeg with concentrated HGCl are created wlth aqueous 6 N KOH, some transformation into a soluble form was also noted. without this pretreatment no soluble fraction is obtained. Procedure 13 Preparation of solutions of protactinium in nitric acid, according to C. J. Hardy, D. Scargill, and J. M. Fletcher, J. Imorg. Nucl. Chem. 7, 257 75 (1958) Milligram amounts of protectinium-23i were available in a - HC1-HF solution at a concentration of 0.3 mg./ml. Stock solu- tions (of the order of 10-3 to 10“4_fl_Pa in 6,&-HN03)were‘_ prepared from this by evaporating almost to dryness with HNO, .- several times, followed by three precipitations by NH40H; to assist in_the decontamination from fluoride, with re-solution each time in cold 6 M HN03. It was found necessary to dissolve the hydroxide precipitate shortly (<5 minutes) after its formation to prevent aging to. HNO4=insoluble compounds of protactinium. % . Procedure 13 (Continued) The solutiohs'so-prepared~always contained smali émounts of alpfia activity (approximatelj five per cent of the total) inextractable by tributyl phosphate, Prolonged centrifuging ~ and heating to 100°C, in sealed tubes reduced the alpha-active inextractable materiallto one per cent; this-was-due to _daughters of pxbtactinium-ZBl; Aqueous stock solutions Wére obtained free from inextractable alpha activity by a preliminary solvent extractlon cycle, | e.g., by extraction from 10 M HNO3 for two minutes with 50 per cent tributyl phosphate, stripping with. 2 M HNO5, and scrubbing with benzene to remove traces of tributyl phosphéte. Procedure 14 Separation of protactinium and niobium according to F. L. Moore, Anal. Chem. 27, 70-72 (1955) Polyethylene bottles were used in all the extractions. The original aqueous phases contained 1 mg./ml. of Nb carrier (dissolved in 0.18 M H,C,0,) and a total radioactivity of - 95 1,46 x 106 arma counts per minute or Nb 'radioactivity of & P & 4 gamma counts per minute. Separate extractions were 3.4 x 10 done under the same conditions for Pa233 tracer and Nb%> tracer. Three-minute extractions were peffdrmed with equal volumes (9 ml.) of diiéobutyicarbinbl that had been pretreated for three minutes with HF of the same concentration as the 57 | Procedfire 14 (Continued) original aqueous phase. The organic.phasés were separated, centrifuged, and washed for ome minute with an equa1 volume of a solufiion of the same HF-HZSO4 concentration as the original aqueofis phase. 0 -- <0.1 0.5 <0.01 87.8 | 1.0 . <0.02 92.5 2.0 . <0.02 9.8 4.0 <0.02 98. 4 6.0 | <0.01 | 98.2° a Each aqueous phase was 6 Y in H,50,. b A second extraction left no detectable Nb in the aqueous phase. IProcedure 15 Paper chromatography of protactinium, - according to Jacques Vernois, J. Chromatography 1, 52-61 (1958) quyéthylene was used throughout. Chromatograms were developed by ascending elution, Separations were carried ofit-in a cylinder which was 17 cm. in diameter and 27 em. high. Sfieets of Whatman No. 1 chromatographic paper (22 X 22.cm.) were rolled into cylinders and placed in the.bofitom of the reservoir. -Solutions.were depositéd on_the-paper with the aid of a poly- ethylene microPipét. Chromatograms were developed over a 59 Procedure 15 (Contlnued) period of about ten hoyrs, after which the paper was removed and ailr-dried. l. Separation of Pa-Ta-Nb with a solvent mixture con- sisting of 25 ml. of 12 N HCl, 50 ml, butanol, one ml. 20 N HF, 24 ml. H20. The Rf values were: Pa - 0.50; Nb - 0,.82; Ta - 1. | | | | 2, Separation of Pa-Ti-Bi with the mixture: 25 ml. of 12 N HC1l, 5 ml, 20 N HF, 50 ml. butan&l, 20 wl. Hy0. The Rg¢ values were: Pa - 0.45; Ti - 0.66; Bi - 0.66. 3, Separation bf Pa-Fe with the mixture: 33 ml., of 12 N HC1l, omne ml; 20 N HF; 50 ml. butanol made up to 100 ml..with. HZO' The Rg valfies were: Pa - 0.46; Fe = 1. 4. Separation of Pa-Po: an unspecified mixture of HCl- .HF-butanol-HZO (similar to those above) easily separated Pa from Po. The.Pa moves about half-way, while the Po moves with the solvent front. Procedure 16 Determination of protactinium in urine, .according to E, R. Russell, U, S, Atomic Energy Comm. Report AECD-2516 (1958). 1. Transfer 400 ml. of urine specimen to a beaker, wash the container with 100 ml. of concentrated HNO, and add the wash to the beaker; Evéporate to dryness, and ash to a white solld with alternate treatments of concentrated HNO3 and superoxol. 59 Procedure 16 (Continued) | 2, Treat the white residue witfi 50 ml, concentratedfl HC1 and evaporéte to near dryness on a low-temperature hot plate. | | 3. Add 60 ml. of 10 M HCL and heat 10-15 minutes with occasibnal stirring. 4. Let the.salts settle, and decant the hot solution to a 125-ml. separatory funnel. . " 5. Wash the remaining salts with 20 ml. hot 10 M HCl "and decant to the se-paratory-l funnel. 6. Add 25 ml. of diisopropyl ketone to the hot solution and shake the mixture 8-10 minutes.' | 7. Digcard the aqueous layer and collect the ketome in a beaker. Wash the ffinnel with 5 ml. of ketone, and add the wash to the beaker. \ 8. .Evaporate the.ketone in a d:ying oven at.100-110°C. Avoid higher femperatufes. | | | | 9. When the ketone is ccmpletely evaporated, ignite.the' beaker in a muffle-furnace at 250-30090 for 5-10 minutes. 10, After the beaker is cooled, take up the resldue in warm concentrated flNOs, and evaporate éliqudts on counting ~dishes. | Average-fecovery'in-eight samfiles analyzed was 8416 per cent. (Reviewer's Comfient: - We have not evaluated this procedure in the laboratory, but it is easy to agree with its author tha; “Becausé‘of=the tendency'of Pa to undéfgo hfdrolfsls and to become colloidal, it is difficult to obtain reproducible 60 ' Procedure 16 (Continued) results. The urine procedure used in this laboratory is basically the same as that used for all pther.aétinides (See Procedure 17). In this reviewer's opinion, urinalysis for protactinium is an exercise in futility. Ingested protactinium is far more likely to be found in the feces.) Procedufe'17 Determination of protactinium in urine, according to H, W. Kirby and W. E. Sheehan (Unpublished -- based on U. 5. Atomic Energy Comm. Report MLM-1003, August, 1954) 'Collection_Procedfire: Personnel are.requested to collect every bladder discharge'in one fu11.244hou: day, beginning with the first voiding in the morning either on Saturday or Sunday. As an alternate, they are permitted to collect the first voiding in the morning and the last voiding before retifing on both Saturday and Sunday of the weekend.the sample "1s to be collected. The first procedure is preferred. 1. Transfer the urine specimen to a 2000-ml. graduated cyllnder. 2, Dilute the urine if necessary in the graduate to a .volume of 1800 ml. with H,O, 2 _ 3. Transfer to a 3000-ml. beaker and add 25 ml. of concentratedZNH40Ha. Stlr the sample in the beaker for ten minutes. 61 Procedure 17 (Contimued) 4. Transfer the solution back.to-the_ZOOO-ml. graduate - éhd allow the precipitate to settle fof two'hoursb., 5. Siphon off the supernate to within 106 ml, of the precipitate in the bottom of fhe cylinder and discard the supernate.- :6. Transfer.the precipitafe to fwb 250=ml, centrifuge bottles and centrifuge for 15 minu;es; - 7. Siphon off the pupernate from the bottles and discard. | | 8. Dissolve the precipitate in one of the bottles with five ml. of C6ncentratéd HHO3 and combine this solution with the precipitate in:;he other bottle, - 9. Wash the emptf centrifuge:bottle with Héo afid add " to the second centrifuge bottle containing the precipitate, Dllute the precipitate to 100 ml. with'Hzo; | --10. Stir the solution in the éentrifuée bottle until all the precipitate_is dissolved and then add ten ml. of concentrated,NHaofi. Stir ffir five mifiutesf- - 11. Centrifuge for 15 minutes, siphon off,'énd'discard the supernate, B | 12. Redissolve the precipitate in 25 ml. of concentréted HN03. When thelprecibitate has dissolved, transfer the solu- tion to a 100-ml. beaker. Rinse the qentrifuge bott}e with ‘two 3-ml. portions of HNO3 and add to the beaker. " 13, Evaporate fhe HN03 éolfition'on a hot-platg to 3-5 c ml. . Allow to cool. Procedure 17 (Continued) 14. Add 2 mg. of Ce as Ce(NO4),; to a 50-ml. centrifuge tube. 15. Dilute the solution in the 100-ml. beaker with approximately 5 ml. HZO, swiri, and transfer to the 50-ml. centrifuge-tube containing the Ce. 16. Rinse the 100-ml. beakér with two lO-mi. portions of Hy0 and add to the centrifuge fube.' The totai volume in ‘the centrifugé tube should not exceed 30 ml. | 17. Add two drops of methyl orange indicator'and,'while stirring, adjust to pH 4-5 wilth NH40Hd. Stir for 15-minutes. 18. 'Centrifuge five minutes and discafd the supernate, ) 19. Rinse the sides of the centrifuge tube.with 20 ml. of 2 N HCi. Any precipitate clinging to the stifring rod used in Step 17 ghould be rinsed off with 2 N HCl into the centrifuge tube. 20. Rinse the sides of the centrifuge tube with five ml. of H,0 gfid add one drop of methyl orange_indicétor. 2l. Adjust to pH 4~5 vhile stixting,by the dropwlse addi- tion of concentrated HN4OH. Stir for 15 mifiutes. 22. Cefltrifuge fotjfive minutes.and_discard the supernate. 23. Cover fihe precipitate with 10 mi; of 1% NH,Ho PO, and stif until the slurry is homogeneous;__Cent:ifuge the precipitaté and discard.;he wash. | | 2@. _flbunte the précipitate; as a slurry in approximgtelf 2 ml. of Hy0, on a stainless steel disk. Ignite the samfile for 15 seconds over a Meker burner and count in_a:low back=- ground alpha counter. 63 Procedure 17 {Continued) ° Footnotes to Procedure A - ApH of 9.0 or greater 1is desiréd. 1f necessary, add 5-ml. portifins of concentrated NH,OH untill u?ine is at pH 9-10. | | o b - If at the end of two hours the precipitate 1e gredter than 350 mlfi; éllow it to settle until'fhat volume is reached. Occdsionall&,.the preéipitate may setflé to less than 100 fii. When this is the case, retu;fi the suspension to the 53060-m;. beaker, add concentrated HNO, until the solufiipn 1ls clear, then add iOO mg. of da as Ca(N03)27 _Re?eat the addition of Nfladfl, gtir, and return the suspension to the 2000-ml, graduated cyiinder. Allow the precipitate to. settle for two hours. - | c - If the solution boile dry, fediasolve in 5 ml, of concentrated HN03 . | d - It has been_ffiund that Pa will co-precipitaté with Ce Better from solutions of high salt concentrations. :The high salt:cohéentrétlon at tfiis_point necessltates a certain amount of caution on the part of the operator. The adjust=- ment of the pH with NH;OH gust be dohé.slowly,.gr large amountQ of Ca salts may.be precipitated along with the Ce. - It 15 recomnended that the following procedure be used in adjusting the pH: While stirring vigorously, add the con=- cénfrafed NH,OH one drop .at a time from a dropping bottle, _allowing the particles forméd to diaaipgté-béfore makiné the next addition. Add 10-15 drops in this manner. :Continug 6 Procedure 17 (Continued) adjusting the pH by adding 3 N NH,OH dropwise until the end- point is near. Complete the pli adjustment with 1 N NH,OH and, if neceséary, 1 N HNOs3. | e - Samples are-mounted on. stainless steel digks 1-7/8 inches in diameter and 0.018 inch thick. Beforé use, the disks are washed in a solutioq'of a déte:gent, rinsed in wéter, and dried. Since aquéous solutions-ao not spread fiell on bright staifiless steel, the disk is held in the flame of a Meker burner until the surface is slightly oxidized - (color of brass). The disk is allowed to cool énd a ring ofl -Zapon lacquer or collodion, 2-5 mfi. wide, is applied with a brush to the outer edge. The lacquer is dried under an infra- red lamp, and the disk is allowed to cool.- The CePb4 slurry is then transferred with the aid of a transfer pipefi'to_the area within fhe'lacquer ring. As many as three'one-ml. water washes may be added without danger of overflowing. fl(ngigugzlg_yg;gf - The éerium used in this urinalysis_pro- :éedure should have a radiochemical purity of one count pér hour per milligram; At Mound Laboratory the cerlum islpuri- fied by a solveqt-extraction method. Yields of greater fhan ‘90 per cent are exfiected.) VIL. ' APPENDIX Summary of the Protactinium Project at Mound Laboratory The production of approximately one gram of protactinium-231 at Mound Laboratory is dwarfed in significance by the fact, 65 noted elsewhere in this report, that approximately 100 grams ~of this nuclide'waé_recently isolated in Great Britain. Nevertheiess,_it seems worthwhile to describe the operatipn at this LabdratOry for its historical value as well as for the .additional chemical insight aff&rded by the various steps in 'tbe process. It 1ls especially nO;eworthy that.at no point in the.proceas was it found necesséry, or even desirable, tb use fluoride for the solubilization of the protactinium. The protactinium project waé initiated in-1954 at the ;eqfiest of Oak Ridge National Laboratory for tfie.pu:pOSe,of obtaining. a supply of pfétactinifim which could be used to study its macrochemical properties. | The best afgilable source was a resifiué which could be filtered from the aqueous raffinate resulting from the diethyl ether extraction of uranium,. The residue, whose_mdjqr constituents were iron.'aluminum, caicium? magnesium, cbbélt, and copper, ‘contained approximately 0.1 to 0.2 ppm of protactinium. A process was developed and réported6o which gave good recoveries “and purity on a microgram scale, The process consisted of dissolution in 1 N HCl, saturation with NaCl, and boiling to coagulate a small precipitate, which'consisted principally of calcium and silica, and which carried protactinium quantita- tively. The precipitate was digested with NaOH, to remové silica, and the hydroxide reaidfie was dissolved in 9 [ HCIL, The solution was passed through an anion exchanger, leaving protactinium on the resin. The protaétinium was eluted with a mixture of HC1 and HF. On the basis of the apparently simple and inexpensive process, 20 tons of raw material was obtalned from the uranium refineryw Inasmuch as the filtratlon of the precipitate from the aqueous waste stream was not a normal part of the treatment of the. aqueous waste, no stockpile was available, and the raw material was obtained from the then-current refinery operations. When received at this Laboratory (in 80 steel drums) it was obvliously inhomogeneous; the color of the material ranged from a light tan to the dark reddish-brown of ferric hydroxide. Spectrographic analysis confirmed that the material was sig- nificantly different in composifiion from the samples previously received for analysis and process development. Typically, iron was a major constituent, and the aluminum and calcium previously found were either absefit or reduced to minor con- stituents. No two drums contained raw material of identical composition. A single drum was selected which appeared to be intermediate in composition, and optimum conditions for the dissolution and precipitétion of the protactinium were deve10ped61. Plant operations were then begun. The material in the selected drum behaved exactly as predicted, as did one or two other batches. However, the inhomogeneity of the raw material quickly became evident wfien the protac- tinium either failed to dissolve quantitatively in the selected acid (2 N HCl) or, after dissolving, failed to pre- cipitate when NaCl was added and the solution boiled. 67 Since of the 20 tons of raw matefial available, only about half would Be needed to fulfill the commitment for one gram of protactinium, batches were selected on the basié of the solubility of protactinium in 2 H HCl. Simultaneous analyti- cal and process development fSée Procedure 10) showed that the precipiltate which carried protactinium from the NaCl solutlon was nét, as préviously thought, a calcium silicate, but T10,+xPO;, and that the coprecipitation could be made quantitative by addition of TiClj to the HCl solution. (The raw material contained sufficient nitrate ion to oxidize the Ti*3, Precipitatiofi of Ti'3 is incomplete and excessively slow in the presence of ferric ion.) Therefore, failure of the protactinium to coprecipitate quantitatively was corrected by the expedient of adding TiCl; to the process solution. (It was subsequently found that those batches in which prot- actinium failed to dissolve easily were phosphate-deficient and probably required much higher acidities to solubilize the iron. In addition, the protactinium was prbbably held in an insoluble condition by the more refractory Ti0, and Nb,0s.) The NaOH metathesis of the protactiniferous precipitate, which was called for by the original process, produced a residue which was only partially soluble in 9 § HCl, and the protac- tinium which did dissolve.hydrolyied-élowly and reprec¢lpitated. 1t was,_therefqre, not suitable for use as an anion exchange feed solution. Dissolution in HF and separatioh of the iron on an anion exchangérso was found to be impractical because of the excessively large quantities of iron which had to be removed. 68 However, a slurry of the hydroxide residue in 6 N BC1l could be extracted with diisobutyl carbinol (DIBC) diluted to 50 per cent with Amsco kerosené° If the dissolution and extrac- tlon were carried out shortly after the NaOH treatment, about 80 per cent of the protactinium could be extracted before hydrolysis produced "inextractable" protactinium. It is note- worthy that the presence of large amounts of iron decreases the rate of hydrolysis of protactinium in HCI. After extraction by DIBC, the aqueous raffinate was allowed to settle, and the supernate was discarded. The insoluble residue was retained for further processing with H,80,-HC1 (Procedure 10, Step 3). The crganlc phase was strippéd with two successlve portions of one-tenth its volume of water. Although considerable iron was separated by the coprecipita- tion.of protactinium on Tl from HCl solution, the iron which remained was extracted by DIBC and stripped along with the protactinium. When attempts were made to concentrate the protactinlum by recycling through DIBC, it was found that, in high concentration, iron was extracted preferentially and limited tfie degree of protactinium-concentration which could be achieved. The strip solution was made 5-6 N in HCl and extracted with isopropyl ether, which removed a large, but undetermined, percentage of the iron with a loss of oniy about one per cent €9 of the protactinium. Higher HCl concentrations drove more iron into the organic phase, but the loss of protactinium became prohibitive. The aqueous phase was adjusted with H,50, and HCl, and the protactinium was extracted in pIBCO2, The organic phase was stripped with one-tenth its volume of 30% Hy0,. The strip solution was adjusted to 9 N HZSO4 - 6 N HCl, and the protactinium was re-extracted in DIBC, After four cycles of extraction and stripping, appro#tmately one gram of protactinium was concentrated in fractions totaling less than one gallon of aqueous and organic solutions. The work was interrupted at this point and was not resumed for more than a year. By that time, all of the protactinium had hydrolyzed, affording further separation from iron. Dis- solution in H580, and extraction in DIBC yielded 660 ml. of organic solution containing approximately 900 milligrams of protactinium. A spectrographic analysis of the first concen- trate is glven in Table IV¥*, It was apparent that the principal impurities were irom, phosphate; and niobium. The presence of bismuth was highly questlonable, and no specific effort was made to separate it or any of the other reported impurities. Analysis of the final product confirmed fhe validity of the decision. * = The spectrographic analyses were made by Mr. D, L, Roesch of Mound Laboratory. TO Pa S1 Mg Fe Al T1 ~ Be Cu TABLE 1IV. Aud Pt a4 = :]:50%. b - By gamma counting. First Concentrate Per Cent 1.7 0.02 0.42 4.3 0.02 1.97 0.02 0.06 6.58 0.002 0.06 0.26 4,02 Possible Fe interference. Probable Nb interference. SPECTROGRAPHIC ANALYSTS OF PROTACTINIUM2 Final Product —Fexr Cent 65 0.008 0.15 Development of purification methods proceeded concurrently wlth the purification itself, so that, by the time a method had been developed which could be used routinely, nearly the entire batch had been partially purified. It was found that methods which were effectlve at one level of purity were elther partially or totally ineffective at thé next higher level, so that no one method was ever developed which could, with cdmpleté confidence, be used at all stages of the purification. For example, in a typical series of experiments, 25 ml, of DIBC containing Fe, Nb, and about 35 mg. of Pa was stripped with an aqueous 501ution which was 4 N HCl and 10% Hy05. The volume ratio of the phases was varied, and the course of the iron separation was followed with the aid of Fe’? added as a tracer. The percentage of Pa stripped rose sharply with increasing aqueous volume and reached a plateau of 98% at an aqueoug-organic ratio of about 0.15, The amount of Fe stripped also increased, but less sharply, so that, at a volume ratio of 0.14, 95.67% of the Pa was stripped with 2.0% of the Fe. However, when the organic phase was stripped a second time with fresh strip solution in the same ratio, the aqueous phase contained almost 20% of the Fe. 1t is evident that, in solutions of relatively high concentra- tions, the degree of separation by solvent extraction is governed by the relative solubilities of the metal ilon com- plexes in the aqueous and organic solutionms, ratfier than by their individual distribution coefficients. This contrasts with their behavior in more nearly ideal solutions. The HCl-H,0, strip gave no separation from Nb. However, after addition of HZSO4 to the strip solution, the Pa was re- T2 extracted with DIBC, and apprqximatelj half of the Nb remained in the aqueous phase with less than 6% of the Pa. Spectrographi¢ analysis showed that 75% of the phosphorus had | been removed. The intermediate product consisted of 835 mg. of protactinium in 150 ml. of DIBC. The iron-laden organic and the niobium-laden aquebus raffinates were retained, and the protactinium was subsequently recovered and purified. A second, ‘and far more effective, Fe separation was discovered at a later stage in the purification: When 10 ml. of DIBC containing Pa, Fe, and Nb was stripped with a mixture of 4.5 ml. of 18 N H,80, and 0.5 ml. of 30% H,0,, the organic phase retailned 627% of the Nb and 1007 of the Fe, whlle 1007 of the Pa passed into the aqueous phase., The Pa was reextracted into DIBC after addition of HCl to the aqueous phase. Attempts to separate Nb from Pa by stripping the organic solu- tion with an HCl/H20204 mix'ture63 were unsuccessful so long as both elements were present in relatively high concentrations. With the bulk of the Nb removed, the efficlency of separation was lmproved, but was still not completely satisfactory: 1In a single pass with equal volumes of organic and aqueous phases, a mixture of 5% H,C,0, and 6 N HCl stripped out about 70% of the Nb and about 57 of the Pa. When Fe(III) was present to a eignificant degree, the H2C204/HCI strip was almost totally ineffective. A batch countercurrent method was developed which stripped the Nb from each batch of organic solution with three separate T3 portions of the HyCp04/HCl mixture. About 957% of the Nb was removed in the aqueous phases, with about 5% of the Pa. The aqueous phase was diluted with an equal volume of H,0 and heated for 10 minutes at 90°C. Protactinium precipitated, leéving Nb and Fe quantitatively in the supernmatant solution (ef. Ref, 23). The preclpitate was centrifuged, and the Pa was redissolved in H,S0, and extracted with DIBC. Another separation of Nb from Pa, based on the hydrolytic precipitation of Pa from acid oxalate solution, comnsisted of stripping the DIBC solution with 10% H20204 which was 1L N in HCl, A precipifiate irmediately appeared in the aqueous phase, and was found to contain all of the Pa and 207% of the Nb. The precipitate, on being heated with fresh strip solutionm, dissolved almost completely, but a new precipitate formed in a few minutes. The new precipitate contained all of the Pa, while Nb remained quantitatively in solution. The precipita- tion of Pa was somewhat erfatic under these conditions, but could be made quantitative by the addition of one drop of 857% H3P04 to 10 ml, of the oxalate solution. Eliminatioq of phosphate ion was achleved by precipitation of protactinium iodate from dilute H2504. The Pa was stripped from DIBC with 5 N H2504, and the solution was diluted with H,0. The solution, containing 120 mg. of Pa in 35 ml. of 1.4 N HyS0,, was warmed on a water bath. Protactinium lodate was precipifated by the dropwise addition of 15% HIO3. The pre- cipitate was cooled, centrifuged, and separated from the Th supernatant solution. The solution was gamma-counted and contained the equivalent éf between 0.1 and Q.S mg. of Pa, However, gamma-ray spectrometry showed that the gamma activity came almost entirely from actinium~227 and its decay products; the 27-kev gamma peak of protactinium-231 was completely absent. The protactinium iodate was digested with concéntrated HC1 and wafmed gently until gas evolution ceased. The Pa dis- solved initially, but reappeared shortly as a flocculent precipitate, which was centrifuged, washed, and dried at-110°C. A spectrographic analysis of the hydrous oxide is given in Table 1V. Approximately 0.5 g. of Pa was ignited to the pentoxide at 675°C. An x-ray powder pattern showed that the crystal struc- ture corresponded to that of cuble Pa205'12*° The heat output of the Pa205 was measured 1ln an isothermal calorimeter**, and the half-lite of Pa23l yas found to be 32,4801260 years, after correction ffir chemical impurities and decay products. Details of the half-life measurement will be reported in the near future. As a result of chemical operations at Mound Laboratory thus far, approximately 700 milligrams of chemically and radio- * - The crystallographic patterns were analyzed by C. R. Hudgens of Mound Laboratory. *% - The calorimetric measurements were made by K. C. Jordan of Mound Laboratory. 13 chemically pure Pa?3l has been produced. An additional 250 milligrams has been recovered from residues, raffinates, and other process wastes and is now being purified. T6 REFERENCES Ha1551nsky, M. and Boulsgleres, .y Erotactinium, Nouveau Traité de Chimie Minfrale, XI1, pp. 617-680, ed. by P. Pascal; Masson et Cie., Paris (1958) (This should be required reading for anyone working with protactinium. The bibliography, containing 165 references, is complete to November 1, 1957.) Salutsky, M. L., Protactinium, Comprehensive Analytical Chemistry. Vol. I, Chapter 1V, Section 44, 11 pp., ed. by Cecil L, Wilson; Elsevier Publishing Co., Amsterdam (In Press). (Primarily devoted to analytical aspects. &9 references. ) Katzin, L. I., editor, Production and Separation of U233, Collected Papers, U. S. Atomic Energy Comm. TID«5223, 728 PP. in 2 vols. (1952). Available at 33.25 from Office of Technical Services, Dept. of Commerce, Washington 24, D. C. (79 papers devoted to thorium, protactinium, and uranium chemistry, radiochemistry, separations, and nuclear characteristics. Not a true review, but a valuable collec- tion of research papers and data.) Gmelins Bandbuch der ancrganischen Chemie, Frotgectinium und Isotope, System Number 31, 99 pp., Verlag Chemie, G.m.b.H., Berlin (1942). (Reviews the literature to 1940,) Elson, R, E., Thg Chemigtrv of Protactiniium, The Actinide Elements, Chapter 5, pp. 103-129, National Nuclear Energy Serieg, Divigion IV, Plutonium Progevc Record, vol., l44A, ed. by G, T. Seaborg and J. J, Katz, McGraw=Hill Bocok Coe, New York (1954). {69 references, the latest original reference being dated 1931.) Hyde, E. K., Radio; dcsi Separationz of the Actinide Elements. Ibid., Chapter 15, ppa 542=95, therature Survey on: 1. The Chemistyy of Actinium and Protactinium -= Especiglly in Aqueous Solutiong. 7T 10. 11, 12, 13. 14, 15. 16. 17. 18, 19. 20. 21. 22. 23. 24, 2. DflL::mina;iQn_9i_Asnininm_flndhzznnassinium 3. Iech- . Anon., Atomic Energy Commigsion, Tel-Aviv, Israel, LS-6, 34 pp. Strominger, D., Hollander, J. M., and Seaborg, G. T., Revs, Mod Phys. 30, 585=904, April, 1958. Zijp, W. L., Tom. Sj., and Sizoo, G. J., Physica 20, 727-35 (1954), Maddock, A. G., Private Communication, September, 1959. Grosse, A. V. and Agruss, M., J. Am. Chem. Soc. 3§, 2200 (1934). _ Sellers, P. A.,, Fried, S., Elson, R. E;, and Zachariasen, W. H,, J. Am. Chem. Soc. 78, 5935 (1954). Ferradini, C., J. Chim. Phys. 53, 714 (1956). Thompson, Roy, U. S. Atomic Energy Commission Report AECD-1897 (1948). (Also reported in TID-5223, p. 294 - See Section I., General Reviews.) Kirby, H. W., Unpublished Work. Burgus, W. H., Private Commmication, October, 1959, Hardy, C. J., Scargill, D., and Fletcher, J. M., J. Inorg. Nucl, Chem. 7, 257-275 (1958). Goble, A., Golden, J., and Maddock, A. G., Can. J. Chem. 34, 284-292 (1956),. Casey, A, T. and Maddock, A. G., J. Inorg. Nucl. Chem. 10, 58-68 (1959). Haissinsky, M. and Bouissidres, G., Bull. Soc. Chim. France, 1951, 146-148, No. 37 (AEC-tr-1878). Golden, J. and Maddock, A. G,, J. Inorg. Nucl. Chem. 2, 46-59 (1956). : Grosse, A. V., J. Am. Chem. Soc. 52, 1742-47 (1930). Bouissiéres, G. and Odiot, S., Bull. Soc. Chim. France, 1951, 918-19, (5) 18. Katzin, L. I. and Stoughton, R. W., J. Inorg. Nucl. Chem. 3, 229-32 (1956). 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 3é6. 37. 38. 39. 40. 41. 42. 43. Kraus, K. A. and Van Winkle, Q., U. S. Atomic Energy Commission Report ORNL-239. (See also TID=5223, paper 6.11, p. 296.) Goble, A. and Maddock, A. G., J. Inorg. Nucl. Chem. 7, 84 (1958). Goble, A., Golden, J., Maddock, A. G., and Toms, D. J., Progresg in Nuclear Epergy --ILI, FProcess Chemlstry 2 pp. 86-98, Pergamon Press, London (1958). Nairn, J. S., Collins, D. A., McKay, H. A. C., and Maddock, A. G., 2nd U. N, Intl. Conf. on Peaceful Uses of Atomic Energy, A/CONF.15/P/1458 (May, 1958). Peppard, D. F., Mason, G, W., and Gergel, M. V., J. Inorg. Nucl. Chem. 3, 370-78 (1957). Moore, F. L., Anal. Chem. 27, 70-72 (1955). Moore, F. L., Ibid. 29, 1660-62 (1957). Fudge, A. J. and Woodhead, J. L., Chem. and Ind., 1122 (1957). Oliver, J. R., Meriwether, J. R., and Rainey, R. H. U. S. Atomic Energy Commission Report ORNL-2668 (Aprll 1959). Kraus, K. A. and Moore, G. E., J. Am. Chem. Soc. 72, 4293-94 (1950). Kraus, K. A. and Moore, G. E., Ibid. 73, 2900-2 (1951). Kraus, K. A. and Moore, G. E., Ibid. 27, 1383 (1955). Kraus, K. A.,, Moore, G. E., and Nelson, F., 1lbid. 78, 2692-95 (1956). Maddock, A. G. and Pugh, W., J. Inorg. Nucl. Chem. 2, 114=17 (1956) Kahn, S, and Hawkinson, D. E., J. Inorg. Nucl. Chem. 3, 155-56 (1956). Barnett, M. K., J. Inorg. Nuecl. Chem. 4, 358-66 (1957). Lederer, M., J. Chromatography 1, 172-78 (1958). Jakovac, Z. and Lederer, M., Ibid. 2, 411-17 (1959). Vernois, J., J. Chromatography 1, 52-61 (1958). Camarcat, M,, Boulssidres, G., and Haissinsky, M., J. Chim. Phys. 46, 153-57 (1949). 79 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55, 56. 57. 58. 59. 60. 6l. 62. 63. Ferradini, G. and Haissinsky, M 1., Ibid. 533, 722- 25 (1956). Ferradini, C., Ibid. 50, 589-90 (1953). Danon, J. and Ferradini, C., Compt., rend. 234, 1361-63 (1952). Guillaumont, R., Muxart, R., Bouissidres, G., and - Haissinsky, M., Compt. rend. 248, 3298-3400 (1959). Fried, S. and Hindman, J. C., J. Am. Chem, Soc. 76, 4863-64 (1954). Brown, D., Smith, A. J., and Wilkins, R. G., J. Chem. Soc. (1959), 1463-66. Miles, F. T. Heus, R. J., and Wiswall, R. H., Jr., U. S. Atomic Energy Commission Report BNL 482(T-109), (Nov., 1954). Hyde, E., K., U, S. Atomic Energy Commission Report UCRL-' 8703, p. 6 (1959),. Hahn, O, and Meitner, L., Ber. 32, 1812 (1919). Kraus, K. A, and Van Winkle, Q., U. S, Atomic Energy Commission Report CC-3365X (June 30, 1945). (Also see TID-5223, paper 6.2, p. 259 (1952). Ong Ping Hok and Sizoo, G. J., Physica 20, 77 (1954). Heath, R. L., U. S. Atomic Energy Commission Report IDO-16408 (July, 1957). Mc Isaac, L. D., and Freiling, E. C., Nucleonics l4%, No. 10, 65-7 (1956). Fudge, A. J. and Woodhead, J. L., Analyst 81, 417-26 (1956), Van Winkle, Q., Larson, R. G., and Katzin, L. I., J. Am. Chem. Soc. 71, 2585-86 (1949). - Salutsky, M, L., Shaver, K., Elmlinger, A., and Curtis, M. L., J. Inorg. and Nucl. Chem. 3, 289 (1956). Barnett, M. K. and Elmlinger, A., Unpublished Work. Jones, L. V., Unpublished work. Moore, F. L. and Reynolds, S. A., Anal. Chem. 29, (1957). (Also see Procedure 1l4.) Bibliography closed December, 1959, 80 USAEC Offica of Technlo! Information Exterslan, Ock Ridge, Tennames