NAS-NS-3060

RA OF NEPTWWM’I

NUCLEAR SCIENCE SERIES

National Academy of Sciences-National Research Council

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HADIOCHEMISTRY OF NEIPTUNIIUM

by

G. A. krney and R. M. Harbour

Savannah River Laborat cIry E. 1. du Pent de Nemours, G Co. Aiken, South Carolina U3801

Prepared for Subcommittee on Radiochwnktry National Academy of Sciences - Nationa I Research Council

IssuancffDate: Dacewnber191~1

Published by Technical Information Center, office of Information Sewices lu~lTE~ STATES ATOMIC ENERGY (:OMMl:~l(JN This paper was prepared in connection with work under Contract No. AT(07-2)-l with the U. S. Atomic Energy Cmaission. By ●cceptance of this paper, the publisher and/or recipient acknowledges the U. S. Government’s ri[~ht to retain a non- exclusive, royalty-free license in and to any copyright cover- ing this paper, along with the right to reproduce and to authorize others to reproduce all or part of the copyrighted paper.

-.,.-...... —...—~-*~mdM--- ,,———. .- —--- Foreword

The S&committee on Hadmchemiswy is one of a number o’f iubcommitmes working under tl~e Committee on Nuclear ‘Sciencewithin the Natmnal Academ} of Sciences-National Research Counci 1. i!s members representgovernment, industrial and (UniversityIaboratories in Ihe areas of rrucfmr chemistrvand analytical chemistry. The Subcommittee has concerned itwlf with th~ are,~ of nuclear science which revolve the chemist. such as the collectmn and distribu$eon ID”radiochemlcal procedures, the rtitochemicai purity of reqpnts. the piace o! radiochmnistry in college and university PfOiFams.and radiochemistrv in environmental soence. Th!mseries of rnmwxyaphs has qown out of the need for cornpilat!ons of radiochemical information, procedures. and techmques. The S@committew has endwvored to present a serws that will b d maximum use to the working scientist. Each monogrwh presents pertinent information rmqwredfor radiochcrnical work with an indivm!ualelement or with a specialized technrque. Exprts in the Particulu radmcfwrnical technique have vvrittm the monographs. The Atomic Eneruv Commission has sponsod the printing of tht sems. TM Sukomrrtittee is confident these publications will te useful not only to radiochemmts but ahio to rtrwarch workers in other fiefds such as phvsic$.b ochemistrv. or nwdlcine who wish tow radiochemicat tswhniques to solve specific problems.

Gregory R, Chopp in, Chatrman %bcomm!twe on Radlochemis!rV

“l- CONTENTS Paqe

I. General Review of the Inorganic and Analytical Chemistry of Neptunium ...... s

11. General Review of the Radiochem.istry of Neptunium ...... 7

III. Discovery and Occurrence of Neptunium ...... 8

Iv. Isotopes and Nuclear Properties of Neptunium . . . 9

v. Chemistry of Neptunium ...... 12 A. Uetallic Neptunitm ...... , ...... 12 A.l Preparation ...... 12 A.2 Physical Properties ...... 12 A.3 Chemical Properties ...... 14 B. Alloys and Intexwtallic Cmpmds ...... 14 c. Coqmunds of Neptunim ...... 16 D. Neptmium Ions in Solution ...... 20 D.1 Oxidation States ...... ,.. . 20 D.2 Oxidation-Reduction Reactions , . . . . . 24 D.3 Dispmportionatim of Neptunitm . . . . . 24 D.4 Radiolysis of Neptunium Sslutions . . . . 29 D.5 Hydrolysis of Neptunim ...... 31 D.6 Ccqlex Ion Fomation ...... ,.. . 33

VI. Preparation of Neptunim Sa@es for Analysis . . 39 A. Neptunium Metal and Alloys ...... 39 B. Neptunim Co~ds ...... 39 c. Biological and Environmental S.qles . . . . . 40

VI1. Separation Methods ...... 4) A. Coprecipitation and Precipitation...... 41 B. Solvent Extraction ...... 54 c. Ion Exchange ...... 88 D. Chrowtography ...... 104 E. Other Methods ...... 107

VIII. Analytical Methods ...... 109 A. Source Preparation and Radiow:ric Methods . . 109 B. Spectmphotometry ...... 114 c. Controlled Potential Coulomet~/ ...... 119 D. Polarogmphy ...... 121 E. Titration ...... 123

-2- PaiJg

F. Emission Spectrometry . . . , ...... 124 G. Gravimetric Methods ...... 12s H. Spot Tests ...... “.,.. . . 127 1. Mass Spectrometry ...... , ...... 129 J. X-Ray Fluorescence Spectrometry ...... 129 K. Neutron Activation ...... 130 L. Other Methods ...... 131

IX. Radioactive Safety Considerations ...... 132

x. Collection of Procedures . . . . . ,...... 134 A. Introduction . . ., ...... ”. . . . 134 B. Listiniz of Contents ...... ,. 134 Procefiiire 1. Separation of NF1by lTA Extraction ...... 138 Procedure 2. Separation of P@ by TTA Extracti(nl ...... , . . . 141 Procedure 3. Determination of 23’Np j.n Samples (kritaining LIBPu, and Fission Products . . . . . , . 14s Procedure 4. Determination of Np ...... 1so Procedure 5. Determination of Small Amounts ofNpinPuMetal ...... 1s5 Procedure 6. Determination of Np in Samples Containing Fission Products, U, and Other Actinides ...... 1S8 Procedure 7. Detensination of Np in Samples of U and Fission Products . . . 161 Procedure 8. Extraction Chromatographic Separation of 23%p from Fission ami Activation PTO- ducts in the Determination of Micro and !’@-microgram Quantitie:3 ofU . . . . ,, . . . 163 Procedure 9. Separation of U, Np, Pu, and Am by Reversed Phase Partition Chromatography . . . . 16S Procedure 10. An Analytical Method for .2;7NP. Using Anicm Exchange . . . . . 167 Procedure 11. Separation of U, Np, and Pu Using Anion Exchange . . . . . 169 Procedure 12. Separation of Zr, Np, and Nb Using Anion Exchange . . . . . 171

-3- . . .

*

Procedure 13. Separation 0. Np and Pu by Anion F.change ...... 173 Procedure 14. Separation of Np andl Pu by Cation Exchange . .’. . . . . 175 Procedure 15. Separation and RadiQchemicaI Determination of U and Transuranium Elements Using Barium Sulfate ...... 176 Procedure 16. The Low-Level Radio:hemica~l Determination of 23’Np in Environmental !hmplos ...... 179 Procedure 17. Radiochemical Procedure for the Separation of T::ace Amounts of 237Np fn)m Reactor Effluent Mater . ,, ...... 184 Procedure 18. Determination of ~ in Urine . . . I 86 Procedure 19. Determination of 2’1:’Npby Ganma Ray Spectrometry ., ...... 189 Procedure 20. Spectrophotometric [letermi- nationofNp ...... 193 Procedure 21. Microvoltnetric Coqlexometric Method for Np with EDTA ...... I 97 Procedure 22. Photo~tric Determination of ,h@as the Peroxide Complex . . . . 199 Procedure 23. Separation of Np for Spectrographic Analysis of Impurities ...... , . . . . 201 Procedure 24. Photometric Determination c)f Np as the Xylenol Orange Complex...... ,. 204 Procedure 25. Analysis for Np by ICmtrolled

Potential Coulometry . . . . . ,“ 206

References...... 209

-4- RADIOCHEMWTRY OF ~dEPTUNllUM*

by

G. A. Bumq’ and R. M. Harbcmlr

Savannah River Laboratory E. 1. du Pent de Ncanurs & Co. Aikan, South Carolina 29801

I. GENERALREVIEWOF THE INORGANIC#J’4DANALYTICALCHEMISTRYOF NEPTUNIIB!

1. J. J. Katz and G. T. Seaborg, The Chemh?tw of the Actinide Eh???IQnt8, Chap. VI, p 204-236, Johm Wiley and Sons, Inc. , New York (1957).

7 e. C. F. Hetz and G. R. Waterbu~y, “The Transuranium Actinide Elements,” in 1. M. Kolthoff and F. J. Elving (Ed.), Treati8e on AnaZyticc~l Chemistry of the Eze?TW?Zt8, Volume 9, Uranium and the Ac!iinide8,, p 194-397, John Wiley and Sons, Inc., New Ycl~k (1962).

3. “Neptunium, “ in P. Pascal (Et.), Noxveau Trvri:e C& Chimie Minerale, Vol. XV, Trcnaurankns, p 237-324, Masson et Cie, Paris (1962].

4. “!leptunium,” in P. Pascal (Et.), No:xtwzu Traite de Chinrie Minerakz, Vcl. XV, Trcnauraniee8 f’Supplement), p 1-91, Masson et Cle, Paris (1962).

.5. Il. B. Cunningham and J. C. tlindman, “The Chemistry of Neptunium,” in G. T. Seaborg and J. J. Katz [Ed.), The Actinide Elements, p 456-483, Vol. 14A, Chap. 12, McGraw- Hill Book Co., New York (19$4:).

%e information=ontained in this axticle was developed during the course of work under Contract A’1(07-2)-1 with the U. S. Atomic Energy Commission.

-5- 6. J. C. Hindman, L. B. Magnusson, end T. J. LaChapelle, ‘Chemistry of Neptunium. The Oxidation States of Nuptunium in Aqueous Solution,” in C. T. Seeborg, J. J. Katz, and W. M. Manning (Ed.), The !l”mmeurunin Ekmenta, p 1032-1038, Vol. 14B, McGraw-Hill Eook Co. , New York [1949) .

7. J. C. Hintian, L. B. Magnusson, and T. J. LaChapelle, ‘themistry of Neptunium. Absorption Spectrm Sttiies of Aqueous Ions of Nept~ium, ” in G, T. Senborg, J. J. Katz, and W. H. Manning (Ed.), The f’mneumniaun EZenm~, p 1039-1049, NcGraw-Hill Book Co., New York (1949).

8. L. B. Magnussat, J. C. Hindman, and T. J. LaChapelle, “Chemistry of Neptunium. First Prqamtion and Solubi li - ties of Some Neptunium C~mds in Aqueous Solutions, ” in G. T. Seaborg, J. J. Katz, and W. ht. Manning (Ed.), The !l’raetiun EZmente, p 1097-1110, McCrau-Hill Book Co. n New York (1949).

9. S. Fried end N. R. Davidson, ‘me Basic Dry Chaistry of Neptuni~, “ in G. T. Seeborg, J. J. Katz, and W. M. Manning (Ed. ), The ~wn EZ&nants, p 1072-1096, McGraw-Hill Book Co., New York (1949).

10. C. Keller, The Chauiatq of the TM MIUWZ{WI?EZanenti, p 253-332, Verlag Chem.ie, Germany [1971).

L1. G. A. Burney, E. K. Dukes, and H. J, Groh, “Analytical ~%amistry of Ncptuni~, ” in D. C. Stewart and H. A. Eliom (Ed. ), l%vgresin in Rucle~ l?ne~, Seriee IX, Anal@?al C’kmhtry, Vol. 6, p 181-211, Pergmon Press, New York (19M) .

12. J. Korkisch, Mdexm Methode for t?w Separation of Ram?r MetaZ Ione, p 28-196, Pergamn Pre:,s, New York (1969) .

13. J. Ulstmp, ‘Wthods of Separating the Actinide Elements ,*! At. he~~ Rev. 4(4), 3S (1966).

14. A. J. Ibses, The Ana2@imZ c~8ii~ of the Actinide l%mmte, Uacltillan Co., Nw York :1963).

1s. A. D. Gel’man, A. G. Moskvin, L. M, Zaitssv, and M. P. Mefod’eva, “Coqlex Compounds of Transuranides ,“ Israel Pro~am for Scientific Translation j (1967), translated by J. Schmorak.

-6- 16. P. N. Palei, “Analytical Chwmistry of the Actinides,” translated by S. Botcharsky, AERE-LIB/TRANS-787. [See alsoJ. AnaZ. Chin. USSR 12, 663 (1957)]. 17. u%lina Nwuibuch &?P Ano~ar.iachen Ckmie, Vol-me 88 Tranawzne, Part C (1972].

18. &nelina Hwuibuch der Anoqpri8chen Chemie, Volume 8, T~suMe, Parts A, B, and D (1973).

19. V. A. Mikhailov and Uy. P. Novikovp “Advances in the Analytical Chemistry of Nepluniurn [A Review] ,“ J. AnuZ. Chem. USSR 25, 1538 (1970).

20. V. A. Mikhai 10V, Am Z@ica Z Chemiat~ of Neptunium, John Wiley 6 Sons, New York (1973).

21. B. B. Cunningham, “Cheaist~- of the Act~:[ide Elements, ” in AnnuuZ Rev. Nucl. S&. 1+’, 323 (1964).

22. K. K. Bagnell, The Actinide EZement8, Elsevier Publishing co., lmdon (1972).

II. GENERALREVIEWOF THERAOIOCHEMISTRYOF NEPTUNIU4

1. E. K. Hyde, “Radiochemical Separations of the Actinide El~ts,” in G. T. Seaborg and J. J. Katz (Ed.), The AetJnide EZewenta, Chapter 1S, National Nuclear Energy Series, Div. IV, Vol. 14A, McGraw-Hill Book Co., hew York (1954).

2. E. K. Hyde, “Rdiochemical Separations Methods for the Actinide Elements,” lnternationaZ Confemwe on the PeacefuZ Uaea of Atomic lhte~, 2nd Ceneuu, 7, 281 (195S].

3. H. Page “Separation and Purification of Neptunium,” in 2kmeumnienn, p 249-272, Masson et Cie, Paris [1962).

-7- 111. DISCOVERYANDOCCURRENCEOF NEPTUNIUM

Neptunium was discovered in 1940 by NcMillan and Abelson. l

They bombarded a thin uranium foil with low-energy neutrons and showed that the 2.3-day activity tha: was formed was an isotope of element 93 produced by the nuclear reactions:

It was shown in 1941 that the decay product of 23gNp was 239Pu.2

23gNp is produced in large quantities as the intermediate in the nuclear reactor production of 239.*, but because of its short half-life it is used only as a tracer.

Wahl and Seabarg3 discovered the long-lived isotope 237Np in 1942. It was produced by the nuclear reactions:

The first weighable quantity of 237Np (U5 ~g of Npo2) wa5 isolated by Magnusson and LaChapelle in 1944.4 These workers were the first to measure the specific a:tivity of 237Np.

As a result of these reactions, Np is produced in relatively large quantities in nuclear r:actors fueled with natural U. When fuels enriched in 235U ~d 23qJ are used in nuclear reactors, the following reactions are increasingly important.

-8- ..- ......

Since about 1957, the U. S. Atomic Energy Cwmission has

=covered and purified byprmduct Np in its production facilities.

‘a’Np is used as target for the production of 23EPu, an isotope in demand for fueling ~adioisotopic p>wer sources. S

The half-life of ‘J7Np is very shofi compared to the age of the earth. Therefore?, it is found only in trace quantities in U minerals where it is fotmed continuously by neutron reactions described previously.G It vas found that the abundance of 2s’Np in a s~le of Katanga pitchklende was 2.16 x 10-12 atoms per atom of 23%, while that of zss~ was 3.10 x ]0-’2 atoms per atcm of 230u.7

IV. ISOTOPESANDNUCLEARPROP[:RTIESOFNEPTUNIUM

The known isotopes and selected r.uclear prope-ies of

Np are listed in Table 1. The rad.ioar.alytical chemist works mostly with long-lived 2s7Npand short-lived 2’gNp and ‘seNp.

The decay schemes of these wst important isotopes of Np are presented in Figure 1.

Thermal neutrmn cross sections and resonance integrals for Np isotopes are shown in Table 2.

-9- Maa@ Half-lifa 22s= 60sac 224 4.0 tin

2s “%r#,4a)

231 Somm 3.s14 1 10” E a ■ 6.2S ‘S%(d.tia) [email protected]) ‘D%(d.h) 252 13 da 1.s44 I 10” a l’%J[d, Sm) as%(d, h)

2ss Ssda s.117z 10” E “%l[d. h) a(?x 10-’) Ea = S.ss ‘Shl[d, h)

1s4 K ■ 0.0 1s%J[d,5m) ‘e a(clO-’)

2ss 3.1141 10’ m I?a■ S.0SS(48)a%[d,ln) m(%lo-‘ ) S.ols(sst] 4.92s(lm 4.s64(18] 24s 22 h S.m x lo’~ R(O.4S] = O.SII(WI) “’U[d, n) ‘a- 0-(0.s2) o.56(4a) Z“u[m,za) 2s6= ●- fr o- l“U(d.4n) 227 2.14 x 106 yr 1.s64 s 10’ % Ea = 4. 7M(42t) J%lm,h) Sf(s E 10-”) 4.74s(m) “’urm.7)’ 4.764(s8) *s’U(O--dmy) 4.*1(5. it) 4.62d(6t) “lh[a-dacay)

2s4 2.12 day 5.744 1 10” B- = 1.2S(4S11 “’wpm,v) ‘B- 0.26(s48) “%(d.h)

~ ■ 1.027(2SW ‘i%(a,p) 0.965(261) 2ss 2.ss dmy S.la 1 10” = O.?ls(?t) “’U(B.T) o-q ‘n- Sf(a 1 10-”) o.4s7(46u ?’%J(B*Y) o.263(lm O.n?(zrb)

~ ● O.m(ln) o.220(12b) O.llx(mb] = 2.lc[sa) “’u(B-d-y) 24e 7.s da 2.s19 m lo” e- ’13- I.so[nt) 6? mlm 2.s95 s 10” B- = O.m(lwl) ~“u(m.pal 24a ‘B - 241 16 mla 1.a2 z 10” 0- ■ 1..M “’u(m.p) ‘a-

-1o- %p W?*

~ VW

**) m+) Spm Y and panty 3. Vn+l 2. (s/2+) :, sR- 7/2- <.. Ilr# h . l).

-- En9rgY Spm and thv 1 pvlty

ml., 5119 50s3 !m-1 Lgl’1 m. LU9.3 ml-i 3916 ml. }

3301 ?12. 265s Sn. $6375 Wlb

?5 ?! v.?‘ 5727 %2. ? 85 Y1., w?!..

F~glure1. Decay Schemesof the Most hn ~rtant Neptuniun Isotopes,237NP, 238Np,and ‘39Np.8$10

-11- TAOl.E2

CROSSSECTIONSAND RESONANCEtt4TUWtLSa FORNEPTUNIIW ISOTOPES’

Nat mm Cspture Fis! ion ——- — 3“ Nsss NudMm .. ) !.(SLQ “f .k%z!!l 2.34 9cm ?3s 148~

236 i?,8(M)

.!37 1.85 600 0.02 0 o.ol)13~ ;.4$

23a 1.600 600 2,070 ml

2Se [to **’NP) —.— .— a. Cross-sections expressedin barns, 10- Z*C81. tJ. J. H. Lsndru. R. J. Nasle,N. Lindner.W3tL-slZ63(l!l~2). l-. For neutrons with the fission spectnu. ,.i For 3 MN ntmtrms. t?. For ..reactor matrons’..

V. CNEMISTRYOF NEPTUNXLU A. METALLICNEPTUNIUM

A.1 Preparation

Npw?al was first prepartxi by Fried and Duvidsoa in 1948 by the reduction of SO ug of NpFj with M vapor as 1200*C. ti A sitilar method was used by Uestmn snd Eyriq,, L2 Reduction of NpF+ by excess Ca metal with iodine as a bocmter’)- ‘* was used to produce mltigrsa quantities of * metul.

A.i! Physical Properties

Pure Np is a silvery ductile matal with s melting point of 6.3’79C. ?%e =tal undergoes three allotropic modifications below the 9eltin8 point. The physical properties me ~rizsd in Table 3.

-#z” TABLE3 PHYSICALPROPERTIESOF NEpTIJNI~~T~&~’J7*L$

A. Appearance: Silvery white [slowly ccatod with oxidel in dry air ●t rcom toaperature) B. Melting Point: 6376C c. Boiling Point: 417S*c (extrapolated frtm vapor pf;ssun measuremmts of liquid Np )

D! . )ieat of Vaporization: AH 1800”K H 94.3 kcall(g-mm) E. Properties of Various Aliotmpic Mifi-tio-: a B Y Transition teaporature to next higher phase, ●C 280 577 637 !Mtmity, glcm’ (at T*C) 20.48 19<40 18,04 Crystal Structure Orthor- Tw:ragonali Cubic hoabic

Wtphens a’ detmmined tke pressure-taqmmturw relationship for Np. The ~~ific hst (Cp) ofNp fis h!il:h. Thm Duhng and Ptiit walue off W is reached at 140’K and 7,093 cd/(aiol-e8t) at

27”C.*1’ Tbehigh specific Mm can k entiwtly acmuntod for by tho wv bi~ ●lectronic contributions. No imgvutie orderIn8

in a-!tp occurs * to i.7”K.a2 A.3 Chewlcal Properties

HP is a reactive ~tal. The potential Fl>r the couple

NP”~3+ ‘ ~- i$ 1.83 vo~ts. ~ta~li~~ is S~OUIYCOV@* with ● thin oxide layer when exposed to dry air at @out 20”C, and rapid oxidation to Np@ occurs at higher temperatures especially in mist air. Hydrogen, haIogens, phosphorus, and sulfur react with Np metal at elevated temperatures, Hydrogen resets to form the hydride at relatively low temperatures.

F@ ferns intexnetallic compounds of intermediate solid solutions with U, Pu, Se, Al, B, Cd, Ir, Pd. and Rh.

Np dissolves readily in&-Kl at room tmperature andHzS04

●t elevated t~rature. The behavior of l{]) toward various solutions is given in Table 4.

E!.,AL1OYSAND INTERMETALLICCOWOUNDS Co@ete phase diagrams are reported for Np-Pu and N\p-U.23-2c

Complete miscibility has been reported betb’een y-l$p and y-U and between y-Np and Z-PU. Np is a unique elment because of lts emt-ly high volubility in both a-Fu and &.Pu.

The intermetallic co~unds of Np with Al and Be (NpAlz,

~13, NPA1*, and Np8e13) are prepared directlyby reducing NpFq with an excess of metallic Al or Be. The boride:; (NpBz, NpB~,

Npltc, and NPUIZ) and the intennetallic cmrpounds NpCdGand

NpCdlz ●re obtained directly from the e’lments.27-2q Several

-14- . .

TABLE4 BEHAVIOROF NCJMETALIN VARIOU:iSOLUTIONS’1 ObservntIons Solution— ConcentrationW) Initiai——. -— After4 &ys H20 Very slowlyatta:ked

HCla 1.s Irndiate vigorols Coql,ctelydissolved reaction ,, 6 ,, ,, 12 ,, 2 NOvisiblarmction Someturbidity, hydrated oxide 8 ., ,’ 15.7 ,* No reaction- clearsolvent 2.25 Slowreaction So reaction- cl?arsolvent 9 ,, $, 18 NOnoticeable reaction ,, (nlcoot# 2 Slight.initialr*action- someturbidity cessed hydratedoxide 8 ,, ,, 16 NOvisible r.action NO rmction- clearsolution HC104 Cone. Rapid diasoluticn ,!, uha hoatai Iinim CQnc. Rapiddissoluti(m !, whenhosted 14s0Jrw Rapid dissolutkn ,, uhon hooted lConc.HNOS- Dissolution uhal refluxod ** trace HF

‘z. At ambienttaqwratum.

-ls- compoundswith noble metals, such as NpPt3 and NpPt5, have been p’repareti by hydrogen reduction of NpOZ at 1300°C in the presence of platinurn.’” Also, Erdinann31used the same method

10 prq?are several other compounds, NpIr2, NpPd.3,and NpRh3.

(;. CWPOUNDS OF NEPTUNIUM

Cmpounds of Np for the III, IV, V, VI, and VII oxidation states have been prepared. The solubilities anc compositions of some of t’he compounds have not been verified because they were initiallydeterminedwith smaIl amounts offNp shortly after discovery and therefore may be semi-quant:.tative. Uhere studies have “been made with larger amounts of neptunium, i.e., oxalates and peroxides, more quantitive data is available.

Numerous Np compounds, such a$ nitrates, chlorides, and possibly thiocyanates, are readily soluble in s~lvating organic soiverms such as diethyl ether, hexone, TBP, and other acid- contai.ning solvents saturated with water.

l[nvestigation of co~nds containing trivalent rqt.unium has been limited because of the instability of Np(lII]Iin aqueous solution in the presence of atmospheric oxygw. Np(III) is produced mder hydrogen (on ● platinum catalyst), by electro- chemical reduction and with rongalite, IW+SO2.(H2O”2H;1O.Wfod$eva at al.’2 haw prepard several Np(IIl) COWWCIS from Soiution with protection from oxygen. All the reagent solutions and water were

-m- purged with pure argon. The precipitation and subsequent operations (centrifugation and washing) were conducted with a layer of benzene over the solution. rhe solids were washed with acetone or ether and dried in a stream of argon. Np(III) oxalate was prepared, but it was appreciably oxidized in a few hours.

The solid was brown and was in the fo:a of tetragonal prisms.

Np(III) phenylarsonate is rose-lilac t:olored with the composition

NpZ(CGHS~09)S”nHZ0 when well dried; the compound is stable for a long period at room te~rature. Np(III) salicylate and grayish- lilac Np(III) fluoride were also precipitated under controlled conditions. h c~lex double sulfates of Np(iII], KsNp(S06)5 and NaNp(SO~)z-nHaO,were precipitated. In the dry form, these salts were stable to oxidation during prolonged storage even at increased teqerature.

Only one solid coqnmnd of Np(VIl), Co(NH~)GN@S”3Ha0, has been reported.]’

Coqounds of Np(IV), (V), and (VIl are shown in Tables 5 and 6. Table S includes cmpounds prodtied in aqueous solution, and Table 6 includes coqounis produced by other

●ethods.

-17-

,. TABLE5 wPTuN1iMcmoums PRECIPITATED~ A-!; 5MiiTI@l Coqoeition Color _ of 3olution ScJ.ubiliw(mNp/1) B1uk - NaNO, Di!solw.sin either *%; to 9 uid or base

,- gm lM N#Xl - 3t04 34 ~ NaNKiI Greea m Nmat- 2s dilute ~ia Brwn lM Mt,ai - 3s O.w (Mt.]@h Purple 2.W m~ - 1; 36 6.3NH20Z G?~yish O.m W1 - 32 111= O.m HF (mm ●tm) Green lHHNog- 37 M HF Green lNHF- 34 0.02NWlmF GM 4MHF -lMIF m 3D Tm %mm lM Ml - O.lMKIO* Brwn Gre,n t. 32 40 Green 41 Grey groeo 42 Tan HJO .0 43 Greenishblu H*O. 13 44 0.E4K203,

Greenish blm 44 Green 0.7M14230.- 3S O.omw!!, - m SmCzll]ol

lhwll lMIKl- O.m 36 45 II#0. Bluish lilac 0 32

81W 0.3Nml - mm tl 32 KzS4. - O.a H@b Green 0.lM C,ll,AsO,H, - s a O.sn Imi 0.04MCdlIA@lll; - I 40 46 0.3Mml 34

-18- TABLE6 OTHERNEPTUNIWCOMPOUNDS Compound Color LatticeSymnetz> Reference Np112 Cubic 47 NpH, Hexagonal 47

W2 Green Cubic 48,49 Np20~ Dark broun Monoclinic 49a Np~00 Darkbrown Orthorhombic 50,s1 Np09=H20 Redbrown Orthorhombic 47 A ~a ~ap d t@-Lf ~PoLb-Y o=~~eof Np(vII), @(VI), @(V), & J’@(IV)ztith ali.alimetzZa and alkaline earth mataik am know. Abo, tt$tikzr ooqounda me zwported &th the mzw earth, other aotin~.ba, and a?kmzts in Grape 4 to 7.=2 NpN Black Cubic 53 NpF, Purple LaFs 54 NpF~ Green 55 NpFc Orange Orthorhombic 52,56 A ZaWe tier of fhoro ompozde of alkali or alkalina emth wtile Uith hfp(IV) and fluoride .haoe bum raported~2a fcm .rzioh ~ozmde & th i@(V)ad @(VI) ai%O m zqwrtd. r4@2F Green Tetra~,onal S7 N@F I Green Rhodmhudral M

NP02F2 Pink 57 NpCIS Groan 11 NpC1. Orangebrown 11.s8 N#)CIZ Ozmnge 59 NpBrS Green 60 NpBrb Dark red fll w s Brown 62 NpS cubic 63.64 Np# ~ (4 dj fferent 63,64 Strlx tulm) slp~ss Orthorh-ic 63,64 Np2Ss Tetrugonml 63.64 NpS~ Mnoclinic 63,64 0. NEPTUNIUM IONS IN SOLUTION

D.1. Oxidation States

Neptunium exists in the (III), (IV), (V), (VI), and (VII) oxidation states in aqueous solutions. The heat of formation, the entropy of the individual ionic species, and simple methods of preparation are listed in Table 7. The first four of these oxidation states exist as hydrated ions in the absence of coqplexing agents. Np(VII) is stable only ir, alkaline solutions; reduction to Np(.VI)occurs in acid solutions.

The singly charged, hydrated neptunyl itm, [Np02(H20)EJ+, is the most probable oxidation state in solnx~ion. Because Np02’ hydrolyzes only at pH ~7, disproportionates >nly at high acid concentrations, and forms no polynuclear complexes, it is stable compared to the other pentavalent actinides. The standard potentials and formal electrode potentials in lM HC104 of pairs of neptunium ions are shown in Table 8.

The formal oxidation potentials for Np couples in various

M solutions are given in Table 9 ~ with the hydrogen electrode in the stated medium as the reference. The change in the potentials in l.OM H2S04 as compared to lM solutions of HCI04,

HCl, and HN03 indicates strong complex formation c,f Np4+ with wlfate ions.

-20- ~,,,°K !;,,,~~ mi&tim WA ● lmicFam CalOr (kal/ml) ~;-,tm-”K)l

.s WIH,OI 1“ Blua violet -117 -, 3.9 NP(>III: . H,/P! Electrolytic reductlm

.4 W(M) :“ Yalla ~ -112.5 -. B *’- “ (), Np~Vi . W* ?/Po’) ● I-(5M HCl]

.5 WI (MM; Cram -231 - *.2L’ w“” . mm, (hat! Np(Vr] * stoichiutric I“ YIP(V1] . W120H

.6 N@l(HIO]~’ Pink or red -204 -.d Np(

+7 NP2:- Gr40n* nissolutlm of die-l lY pwpuvd Ll,N@L In dllure ●lkmlis NP(VI) . maw (or MZj, KjS#h. p9rldnta) in 0,S to 3.SM W

a. J. C. Hi diw. J. H. ~]-. Ilk?m. -. Il. 9s2 (1970). ii J. R. Rraodt; ”J. M. MIa. J-: b. 9.-912 (i970). e.c. * In IKlo.. J.C.Sulltwsmd A.J.Zimlcn. IllLq. hot. m,. Latt#m 1. 927 (Iwo).

,

-21- TABLE8

STANOARDANDFOR?4ALREOOXPOTENTIALSOF PAIRS OF NEPTUNIUMIONS”

Standaxd Fonual Poten- Potentit.ls tials in lM Electrode Process -L !iclob (Voits) Np = Np’+ + 3e- -1.astl -1.83 2Np + 3Hz0 = Np20J + 6H+ + 5e- -1.42(} . Np201 + H20 = 2Np02 + 2H+ + 2e- -0.96;! . Np203 + 5H20 = 2Np(OH)b + 2H+ 2e- -0.92[1 Sp3” = Np*+ + e- -0.152 0.1s5 Np]+ + 2H20= N@12 + 4H+ + e- 0.337 Np’+ + 4H2G = Np(OH~) + 4H+ + e- 0.391 Np3” + 2H@ = Npol + 4H+ + 2e- 0.4s1 0.447 NP(OH)* = N@~ + 2H20 + e- 0.S3D !U@lZ= N@~ + e- 0.S64 Npb+ + 2H20 = NpO~ + 4H+ + e- 0.749 0.739 N@z M NpO~+ + e- 1.149 1.137 ZNp{OH)~ = Npz05 + 2H20 + 2H+ + 2e- 1.219 2NpOZ + }{zO= Np@5 + Z{+ + 2e- Np205 + H20 = 2N@)3 + 2H+ 2e- 1.310 Np(lr + H20 = NpOl + 2H+ + c- 1.9s10 Np3” + 2H20 = N@~+ + 4H+ + 3e- 0.677 Npb+ + 2}{20 = NpO~+ + 4H+ + 2e- 0.938

-22- TABLE9

REOOX POTENTIALSOF NEPTUNIUM(IN VO1.TSAT 25”C) “66-6*

:1. 1.(H4 HC1O, -0.477 -1.137 (-l.236)a rl-”—–— -0. 1ss 7 +1.83 Npo;+— --Np”~ Np3+ Np L -0.938 J -0.677 1 ..— J ,2. 1.(IM Hcl

-0.437 .— -1.13!5 I -0.737 -et.137 1 1.87 NpO$+—— N@~ Npb‘—-— Np3~- Np. L- -0.936 I -0.670 [ 1 3. l.IOMHzS% -1.084 -0.99 +0. Ii NpO$+ NpO~ NP*+--- Np3+ I -1.04 4. 1.02k! HN03 -1.138 NpO;‘—— NpO; s. 1.W NaOH -0.48 -0,39 +1.76 +2. 2s Np02[OH);Z Npo20H Np(04) Q—— Np(oH] ~ Np (-0.’43) L J 0.S82 Np(VII] -—-.---- Np(VI)b ——. a. Standard potential b. According to the half-reaction NpO?- + e- + H20 -Npoi- + 20H-~g the dependence of EO on the OH- concentration is expressed by70:

Eft = 0.600 + 0.059 ● log [OH”]-”

-2.3- The current-voltage curves for oxidat~on.reduction

reactions of Np in aqueous solutions are sliown in Figure 2.

[).2. Olxjdation-Reduct~on Reactions

Table 10 lists reagents and condition\ necessary to change

c~xidati.on states for Np ions. For cases w~ere only one electron

jlSt-~sferred, e.g., NpJ+/Np@+ and NpOZ+/Np022+, the establish-

ment of redox equilibria is rapid. Redox reactions that involve

fomaing or rupturing of the neptunium-oxygen bond, e.g.,

Np*+/NpQ2’ and Npk’/Np022+, have a slower reaction rate.

Rate constants (k) and half-conversic,n periods of the

redox reactions in lM acid solutions at ;!:)*C are given in

Table 11.

0.3. Disproportionation of Neptunim

Only the Np(V) oxidation state under~oes appreciable disproportionation. The reaction 2Np02+ + 4H+ - Np4+ + NpOZ2+

+ 2HzC)shows that disproportionation of Np(V) is favored by high acid concentrations. Because Np4+ and NpO;:2* form more stable complexes than the Np02+ ion, the disproportionation of

Np(V) is promted by the addition of completing agents. The equilibrium constants, K, for various acid solutions are listed

in Table 12 where

~ . JNP(IV)][NP( VI)] [Np(V)]2

-24- 140 P4W)-NP(V) ml h 90 - *(V)- Np(vo Iwxn--*[lv) 80 -d ‘V+ NP(W) 4 NPI,IV)+NP(V) Em - Np( )-NP(IV) Jt -%0 - ii 3 ~o v w - I x 30 - ~J(- Hz Oi9Chq8 02 D49chOfgs- 1 ; 20 - 4 10 0 hd!!L#f 0 -a2 -OA -04 -Oa -1.0 -1.2 - 1A -!.6 -1.8 -2.0

Figure 2. Current-Voltage Curve for Red(tx Reactions of Neptunium. 7*

-25- ‘1/: .1* 9+*

l,;: .1% ● e ‘l~; ..4 ● ,.

~!).!20 .,.

81)J to ● @8

~[wfl) - OpIvll ?0,0,

-26- 0.* t’ ;:

I ● w’

I * W“’

●,e*k. &,+*+ $j%$ 6S+*’96,.,;*

*t * W’”

t.; ● *“” .,. , .,.:.!+., ,,,.,,,,.

TA6LE 12

EQlJ1L1~[lS4 COUSTAMTS F(R D1SPROPUUIOMTION ~ m(V) IN VNtIOUS M1O SOLUTIWS AT 25°C $*

solution —- Ica Ml Hclo, 4 x 10-7 S.S4M HC1O* 0.127 8.67M HC1O* 200 lM HISO* 2.4 x 10”2 1.$6H H2S0. 0.16

IV)] [NP(VI~ t2. a* 1*( PJPm2

-2a- The reverse reaction

takes place rapidly in weakly ●cid .w)lutions. The rate

constant in lhl K1O+ is 2.69 (M*ain]l”’*. J*

0.4. Rdiolysis o~Neptunlm Soluttcms

The radiolysis of Np(VI) by self’-radimtion of 2J7Np

causes reduction to Np(V) with a rate constmt of

(3.1 tO.2) X 10-s see-] (0.5 to 1.7N HCIO~) and a radiolytic

reduction yield (G) of 6.4 ions/100 ek’.’’-’~’ fh~ared to other hexavalent actinides, Np(Vl) has a much lower rate of radiolytic reduction.

For the ‘*CO irradiation of O.lhl Np(VI) in 1.lIM HCI04,

~ m 3.4. The radiolytic yields for mdiolysis of ~p solutions

(saturated with ●tmospheric oxygen] exposed to a% 1 MeV electron bean?”’s: are shown in Tablo 13. Np(V) has a compara- tively high stability to radiolysis. Np(IV) is oxidized to

Np(V).

When 23gNp is prepared by neutron irradiation clf uranyl salts, 80 to 90% of Np is in the tetravalent state,*2

-29- RadJolytAc Acid Con- Yield G Cent SW ion (Iuabm’ of !hll —. ion Acid N@l* + Np02+ Klob 0.018 4.4s 0.80 S.76 0.126 6.7 0.? 6.7 il. s 4,7’ 3.4 1.9 0.05 8.2 o.ab 3.0

0,8 2.1

-so- 0.5. Mydmlysfs of MSptunlm

li’b hydrolysis of a matd ion is m SpOCial caso of coaplox

fON%i On with ~- ion. Hydr’dysis consists Of the transfer of ● proton fron 8 coordinated water molecule to a wstor mlcculu in tha outer sphorw, s.g. ,

with

TheJ most recant snd extensive hydrt}lytic studies of Np were msde by A. 1. Moskvin. ” !+ydmlys:,s constants, l%, are listed in Table 14 for Pip(IV), (V), and (W] .* The ttmdency for Np ions in dilute acid solutions to undergo hydrolysis increases with increasing ionic potent ill [d) where d = Z/r,

Z is the ionic charge, snd r is the ionic radius, Thus, the tendency to undergo hydrolysis increases in the order:

]W2+

Successive hydrolysis reactions in Pu(IV) solutions result in the formation of colloidal aggregates. Tho polymer pre- sumably forms irreversibly with oxygen cm hyd:roxyl bridges.sc

*The stability constant KI of the Np hydroxo complexes may be % calculated from KI ● ~ iY the icmicproduct of T ‘here water,, 10-1”.

-31” TABLE 14

FIRST HYDROLYSISCONSTANTS4N0 SCMJBILITYPROOUCTSFOR NEPTUNIUMIONS

.—Ion !!YQQwS ‘8P Hydrolysis Produc~ ——-% Reference NP’+ * (~)* 6 X 10-S’ 83 (NpOH)‘+ !5 x 10-3 84 j) x ~()-~ 34

W2+ Np02(OH] 9.s x 10-1° NpO@H 8.3 X 10-l S 86 1.3 x 10-9 8S 8 X 10-10 1o-1o 34

NpO;+ N@2(m2 2 x 10-2’ [Np02 (OH)]+ 4.3 x IO-* 83

-32- tiskvin’g repo~s evidence for formLtion of polymer fom of

Np(IV) in queous solution mt [H+] “:0. 3M.

0.6. ~l~x Ion Fomstlon

Tho fo~tion of w~lex spocios by the sctinides in different oxidation states with ● vuriety of ligands offors jmtential for separating the sctinidos fmm each other and fmm other cations. Coqlex formation and hydrolysis are coqmting reactions. The ~chanism of complex ion formation can be repromnted ●s successive rmctions between water mleculos from the inner sphere of Ihe hydrated cation and anions, A, e.g.,

Np(H*O)/+ +A- =NpA(HzO)7:+ + H20

The ability of an ion to form complexes is dependent on the

=gnitude of the ionic potential. The relative tendency of

Np ions to fom co@exes is usual]):

Np’+ >Np’+>Np023+NpOZ2+>Np02+

Neptunium (111)

Np(III) exists in aqueous solutions as Np(HaO)es+.

The chloride and bromide coqlexes cf Np(III) have been studied spectroscopically in concentrated LiCl and LiBr solutions

(see Table 1S).

-33- rmt.f 15

Bs&A’ -m - ua t] - 2.42 u h - 4.s - U* s, - S.4S 40 s, - 6.s4 1.a4m% 01 - 0,04 49 0, - 0.24 b, - O.bt I.m mob n, - 0.51 w 2.a ncm, 0, ● O.M C9 0, - 0.16 4.* =10. 0, - 0,10 91 8, - 0,10 i.a ml% W’* 6, ● 4.81 02 WI” E, ● 757 w 1“ B, . 9.s1 Wm n, %11 l.a ml% 14pm,) ‘* 01 . 0.24 B9 Ww)r B, ● 0.01 m=,) 1“ B, - 0.16 I.m mm. B, . 0.24 90 z m mob 0, ● 0.24 tf a.m UIO. BU - 0.15 91 B, - 0.7s 0.2 to m 14210. *’. El .11.: n z. a mo. [m-m)]’” 0, ● 1.4s 93 PIP(S.I a 0, ● X47 s.a -m B, * 2.49 w n, ● 5.57 4.mIan. n, ● 2.70 92 0, ● 4.16

[NP(C,O.)]J”” 0, ● 1.ss 9s *(CA%]a s, .17.s3 [b[c@*) ,1‘“- B, .25.98 rmcnw,I”- B. .27.40 l.m mom 8, - 7.40 96 s, .1s,62 8, .19.44 l.m 2cI0. B, . 0.19 0, .16.42 0.1 to 0.s ~ 8, . ?.7 n o.m 2WCI 6, - Z.u 97 0, ● 4.76 0, ● 7.bm

0. ● 9.47 en .I1. o a, .14.7 0, .1?,4 B* .20.2

-34- T*I. 15. cwtlwcd h~ ~ l!@Il 1lbrlm Cclmtmt Mfasc

O.lM !6hclo, np(ml, e. .4s.2. 98

s,7-olchlom- o.lM W,C1O, flp[rm:. B, .46.0S 08 I-hmw- I@mllutm m-) Etl@aD- o.st4 (Wl) np(mh) 0, .26. S 94 dlAw- cat~ata lE~A) ‘ - O.lM I!xF, NP(YTA, J . s.ls” lLM

In I’Klo, ~(mp.~]” r, . 29.79 101

2.CN Hcl Np, c 0, - 0.30 1P: d,ml Hclo. n, ?.s1 91 [t.yo,m,j - B, - 1.ss I.w =10. up*lml, e, - 0.25 101

4.OM tclo. e, - 1.6 QI

[N@,: KI,,, ]- et 1.4 1O-’M 1oo, N@,al ~,-- !..1 74

e, ~, 4 d6

[N@,’s~,)~ fll ● :.15 III] [N@ ‘so,l;’- e, - S.KI

Nflz(lrn,) t?, . 2.41 103

O.ow m.clo., [NpY,’czo. )1 - 0, . 4,0 134 d, .-.3

NPz (W fl, . 1.3! I 05

[N@,’AC;,l- fll . 1.80

1.5M M’1.clo, 6! . I.at

B, . !.s5

8-htirow- o.lM N4.CIO, N@It (01) @l . 6.s1 ILM ~lmllmca (01) - [w,’oKl,w- n) .11. s0

Glymlmto O.IM M4, CI0, TI@, [l;LYC) ~! - 1.51 lo~ (GLTC)-

Lactara O,lM WI.CIO. N@, (lAm) B, . ;.?5 1(J7 (wm)- O,m Nt,clo. [NpO,:Wl), ]- 0, . 1.20 105

IS. dlntm. diitributim .8— Ls; I*1, lM ●lchnll@; 3*, tpsct-qhotmmrf; U9r, ml*ctmtlw* fome: *O,. mf with radm elrmmdo; p, @ Wtfd. 3. Smbility comtmts W@ Ilnn m Ioprltk to bug 10 of tha qu llbrim cm!tmt8.

Fer ttw twsctlm of # cnt L.m ❑ ●Ith llInMII L, !hc cemtw+t K ml B ● m daflnd ● ,:

“-e’- %’’-k%”t’-%”t’

““*’’”*”’

Thomfon n, - 1,1,. B, ● 1,1,1,. me.

c “--

-35- Ty84n WYti 1

M a, ● 2.17 Im

6, ● S.07

#, ● 1.s1

Jo % ● a.n 110 m, . l.= m, . a.m

s, ● 6.1s Cltnuw . :.* ,In Jo % IClll)’, 8, ● K 6? n 8, . 4.m Ill on . 7.m

n B, . z.- 111 0, . S.40

s o Im UC1O. 0, . S.SJ 112

m % . l.’? 115 s, . 6.09

2s [w,m-ml’- 01 . 4.00 11s l*,(EmA)l’-P, . ?.l J

:s o al Uclo. a. - 0.1: I Is ?& a lclo, s, - 0.1s *I x o n 4cI0. m, - O.n I 14 n m Ulo, 9, . O.M 91 F19rl& JI I a Ulo. e, . s.- 111 s, . 6.>? :s 1 m Um3. n, . I.m Ilb

s, ● a.n 3,.1.s. M n, . ho 41 Ii n, . ●.u

s, . Z.m w m, . 4.U k, . b.m Jo 0, . J.u 117 s, . ~.n 1, . 6.0 b 0, . a.m !10 c, . 6.lJ

““’’- R”Efh””lEth”” Eth””’ 0’ “Eil’b”“ “+M” -

-34- Neptunium (I1r.J

Np(IV), which exists as Np(H@)c@+ in aqueous solution, forms strong complexes with most anions. Analogous to Ll and Pu, Np(IV) fores negatively charged chloro and nitrate coraplexes in concen- trated H(3 and HN03; these complexes are sorbed cm anion ex- dangers. Np(C20s)2 is soluble in dilute (NH~)zCOS solution in- dicating that the carbonate coqle~,es, which have not been studied in detail, are more stable than the oxalote complexes.e

Definitive studies of the nature au~d composition of peroxide coqlexes in solution have not beml made. A purple-gray Np(IV) peroxide precipitate is formed by !Iddition of Hz[hto a solution of Np(lV) in nitric acid.

From the stability constants listed in TabI@ 15, the following series of Iigands were a::ranged, according to in- creasing strength of the complexes formedi by addition of the first Iigand to Np*+:

C104-

M7ptainiwu (VJ

~~), present in aqMOUs solution os singly charged neptunyl ion, NpOZ(HaO)6+, is u Pom completing agent because of its large size and low charge. The n~aptunyl complexes, 2+ which ●re comparable in stability to Mg2*$ Ca , snd Zn2+

-37- complexes, 87are much more stable than pentavalent uranium,

P~lJtG~iU.!7!F and alIR3riciuIB COlUpi8X8S.

Studies of cationic complexes of 14p(V; with IJOt2+,

Cr:~+, Fes”, 1%”+, and other cations in HCl(lt solutions have been mde.&

From the stability constants listed :bt Table 1S, th{e following serit?s of ligands were arranged ;lccording to in- creasing strength of the complexes formed ‘>Ythe addition of the first ligand to Np02+:

?kptunim (111)

Np(VI) exists in aqueous solution as NpOZ(H:lO]~z+. From the stability constants listed in Table 1S, the following series of ligands were ~rr =:iged according to increasing strength of the complexes formed by the addition of the first ligand to

Npf322+:

C1O*”

Neptuniwn(VI ‘J

Very few >tudies of N&(VII) complexes have been uade.

Sulfate compiexes of the Np023+ ion in acid solution show that

Np02 ‘+ has a higher tendency towards complex formation with

-38- sulfate ions than the neptunyl Np022+ icm. This is reasonable

because the char~ of the NpQzn’ group :.ncreases from hexav~lent

to heptavaIont neptunium.

!/1. PREPARATIONOF NEPTUNIUMSAMP1)ESFORANALYSIIS

A,, NEPTUNIIMMETALANDALLOYS

Neptunim metal dissolves in HC1, otlier halogen acids, and sulfamic acid but not in HN03 or concentr~ted Hl,SO~. Hot dilute

H2SO~ attacks Np slowly. Np is dissolved slowly in hot concen- trated nitric acid containing fluoride.

Np-Al alloys are soluble in 6 to 1(IMHN03 containing @.05M iilg(NO~lz and ‘W.02M KF; they are also sclluble in HCl and HClO~.

Am alternative method is to selectively c[issolve the Ail in a solution of NaOH-NaNOs; the Np and other actinide elements are separated by filtration or centrifug~ltion and are :501uble in boiling HN03-HF or HC1.

IB. NEPTIJNIIMCOWOUNDS

Np02 prepared by ignition of the oxmlate at 400 to 600°C is soluble in hot 10M HNOs. When ignition is done at higher tempera- tures, refluxing in strong nitric acid for a long period, even with the addition of HF, is required. Fusion with potassium bisulfate and dissolution of the melt in dilute acid is useful for dissolving

NpOZ fired at very high teqeratures. Blp fluorides are readily soluble in nitric acid solutions containing aluminum or borate ions.

“39- NpOZ.-Al targets are soluble in hot strong nitric acid solu-

tions containing mercuric and fluoride ions.

c!. BIOLOGICALANDENVIRONMENTALSAWLES

Np in these samples ranges from readily soluble metabolized neptunium in excreted saqles to extrewly refractory fallout sqles. Most procedures for dissolving, fallout or othler environ- mental samples involve treatment with HE: or a basic fusion step which renders Np soluble in acids. There has been little investigation of Np in these types of samples; however,, numerous cleterminations of plutonium in tissue. bcme, feces, urine, vegeta- tion, soil, and water have been reported and the same methods of dissolution would probably be applicable for Np; Nielsen and

Beas ley 11’ have smrized many of these methods. Dissolution of biological sa~ies and vegetation is l;enerally accomplished by multiple wet ashing or a combination of \let and dry ashing. In wet ashing” strong oxidizing agents sucli as perchloric acid and nitric acid are used [individually or iii combination), or sul- furic acid and hydrogen peroxide. In some cases the sample i.s fused with sodiun ox potassium carbonate: and the stelt is dissolved in water or dilute acid. 120

-. 40 - Wr. SEPARATICW METHODS

A. COW?ECIPITATION AND PRECIPITATIUY

C!=cipitation is the “classic” -thod fc~r s~arating

tracer quantities in radiochemical analyses. llecause ,Np in

aqueous solution is easily converted to (iiffemmt oxidation

states that exhibit markedly different lbl~havior in coprecipitation,

separation from other elements can be aft~ained. However, ion

{exchange , extraction chromatography, and solvemt extraction

:separaticm are used alaost exclusively Ix:cause more co~lete separation is attained mre rapidly.

Precipitation of neptuni~ oxalate :.s regularly used in

large-scale processing of neptunitm 8s u) intermediate to neptunium oxide. Precipitation of other Np coapowlds ils very limited.

The coprecipitation behavior of the different oxidation states of Np is sh~n in Table 16.

Lantha?u4m Fkwid%. The first separation of a pure Np

compound described by Magnusson and LaChrnpelle4’ used LRF9

,coprecipitation. Np[IV), Pu(III), and RJ(IV) are carried almost

lquantitativcly by lanthanum fluoride from mineral acids. U decon-

tamination i!;best from H2SO~ because of the strong uranyl sulfate

complexes. Np is reduced to the tetravalent state and precipitated

‘by adding fluoride and lanthanum ions. [nsoluble fluorides

- 41 - TA8LE 16 COPUECIPITATIOM&EMit~litI&TRACE AMOUNTS

carrier Compwnd !!QQM. igQgQ NEfY1’lP Lanthanu Fluoride (Y c NC Zircotiw Phosphate c Nc NC ThOrim Oxalate c Lanthaaa9 oxalate Id’ ThOrim Mate c w Zirconim Phenylarsonate c Poor Nc ZimOniw Benzenesulfinat,e c K K %dim Umnyl Acetate Nc Poor c Thmhm Puroxide c Bismth Plmsphate c M Nc Barium Sulfate c Nc Nc Potassium Lanthamm Sulfate c K NC Potassium Uranyl Carbonate Nc c c Hydroxides c c c

a. C indicates co-precipitation near.llj’ complete ulwier proper condition. b. NC indicates co-precipitation less than a few percant under proper conditions.

-42- includin~ the rare earths and Th also prec:ipitatc. Hold-back carriers me added to decrease the precipitation of Zr md alka- line earths. The fluoride precipitate is converted either to acid-soluble sulfates by evaporating untjl~. fumes of HzSOU appear, oIrto hydroxides by metathesis with alkallj. hydroxide. Oxidation at room temperature with bromate yields K.uoride-solubl(e Np(VI), but other acti.nides and lanthanides are m}t oxidized and, hence, are precipitated in a subsequent LaFs pre[:ipitation stelp. After removal of solids, Np is reduced to the Ix)travalent state and again coprecipitated with LaFS. Pa is co~trecipitated WILthmanganese dioxide preceding the LaFs precipitation zis required.12i LaFt precipitation has been used to separate NI~(IV) and Np[Vl from

Np(VI). 122

Zimoni.wn Phosphate. Tetravalent io]~s of Np, Put Ce, Th, and other elements are coprecipitated witl~ zirconium phosphate.

A variation of this method by Magnusson, “fiompson, and !3eaborg121 it; based on oxidation-reduction cycles. f~fter zirconium ion and

NaBi03 are added, the solution is heated ::0 oxidize Np and Pu to the hexavalent state. H3P04 is added to ~:arry tetravalent ions.

The supernatant solution is treated with Isxcess hydrazine to destroy bismuthate and then with ferrous :Lonto yield Nlp(IV) and

I%~(IIIj; Np is carried with zirconium pho:~phate, but Pu(III) and

U(VI’j are not carried. The zirconium pho$phate is dissolved in

X!No3 - HF, and Np is separated from Zr by coprec:ipitation with LaF$.

-43- Barium Sulfatu. Ce, Ba, La, and ?dp(iti)in quantities from carrier-fne trace levels to 1 mg are coprecipitated >99.7% by barium sulfate from strong sulfuric acid solution:~ containing potassim salts and hydrogen peroxide. This causes a separation frcm most other ele~nts, Np was separated by dissolutiawt of the bariw sulfate and reprecipitation from concentrated sulfuric acid containing chromic acid; ,pN (IV) was net carried with the Ce,

Bat and La. The Np in the supematant was reduced to Np(IV) with hyclrogen peroxi& and again coprecipitated with bariu sulfate.

After the precipitate was filtered, 23’Np \/as determined by gamma co{mting of the filter. ]z’ The method has been further modified~z” ami also applied to a wide variety of envi::onaental and biological sal@es125 {Procedure 1s, p176).

Hyiraeich . Insoluble hydroxides copreclpilate all oxidation states of Np except Np(VII).4SS127-129 Generally, the trivalent and tetravalent states are carried most effectively, The choice of reagent for precipitation depends on the composition of the solution. Strong bases are used when the solution contains cations that are’ amphoteric (Al, Pb, Zn) cm when the solution contains organic coaplexing ligands. When the solution contains cations thiat foxm amine complexes or are insoluble in strong base (Cu,

Cc), Ni, Ca, Mg), mnia is used as preci.~itant.

-44. Other In.qmnio Copmtipitants. Np(IV) is coprecipitated with bismuth phosphate and the double sulfate of lanthanum and potassium. Coprecipitation with lanthanum pot~:ji~ double sele - nate gives results similar to those described for the double sulfate but does not have any advantages.lso

The pentavalent cations of the transuranium elements are cop~cipitated with potassium uranyl tricarbonate. ’31

Dupetit and Aten132 described the coprecipitation of tetrava- lent actinides with thorim peroxide and uranium peroxide.

Neptunium is completely carried by thorium peroxide, but results were pmr with uranium peroxide. l%is was attributed to the presence of Np[V).

Other less coauon carriers for Np(IV) include thorim and

Lanthanm oxalates and zirconium, thorium, and eerie iodates.

Othfm~cznic t@%?&p~t~t8. Zirconium phenylafionate and zirconium benzenesulfinate are specific fo”? coprecipitation of the tetravalent ions from solution. The twtnsuranium elements are separated from other cations and from each other by a series of oxidation-reduction steps similar to those outlined for zirconium phosphate. 133

Kuznetsov and Akimova13* have proposed a number of organic reagents for concentrating the tetravalent cations of the txzms- uranium elemmts from very dilute solution!;. Np(IV) and Pu(IV] form he~nitrato species in nitric acid-nitrate salt solutions,

-45- and these cations are coprecipitated with the nitrate precipitates of heavy organic cations. Of the rwagents ~tudied, butylrhodamine was the -st effective organic cation. In mncentrated nitrate solutions, U(IV), fi(IV), and Ce(IV) coprecipitate! with Np[IV) and Pu[lV). Other coprecipitation was with quaternary ammonitan bases, dimethyl dibenzyl mnium, and benz?lquinc~lium colqounds.

Excellent separation from rare earths, iron, chmmim, manganese, and copper was attained.i’s

With many organic reagents containing 3ulfonic groups, tetravalent elements fom soluble cyclic salts that are {coprecipi- tstad with precipitates fomed by the catiom of a ba:.:c dye

(arsenazo] and the cyclic organic reagent. Compami to the organic nitrates shove, the precipitation is more (c(mpletel but less selective. ‘S’

Np(Vt) is carried with sodium uranyla~~tate.

Prvaipitatwn. Precipitation of macro quantities of Np is seldom used as an analytical or radiochernicul method. If other cat:lons that fom insoluble compounds are ljresent, these must be $teparated first. When the solution is :r(:latively free from other ions, a method such as alpha cotatting is usually mo:re rapid and offers less health hazard. A nusber of Np compounds have

10U solubilities in aqueous solution; howevlm, indefinite stoichiometry or necessity for calcination i:o the oxide limits the usefulness of direct gravimetric deternunation.

-46- @ihti&8. No information is available on Np(III) “hydroxide, ” probably because it is rapidly oxidized even in an inert atmosphere.

Np(IV] is precipitated from mineral acid solutions by sodium, potassium, and ammonium hydroxides as tho hydrated hydroxide or hydrous oxide. The brown-green gelatinous solid is difficult to filter; it is easily redissolved in mineral acids. No formal volubility studies are reported, but the volubility in lM NaNOJ - lM NaOH is <1 mg/1.

Np(V) “hydroxide” is green. The volubility in dilute ammonium solution is 0.18 g/l; in lM NaOH, 0.017 ~!/l; and in 2.2M NaOH,

0.014 g/1.35 There was speculation in tile early Iiterature38 that Np{V) might precipitate as NHqNp03-:ti20 or an analogous sodium compound as well as NpOz(OH]9HZO; however, the exact nature of the precipitate has not been confirmed. Np(VI) is precipitated as dark brown (NH4)2NP207”H20 with exces:; ammonia from mineral acid solution; the volubility is given a:; 25 mg Np/1. ‘5 When sodium hydroxide is the precipitant, a brown compound with reported co~sition Na2Np207”xH20 is precipitate(i. Studies on the variable composition of the uranates leave some question as to the composi- tion of the neptunates given above. 137

Fzuotid88. Grayish-lilac colored Np(III) fluoride is pre- cipitated by adding a dilute HCl solution of Np(III) containing

Rongalite to a solution of ammonium fluo::ide or hydrofluoric acid in dilute hydrochloric acid while sparging with argon. The dry compound was quite stable to oxidation.3~ Np(IV) fluoride hydrate

-47- is precipitated when hydrofluoric acid is added to an acid solution

of Np(Iv),

Ammonium Np(IV) pentafluorideprecipitates as a bright-green

granular solid when hydrofluoric acid is added I:oa solution of

Np(IV) containing NH~+ ions. A similar precipitation in the pre-

sence of potassium ions yields a bright-green precipitate that

X-ray diffraction indicates is KNpzF9. ‘Tiesupcrnatant lM HF -

O.OIM NH,,’>from precipitationof the ammo:liumsalt contained 1.1

mg Np/1 two hours after precipitation; t!h:solut~ili.tyof the potassium salt was 1.7 mg Np/1 after 16 hours in O.SM HISOb -

0.5M K2SOJ4- ;!MHF.3*

A double fluoride precipitate of La :md Np with an approximate composition LaIZNpFIOOXHZOis obtained by ilddinghyd.rofluoricacid 3+ to an ac~d solution o equivalent amounts of La and Np&+. The volubility of the salt in water was 4 mg/...39

Rubidium neptunyl(V) fluoride was prf:paredby injecting a chilled W.IM HN03 solution of Np02+ into a chilled solution of

%12M Rbl:at O°C. The gray-green precipittltewas washed with small amounts of water, methanol, and acetone followed by air drying. 13*

0XUikt88. Brown NpZ(CZOq)3*nH20 (n ~111)is precipitated by adding oxalic acid containing Rongalite i.rtoa dilute acid solution of Np(IIl) also containing Rangalite.,The compound is appreciably oxidized within a few hours.32

-48- After valence adjustment to Np(IV) with ascorbic acid, ko

bright-green Np[C20~)2D6H20 is precipitated from solutions

originally containing 5 to 50 g of Np(lV), [V), or (VI) in 1 to

4M HN03 by the addition of oxalic acid. T.le volubility varies as

a function of the concentration of nitric i~cid arid oxalic acid

(Figure 3). At oxalic acid concentrations near O.lM, the volu-

bility varies between 6 and 10 mg/1 as the nitric acid concentra-

tion is varied between 1 and 4M. The solukility is very tlependcnt

on maintaining all the neptunium in the tetravalent state,

Significant separation from a number of cations is attained.

The salt (~U)Q[~(C20~)~]-(~~)2C20~= XH20 has be~., isolated. ~3g

The soluble aqueous complex was cooled to O’C to remove cxccss

ammonium oxdate. Ethyl alcohol addition produced an oily, dark-

green liquid that yielded dark-green crysta..s when treated with

96% ethanol.

Green neptunyl(v] oxalate (Np02C20~H”2}120) is precipitated when a solution of Np(V] in lM HC1 is treat~d with a 10% solution of oxalic acid in tert-butanol. bl

Neptunyl(VI) oxalate (Np02C20~”3H20), a grayish-~reen crystalline solid , is precipitated from 2M HV03 - O.OSN KBr03 containing 20 to 40 g Np/1 by adding oxalic zcid until the solution is ‘IJO.3MH2C20Q.42 The volubility in 0.5MHN03 - CI.023MHZCZ04

increased from W.5 to ‘v1.5 g Np/1 over the temperature range O to

20”C. In lM INOJ at 14”C, the volubility varied from %3.8 to

-49- 100r - ——

:1’:”’”:230’’’’/“ 0.7[3

1.64 to-– •~ _ -2.813 : B- 3.7fi 1

3 ~~ 0.’01 o. I I.0 ~1Omlic Acid, M

Figure 3. Volubility of Np(lV) oxalate

-so- %0.75 g Np/1 as the oxalic acid concentration varied from WI.002M , to w. lSBL

Pervti&. Np(IV) peroxide is precipit:lted from solutions

containing Np(IV), (V), or (VI) in >3M HNOJ by the addition of

hydrogen peroxide. ~”o The higher valence states are rapidly reduced to Np(lV), and gray-purple neptunium peroxide precipitates.

The precipitation does not progress through the highly colored, soluble peroxy complexes that are characteristic of plutonium peroxide. fio crystalline forms were prepared depending on the acidity of the precipitation solution. The volubility is reported as a function of the concentrations o: nitric acid and hydrogen -% peroxide. A minimum volubility of ~lO-uM neptunium occurred in solutions 1.5 to 2.5M HNOJ and 4.5M H::02. The solubilities were not readily reproducible at nitric ac;.d concentrations of <2.5M.

Iodate8. Precipitation of Np(IIl) iodate has not been reported. Np(IV) iodate, a tan-brown solid, is precipitated when

HIOJ or KIOg is added to a dilute mintral acid solution. The volubility in lM HC1 - O.lMHIOS is 0.8 g/l; in lM HC1 - O.lM K103,

0.08 g/1.35 These solubilities appear to be high, possibly because some Np was in higher oxidation states.

Amtate. Rose-colored N~@Z(C2H@z)s is precipitated when a sodim acetate - sodim nitrate solution is added to a dilute sulfuric acid solution that has been heated to 90°C in the pres- ence of potassium b-te to give NpOZ2+. The volubility is

M.1 g/1 in 0.5M H2SO* - 0.07M NaNOs - 2MNaCzH~02.38

-sl- Ccmbo?latea. No sinple carbonates of NF(III) and Np(l V) are rqor~al A light-colored precipitate of NF(V), KYpOaCOs, is precipitated by addition of solid alkali carbonate (to about pH 7) to a solution of Np(V) ❑ade by reduction of Np(VI) with iodide ion,~3

Phosphate. A green gelatinous precipitate, Np(HPOb)a”xHaO, is formed when phosphoric acid is added to Np(IV) in hydrochloric or nitric acid. The volubility in lM HC1 - O.SMHsPO~ is W56

❑g/1, and the volubility in lM HNOJ - lM H#O~ is %134 mg/1.+5

sulfates. Mefod’eva and Gel’man32 report precipitation of

Np(lII) as the complex sulfates KsNp(SO+)b und NaNp(SO~)2*nH20.

Np(III) is produced in dilute hydrochloric and sparged with argon at %SO°C using Rongalite mductant. In the dry form, the complex sulfates are stable to oxidation even at increased teqenture.32

Np[IV) is crystallized from hot concentrated sulfuric acid as a bright-gnen compound, presumably Np(SOk)2*:cH20. The volubility is %16 g Np/1. Sulfuric acid solutions of Np(V) and Np(VI) have been reported, but no data are given on volubility.3S Although not reported, it is expected that Np(IV) colpounds analogous to

Pu(IV) co~ounds could be precipitated fmm a solution containing sulfate salts, alkali metal ions, and Np(IVj.

Other Conpounda. Several Np(IV) chlor’Lde coaplex salts have been prepared. Yellow CszNpCls was precipitated by ❑ixing solutions of Np(IV) and CSC1 in 2 to llM HC1 and saturating the rwsulting

-52- solution with hydrogen chloride. 19N3volubility in ~lOM HC1 is

<0.DIM ~d increases to w1.4M in %lM lIC1. ‘“~ A similar compound,

[( C2HS)~N]zNpC16, was precipitated by adding tetraethylammoniwn chloride in 12M HC1 to Np(IV) in 8 tc) 12M HC1.1”2 Several other complex salts of Np(V) and Np(VI) have been reportecl. Yellow

[(C2~5]4N]2Np02C14was precipitated by the same procedure used for the Np(IV) salt,1”3 and Cs2NpOC15 (bright yellow), (Ph4As)2NpOC15

(bright yellow), CsSNpOC14 (turquoise), and CszNpOzClk (dark yellow) were made by variations of the same pr>cedure. ‘q

The phenylarsonate and salicylate of Np(III) have been reported.32 They are quite stable at :unbient temperature when dry.

-s3” B. SOLVENT EXTRACTION

Solvent extraction of Np from aqueous solution into immiscible

organic solvents is probably used most often for wparation because

of its rapidity, simplicity, and reliability). Solvent extraction

of Np is usually ❑ade from nitrate systems. Generally the effi-

ciency and specificity are decreased from ch’loride systems; other

systems,such as fluoride, sulfate, and phosphate,form complex ions with neptunium,and extraction is inhibited.

There are examples of bath ion association extraction and chelate extraction among the solvent extrac”:ion systems for Np.1bbD1”5

In chelate systems, compounds such as lTAp cupferron, acetylacetone, and 8-hydroxyquinoline replace coordinated water from neptunium ions and form neutral, almost covalent, cheiate compounds that are soluble in such organic compounds as hydroc~rbons. In ion associa- tion systems, several ❑echanisms are possible by which uncharged, extractable compounds are formed by electrostatic attraction between oppositely charged ions. In one ion association system, an oxygen-containing organic compound such as ether is coordinated to Np(IV), and the complex cation is associated with nitrate ions to give an uncharged extractable species. Ion association solvents conmonly used for Np extraction include TBP, hexoneo diethylether, isoamyl alcohol, pentaether, and dibutyl carbinol. For solvents such as hexone and diethylether, which fom coordination complexes with actinide nitrates, the order of extractability of the various

-s4- oxidation states is usually (VI) > (IV) >> (111) nd (V)~ with the

last two states generally considered to bm nonextractable. The

(IV) oxidation state is poorly extracted by diethylether but is

extracted into hexone and dibutyl carbinol.. For TBP and chelating agents, which fom coordination complexes with the ❑etal nitrates,

the stable oxidation state giving the strongest complex is usually extracted most efficiently. The tendencies of the actinides to form complexes is (IV) > (VI) > (111) and (V). Thus, TBP, TTA, and other conrplexing agents usually extract the (IV) state most effectively. An exception (Table 17) is lJp(IV]-TBP; however, these exceptions may be the result of the instability of the oxidation state in the aquebus solution.

Groh and Schlealh6 and Schulz and Benedictg have reviewed production-scale neptunium processes, including solvent extraction.

C71ezute s~atema. A large number of ~i-functional reagents that form strong coordination complexes tiith metal ions have been investigated. These complexes are mme soluble in nonpolar organic solvents-such as benzene or CCl~rthan in the aqueous phase. Of these compounds, the fluorinated B-diketone, 2- thenoyltrifluoroacetone (TI’A) has been most widely used for extrac- tion of ?+@in radiochemical and analytical appl:lcations. 1’7~*’a

Many variations include TI’A extraction as a part of the total separation schek before the analysis of Np or the determination of its oxidation states. i27~]92#*”9D1’0

-55- .

TAUE 17

VAAIATIOUW ESTRACTIOIICOEFPICIU(TSMITMOXIlhTIOR STATE

QElmkkll##t— Aewau Pmula !QQw_&MM_ YFXQ__!Mw_ .!Mw_&Qv_wQ -(III) m 1* TW-korosem m Imi)* 3.0 0.13 11.0 0.014 :!l. s z.~, O.m ,.-6 ~o-. ,.-8 ~@ O.sm nA-xylOm 1J4 HloB 10’ 10” ‘ 0.(104 10-0 Di*thyl ●Clwr edk tNoB 0.1 0.3 4.6 ..31 lM MEb-sat 1.:!

m,mo,

Ibx$nw Ossm tmm-11.lm 0.14 l.” 9.e

m8N08 C* H40, 0.3 1.’ ,a.5 ~lw

-56- Some data for the extraction of Np and other cations into

0.5M TTA in xylene for a range of nitric a,cid concentrations are

given in Table 18. 1

Shepard and Meinke have compilti a useful set of TTA extrac-

tion cunres showing extraction as a function of pi-l for a number

of elements.lso The data show that by judicious pH control, ?TA

extraction is useful to separate neptunium from many other

elements.

Basically, the lTA method depends on quantitative reduction

of Np to the highly extractable tetravalent state while inter-

fering ions are stabilized in inextractable oxidation states.

(Procedures 1 and 2, p 138 and 141], Neptunium in lM HNOs or lM

IKl is rapidly and co~letely reduced with femous sulfamate,

hydro~lamine hydrochloride-potassium iodide, or hydroxylamine

hydrochloride-ferrous chloride. NplIV) is eXtrdCted into the ‘ITA,

and Pu(III] and U(W) remain in the aqueous phase, If no inter-

fering cations are present, the extract can be evaporated

directly for Cotmting. The efficiency of separation from other

alpha emitters 1s verified by alpha pulse height analysis.

Fe(III), Zr(IVl, and Pa(V) are strongly extracted f- lM HN03,

but separation is attained by stripping the Np(IV) from the

‘lTA-xylene into 8M Ii?#3s. Trivalent actinides and lanthanides

do not interfere. Sulfate, phosphsI:e, oxmlate, and chloride,

if present in the aqueous phase, aro camplexed with Al’+ before

extraction to prevent interference.

-57-

. . .. . TABLE 18

EXTRACTION COEFFICIENTS FOR VARIOUS IONS IN1-O 0,5M TTA-XY1.ENE1’9

Extraction Coeft:lcient at 25*C .—. Ion !!!Qd?Q —. —— NP(III) 1.0 <3 )( Jo-s @(IV) 1,0 1 x 10’ 8.0 Np(V) 0.8 <5 x 10-’” f@@I) 0.8 <1 x ]()-’ Pu(III) 1.0 1 x 1.0-6 Pu(IV) 1.0 1 x 10’ 8.0

-S8- The relative standard deviation for a:he analysis is 22%.

The nominal decontamination attained from plutonium is 10g to

M 151 #152 10 . Some data on the extraction of Np from sulfate and perchlorate systems with TTA have been giren by Sullivan and

Hindman.93

ITA extraction preceded by a LaFs coprecipitation cycle has also been described.153-L56 Np has been separated from numerous special materials where a combination of method:J including lTA extraction was used. Holcomb157 has described m method for separating 17 gamua-emitting radionuclides, including 23gNp, from heavy water mderator by ‘ITAsolvent extraction and anion exchange.

The individual nuclides were determined ty gamma counting and gamma spectrometry.

8-Hydroxyquinoline forms the following chelates with Np:

Np(CSHGNO)~with Np(IV) and H[N@*(C9HGN(~)~] with Np(V]. Extrac- tion of a number of elements as a function ofpH into O.lM

8-hydroxyquinoline in CHCIZ is shown in Figure 4. The trivalent actinides extract only at pH 4-6, and at this @i appreciable hydrolysis of the metal cation occurs.’ ~’] Np(IV) cupferron is extracted almst quantitatively into chlomfom from lM HCl and is back extracted in 8H HC1. i50a

Separation with acetylacetonate has been reported for U and

Pu and probably has application for Np.

-s9- I ~- ‘7 1

PO(v) p(w) cffdUI Acum RO(m PO(v)

Am(m)

; ;/\ -1et(m) +- L 4 6 8 - 10 pl’t

FIGURE 4. Ftercentage Extraction of Tracer Quantities of Ac(I!II), Am(III’), CM(III), Cf(III), N (IV), and Pa(V) with 0.lM8-Hydroxyquinoline /’CHC13 and of Ra(II ! with 1.OM 8-Hydroxyquinoline/CHCls [p = O.lM [Na, NH*, H)CIO~, 25”C]. [C. Keller and PI. Mosdzelenski, Radiodfim. Ada. ?, 185(1967) Supplemented].

-60- Extraction of plutonium dibenzoylmethaneor salicylatehas been

reported. 1‘g~ 1‘o Neptunium dibenzoylmethane is unstable in aqueous

sc}lutiont so Pu and U, which form extractable complexes, can be

separated.l 59’!S1

Chmutova et CZZ.extracted PuIIV) from 3M HNCSwith a chloroform

solution of N-benzoylphenylhydroxylamine; IJOZ2+, Am(IIX],, (V), and fission products (except Zr and I%) do not extract.~62

Np(IV] is strongly extracted from 1 tcl 4M HNDa and 1 to

6M HCl with 4-benzoyl-3-methyl-l-phenyl-ppazolin-5-one; under the same conditions, Np(V) and (VI) are not extracted.1s3 Np is ex- tracted at pH 9’ to 10 with l-nitroso-2-napthol in n-butanol and isopentanol and is separated from U and Pu.’6b

Ion A880CiatiOrI @8t4w18. The TBP-HNOS system is a useful sYStm for large-scale processing but is not, widely used for quantitative analyti~al separation. TB~ forms an organic- soluble coordination complex with the metal nitrate, generallyof the type M(N03)149ZTBP.lb> Increasing the nti,trate concentration by adding nitrate salts of Al or Ca favors ext::action. Other factors that affect the extraction include complexirlg ions, reagent puritY, free TBP concentration, temperature, and mi],ing time. A S_rY of the early work with TBP has been given by Geary,lsG The physical and chemical properties of TBP as an extracting a,gent have been summarized by McKay and Healy. *G7 Other discussions ‘f the use of TBP are in References 168-170” ‘xtract~’on Coefficimts

-61- for many elements for a variety of aqueous solutions anJ TBP 149 concentrations have been reported by Schneider and Harmon;

data are shown in Table 19.

Np(VI) is almost completely separated from Al(III), Am(III),

Cr[III), Fe[II), Fe(III), Na(I), Zn(II), and many other cations

in one stage of TBP extraction. Separation of Np from Pu and U

involves either oxidation of Np to the (VI) stat{! for extraction

and subsequent stripping of Np(V), or stabilizat:.on of inextract-

able Np(V) followed by extraction of Pu and U.

The following sequence of extractability ha: been found for

the various oxidation states of the actinides: PI(IV) > M(VI) ~~

M(III) > M(V). For the tetravalent actinides tht sequence is

Pu(IV) > Np(IV) > U(IV) > Th(IV], while among thw hexavalent

actinides the extractability decreases with incratsing atomic n-or: U(VI) > Np(VI) > PU(VI)’GS (Figures 5 ar,d 6).

The tetravalent and hexavalent actinides are extracted from

HCl solutions with similar relative distribution coefficients as

from nitric acid but exhibit no maxima. Lower d:.stribution coef-

ficients are observed for extraction from perchloric acid solutions

because of weak coqlexing by the perchlorate ion. Strong couplexing

agent% such asOSOb2-, P@k3-, and F-, reduce the extractability of

all actinides appreciably; however, cations such as Al that form

quite stable complexes with these anions partially negate the

deleterious effect on actinide extraction. Distributicm

-62- TABLE 19

EXTRACTION Coefficient DATA FOR TBP1bg Extraction Coefficient 1on Solution TEP (%) At 25°c Am{III) 4.OM HN03 30 0.013 Al 4.7M 15 0.0003 Ca 4.7M 15 0.0003 Co{II) 2.14M Co(NO,)l 60 0.002 Cr(III) 3.OM HN03 100 0.0001 CU{II) 3.OM 100 0.0004 Fe[II) 4.7M 15 0.005 Fe(III) 2.Cm4 12.5 0.003 Mg 4.7M 15 0.0003 Na 2.OM 12.5 0.003 Ni(II) 3.OM 100 0.00006 Np(IV) 4.OM 30 3.0 Np{vI) 4.OM 30 12.0 Th 4.OM 30 2.8 Pa 4.(M4 50 2.8 Zn 2.OM Zn@03)2 12.5 0.0001

Ru 2.OM HN03 30 0.1s Zr 2.OM 30 0.09 Nb 2.OM 30 0.03 Rare earths 2.OM 30 0.02 Pu(III) 5.(X4 20 0.012 Pu(.IV) 5.OM 2G 16.6 Pu(VI) 5.(IM 20 2.7 U( IV) 4.OM 25 10 U(VI) 4.M 25 23 HM13 2.OM 30 0.26

-63- .,

HMO,* mola/4

Figure 5). Dlstrlbutlnn Coefficients for tte Extractlm of ‘Tetravalent Actinfdes by 19 ~ol % TBP.-Kerosene from Nftric Acid S~lutforl. l&5

-64- ~lgure!6. Dlstrfbution Coefficients for the Extraction of Hexavalent Actinlde% by 19 vol Z lBP-Uerosene from Nitric Acid Solutlon.’G:

-6S - coefficients for Np(V] and trivalent actinides are appreciably

lower171 than for tetravalent and hexavalent actinides,

For Np02+:

‘2+[aq) + ‘3 [aq) + ‘Bp(org) “ ‘W’02‘W3) ‘Tap] (erg)

For analytical applications with small volume:;, equilibrium is

atta~ned in less than five minutes with good mixing.

The extraction properties of many >ther cmganophosphorus

compounds have been studied; however, F:w separation methods for

Np have been defined. Higgins et aZ. wm:king with the butyl series

found the order to be phosphate ((RO)SFY1) < phosphonate (R(RO)2PO)

< phosphinate (Rz(RO)PO) < phosphine ox:~de (RsPO).i72

‘The distribution coefficients for I.he extraction of some

tetravalent and hexavalent actinides wilh various trialkyl phosphates are given in Table 20.

Burger t7b*175and Petrov et a2~76 f’ound that electronegative

SUb!3t~ltUUIItS in the alkyl chain, such as, chloride and phenyl,

strongly depressed the extraction. Sidda1173 found that increasing

the length of the alkyl chain in the phosphate series made little difference for up to eight carbon atoms for tetravalent and

hexavalent actinides. The effect of branching the alkyl chain is

to increase the extraction of U, Np, and Pu, but to strongly depress

extraction of Th. The extraction mechan~sm of these cimapounds is

generally the same as that for TBP, but the Solvstion number is not

“66- TABLE20 DISTRIBUTIONCOEFFICIENTSFOR THE EXTRAC1’]ONOF TETRAVALENT ANO HEXAVALENTACTINIDESUITH 1.9MTRIAI.IYLPHOSPHATE/ n-DODECANE FROU ZM HNO! AT 30°C7’

Distribution.——Coefficientsa Extractsnt Th Np(IV)b h(IV)O J(VI] Np(vI)~’ PUNI) —— —— —. —— Tri-n-butylphosphate 2.9 3.2 16.1 26 15.6 3.5 Triisobutylphosphate 2.4 2.? 11.8 22 15.9 3.4 Tri-n-amylphosphste 2.9 4.2 15.6 32 19.3 4,1 Tri,imamylphosphste 4.2 4.7 17.8 34 18.9 4.4 Tri-n-hexylphosphate 3.0 3.6 1S.6 38 20.0 4.s Tri-n-octylphosphste 2.4 3.4 15.3 33 1s.7 3.9 Tri-[2-ethylhexyl) phosphste 2.s 4.3 25 58 23 5.7 Tri-[2-butyl] phosphate O*4S 4.9 28 42 4.6 Tri-(3-amyl)phosphate 0.22 3.5 18.1 49 5“0 Tri-(3-methyl-2-butyl) phosphate 0.18 3.(? 24 47 25 S.4 Tri-\(4-oethyl-2-amyl) phosphste 0.047 3.5 22 38 24 4.9

a. For traceramountsof the givenelements. b. The aqueousphasecontainsO.OIMFe(?WzSO~)t. u. The aqueousphssecontsinsO.OIMN8NOt. d. The aqueousphasecontsinsO.OIM (~)2Ce(10,1{.

- 67 - necessarily the same for all elements.1”

A method with mono[2-ethylhexyl]orthophosphoricacid in contact with 12M N(21+ O.lM hydroquinone has been effective for separating Np(I’!/) from U(VI), Pu(III), Am(I[I), Cnl(lII), and trivalent rare earths. The K value for Np([V) is ‘V103,and for the other cations,mlO-l; thus, separation i:5 attained by a single contact followed by multiple scrubbing of tl~e organic pha:$e.~’~

K. Kimura178 has determined the acid depend{mcy of the distribu- tion coefficients for many elements extract~ti by SO vol% bis(2-ethylhexyl)orthophosphoricacid(HDEWP: from HCl solutions

(Figure 7), These data offer the basis for separating Np from many cations.

The distribution coefficientsof Am(Ill:], Pu(IV), NP(V), and

U(VI[) in HDEHPfrom HNOo are given in Figure 8.179 The dis- continuity in the Np(V) curve at high acid concentrations is probably due to disproportionation cJf Np(V) into Np[IV] and Np(V[), both of which are more extractable than Np(V).

Np(V)Iin dilute nitric acid has been separated from U(VI),

Pu(IV), and Th(I’V) by HDEHPextraction; however, there was evidence that a few percent of the Np(V) was reduced to Np(l’V) and not separated by a single extraction. 180 Kosyakw et C[ZjT9 used

HWH!P to purify Am(III) from other actinides in higher valence states and,to accomplish their mutual separ~a:ion.Am(III), Pu, and U were extracted from O.OIM HN03 after stabfl:[~ation of Np in the

-68- Fr c + DFP wlks.stusiqmM4allW~da& --CABLMtAIXCAMabmwl#. *T1 DatJ#TMi=ui. N *EN Ma of EMhmurJ, Xd Elrl$l s Scrlibitq -. ?

Figure 7. Extraction of Elements frcm HC1 Solution by 50% HOEHP in Toluene as a Function cf Acid Concentration.17*

-69- Log [HN03]

Figure 8. Extraction of Various Actinicl~!s into o.5MH(lEHP (Isooctane diluent) from HNO:I Solutions. lTg

-70- pentavalent state with sodium nitrite. I@(V) was then oxidized to Np(VI) and extracted with HDEHP. Np(VI) was reduced to HP(V) and recovered from the organic phase by washing with O.lM HNOs.

Am was back-extracted f- the HDEHPwith W HNOs and Pu was reduced to Pu(III) and recovered by back extraction with 3M H?U)9*

U(VI) was recovered by back extraction w:.th lU (NH~)z COs.

Chudinov and Yako*~lati’-o extracted IJ and Pu from Np(V) with

HDEHPas a preliminary step in the colorflbetric determination of

Np(IV) with Arsenazo(IJI).

Peppard et a2!7”’D’al studied the extraction of several actinides by mono-2-ethylhexylphosphoric acid (HzMEHP) from HC1 solutions

(Figure 9). The distribution coefficient for Np(IV) in 12M HCl was ~103, 104 times larger than the non- “:etravalent species studied.

Gindler et UZ.’B2 used this method to puvify 2’GPu for fission counting. The Np(IV) can be returned to the aqueous phase by addition of TBP to the organic phase, re:;ulting in a great reduction in the distribution coefficien-:.

Kosyakov et U2. *79 dete~ned the d:Lstribution coefficients of Am(III), Np(V), Pu(IV), and U(VI) in I{zMEHPfrom nitric acid

(Figure 10). ~ey are generally higher :For the same aqueous conditions than those for HOEHP.

White and ROSS183 have written a general review of the extractive properties of tri-n-octylphosphine c~xide ~m).

-71- ‘R17

-1

Figure 9. ExtractIon of some Actinide Cations into 0,48M H2MEHP in Toluene as a Funct’on of HCl Concentration.177

-. 72 - 6.a

5.0

4.0

3“0 $3 ~ 2,,0 d

I !,0

o

-1.0

-2.c)~.L--J_. -1.0 -0.5 0 0.5 I.() LAW[HN03]

Figure 10. Extraction of Various Actilnldes into 0.2!4 H2MEHP (Isooctane diluent) From HN03 Solutions.~79

-73- Extraction data for Np and other actinidos into TOPO have been

sunmnarizedby Weaver and Homer. leb

Extractionwith methyl isobutyl ketone (hcxone} is based on the solvent power of hexone for the covalent nitrates of the (VI] oxidation states. Hexone was used for large-scaleprocessing of irradiated nuclear fuels (“redox”process) but has been supplanted by other sol,ventsboth in plant and labflratoryapplications. A two- cycle extraction system for the separationof neptunium from uranium-fissionproduct mixtures has boon given by Maeck.195

Hexone extraction of Np(VI] from acid-{il:ficientAl(NOJ)S was followed by TTA extraction. Excellent separationfrom U, l%, W, and Zr was attained. Also, Np has been separa~tedfrolm Pu and La.

Np(VI) and IPu(VI)were produced by oxid~tion with KBr03; both were extracted into hexone from an A1(N33)3 solution. Back extraction with an aqueous sodium nitrite solution yielded Np(V) and Pu(III), neither of which is soluble in hexone. The hydroxides were precipitated and dissolved in nitric acids and ferrous sulfamate was added to give Np(IV’Jand Pu(III). Np was extracted into a solution of tributylaminein he>,one,leaving the Pu in the aqueous phase.*2g

Extractioncoefficients for ions :.ntohexone from several different aqueous compositionsare shown in Table 21,

Dieth:yletherquantitativelyextra,:tshexavalent Np, ?%, and

Am from salted solutions containing a strong oxidant (Table 22).la6

.“74- TABLE1!1 EXTRACTIONCOEFFICIENTSOF VARIOUSSOLUTESINTOHE)(ONEAT 25°C1°

Extraction Salting Agent (M) Nc~- (M) !wd!!!l Coefficient Al(N3s) s 1.3 4.0 0“1 0.02 1.3 3.9 0.0 <0.0001 2“0 6.1 1.7pH 0.011 2,0 6.1 0.1 0.0003 1.3 4.4 0.5 2.1 1.95 6.3s 0.5 0.0018 1.3 $.4 0.5 1.5 1.s S.O 0.s <().001 0.7 2.6 0.5 1.7 1.0 5.4 0.4 0.82 1.5 JI.5 0.0 1.1 1.0 :;.s 0.5 0.009 1.0 :;.2s 0.2s 0.01 1.0 :i.1 0.10 0.10 1.3 4.1 0.20 0.12 1.4 4,,6 0.4 0.10 HH,HO, 8 E.2 0.2 0.004 8 8.2 0.2 0.0005 11.1 11.6 0.5 1.7 ill 11.6 0.5 9.8 11.1 11.6 0.5 0.14 Al(HO$)S 2.0 6.3 0.3 .50.0 A1(HOY)S 0.s 1.8 0.3 0.1 1.0 3.3 0.3 2.0 2.0 6,3 0.3 30.0 tai,tq 4.3 4,6 0.3 0.18 8.7 9!0 0.3 2.0 11.0 1~ 3 0.3 14.0

—— a. Concentrationof all solutesis 2 g,f: b. h-emitting fissionproductsaftel’144-daycoolingperiod.

7s .. TABLE22

E.KTRACTIONOFNEPTUNIIH,PLUTONIM,AND MERICIW INTO VARIOUS SOLVEWS

\ Extrm:ted —-.——— Aqueous Phase ~ (xv)b —— Solvent !ko2. !P.u!l !!LQIQ w WQ!!l Ethyl ether 1!4 tiW3; sat IWbW, a 100

bN HNos 9 17 12 70

ml HNo, 17 6S !2 89

Dibutyl W tfl’o, 1-7 23 )1 8:

carb i no 1 7 co w Iiuws 23 48 1’9 95

DBBP,= .Jot dlM HND, 91

% Hm, 15

D~,d 85$ 2.4M ca(K)$)*; 0.6)4 w, 11 ?i.4Mca(ND1)2; o.oSN ~~ 0.3 41 .— a. High efficiency; no value given. b. Np(IV) unstable in W40J. c. Dibutyl-butyl phosphonate, DBBP. d. Dibutyl ether. @BE, * i’th 15% CCIQ.

-76- Other elements that extract strongly are Ce(IV), Au(III), and

SC{III); P, Cr(V1], As(V), Hg(ll), T1[III.1, III(W), and Bi[III) are partially extracted. After back-extraction with dilute acid, ferrous ion and urea orhydrazine are added to reduce Np(VI) to

Np[Vl; IWNOS is added for salting. A second extraction with diethylether further separates Np(IV) fron U(VI).127~i@’

Distribution data for several of the actinides, including neptunium,as a function of nitric acid concentration into dibutyl carbitol are reported.l”’oloo

Amine extractants, including long-chmin alkyl or aryl primary, secondary,and tertiary mines, and quaternary amine salts react with acids to form an ion-association complex which is soluble in the organic phase. The mechanism is illu:itrated with a tertiary amine:

+ + R3NH ---- A- ‘3N(org) “ ‘+ (aq) + A (aq] (org)

A- may be either a simple anion or the an:.on of a complex metal acid. The complex may undergo a further reaction with another anion in a ❑ anner analogous to anion exchnnge.

R3NH+ .-. A (erg) + B (aq) + ‘9NH+ ‘“.- B (erg) + A {aq)

The higher araines are excellent extractanl:s for Np(IV), PuIIV], and U. The advantage of amines over orgamphosphoms ccqounds is the greater stability to radiation and hydrolysis in radioactive solutions. The amines are usually dissolved in an organic

-77- solvent (xylene, benzene, or chloroform). TCI ●chieve rapidlphase separation and to prevent formationof a thixd ph8sB during extraction,a s-1 amount [3 to S vol%) of a long chain aliphatic alcohol is added to the organic phase. The l’elative extractztiility of Np in nitrate solution is Np(IV) > Np(VI) > Np(V), although the selectivity depends on the structure of the umine and the composi- tion of the aqueous phase. The extrsctive pfwer of the asdncs in nitrate and chloride solutions varies in the order Quarternary

~nium > tertiary > secondary > primaryJ’$i from H2SOS solutions, the squence is reversed. The distribution l:oefficient of tetra- valent and hexavalent actinides from IiCland HW~ acid solutions decreases in the sequence Pu ~ Np > U > P- > Th.

Keder et al. 190 have rqorted distributim coefficients for several actinide elements (more than one oxitiation state) from nitric acid solutions with tri-n-octylamine (TOA) cliluted with xylene (Figures li, 12, and 13).

The tetravalent ions show a second power depende,tce on the amine concentration, indicating that the extracted complex involves two amine molecules. Extraction of Np(IV)mIci Np{V’[) with trilaurylamine (TLA) from nitric acid is reported. 1’]*1$2 A review of :Iiquid-liquid extraction with high molecular weight amines has been publi:nrci.lg’

Np(IV) has been separateo frm U(VI), 1’u(III), Am(III), and fission products by extraction of Np(IV) info tri-iso-octyhmine

-78- o

b 1.0P---dI

Figww 11. The Extractfofi of tlm QwIrawhnt Acti nt& llftrat8s by 10 vol %TOA In Xylem. ;’s

-79- “r-vl t

b

lo4

no+ 02468 m 12 14

Ffgurt 12. The Extraction of tktlcxavalent Actfnfdk Nitrates by 10 vol Z TOA in Xylene. ~g’

-80- Ioo# w- ——

-1

AQtJoan Hrws, M

-81- (TIOA) in xylene from aqueous SM nitric acid solution containing

ferrous wlfamste. For further separation, the neptunium-bearing organic solution was scrubbed with SM HMO$containing ferrous

Sul.famate. Final purification of Np was ●chieved with a TTA extraction. 19’’~”s 239Np has been separated frm 2*~AJSby extraction with TIOA.*g’ Np(IV) was extracted [i# > 20] froa 0.1 to IOM HPKlgwith O.lM tetraheptyl ~ni~ :litrata in xyltme.

Ihe ~was ~2000 in lMNNO1. l$’ O~stributilm data for a large ntaber of elements in quaternary anmonium c~~ds fron various solutions have been determined, and a proc~lure for separ~~ting

Np and Puuith this system has been SWpOrtaX1.isC

Kedertiss has reported the distribution coefficients from tetra - and hexavalcnt Np, Pu, and U from HICl solutions into TOA

(Figures 14 ●nd 1S). Pu(lV) is much more extractable than Np(IV] and U(IV) under the same conditions, and the hemnmlent actinides are umc extractable than the tetravalent in this :\ystem.

Np(IV) ●nd Pu(lV) were strongly ext?actsd from sulfuric ●cid by the primary amine “Primene”* JH-T in XYlonc. In guneral, the order of extraction of Np(IV) and Pu(lV) from mlfate solution

W8S primary >> secmdsry ~ tertiary ~Jne*20Q *n)’ ~re Proce” durcs for aciinuextraction have been reported for U and Pu, sndi these methods also offer potential for Np separmtic}n.es”i’]~ze’

Mixed &xtruotunt8 (ditwntaj. The torn synergism is iusod to denote enhanced (or depressed) extraction of metaks by mixed extract~nts (diluents) as c~ared to extraction by each extractant

~’gfstered tradcnamc of Rohm ●nd Mas Co. -a2- Jd-L-Ld_d.-s024 SOK) Hcl. l!

Figure 14. ExtractlonoVU(IV) and NpI(IV) by 10X TM and Pu(IV) b{$!,m

Tu frm MCI Solutl on% ●

“8s - too

10

w’ E-. /.

2 4 6 10

Figure 15. ExtractIon of Hexavalent U, NP, ml Pu fmm HCl 5olutlon with 1.0% TOA in Xylene.1’9

-64- (diluent) taken separately. The rangl~ of phenomena described

under the term synergism is diverse, l:omplex,and not completely

understood. A reviw of this subject is given by Marcus.*”

Although the subject has received con~iderable attention, only

a few examples sre reported for Np. Lebedev et a2.202 have

reported a procedure to determine 2“3Am through its daughter product 2Y9Mp in solutions containing large quantities of curium and fission products. O.lM l-phenyl- 3-methyl-.4-benzoyl-pyrazolon-S

(PMBP) and 0.2SM tributylphosphate (TEP) in benzene were used to separate Np(IV~ from Zr, Mb, Cs, Ce, h and Cm in O.SMHNO, and lM HIP04. More than 99% of the Np wa~ extracted with zO.1% of other elements. The ““AR was determined by measurement of the gm activity of the extracted 239Np,

Taubezog has d~scussed the inflwunce of polarity in two- component diluent ●ixtues of chlorofl}rm, benzene and carbon tetrachloride on the extraction of Np(IV) ●nd Np(VI) cooplexes with several phosphate and amine extracta’nts. The results are inter- preted in terms of the size of the complex npucies, the diluent structure,, dipole interaction between complex and diluent, and other factors. Figures 16 and 17 show t~~e effects of variation of diluent mixtures on the dis+ributicm of Hp(IV) and (VI) into

TBP and tetrabutyl~nium nitrate frm nitric ●cid.

-8s- . ,.. / . “--E 4

“c.: L d 2 0.1--- v k

—— 0 002 OA 0.6 0.8 I.0 Mds Fmctiom of Dilusnts

Figure 16. Heptunlm ExtractIon with TBP from W HNOS Into Dlluent Mxtures.2ss

-a6- Mol.Fructions d Dihmts

Figure 17. Of stri button Coefflc

-87- c. ION EXCHANGE

hhny variations of ion exchange are used for separating

14pfrom other ions. Np ions in dilute nineral acids with no strong completing ions are sorbed by strongly acidic cation exchange resins, such as sulfonated polystyrene. In general, the ability of cations to be sorbed on cation exchangers increases with increasing charge and decreasing hydrattd radius. Thus, the order of sorbability on cation exchangers for .Np is Np(IV) ~>Np(III) >

~22+ > W}* All Np species are sorted at low acid concentra- tions and eluted with high uoncentraticms of mineral acids; elutio,~of NpO~ proceeds first and Np(I\) Ss last. Some anions form neutral or anionic complexes with different oxidation states of Np, so that Np may be eluted by this mechanism. Both Np(V) and

Np(VI) are slowly reduced to Np(IV) by common organic base resins.

For this reason and because cation exchange of Np(IV) offers limited selectivity in the separation from other multivalent cations$ this method has not been used ~idely for analytical applications.

Anion exchange is one of the techniques mc)stuseclfor separation of Np in analytical and process applications. The method is simple to perfom and yields excellent separation from many other elements, including most of the fission products.

Ion exchange ha~ been the subject cf many reviews. The books of Helfferich,20° Samuelson,zos Anrphlett,20&and Rieman ant

-88-’ Waltonzo’ are good references to the theory end applications of ion exchangers. Other reviews of ion exchange include Massart,20e

Korkisch,20s’2il and Faris and 8uchanan. :10

Anion Erohunge. Np(IV) forms anionic nitrate and chloride complexes that are strongly sorbed by anion resins; the anionic species provide separation from the cations of many other elements.

The hexavalent state of the actinides al:;o fozm strongly sorbed anionic chloride complexes. Greater sep:ltation of Np is attained from most other elements in the nitrate :;ystem than in the chloride system. The distribution coefficients of many elements over a wide range of nitric acid and nitrate concentrations have been reported.212 Data are given in Figure 111.

In a typical anion exchange cycle, :~ sample containing Np is adjusted to 7 to 8M HNOs for optimum :\orption of Np(W~)G2- ions, and 0.01 to 0.05M ferrous sulfamatc is added to ensure that all Np[V) and Np(VI] is reduced to Np(IV1. The solution is heated to 55*C for 30 minutes or treated with sufficient sodium nitrite to react all the sultlmate and oxidize e.rcess Fe(II) to Fe(III); this treatment is necessary to prevent e.~cessive gassing in the resin bed. The resin is washed with strong nitric acid to remove

Zr, Ru, Pa, Fe, Al, rare earths, U, transplutonium elements, and most other cationic contaminants. ‘l’h(IV) and Pu(IV) are not separmted; howevez, washing with 5 to 15 bed volmes of 5 to

6UW3-O.05M femous sulfamate-0.05M hydrazine reduces Pu(IV) to

-09- I

Figure 18. Sorption of the Elements from Nitric Acid Solutions by Strongly Basic Anion Exchange Resins.212 Pu(III), which is removed from the column. Washing with W

HCl removes Th. The Np is eluted with 0.3M HNOg. Cross-linking

and particle size of the resin greatly influences the separation

from other cations as well as elution ofthc Np. i52’zi3-215

Macroporous anion resin is superior to gel-type anion resin for

separation of Pu from Np. 21sa A number of similar procedures with

variations in acid concentration and substitution of semicarbazide

or aminoguanidine for hydrazine have been reported.

The separation of tracer amounts of Np(VI], Th(IV), Am(III), and Pu!IV) in nitric acid by anion exchznge has been reported.21G

The feed was adjusted to 7.2M HN03-0.054 NaN02 at 50”C to yield

Np(VI) and Pu(IV). After sorption on “Jowex” l-X4 resin, the 2+ column was washed with 7.2M HNOg to elute Am(III) and Np02 , then with 4M HN03 to elute Th(IV), and Finally with 0.35M NN03 to elute Pu(IV). Other work with macro quantities of these cations has shown incomplete separation of Np probably because of some reduction to Np(IV]. Also, Th([V] and I%(IV) were not completely separated. The separation o:: Np from fission products in 7.SMHNOY using ascorbic acid reductmnt is reported by

Ichikawa.217

Radiochemically pure Np has been p::epared for production of high purity metal with one nitr~te anion exchange cycle and two chloride anion exchange cycles successillely.zie

The distribution coefficients of mnny elements over a wide range of hydrochloric acid concentrations have been reported.

-91- These data are used to design separation systems :forchloride anion exchange (Figure 19).*2*’zi9 Np, Th, and PU are :}eparated by chloride anion exchange by sorbing the anionic chl~oro-complexes of Np(IV) and Pu(IV) in 8 to J2M HC1. Pu(III) is eluted with

NHI+Iin 8M HC1, NH20H-NH41 in 12M HC1 or Fe’;12in 8MHC1; Th is not retained; and Np is eluted with 0.3M HC1.iss’220 Distribution data for 65 elements on “Dowex’’*l-X8from 2 to 17.4M acetic acid in water have been reported221 (Figure 20), E)(~Fllesof several separations including U and Np are given. Distribution data for

60 elements on cation exchange resin from 1 to 17.4M acetic acid in water have also been reported.222 With !lp(VI) in 7.9M HC?HSOZ, equilibrium was not reached even after 40 hours of mixing.

A method to separate and determine Np, Pu, U, Zr, Nb, and MO in ❑ixed fission products by anion exchange with HC1-HF solutions has been developed.223 Trace quantities of Np have been separated from macro amounts of Zr and trace amounts clfNb by elution with

HC1-HF solutions.22° Also, HCI and HF solutions have been used to separate U, PUB and Np from each other ard from alkali metals, alkaline earths, rare earths, trivalent actinides, Al, Sc, Ac,

7%, Y, and Ni (Figure 21).225 Controlled elution with a series of solvent mixtures was used to separate Np, Pu, Zr, Nb, Mo, Tc,

Te, and U from fission products.22G The chloro complexes were sorbed on anion resin and sequential washes with 12M HC1-NHZOH-NH41(PU)B

10M HC1-Aq H20z(Np), 9M HCi-Aq Hz02(Np and 2r), 9M HC1-ethanol

(l:i, Zr), 6MHC1-ethanol (1:1, Nb), ethanol-lM HC1(4:1, Te],

● Registered Trademark of Dow Chemical Co. -92- I u) M EIMlll-F4 r 0 NM ElEll w. % ~.5 cl ‘-J p tl u I!iilD1@1“ E3fllfillkmEilll *. I Bil w ZI+I.14a.1 , m. *I l:+ -. i .;, ., 1 I ,[. 4 id Q: Kit!!EilEliilkill m~E w’.. km). w Cdq ‘w’ ., 4-4 n ml::5..m1!1 L L$lRIpd#i “w IalIEwF#l WI Ei34d HJ# ULlIiLi.1 EfElEEEwH Em-1 lEm ,, 81 Ewu EiEili

Figure 20. Sorption of the Elenwnts from Acetic Acid Solutions by an Anion-Exchange Resin ?2J T—-----71 1 I 4 k-!50”

Elu@nt W&moo column VdUCWB9

Figure 211. Uraniun-Neptuni uwPlutonlwn Sel~aration b y Anion Exchange (“bwex” 1-X1O, 400 Nesh, 0.25 cm2 x 3 cm Column). **s

-9s - ethanol-W IK1(4:I, *), O.IM Kl(ll)o and 4M tMls(Tc).

Other literature has included a study of the elution charac- teristics af xp, PU, II. Pa, WJ Zr in 1~1, Imos, ●n’d ~b~h ~y~t~s with ‘Skuex”-2 anion resin. EquiIibri~ data wru given for each acid fm O.lV CO concentrated, and pss~ble separations bmsed on eqvilfbri- da:a were summarized.*” Equilibrium data wre 8iven for a ndmr of elements lnclwl~ng Np in 0.1 to WN NtPO. with

“lbuu#-2 resin. Separation ofSp frtmCs andleuas attained, hut data were erratic.~a’

Sp has hem separated fmm Pa by elution uith 1231 K1-O.5N W ukth Pa elut{ng first.’” Separation has also hem achieved by clution u~th S!UIUl frm an~on resin, in which case Sp elutes f~rst.zz*

!JJ(IV) haz been sorbad quant~tat~vely on ‘*R’”-l fsxm O.IN

Sa2CD1 ●nd elutod uith W*CI or dilute MC1.Y’O

Np(Vll] fores stahlc mlkal~nc s01ution9 as sk :+OS’- Ion.

.Sovikov a: (x:.z” studid the anion exchange behavlw of this soluble complex as a poss~ble has~s for separation from other elmts. lhe sorption was irreversible for all experimts; this was attributed to the redxtion of the ~(~11] by the resin.

-%- An anion exchange method using the nitrate system has been

reported for removal of Np before spectrochemicaldetermination

of catioinicistpuritiesz]z(Procedure23, p 200),

In several reported instances, anion exchatn:le resin exploded or ignited after use in nitric acid or strong ni’:rate ~olutions.233

Tlw!se ●ccidents are thought to be due to nitration of the skeleton of the exchange resin, leading to the spontaneous! reaction in the presence of heat. Anion exchange resin in the nitrate form should not be stored in the dry state, and temperature should be carefully controlled ●t <60*C when used in stronji nitric acid.

The nitric acid concentration should be <8.SM, a~~d flow to the col,un should not be interrupted, particularly wlmn high levels of radioactivity are in the col~.

cation &Ywhf.znge. Sulfonic acid type resins have had limited applications for Np separations because both Np(uI) and Np(V) are reduced S1OU1Yby the resin.:Sh Several separations hove been reported for the pentavalent state of $ip. Y. A. Zolotov and

D. Nishanov235 reported the separation of Np from U, PI),and fissioc products by elution of Np(V) ●head of U(~’1)with IN MNOj frou a cation resin in the hydrogen form. Np was initially oxi- di:tedto the hexavalent state with bmsate. Separation of Np dqpended on reduction to Np(V) by the resin. Also, cation exchange has been used for partial separation of Np from Pu(IV), lh(lV), and Zr(lV). Np was ox~d~zed to Np(V) in dilute nitric

-97. acid before sorption on the resin, but a fe~rpercent of the Np(V)

was reduced to hlp(IV) by the “Dowex’’-5OWrosin and was not

separated from the other cations.23G

The distribution coefficients for many of the elements were

detmmined in 0.1 to 12M HBr with “Dowe~’-5G resin. Conditions

for separation of U(VI) and Np(IV) and separation of Np(IJ’)and

Pu(III) were given (Figures 22 and 23), Mary other separation

methods fcm Np could be devised from the distribution data

(Figure 24).237

Np and Pu have been separated by elution from cation resin

with HF after reduction to Np(IV) and Pu(III) with S02.238 Np(IV)

was eluted first with 0.02M HFZ3’, and then Pu(III) was eluted with 0.5M HF. Also, Np was separated from Pu by cution exchange with HBr follGwecl by TTA extraction.2’0

Pressurized elution development chromat~graphy on cation resin at 70 to 90*C with a-hydroxyisobutyric acid has been very useful

for separation of trivalent actinide elements both in the labora-

tory and with macroscopic quantities,z~~ Although no specific separations of this type for Np are reported, the m~ethod is useful

for highly radioactive solutions.

Distribution data for many of the eleme~ts on “Dowe3@’,-50resin over a range of hydrochloric acid concentrations and also over a range of perchloric acid concentrations have been reported (Figures

2S and 26).1$’

-98- a- Smp18 9M WI

9M HBr

,,, .,,.

o ~ C)-2 .44J-.-JQ6 8 m Column Volumos

Figure 22. Separation of U(VI) and NP(IV;) bY Cation Excllan9@ (“Oowex” !iO-X4 0.2 cmz x 2 cm Column@ 25 °}?37

3

-m + Sarrrpk

6M HBr 9M HBr-CL2M HF 2 ~MfJ(lv)

I

t,

,{ o -EkJ#.. 0 4 8 12 Column Volumes

Figure 23. Separation of Pu(III) and Np(I\) by Cation Ex$~~nge (“Oouex’’5O-X4, 0.28m2 x 3 m COl~~, 600).

-99- t

Figure 24. Sorption of the Elements from tiBr Solutfons by a Catfon Exchange Resln,2$7 Figure 25. Sorption of the Elemen:;8from HC1 Solutions by a Cation Exchange Resin. I

I

Figure 26, Sorption of the Elements from HC104 Solutions by a Cation Exchange Resin.23@ i!no~anio Ion ticdzangera. Inorganic exchangers have been

largely superseded by synthetic resins principally because of

higher capacities and more useful physical characteristicsof

the synthetic resins. However, inorganic exchangers have the advantage of greater resistance to radiation dumage. The distri- bution coefficients of 60 cations, including Np, on hydrous zirconium oxide, zirconium phosphate, zirconium tungstate, and zirconium molybdate have been ❑easured.zbz Shafiev et al.2k3 have studied the separation of Np, Pu, and Pm on zirconium phosphate. Np(V) is not retained while trivalent elements are readily eluted with lM HNOq. Pu(IV) is eluted with 0.5M HN03 containing reducing agents such as ferrcus sulfamate or hydro- quinone. Zirconium phosphate does not change the oxidation state of Np{V). The sorption of Np, Th, and U from HN03, HzSOb, and

HF solutions on amonium molybdophosphale (AMP) colunns has been dete~ined.2b~”2”s The sequence of so~ltion is Np(IV] > Th[IV) >>

U(VI) ~> Np(VI) > Np(V). These same woy.kers demonstrated the separation of Th, U, and Np using columns loaded with AMP.24G

Tsuboya et aZ.247 demonstrated conditions in a HNOJ system for separating Np(IV) and U(VI] with a tung:;tic acid exchanger; Np(IV) is much nmre strongly retained than U{VI) from 0.S to 2N HNOS.

- 103 - D. CHRWATMRAPHY

Emhwction C?w0watog3up@. Extrac::ion chromatography has been applied to the separation of Np, PUB Am, and U with 100%

TBP sorbed on diatomaceous silica. The diatomaceous silica was initially exposed to dimethylsilane vapor, then treated with TBP, and used as the stationary phase. Nitric acid, with and without reducing agents, was used as the mobile :~hase.zho Other workers2b9 used this system for a similar separation of NF and found that modifications were required to prevent reduction of Np(VI] to

Np(V) and to improve separation from some fission products.

Eschrich250 used the same system to determine the oxidation states of Np by eluting with 0.5 to 2M HN03. The order of elution was

Np(V), Np[IV), and Np[VI). It is probable that some reduction of

Np(VI) occurred.

23gNp was separated from fission proclucts and U on a column of TM sorbed on glass powder.251 The chzomn.~a~raphic method gave - much more effective separation than batch extraction; recovery was adequate so that isotopic dilution was not necessary. However, ‘ two column separations were necessary to separate Np frm Zr.

Wehner et aZ. 252 have also reported separ;ltion cf ~3gNp from fission and activation products on Poropak..Q impregnated wi~h lTA-o-xylene.

Some workers have used “Kel-F”* or ‘~eflon”** powders coated wkth an organic extractant as the stationary phase for extraction

● Registered tradename ofM. K. Kellogg Co. ●*Registered tradename of Ou Pent.

- 104 - chromatography separations. “Kel-F” powder :oated with trilaurylamine

nitrate has !]een used to separate Np from U, Pu, and fission

products. The feed was adjusted to 2M HN03 - O.lM Fe(SO~N}12)2 and

passed through the bed. After the column wa:i washed with .lMHN03

containing Fe(S03NH2)2, thu Kp was eluted with HzS04 - HN03.

The method is very selective for Np(IV) and has yielded chemically

pure 23gNp when the weight ratio of U to Np was >1010 in the feed?s3

The separation requires one to two days. A :imilar method was

developed for the coseparationof Np and Pu from U.zs”

PapeY C?uwmatograp)qf. Paper chromatography Rf values for

elements Ac through Am in many mixtures of either tCV03 or HC1

with methanol, ethanol, and butanol have been determined by

Keller.zss It was necessary to reduce Np(VI) to Np(V) or [IV)

before starting the separation because Np(VI) is slowly reduced

in the column resulting in poor separation of the bi~nds.

Neptunium(IV) was separated from III(IV) with 12M HC1-butanol and

>8M HN03-butanol mixtures. Also, good separation of Np(IV) from

U(VI) was attained with >lM HC1-butanol; Np(V) was separated

from U(VI) with 2M HC1-ethanol as developer.

Clanet2sb measured the Rf values for ele:~ents with atomic numbers 90 through 96 in mixtures of mineral .~cids with alcohols and discussed analytical applications.

Rf values for Np(IV), (V), and (VI) have been reported for paper treated with TOA using 0.5M HN03 developer solutions

- 105 - - ...... ,,......

containing LiNOS, NN~NOS, or Al(~s)3. The valuss are well

separated for the different oxidation states of .Npand for the

different actinides.zs’ Rf values were also obtained for paper

treated with solutions of tetrabutylhypophosphate in acetone- water (20:1) using developer solutions of nitric and petrchloric

acid.2se

Twelve fission and neutron capture isotope:; including 23gNp,

have been separated from irradiated uranium with aqueous hydro-

fkuoric and methylethyl ketone-hydrofluoric acid mixtures as developers.259

Thin Layer (%rcxnatography. Rapid separation of different valence states of Np from each other and from ether actinide elements by thin layer chromatography on ‘7eflcm’’-4O powder saturated with O.lM tetrabutylhypophosphate solution has been demonstrated.2 ‘e

Gza Chrcwfatogq?ly. Effective separation of the transuranium elements by gas chromatography of their chloriies has been demonstrated.z 60 The volatile chloride comploxes were synthesized at %SOO°Cby adding A12C16 vapors into the carrier gas. The

experiments were carried out in glass capillaxy colums maintained at %2500C with less than one microgram of each actinide. Cm, Am,

and Pu were eluted in order of decreasing ator~ic number in about

the snme position as lighter Ianthanide elements in a similar

experiment. The retention times of W, U, and Pa are much

- 106 - shorter; it is postulated that the tetra{:hloridesof these elements

i~re produced. The chromctogram is measu]’edby collecting fractions

of A12C16 condensate at the exit of the c:olumn. The actinide

hydroxides are carried with La from strcxlglybasic solution and

separated from Al. Then the actinide is deposited, anclthe alpha

spectrum is measured with a surface barrjer detector and multi-

channel pulse height analyzer.

F. . OTHER METHODS

Volatilization. Separation of more-volatile Np(IV} chloride

from PuIIII) chloride and other less volatile chlorides has been reported.261’262 The actinide chlorides were prepared by passing carbon tetrachloridevapor at 650”C over mixtures of pl.utonium- neptunium oxides or oxalates. The nepturium chloride sublimate was collected with a separation factor of’%3 x 103 for Np initially containing 4% Pu; the yield was w96%. Tie method is useful for obtaining quite pure Np where a quantitative separation is not

~equired.

NpFG is quite volatile, intermediatebetween UFG SLndPuFG.

Separation was attained from UFG by co-scrption of the hexafluo- rides on NaF. Then the F@FGONaF complex was reduced, and the UF6 desorbect. After refluorination,the NpF:cwas desorbed.263

EZectrophore8i8. Clanet256 has developed m electrophoretic method on cellulose acetate membranes tclseparate the charged species formed by elements with atomic rmrnbers90 to 96 in 1 to

- 107 - 12M HC1 and HN03. Mobility curves have beer obtai:nedfor the acid

concentrationrange for both acids. A large number of potential

separations of these elements and the solution conditions are

tabulated, Some of the separationsof Np irclude !Jp(IV)ctr(V)

from U(VI:);Np(IV) from Pu(IV) or (VI); Np(lV), (V), or (Vi) from

Aml’”IiI)and Cm(III); and separationof the clxidationstates of Np.

Electrodepoeition. Although electrodqlositionhas been used

to prepare mOUMS for radiometric measuremc!r~t,electrolys~lshas not been used as a separation method. Ther(!has been one report that U, PtJ. and Np were separated by electrtllysis from HIWlsby var:yingthe pH. Optimum conditions were slultedas current density

7S0 to 1000 mA/cm2 with a plating time of 2 to 3 hours and solution volume of 20 to 30 ml. Np is completely delmsited at pH :* 9, and

Pu and U are completely deposited at pkl C6 ~md pH <3, respectively.2’*

Other workers using different media for ele~:trolysishave been unsuccessful in separating Np from other ac-:inicles. Although partial separation from a number of comon l:ations has been attained, no useful separation method has been reportlxi.

Mi808zkneim8. An analytical scheme Ih,is beer) described uhich yields sequential separation of the elements including Np renaining after neutron exposure of 1 mg of ● fissile dlememt.z’$ ‘The products were separated and isolated for determination of isotopic abundance by -ss spectrometry using solvent extra~ction, ion exchange, extraction chromatography, and prccipitution methods.

- 108 - VIII. ANALYTICAL METHODS

A. SOURCE PREPARATION AND RADIOMETRIC METHODS

Counting. Because counting methods are more :}e:lsitivethan

chemical or spectrochemicalmethods, they ara the primary methods

for identifyingand quantitativelydetenaining Np. The two most common Np isotopes are 237Np ~d 23*Np. 237Vp is uwally determined by alpha counting its two major alpha transitions $~t 4.781 and 4.762

MeV. If 237Np has decayed for a period of shout 6 months or longer, it can be dete~ined by gama ray spectroscopy of its 2y]Pa daughter. [f 2’:’Np is separated from 233Pa lthich h~as an 86.6-keV gam :?ay, the 2~7Np 86.6-keV g- ray can I>e counted dimectly.

239Np is determined by g- counting its gains transitions at

228 md 273 keV.*O

The gross alpha activity of 23’Np can b41 determined with a proportional counter or plastic scintillation) cout~ter. If other

●lpha-eaitting nuclidcs are present, ●n ●iphm pulse height

●nalysis with ● surface barrier detector 8111cws a detemimtion of the percentage of the total alpha counts attl’ibutableto 2:17Np.

Liquid scintillationcounting can be uwd to determina gross

●lpha activity with ●lmost 100$ ●fficiency ard in many cases can be used to determine 237Np in the presence d other alpha-omitting nuclides. l%- energy resolution in giquid %C!intillmtion if~ MOO KeV

-1o9- as coward to 1S KeV for surface barrier (Ietectors.

--ray spectrmetry with either a !la I scintillation detector or a Ge(Li) detector may be used 1:0 determine 2s9Np.

For 23$Np gamma rays (228, 278 KeV), the tw]ergyresolution of a typical coaxial Ge(Li) detector (about 1.0 KeV) is much better than for NaI (about 20 KeV). The efficien:yof such Ge(Li) detectors relative to a 3 x 3 in. NaI dete~tor is 3 to 1S% for the

1.33-MeV g- ray. Ge(Li) low-energy photon detectors (LEP) have an energy resolution of 0.S KeV with lower efficiency.

An o-y coincidence method for determinating 237Np was developed which increased selectivity.2s” The resolving time of the coincidence system was taken as 8 x lC”-6 sec.

A radioactivation method was developfd to increase the sensitivity for determining 237Np.2G5 Thf!activation product is short-lived 23@NP, which is determined by t:ountingits 1.0 MeV gama ray. To obtain maximum sensitivity, the Np should be purified before and after neutron irradiation.

A sunssary of tho sensitivity and sel,?ctivil:y of radiometric and radioactivation methods for determini~g Np is presented in

Table 23. In summary, alpha counting is the ~!;t convenient method for 237Np, and gamma spectrometric methods are preferred for 238Np and 239Np. Because of the contirr~ingadvancements in nuclear radiation detection systems, the sensitivity, precision, and accuracy of the radiometric methods discussed above could be

- 110 - O.ostoo.lmg s m10-b O.u 10 to so I a 1O-B O.oa .. , ,1 m O.OJ -. ,.,s so 0.1 to 0.s ~ o.z 111 Yoto 100 m1 10-~ Ill .. 1,1”

50 0.0s -. It’ M 0.01 to 0.1 q 10 lo tow .. 5m Jo-” .. G.1 Icm I .. 1 ,@l . .

0.1 M 0.s Iq M 1 1 101 uJtozQ sm Ir’ .- .. so 10-m-i .. 0. u In 10 ● .. 0.

(0.1co 1] [0.1 CO 1] 10”’ tm .- Stoa 10”” W1 . . . .

Iw . .

Iw 10-’ 10 (>1) Ic’ 5t000 10-1KI (>1] ●o* (>IM) ●18’

. . 0.1

. . 0.1

. . I [10s) 1 1 T-w-” - tm # ~sa ‘‘*I ●Iw

F? . .

- 111 - improved with available advanced instrumentatim.

Scurce Preparation. Direct evaporation ig the simplest

❑ethod for preparing sample aliquots for counting. The disadvantage for alpha pulse height analysis is the thickness of the deposit, which results in self absorption of the alpha particles. If a surfactant such as tetraettlyleneglycol

(S0 pg/cm2) is added to the aqueous solution, the NIPsolution is evaporated from a film rather than a drop resu,~ting in a more homogeneous deposit.zc’’z~’ The surfactant polymerizes on heating and bums up when ignited. The diluted sample is transferred to a suitable counting plate, e.g. stainless steel disk, and slowly evaporated to dryness to prevent spattering. The direct munt is flamed to dull red heat, cooled, and coated with a thin layer of collodion solution, and the Np is counted.

ElectrodePosition has been widely used to prepare high-quality sample mounts for precise alpha counting. The procedure is extremely useful when samples contain a mixture of alpha emitters that need to be resolved. Electrodepositionresults in excellent sample mounts fmm organic solutions that evaporate very slowly or leave large amounts of residue and fmm ●queous solutions that contain large a-nts of dissolved solids.

Np and other actinides can be deposited from a vmriety of electrolytes ●nd under sewral conditions. Gravessgg described

- 112 - a semiquantitativemethod for depositing 237Np from Li onto Pt.

Ko27~)reported a method for quantitativedeposition of Np from

O.ZM HC1OQ - 0.15M NH4COOH, and Mitche11271 used NH+C1 - HCl to

obtain a yield of’94%. Some systems used by other workers272-274

are formic acid-ammoniumformate, ammonium coalate, ammonium

acetate, ethanol,,isopropanol,and Nli4Clwitt uranium carrier.

Donnan and Dukes275 developed one of the!fastest procedures

for quantitativedepositions by combining Mj,l/chell’smethoclwith

uranium carrier addition. 23aU is added as ii carrier in three

increments to the NH%Cl electrolyte to ensurf!quantitativeyield; only 20 minutes deposition time is required. An average recovery of 99.8% with a relative standard deviation {IftO.2% (n = 10) was obtaind with Pu. Similar results were obtained with Np.

Resolution of 20 keV is achieved consistentlywith electro- depcsited mounts and a silicon surface-barrierdetector.

Parker and Colonomos276reviewed electrodepos;Ltionprocedures and described two new methods. One is a co-depositionmethod for alpha-spectrometry,and the other for preparation of carrier-free

layers as fission detectors. In the co-depc,sitionmethod with uranium carrier,,237NP was deposited quantil.ativelyin 10 min at

170(0V with stainless steel as the cathode.

In other recent work, Np was deposited quantitativelyfrom ammonium oxalate or ambonium acetate solutifm or mixed ammonium

- 113 - oxalate-ammoniumchloride electrolyte.z’’-zgo Alcohol is an excellent plating medium for aqueous and orgalic samples. Methods have been reported for ethanol, isopropanol, md alcohol saturated with ammonium chloride.201-2B3 Deposition from sulfuric, hydrochloric, perchloric, and oxalic acid has been reported by Palei.20+

The effect of variables on the quantitative deposition on Np and other actinide elements has been reported by other authors.:1e5’2aG

Other methods which have a lower efficiency but yield sources with excellent resolution include vacuum sublimation and electro- spraying.28b-2g1 Both electrodeposition and (!lectrospraying have several disadvantages. These ❑ethods take a longer time than evaporation and require special equipment including a specially designed electrolytic cell for electrodeposition, high voltage equipment, and special capillary with a needle electrode for electrostatic spraying.zGG

B. SPECTROPHOTWHRY

Although different oxidation states of NF have sharp absorption bands, spectrophotometric analysis has had liuited use because rmdiometric procedures are mme sensitive. Further, alpha contain- ment is required for the spectmphotometer, anu opermtion within a glove box is tedious. Generally, procedures used for other actinides can be applied to the determination. Np i:~ adjusted to

● single oxidation state, and the concentration is calculated from the nlar extinction coefficient and the absorption of the

- 114 -

..-. solution at the proper wavelength. When more than one oxidation

state is present, appropriateequations ma:~be formulated for the

concentrationof each component.=g=

Abaoz@ion Bade. Important absorptionbands and molar

extinction coefficientsof the different oxidation states are

listed in Table 24. Most of the sharp bands can be used for

qualitativeor quantitativework even though they only obey

Beer’s Law over a limited concentrationrange. The best band to

use for analysis of Np(III) is at 786 mp kecause this band obeys

Beer’s Law. The strongest bands for Np(I\’)(960 mp, 723 mp)

do not obey Beer’s Law, but they can be used with appropriate

calibration and constant slit width. The strongest band for

Np(V) (at 980 mu in lM HNOS) does obey Be{:r~s Law;2qo a high-

resolution mmochromator (e.g., a double-grating monochromator)

should be used. Cauchatier’ and coworker:;2go have developed a

method for determining Np in irradiated nuclear fuels by measuring

the Np(V) band in lM HN03. The pentavalent state is produced by

adding hydrazine to a Np(V]-Np(VI) ❑ixture obtained after evaporation of the nitric acid solution. Correction for Pu(VI)

is necessary. The most useful band for Np(VI) :1s at 1.23 urn;

Colvin developed a method using this band for measurements in nitrate solution.*9’ In this method, Np is oxidized to the

hexavmlent state with sodiID bichromate, and thm the acidity is

●djusted to 1 to 2U. The ●bsorbance is measured at 1.23 urn

- 115 - TABLE24

IMPORTANTABSORPTIONPEAKSOF NEPlUNIltN2g’-2s’

Absorption 8and [w) .—MolaI”Extinction Coefficient Np(II1) 55P 44.5 60~#d 25.8 ~la,d 30.5 ,86b,d 44 (50to 60°C) 84E+ %25 991b W27 1363b -39 Np(IV) 50CF %15 ~wa,d 22.9 590.5=~d 16.1 WOCF % 7.5 cd ~71s ‘ ~ 3.7 7z3b 127 74f’d 43.0 800C %2] 825ad‘ 24.5 961# 162 975= %32 m(v) 428a 11,1 ~l,b,d 22 ~17cJa’ --18 98& 395 W39CF %]80 N’Pwl) 476a 6.4 55P 6,8 1223bJd 45 1230c’d %43 Np(VII) 412* 1370?40 618e 382*1O

a. lM lCIOq. ~1.~ ~lo,. c. IM HNOJ. d. Obeys8eer*sLaw. e. KOHSolution.

- 116 - against a reference HN03 solution that i:;the same HN33 concentration

as the sample. The method has a relativu standard deviation of

?0.5% at 3 g/k. A number of ions, including Pu, do not interfere

when present in amounts ten times that o:: the Np. A study on heavy

water solutions of neptunium salts in wh:.ch numerous well-defined

bands were found in the region 1.2 to 1,11 Um is reported by

Waggener.sOO

color cmph?xe8. Spectrophotometric methods for Np lack sensitivity. Furthermore, the position of the band extinction coefficients are affected by some anions and by the Np concen- tration. These disadvantages are pafi.ially overcome when color complexes that have very high mlar extinction coefficients are used. A ❑ethod with arsenazo III [1, 8-dihydrcxynapthalene-3,

6-disulfonic acid-2, 7-bis(azo-1) benzenn -2-arsenic acid] is reported.301-303 The intensity of the s~:able green complex of Np(IV] snd arsenazo III is measured al: 665 mu. The color forms instantaneously, and its intensity is constant over the concentration range 4 to 6M HN03. The molar extinction coefficient at 665 mp is %105. Chudinov and Yakovlev separated

U{IV), Pu(IV), and Th(IV), which fozm colored complexes, from

NpC)2+by extraction with di-2-ethylhexylphosphoric acid (HDEHP) in carbon tetrachloride. After extraction, Np is reduced to Np[IV], and arsenazo III is added. The lower lirlit of detection is

0.04 vg/ml, and the relative accuracy is between 1 and 7t,

- 117 - Bryan and Waterbury302 separated Np from U cnd Pu by extrac-

tion with tri(iso-octyl)amine(TIOA) before d~!terminingthe

arsenazo 111 complex. They found that of 4S ~!lementsteste:i,

only Pd, Th, U, Pu, and Zr interfered, The :r{!lativestandard

deviation was between 7.2 and 1.1$ in 200-mg :;amplesof 8.S to

330 ppm of Np. (Procedure 20, p192.) Novikolr et aZ. have

studjed the color complex of Np(IV) with Arse]lazoM.30” At

664 mu the molar extinction coefficient is 1.18 x 10s in 7M HCl and 9.5 x 10” in O.SM HC1. Thorln was used by several.workers to analyze ?Jp.30S’30G

The absorbance is measured at 540 mu against a reference solution

not containing Np. The molar extinction coefficientmeasured

with a Beckman DIJspectrophotometeri.s~~14,500. The precision of

the method at the 95% confidence limits is t2.1% fo:r0.63 Ug of

?Jp/ml. Chudinov and Yakovlev used extraction to separate Np from

U and Fu interferences. The thorin method has also been automated307

with the Technican AutoAnalyzer,and the pr~’cisionhas been,

improved.

Np reacts in weakly acidic solution (pHv2) with xylencl orange to form a colored complex with an absorbancemaximum at

S50 mv and molar extinction coefficientof 5,S x 10*.3*8 X,ylenol

orange is three times more sens~tive than thcrin but only clne-half

as sensitive as arsenazo 111 as a reagent fcj~Np(IV), The greatest

- 118 - advantage of xylenol orange is that uranyl ions do not interfere.

Fe(III), Zr, Th, and Bi interfere.

Np(IV) forms a color complex with quercetin that is stable in the pH range 3 to 7 and obeys Beeris Law ove:ra concentration range 0.4 to 4.0 ug/ml. The molar extinction coefficient is z2,3 x 10b at 425 mu. This method requires an extensive purification to remove cations and traces of organic i:npuritie~,30g

The color complex of Np(V) and arsen~zo 111 exists over a narrow pH range and was studied by Chudinov md Yakovlev. 310 A method with the green-coloredcomplex of llp(V)and chlorophosphonazo

111 was also developed by these workers.~:] Chemical separation or masking agents are required for a nurbcrrof elements. Chudinov has studied spectrophotometricallythe interactionof 12 organic dyes of different types with Np02+.312 He concluded that the most promising reagents for pentavalent neptunium are l-(2-pyridylazo) rt?sorcinol (PAR), arsenazo 111, and chlorophosphonazo 111. With PAR, the molar extinction coefficient is M.3 x 10” at 510 mu. c. CONTROLLED POTENTIAL COULOMETRY

Determination of Neptunium ConcentratLo~. Alpha counting is generally superior to coulometry for determining less than a few micrograms of Np; however, controlled potential coulometry is an accurate and precise method for determining;Np above the 10-Dg level.313 The electrolysiscell contains n platinum electrode at which the Np(V/VI) couple is titrated in OSM HzSOd. First,

- 119 - the Np is oxidized to Np(VI) with Ce(IV), the Np(k’1] and Ce{IV) are electrolyticallyreduced to Np(V) and Ce(IIl”], and then Np(V) is coulometri(callyoxidized to Np(VI). T’leintegratedcurrent, in the last step is ~lsedtc calculate the concentrationof Np.

The standard deviation ranged from 6’%for 7 Bg to 0.05% for about

1 mg of Np. AS little as 2 ug was detectl>d. Elements which significantlyinterfere are Au, Pt$ Hg, “rl,and Cl ; Pu and Pd cause only slight interference. Stromatt’s method was used successfullywith a gold electrode insteallof a platinum electrode to eliminate the Pt/Pt(OH)2 reaction repw:ted by Fulda.9i~

Fulda obtained a precision of tO.6% for [5mg of Np. In another applicationof Stromatt’s method, the prot:isionwas O.1% (n = 8) for 9 mg of Np. Also, 3uckingham31s demo]lstrateda coefficient of variation for the coulometricmethod o~:*0.8% for neptunium o~ide and ?1.11$(n = 11) for neptunium nil:ratesolutions.

Delvin and Duncan316 used the same method in the presence of nitrate with H2S04 electrolyte. Plock an(lPolkinghorne]17used coulometry to analyze solutions of dissoltredalloys for both U and i’Jp without prior chemical separation. Plropst318 has reported a coulomtericmethod for Np using a conducltlngglass electrode in a thin-layer electrochemicalcell. Organic contaminants interfered and were removed by bisulfate fusion befo:.e coulometry.

- 120 - Determination of Ozidat ion States. This method applies to

the (IV), (V), and (VI) states and was reportej by strOmatt.’l’

The analysis depends on the fact that Np(IV) i; not clxidized, nor

is Np(V) reduced at a significantrate at a pl~tinum electrode in

lM H2SO~ electrolyte. The procedure is: (1) ~ potential is applied

at the controlled potential electrode to reduc: Np(V1) to Np(V);

(2) Np(V) is electrolyticallyoxidized to Np(V[); (3) Ce(IV) is

added to oxidize Np(IV) to Np(VI); (4) excess :e(IV) and Np(VI)

an? electrolyticallyreduced to Ce(III) and Np(V); ard [S) Np(V)

is electrolyticallyoxidized to Np(VI). Np[VI) is determined in

the first step. The difference between the integrated currents

for the first and second titrations corresponds to Np(V], and

the difference between the integrated currents for Step S and

Step 2 corresponds to Np(IV).

L&termination of &idation-l?e&ction Pot.e~tia2. The potential

for the Np(V)/(VI) couple was ❑easured in sulf~ric, perchloric, and

nitric acids with a platinum electrode.g2 The ~tential in HC1

was not obtained because of reduction of Np(VI) by chloride.

The inability of the method to measure irreversiblecouples, such as Nap/, is a serious limitation. The potential for the Np(III)/(IV) couple was obtained with a mercury electrode.

D. POLAROGRAPHY

Alternating current polarography with square-wave or pulse polarographshas been applied to detemine small concentrations

- 121 - of Np+) Slec and othurs J*’ have reported an analytical method

with square-wave polamgraphy to determine %@in Pu after pre-

liminary separation from Pu by 77X extraction. !tp is Ihack-

extracted froa the ITA into IOMHMI1. After sewer41 evapora-

tions with nitric acid and uet ashing with mixrd nitric

and perchloric acid (to oxidize organic asterixl], the final per-

chlorate residue is taken ~ in i ml of (IKI. ;! mg of W hydmxyi- amine hydrochloride is ●dded, and the solution is evapwated to reduce the wlw to 0.S IS1. Then, 0.S id of IM EDTAis added; the solution is adjusted to @i S.S to 6.$ with several drops of amsonia and diluted to S ●l. Exactly 2 IUI of the dilution are transferred to a polarographic cell and \pargedl with nitrogen.

The Nppeak is recorded at about -0.8V a~ainst the IS4WCUX’Y pl electrodo on the square-wave polarograph. Then an accurately measured aliqwt of a standard Np soiutin prepared in EDTA is added to the cell, and the !Wpconcentration in the ori,ginal solution is calculated from the increase in peak height.

Interference from the oxidation of chloride ions is decreased by adding EUrA to shift the half-wave potential.of the Np peak.

The patential for the reduction of the EDTAcomplex is about

700 mV more negative than for the reduction of neptunium ions; therefore, the peak is shifted well away from the anodic oxidation of chloride ions and is well defined. T~e authors report precision of f2$ and $10% for concentrationrarlgesof 500 and

25 ppm, respectively.

- 122 - Caucheeler ut al,**O reported a method whi~ch makes use of

the Xp(lV)-Xp(lll) couplo for determining Np :iIt solutions of

irradiated nuclear fuels ●nd 2“Xp targets. !ip is reduced

wlactmiyticaliy to Np(lV), and the polarograa is taksm. An

iali~wt of standard Sp is added to the cell, utd the procethm is

‘repeated . The method was used to analyze solutions with a NIp

content >20 mg/t coatainigq Pu, U, Fa, !di, Cr, and fission

[products,with 8 precision of~2%.

FWmography and other methods were used to coq~re the

chemistry of U, ?/p, and Pu by Kraus, at aZ.)2* Jenkins umd a

manual, po ●mgraph to study the nature and stability of EMA,

complexes with Np(II1) and Np(IV).’a’ Np(IIl) and ([V) wem

$tudied in chloride and perchlorate media by Hiwken and

Kritchevsky,8* *

Np was included in a review of eiectroch,aistry of the

●ctinides by Milner.’2* The sulfate complexai of Np(XV) were

studid polarographically by hsikm.a’

E. TITRATIW

Potenthmetfia. 10- to 100-mg quantities cf Np were detomined by redox titration. $2S CC(IV) iS used to titrste ?/p(v) to N@(VI), and iron(II) perchlorate was used to titrate llp(VI) to W(V)* fie methods can be used successively on the same ~lliquot of sasple

if WI is present (to give the required ceri~:oxidation potential]

and chloride ion is absent (it would be oxidi:~ed to chlorine).

123 - . ..--!... ., .!’-......

Stoppered weight burets were used for adding reagents, and a

plmtinu-cal~l ~ystem was used to detect the end points. Relative

standmd deviations for a single determination were 0.15# for

fezmus titers and 0.S9S for eerie titers.

Colnpbttiu Tftzu’tion. Np(IV) is titrated with a solution

of EDTAat pH 1.3 to 2.0 with xylenol orsngw as in.iicator. The

reactim of Np(IV) with EDTA is stoichl~tric and the color

changas from bright rose to light yell- at equal molar concentrations.

The error fordetemining 1 to 4 q ofNp i:~ 1 to 2%. Np(IV) is

produced in 0.01 to 0.05MHC1 with hydroxyl,smine reductant. Fe3+,

Zrh+, Pu’+, Th’+, and ●scorbic acid interfere. Reasonably large

-Unts of alkali, alkaline-earth, rare earth elements, Zn2+,

Cdz”, CO*+, Cr’+, Mn2+, Ni2+, and U022+ do not interfere.32G

(%Wopotentirntric. There hJ~ been little analytical

chemistry done in molten salts , and so c~r the only useful results

have been obtained from electmanalytical methods. 31p(IV] was

dete-ined quantitatively in molten LiC1-KCl eutectic at 400 to

SOO”C with an ●ccuracy of t4S.327

F. EMISS1(M SPECTROMETRY

Np has a line-rich emission spectra with the more-sensitive

lineS at 4~54.5, 4098.8, 3999.5, and 3829 ;1.32S’329 Other methods

are more useful for quantitative determination of Np than the

spectrochemical method, which is generally used only for analyses

of imprity elements. To prevent interferenceby the numerous

spectral lines of Np, a chemical sepamtion is usually made, or the

carrier distillation method with galliw sesquioxide is used. - 124 - A quantitative method for determinaticw of impurities in Np

is reported by Wheat 232 (Procedure23, page 200). The method is

a modification of one reported by Ko for Pui.s30 The neptunium

oxide is dissolved in HNOy, reduced to the tetravalent state with hydrazine and sulfamic acid, and then sorbed on anion

exchange resin. Two cycles of anion exchange are IJWd to separate

Np. The second effluent is evaporated to dryness to decompose hydrazine,, The residue is made water soluble with aqua regia, evaporated to dr~ess, and dissolved in 6M HC1 containing Co as the internal standard for the spectrographicanaiy:$is. The coefficient of variation for a single determinationof a numbe:rof common metal

ion impurities ranges from 9 to 24%. For a 50-mg sample, the minimum concentrationof impuritiesthat cam be analyzed is 0.5

to ;LOppm,

G. GRAVIMETRIC METHODS

Precipitationof Np for gravimetricdetermination is not a

useful method. If other ions which form insoluble salts are present, these must be separated first. When the solution is

relatively free from other ions, alpha counting or some other method is usually more rapid and offers less health hazard. A

number of Np compounds have low solubilities in aqueous sc~lution;

however, indefinite stoichiometryor necessity for calcination

to the oxide limits the usefulness of direct gravimetric

determination. Often the small quantity or’low concentrationof

neptunium precludes the use of gravimeery.

- 125 - ffycbwidr. Np(IV) is cqletoly precipitated from minaral

acid solution by Na, K, or MibOH as the hydrated hydroxida or

hydrous oxide. The broun-green gelatinous solid that fores is

difficult to filter but is ●asily redissalvd in ●cids. 3%.

volubility in lM NaNOl - lM NaOH is ~0.1 rig/L. !Up(V] ‘%ydruxid.”

i:~ green; it is somewha~ mora soluble in a sodiuw nitrate-sodiuu hydroxide solution. Np(VI) is precipitated ●s dark brown

(NH~)2NpaOt~HaOwith excess NH*OHfrom minaral scid solution.)’

Flwrid%a. Np(IV) is precipitated f;rom mineral ac:~d solution

as green hydrated NpFh by adding excess iii:. The compound dissolves

readily in rewgents which complex fluoridl~ ion, such as AIJ+ or boric acid. Wlwn K or NH~F in usad as tlh(l precipitant, tha green double salt KBIp2F3or NHklUpFsis produced.

Pertmide,~. Purple Np(lV) peroxide iS precipitated when a

large excess of H202 is added to a strongly acidic solution of

Nip(IV),,NP(V), or Np(V1), because peroxide rapidly reduces

Np to the tetravalent state. Reduction is much slower in dilute mineral acid. Np(lV) peroxide always irtcorporates SOW! of the i~ion into the crystal and may have diffc’rentcrystalline forms depending on the acid concentrationof the supematant, Np iS

separated from many cations by precipitnl;ion of neptunium peroxide. ~t

Llxalatefl. Green Np(lV) oxalate he:ukhydrate is prl~cipitated

from dilute acid solution with oxalic a~cid. Because quantitative

precipitation is not attained for Np(V) Jr Np(\’I]P a reducing

- 126 - ●gent, such as ascorbic acid, is usul to ensure complete reduction to Np(Iv]. A granular, easily-filtered precipitate is produced under controlled conditions.”o (Nli~)4Np(C20~)k and N@12HC20~ have ●lso been precipitated from P@(IV) and Np(V) solution.

Ioti. Light tan Np(IV) icxiate is precipitated from dilute mineral acid by adding excess potassium iodate.’s

Cdwnata . The double carbonate of Np(V), KNp02C03, is produced by adding potassium bicarbonate to a d:llute acid solution of Np(V], until the resulting solution is O.IM in bicarbonate.

The solution is heated at 90’C for 3 to 4 hours to produce the light tan double salt.-’

Aaotute. Sodium neptunium dioxytriacetate,

NaNp02(C2H~02)~, lS pink by transmitted light and pale green by reflected light. Np is oxidized in dilute acid with KBrOs at

90*C to Npo22+. Sodium neptunylacetate is precipitated by adding an equal voltme of 4M NaNOS - 4M NaCzHS02 solution.38

%08DhUte . Np(IV) di(monohydrogenphosphate)hydrate

[Np(Hpo~)z‘~zo] , a pale-green gel, is precipitated by adding phosphoric acid to a dilute acid solution of Np(IV).35 ii. SPOT TESTS

Spot tests for determining oxidation states of Np and Pu were obtained for 36 organic and inorganic reagents coimnonly used in paper chromatography.331 The tests we::emade on Whatman No. 1

- 127 - paper which was treated with 2M HC1 in descending chromatography

for 12 hours to remove traces of Fe, Mg, and C=, The paper WBS

treated with two successive 24-hour washings “sy migration with

twice-distilled uater. Because of hazamis of these alpha emitters

and the high sensitivity of radioactive measurement, very

sensitive spot tests with an identification limit of less than

1 ug of actinide were selected. Observations were made in white

and ultraviolet light for both acidic and basic mclia with each

reagent. First the acidic media was allowed to dry; then ~nia

was added and evaporated. A standafi scale of colors was used

for comparison. In most cases, a color reaction was obtained with less than 1 ug of actinide, but the color was the s- for

all oxidation states of both Np and Pu.

Diphenylcarbazide gives a color reaction with Np(VI] but not

Np(V); however, Pu(VI] gives the same color ~e~tian. In acid

solution, sodium alizarinsulfonate or arsenazo give a color with

Pu(IV) and Pu(VI), but no color with Np(V) and Np(VI). Four of the reagents, chromazural-S, arsenazo, 4,2-ppidyl -azo-resorcinol, and pyrocatechol, give fluorescent spots under ultraviolet light with all oxidation states of Pu and Np; kojic acid fluoresces

only with Pu(III).

The oxidation states of Np and Pu were characterized from

color reactions on chromatograms and electrclpherograms. 2s&

- 128 - The tetravalent states give characteristic colors with alizarin,

arsenazo-1, and thorin-I; however, diphenylcarbaxide was used for

the hexavalent state.

I. MASSSPECTRCB4ETRY

Subnanogram quantities of 237Np were determined with a mass

spectrometerby Landrum, et al.sgz The instrumentwas a double-

focusing, 60-degree sector type, with a 12-inch radius. The

source chamber contained a tantalum filament (from which the

sample was volatilized) and a rhenium filament (on which gaseous

species were ionized]. After mass analysjs, the ionized Np atoms were collected in a Faraday cup. The method uses isotopic

dilution with ‘35Np or preferably 236~p. This method is much more rapid than neutron activation,and the sensitivity is at least ten times grecrer. The standard deviation fo”:0.1 to 0.S nanogram of Np was 1 to 2%. Isotope dilution with *’gNp has also been applied to determine 237Np.333

Spark source mass spectrometry is ussful fc~r less quantitative measurements of many elements including Np; however, it is most often used for determining cationic impurities ~LnNp and other actinides.334

J. X-RAYFLUORESCENCESPECTROMETRY

The ease of production and simplicityof the X-ray spectra produced for elements of high atomic number allow mixtures of

- 129 - actinides to be analyzed by X-ray fluorescenc,~ spectrometry with considerable precision and accuracy. Either .~olid er liquid s~les can be analyzed by the intenal stsnd,mi technique.

Mixtures of U, Np, and I% were analyzed at ra:ios as high as

1:1:1; results were comparable to standard counting. U, Np, and

Pu in any combination of two elements were ani~lyzed at ratios as high as 1:8 without seriously affecting accuracy. However, at ratios of 1:10, low results of 5 to 7% were ojtained for the element present at lower concentration. The principal L series

X-ray emission lines of elements with atomic nwnbers ’32 through

96 are given by Kofocxi.s35 Novikov et CZZ.3’6 used X-ray fluorescence to determine microgram amounts of Np in pme solutions or in solutions containing Pu. The sensitivity was

0.2 to 0.3 pg ofNp. The relative standard error in determining

1 Dg Np was 5%, ~d the analysis, including s~ple preparation, required 30 to 40 minutes. The Kal and Kaz X-ray energies for

Np, PUB and Am were measured by Nelson, et al.337

K. NEUTRONACTIVATION

Neutron activation was used to determin~! subnanogram quantities of 237NP.332 The unknown sample was i~adiated with another Np sample of known Np content and comparable weight in the same avemge time-integrated neutron flux. After irradiation,

- 130 - the 23BNp was determined by gamma spec:rometry. Conventional

radiochemical separation methods were ?Ised. Isotopic dilution

with mass quantities of 237Np ser~ed t,)determine chemical

recovery.

L. OTHER METHODS

Gamma counting 239Np, the decay product of 2k3Am, has been used to determine 2“3Am in solutions containing large amounts of

Cm. The ratio of the equilibrium amount of ‘3gNp to the amount of 2b3Am was determined by separating (by TTA extraction) and analyzing (gamma counting) 239Np from jample~ in whi,:h~hq.kmand

239Np were known to be in secular equilibrium. The method was compared to determining 243AM by the isotope dilution-mass spectro- metric method. The precision of the msthod was 7% at.the 95% con- fi~ence limits (n = 16) for sample ali~uots that contained 0.1 to

5 Llgof 243AM.33B A similar approach #as reported hy Lebedev et aZ.202

2]3Pa, the daughter of 2;7Np decay, has more-abundant gamma rays, which are easier to measure than 237Np. Cofield33g used this as a basis for determining 237Np-233Pa in human lungs by in uivo gamma spectrometrywith a large NaI SC:ntillation detector in a low-backgroundcounting chamber.

The neutron capture cross section of 23BU was measured by analysis of 239Np produced [23@U(n,y)23gll~-23gNp]. The procedure uses isotope dilution with 237Np to dttermine chemical yield,

ITA extraction for separationof Np ard U, electrodepositionfor

- 131 - Np source preparation, and gamma counting3bofa? analyses.

Characteristic isomer st,iftranges have bem measured fcr several valence states of Np using l&sbaue? resonance of the 59.54-keV gamma ray of 237t-ip. They exteld from about

-6.9 cm/sec to +5 cm/sec for the individualoxijation states of +7 to +3 and are clearly defined.3*1’3”2 The isomer shift characteristicof each oxidation state is useful for !,tudyof bondi~g in Np compounds. Dunlop and Kalvius have also made significantcontributions.3kla

Ix. RADIOACTIVE SAFETY CONSIDERATIONS

TfieSipisotopes emit high-energy alpha pa]hticles,medium- encrgy beta particles, and low-energygamma rays. The tendency of Np tu concentrate in the bones with a biolo~;icalhalf-life of 7.3 x 104 years makes ingestion the primary hazard to personnel.

Studies of the distributionof 239Np in animal tissue showed

60 to SO% of the ?Jpwas Csposited in the bone-.131 Studies have ii[so been ~de of the inhalation, pulmonary absorption, gastro- intestinalabsorption, and short-term retention of 2:17Np in rats.3”3

Because 237Np (T$ = 2.14 x 106Y) is the only isotope of Np which is available in weighable amounts, it presents the only serious hazard. The riidiatim hazard is small due to the low specific activity of 237!Jp and the low energy of its gamma radiation. Table

25 lists body burdens and maximum permissible concentrationsof

‘“SF and 23’Sp for continuotisoccupationalexposure.’”b In

- 132 - handling Iarge quantities of 237Np, standa~.dgloved-boxe:jmaintained

at a negative ~ir pressure with respect to the laboratoryairq~s

should be considered for containment.

Criticality is no problem for 237Np belcausethe bare critical

mass for a sphere of density 20.4S g/m3 is 68.6 kg.’kG

TABLE 25

HEALTH HAZARD OATA FOR NEPTUNIUM [SOTOPE:S3””

Maximum Permissible Concentration for Max Permissible 40-hr Week (pCi/cc) Isotope Organ Body Burden (uC:~L, ——~~ .— Air 2s’Np (s01.:) Bone 0.06 9 x 10-5 4 x 10-12 Kidney 0.1 2 x 10-” :’ x 10-*2 Total Body 0.5 4 x 10-4 ;? x 10-11 Liver 0.s 6 X 10-* 2 X 10-]1 GI(LLI] 9 x 10-4 ;! x 10-7

tinsel.:t Lung 1o-1o G](LLI) 9 x 10-b ;! x 10-’ z ~~~ (sol .:) GI (LLI) 4 x 10-3 8 x 10-7 Bane 30 100 41x 10-6 Kidney 40 200 7 x 10-6 Total Body 70 300 ]*-S Liver 100 Soo 2! x 10-5

(insol,j GI(LLI) 4 x 10”3 7 x 10-7 Lung 2 x 10-6

- 133 - x. COLLECTION OF PROCWLJRE!i

A. INTRODUCTION

The procedures are divided into three cal;egories:

o Procedures for extraction, extraction chromatography, ion exchange, and carrier precipitation or :wme combination of these n.athods with highly radioactive swnples. Most of these ❑ethods utilize alpha counting (alpha pulse height analysis), gaxna spectroscopy, or possibly isotopic dilution. The method of determination is not detailed for all. procedures.

e Procedures used for environmentaland biological samples.

o Miscellaneousprocedures for quantitativedetermination, including absorption spectrometryof color complexes, coulometry, and gamma spectrometry.

B. 1.ISTING OF CONTENTS

Procedure Author —.Title cr—.Method * 1 Moore*”e Separation c~ i4p b:yTTA Extraction 138

,.‘> DorsettlS* Separation (IfNp by TTA Extraction 141.

.3 Smilh3”7 Determinati(mof 239NP in Samples Containing U, Pu and Fission Products 14s

4 Detenninatilmof Np Landrum34B 150 s Slee et C7t.’zo Determinati4mof Small Amounts of :* in F’uMetal 1s5

-134- ——.Procedure Author .Title. ——or Method 6 Schneider)qb Determination0!?Np in Samples Contain:~ng Fission Product!;,u and Other Actjnides 1s8 7 Maeck et aL.185 Determinationof Np in Samples of U and Fission Products 161

8 Wehner et UZ.252 ExtractionChromatographic Separation of 2’]9?4p from Fission and Act:Lvation Products in the [determi- nation of Micro and

Submicrogram @I;Nitit!Lt3S of U 163

9 Eschrich2”9 Separation of U, Np, Pu,, and Am by Reversed Phase Partiticm Chromatography 16S

.10 R,oberts2*” An Analytical Method far 237Np Usjng Anion ExchaLnge 167

11 Nelson et 220223 Separati.cnof U, Np, and Pu (JsingAnion Exchange! ~69

12 Holloway et aZ.*2° !3eparaticnof Zr, Np, amd Nb Using Ar,ionExchange 171

13 Jackson et al,’kg Separatism of Np and Pu by Anion Exchange 173

14 Zagrai et aZ.23g Separatism of Np and Pu by CaticnlExchange 17s

1s Sill123, 124,12S Separatism and Radiochernical Determin$ltionof U and ‘TransuralliumElements Using Bti~biumSulfate 176

13s “ Procedure Author Title— —.or Method Page T@? II 16 Taylor’so The Low-Level Radiochemical Determination of 237Np in Envinmmertal Samples 179

17 Perkins]ss Radiochemjcal Procedure for the Separation of Trace ADounts of 21-Np from Reactor Effluent Uater 184

18 8utler35~ Detemina:ion of’ Np in Urine 186

~pe III 19 Granadelsz Dete2minacion of 2B7Np by G~ Ray Spectrometry 189

20 Bryan et aL.302 Spectrophotometric Deteminution OF * 193 21 Smimov- Microvolmetric Coeplexo- Averin et a2.32G metric Mdwd for Np with EDTA 197

22 Novikov et al. B53 Photometric Determination of Np as the Peroxide Complex 199

23 Uheat 2‘ 2 Separatim of Np for Spectrographic Analysis of Impurities 201

24 Ermoloev et aZ.30s Photometric Determination of Np as the X~lenol Orange Co~lex 204

- 136 - Procedure Author ..Title—— or Method 2s Stromatt31’ Analysis for Np by Controlled Potential] Coulcmetry 206

- 137 - Procedure 1. Separation of Np by HA Extraction F. L. Fbore*”o

i?utl~~ of Mt?tlwd

Np is separated from fission products, U, Pu, transplutonium elements, and nonradioactive elements by extraction into thenoyltrifluoroacetone (TTA). After separal:ion, an aliquot is suitably prepared for either alpha counting of 237Np or gamma counting of 23qNp.

Reagent8 (C.F. Chemica28)

● HC1, lM

● HN03, 10M

● Hydroxylamine hydrochloride (NH20H”HC1) solution, ‘v5M. Dissolve 69.5 g of reagent in 200 ml of distilled water and warm if necessary for dissolution.

● FeCl , w2M. Dissolve 40 g of reagent-grade FeC12*4Hz0 tetrahydrate in 100 ml of 0.2M H(H. Store in a dark glass stoppered bottle.

● 2-Thenoyltrifluoroacetone-xylene:;olution,W.SM. Dissolve 111 g of compound in one liter of reagent- grade xylene.

E@@n3ent

● Extraction vessel with mixing device

● Hot place

● Micropipets

● Stainless steel counting plates

● Counting plate heater

● Meeker burner

- 138 - ● Asbestos board

● Sample carrier

● Alpha proportionalcounter (or gamma counter)

l%etreatment

If interferencesmay be present in salution with the Np tracer, Np is adjusted to Np(IV) and carried on ‘~1❑g of La pre- cipitated as the hydroxide. The hydroxide precipitates are dissolved in lMHNO~, and LaFs is precipitated to carry Np(IV).

The fluoride precipitates are dissolved in a few drops of 2M A1(NOS)S and dilute HC1. While the extraction of Np(IV) :Frm HNOI iB usually very effective, HC1 should be used whenever possible because there is a greater tendency to form extractable Fe(III) ion in the HNOSsystem.

It is desirable to ❑ easure the chemicrnl yield if wch chemistty is employed. A 237Np spike is useful for determining

23gNp recovery; 239Np ❑ay be used for dete:nuining 237Np yield.

Procedure

1. Pipet a suitable aliquot of the swnple into a separator funnel or other extraction vessel,

2. Adjust the solution to lM HCl - llf NH20H”HC1- 0.25M FeCla. KI may be used as a reductant in place of FeC12,

3. Mix the solution for 5 ❑in at ambient temperature.

4. Add an equal volume of 0.5M ITA and mix for 10 ❑in.

5. Allow the phases to separate; then remove the aqueous phase and discard it.

139 - 6. Mash the organic phase by mixing k)ith an equal volume of IM HCl for 3 nin. AI1ow the phases to s,~pa”tteand

discard the aqueous wash.

T t. Strip the Np from the organic phase by mixing with an equal volume of 1CB4HIWs foL 2 min., (If the aqueous

strip is too high in g~ activity for alpha measurement,

the last traces of radioactive Zr and Pa may be removed

by a S ●in re-extraction of the 10M HNOs strip solution

with an equal volume of ITA.

Ordinarily, the small amount of Fe in the ITA causes

negligible self absorption in counting, and the TTA

extract is mounted directly on the counting plate. If

Fe is a problem , excellent separation is attained by

stripping the Np into 10M HNOs.

8. A suitable aliquot of the ITA extr;lct or the 10M HNOS strip is prepared by conventional lrnethods for either alpha counting for 237Np or gaiuna ,:ountinlg for ‘39Np.

- 140 - Procedure 2. Separation of N by llA Extraction R. S. Dorsett15 Y

OutZine ofllethod

Np is determined in the presence of Pu, U, fission products,

and other alpha-emitting nuclides by extraction into thenoyltrifluoro-

acetone (TTA) followed by alpha counting of- the TTA. l-he analysis

consists of three parts: (1) the pre-extractionstep in which

acid and oxidation state are adjusted, (2) the extraction in which Np is quantitatively extracted into ITA, and (3) the mounting and alpha counting of the TTA extract. When additional purifi- cation is required, the Np is stripped fron the TTA, acid and oxidation state are adjusted, and a second extraction is done.

The precision of the method is dependent on the type and quantities of interferences. The interferencescaused by sulfate, phosphate, fluoride, and oxalate ions are eliminated hy addition of A1(N03)? which complexes these ions. A coefficient of variation of 2% is obtained with relatively pure solutions.

Reagenta

● Hydroxylamine hydrochloride (NH20HoHC1), lM, is prepared by dissolving 69.5 g of C.P. grade compound and diluting

to one liter.

c (NaN02), lM, is prepared by dissolving 69 g of C.P. grade compaund and diluting to one litl~r.

s 2-Thenoyltrifluoroacetone-xylene, 0.5M, is prepared by dissolving 111 g of the compound in one liter with C. P. xylene.

- 141 - e Ferrous sulfamate [Fe(NH2SO~)2], 2M, is prepared by dis- solving iron powder in an excess of sulfamic acid with minimum heating. The solution is filtered after dis- solution.

c Aluminum nitrate [Al(NOg)s), 2M, is prepared by dis- solving 750 g of C.P. grade coml)ound and diluting to one liter.

● (tlNOs) nitric acid solutions arl? prepared as required from C.P. grade stock.

o Collodion solution, 0.5 mg/ml, LS preFlared by dissolving S00 ❑g of collodion in one llter of l-to-l ethyl alcohol. ethyl ether.

E@ipmen:!

● Centrifuge cones (with caps)

● Vortex mixer

● Micropipets

● Stainless steel counting plate:;

● Counting plate heater

● Meeker burner

s Asbestos board

● Sample carrier

o Alpha proportional counter

o Alpha pulse height analyser

Pretreatment

FZuotide method. When it is not knc}tin what impurities are present in the solution, Np(Pu) can be caxrier precipitated with

La(OH)J. The hydroxide is dissolved in HNos, and La is - 142 - reprecipitated as the fluoride. The fluoride precipitate con-

taining the actinides and lanthanidesis dissolved in A1(NOS)3

and dilute HN03, and this solution is extra:ted with 77A.

@ in Mbut~Zpho@uzte (TBP). If Np :.s present in TBP or

other organic extractants,it is stripped w:.thdilute HN03(%0.1M)

and then analyzed by the procedure.

Sepamtion ofNp and U. Acid control is very important for

this separation. In the analysis of low-level Np solutions that

contain large quantities of U, the prcblem is complicated because

237Np and 230U have the same alpha energies. Also, the specific activity of 2ghU is 10 times greater than 237Np. Pm accurate analysis is assured by (1) close control of .:heextraction acidity,

(1 tO.lM), (2) a double extraction cycle, and (3) in extreme cases, a fluorophotometric determination of U content of the final ‘lTA extract.

.%oaedme

1. Pipet 103 to 104 dis/min alpha of 29;Np into a lS-ml centrifuge cone.

7.. Add sufficient water or HN03 so that at the end of Step 3 the acid is lM. Mix.

3. Add 1 ml of 2M Fe(NHzSOq)z solution. Mix and let the solution stand for 5 min.

4. Add 3 ml of O.SM ~’A in xylene, and mix for 5 min in a vortex mixer.

s. Allow the phases to separate; then remove the aqueous phase and discard it. Add 4 ml of lM HIXls to the organic phase, and mix for 2 min in the vortex mixer.

- 143 - 6. If the alpha activity due to F% and U is <103 dis/min, proceed to Step 9. If the alpha activity is >lOs, proceed to Step 7.

7. Remove the aqueous phase from Step S and discard it. Add 1 ml of 8M HW3 to the organic phase, and mix for 5 min in the vortex ❑ixer.

8. Discard the organic phase. Repe~t~Steps 2 through 5.

9. WITI on the counting plate heater, heat to 175° to 190”C, Id place a clean stainless steel counting plate on the heater. 10. Pipet an aliquot from the organi.: phase that contains %103 dis/min Np, and add it droptiise to the plate. Rinse the pipet twice with xylene, and add both rinses to the plate. Heat the plate until dry.

11. Heat the plate over a Meeker hurler flame until the plate is a dull red color. Place the :~late on an asbestos board to cool.

12. Uhen the plate is cool, add 1 dr.)p of coilodion to cover the surface. Allow the plate to dry several minutes before counting.

- 144 - Procedure 3. Detenninatlon of 23gNp fn Sanples Contalnfng U, Pu, and Fission Products H. L. Smlth3k7

Introduction

The procedure for determining 23gNp affords excellent decon-

tamination from milligram quantities of U, the fissim products

obtained from 1013 fissions, and Pu. The decontaminationfactor

for Pu is about 104.

An initial fuming with H2SO~ is required to ensure exchange between the 237Np tracer employed and 23gN11,and also to complex

U(WI] . If the sample is a dissolved U foil, HN03 must be added before the fuming step to convert U to the VI oxidation state,

NPIIV) and (V] are carried by LaFg precipitations in the presence of Zr and Sr holdback carriers. ‘l%epreci~itationsprovide decontaminationfrom the activities of Zr and Sr as well as from

IJ. LaFs scavenging with Np in the VI oxidation state decontaminates from the lanthanidesmd partially from Pu.

The chemical yield is about 50%, and eight samples can be analyzed in one day.

Reagen ta

● La cnrrier: 5 mg La/ml, added as La0J0J)3. 6H20 in H20

● Sr carrier: 10 mg Sr/ml, added as Sr(N03]z. 4H@ in H20

● Zr carrier: 10 mg Zr/ml, added as ZrOC12 in H2C)

● 237Np standard solution: S,000 ta 10,000 counts/(min-ml) in 2 to 4M HC1 or HN03

- 145 - ● HC1: O.lM; 2M; concentrated

● H2SO~: concentrated

● HN03: concentrated

● H3B03: saturated solution

● HF: 1:1 H20 and concentrated HF

● HI-HC1: 1 ml 47% HI + 9 ml concentratedHC1

● HF-HN03: equal parts by volume of 2M solutions

● NH20H*HC1: SM (or saturated)

● KMnOk: 10% solution

● NHbOH: concentrated

● “Dowex” 1-X1O anion exchange resin: 100 to 200 or 200 to 4n0 mesh, slurry in H20*

%ocedure

Step 1. Pipet 1 ml of 237Np standard into a clean 12S-ml erlenmeyer flask, and then pipet in the samrle. Wash down the sides of the flask with a little H20, add IC drops of concentrated

H2W4,** and evaporate nearly to dryness on a hot IPlate. (No harm is done if the solution is permitted to evarorate to hard dryness.)

Step 2. Dissolve the residue by boilirg briefly in a minimum of 2M I+Cl. Transfer the solution to a clear 40-ml Pyrex centrifuge

● The resin is supplied by the Bio-Rad Laboratories, Richmond, Calif., who purify and grade the resins manufacturedby the Oow Chemical Co.

● * [f the s~le has been obtained from more than the equivalent of 50 ❑g of soil, do not add any H2SOk sj.nce CaSOh will pre- cipitate and carry NP to some extent.

- 146 - tube; wash the fla>.. once wit H20, and transfer the washings to

the tube. The volume of solution shou:.dbe 5 to 10 ml. (Ignore

any small residue.)

Step 3. Add 5 drops of La carrier and 3 drops of Zr hold-

back carrier. Add 2 drops of NH20H”HCI for each ml of soIution,

stir, and Iet stand for a few minutes. Add HF dropwise until the

yellow color of the solution disappears and the solutio.1becomes

cloudy (LaFJ). Centrifuge. Remove ant discard the supetmate.

Wash the precipitate with 1 to 5 ml of HF-HN03,

Step 4. Dissolve the precipitate by slu:rryingwith 3 drops

of saturated H3B03 and adding 3 drops of concentratedHC1. (Ignore

any small residue.) Add 3 ml of 2M HC1 and precipitate La(OH)g

by adding about 1 ml of concentratedNH40H. Centrifuge, and

discard the supemate. Wash the precipitate t)y boiling it briefly

with several milliliters of H20. Centrifuge and discard the

supernate.

step 5. Dissolve the precipitate in about 5 ml of 2M HC1.

Reprecipitate LaF3 by adding 10 drops of HF; centrifuge, and discard the supemate. Wash the precipitate with 1 ml of HF-HN03.

If the precipitate volume is greater thwn 0.2 ml, repeat the hydroxide and fluoride precipitationsuntil the volume of LaF9 precipitate does not exceed 0.2 ml.

- 147 - Step 6. Dissolve the fluoride precipitate in 1 drclp each c:f

saturated H3803 and concentrated HNOg. Add 10 drops of KMn(lq,

and allow to stand for S min. Add 2 drops of HF, and allow the

solution to stand for a few minutes. Centrifuge, and transfer

the supernate to a clean centrifuge tube. Wash the precipitate with 1 ml of HF-HN03, centrifuge, and add the supernate to the previous one. Discard the precipitate.

Step 7. Add 2 drops of La carrier to the sclution, stir. centrifuge, and transfer the supernate to :1clean centrifuge tube. Wash the precipitate with 1 ml of 1{1:-HN03,add the washings to the previous supernate,and di!;cardthe prec:Lpitate.

Step u. Add 5 drops of NHzOH*HC1 and 2 drops of Zr carrier, and let stand for a few minutes. Add 2 drc~psof La carrier, stir well, cent.rifugepand discard the supernatc. Wash the prec~icate with 1 ml of HF-HN03, centrifuge, and discmd the supermtc.

Step 9. Repeat Steps 6 and 7,

Step 10. Add 5 drops of NH20H-HC1 ard 2 drops of Sr hold-

back carrier, and let stand for a few minwtes. Add 2 drops of

La carrier, stir well, centrifuge~ and discard the supermate.

Wash the precipitatewith 1 ml of HF-HN03, centr:Lfuge,and discard

the supernate.

- 148 - Step 11. Dissolve the precipitatewith 1 drop of saturated

H@C)3 and 10 drops of concentratedHCI. Pass the solution through a “Dowex’” 1-XIC) anion exchange column, 3 crIx 3 mm, and wash the column with 1 ml of concentratedttC1. The Np, now in the It’ oxidation state, is sorbed on the column. rf necessary, remove

Pu from the column with H1-HC1.+ Add applm~ximately1 ml of

O.lM HCI to the reservoir of the column. I)iscardthe fi:rst2 drops that come off the column, and then collect approximately0.2S ml in a clean, dry centrifuge tube. Use no aLr pressure when eluting the Np. Pick up the solution in a transfer pipet and evaporate by stippling on a 2.5 cm Pt plate. If possible keep the deposit within a 1.3 cm circle. Flame the sample to duI; red in a burner, mount with double-sided Scotch tap~ in the center of an

Al plate, and a- and $-count on 3 successive da:?:;.**

..——. * The procedure should remove 9S% of the F’uinitiallypresent in the sample. If, at this point, there remains enough Pu to interfere with the determinationof the Np yield, that is, more than 1% of the Np tracer, Pu may be removed more efficiently in the followingway: Allow 1 ml of HI-HC1 solution to drip through the column with no added pressure. Wash the column with several ml of concentratedHCl, and discard the effluent, which contains Pu in the III oxidation,state, and proceed with the rest of Step 11. One elution step such as the one just described removes 99,5% of the Pu. *“ Alpha-counting: The sample is counted in a 7.5 cm id. methane- flow proportional counter with a loop :.node,~perateclin the a-pllateauregion. Beta counting: The sample is placed on the third shelf of a methane-flowproportional counter with a window thickness of 4.8 mg/cm2. An absorber (about 5 mg A1/cm2), placed on the first shelf, stops soft lletasand alphas. The individual counts are corrected to to,,using a half-life of 56.6 hr, and are then averaged.

- 149 - Procedure 4. Determination of Np J. Landrum34e Outline of Method

After the sample is dissolved, the vo~,ume is reduced by evaporation. Np and other hydroxides are precipitatedwith SO%

NaOH to separate Al. The precipitate is d:.ssolvedin concentrated

H71, and Np is separated from many impuritiesby chloride anion exchange. Further separation is attained by performing in order:

ITA extraction,cupferron extraction, and {:hlorideanion exchange.

The plate for counting is prepared by electrolysis.

Reagent8

● 50$ NaOH

● La carrier, 5 mg La/ml (as La(NO:l)g06Hz0in H20)

s Concentrated HC1

● 55% HI solution

● HC1 gas

● Bio-Rad AG 1 x 8, 50 to 100 mesh resin

● 10M HC1 - O.SM HI

● 5M HCl

● lM HCl

● 0.4M lhenoyltrifluoroacetone(TM) in xylene

● 6% Cupferron

● CHC13

● Saturated NHkCl solution

● ConcentratedNH@H

- 150 - l+ocedure

1. To the sample add about 3 x 10: alpha counts/rein 237NP stan- dardized tracer. Add W2 mg of La3+ carrier and 2 ml S5% HI (no inhibitor), and boil the sclution until the volume has been reduced to about 10 ml. Transfer to a 40-ml cone. Add suffi- cient SO%NaOH to dissolve any Al that may be present. Heat in a water bath, centrifuge, and discard the supematant 1iquid.

2. Wash the precipitate with 10 ml of 10M NaOH. Again heat, centrifuge, and decant. Wash the precipitate thoroughly with 30 ml of H20 (to remove most of the Na+ salts), centrifuge, and decant.

3. Dissolve the precipitate in 10 ml of concentrated HC1. Add 2 drops of 55% HI (no inhibitor).

4. Cool and saturate the solution with HC1 gas. (If white salts precipitate, centrifuge them and decant.) Pass the solution through a “Dowex” l-X8, 50 to 100 mesh column, 6 ma I.D. by 11 cm, pretreated with concentrated HC1 - O.SM HI. Discard the effluent. If 23tPu is to be measured, save the effluent and note the time of Np-Pu separation.

5. Wash the column with 15 ml of IOM HCl - 0.5M HI, and collect the wash with the effluent.

6. Elute the Np with three S-ml portions of 5M HC1, and allow a minute or so between elutions. Collect the eluate in a 125-ml Erlenmeyer flask.

7. Add 2 drops HI , and boil to ne~.r drfless. Transfer to a 40-ml cone with lM HC1. Add lM HCl to ❑ake approximately 15 ml.

- 151 - 8. Add 10 ml of 0.4M ITA in benzene, toluene, or xylene, and equilibrate for 30 ❑in. ,Soparate the layers by centrifuging, and transfer the organic layer into a clean 40-ml cone. Repeat the extraction with 5 ml of 0.4M ITA for 10 min. Combine I:heorganic fractions. Discard the aqueous fraction.

9. Wash the organic with 5 ml of IM HC1 for 2 min. Centri- fuge, and discard the aqueous.

10. Back-extract the Np by equilibrating the TTA with 2 ml of 9M HC1 for 10 min. Separate the layers as before, and transfer the aqueous to a clean cone. Repeat the extraction with 1 ml of 9M HC1 for S min. Combine the aqueous phases.

11. To the combined aqueous phases, add 2 drops of 6% cupferron and 5 ml of CHC13. Equilibrate for 30 sec. Discard the CHC13 (lower layer). Add S ml of CHC13 and repeat the extraction. Again discard the CHCIZ. This step is designed to remove trou~lesome Nb activity.

12. Transfer the solution to a 125-:nl Erlwuneyer flask, add 1 ml concentratedHNOS, and boil to near dryness. Add 5 ml of 9M HC1 and 1 ❑l of concentrated fo:nnic acid. (CA~ION: The reaction between HNOSand formic acid may be violent if too much HN03 is present.) Warm th(g solution until the HN03 has been destroyed. This step oxid:.zes U(VI) and reduces Np(IV) .

13. Add 5 ml of fresh concentrated HC1 (final HC1 concentration should be >1OM, use HCl gas if necessary). Pass the solution through a “Dowex” l-X8, 50 to 100 mesh, 6-mm I.D. x 5 cm column, pretreated with 10Y HC1. Wash the column with 5 ❑l of 10M HC1. Discard the effluent and wash.

- 152 - 14. Elute the Np as in Step 6, but with 10 ml of SM HC1. Collect in a 125-ml Erlenmeyer flask.

1s. Repeat Steps 7, 8, 9, and 10. (ITA extraction)

16. Examine on a NaI detector for ganm contamination. If the sample is radiochemically pure, plate the sample.

Electroplating

8oil the solution from Step 10 to near dryness. Add 1 ml of saturated NHtiCl and one drop of ❑ethyl red indicator, and adjust acidity with NH40H and lM HC1 so that one drop of lM HCl turns the solution red. (Volume should be 3 to 4 ml,] Transfer the solution to an electroplating cell fitted with a Pt hire anode and a l-in.- diameter Pt disc cathode. Pass approximately 1.5 amps through the cell for 15 min.

Add I ml of concentrated NHkOHto the cell while electrolysis is in progress. Continue plating for another 15 to 30 sec. Remove the solution from the cell, and check it for activity in a well counter. If appreciable activity is present, repeat the plating procedure without the addition of NH4C1.

Dismantle the cell, flame the Pt disc to a dull red, and alpha count for chemical yield. Gamma and beta count for 23gNp and 290Np.

Notea

1. Using this procedure, Np is separated from solutions whose contents underwent 10 15 fissions [one week previous) and up to one gram of dissolved soil. (:amma-ray spectroscopy showed no activities Other than 23eh’pand 23gNp,

- 1s3 – 2. 10 to 12 hours is required for six samples.

3. The yield for this procedure is 30 to 60%.

- 154 -

.-. . ‘ocedure 5. Determination of Small Amounts of Np in Pu Metal L. J. Slee, G. PhIlllps gnd E. N. Jenklns320

titZine of Method

Pu metal is dissolved in HC1. The Np (lCI to 2000 ppm) is parated from Pu by 7TA extraction and determined with a square- ve polarograph,

Retzgenta

● Distilled water

● HN09, analytical-reagent gradt

● Hydroxyamine hydrochloride (NFzOHOHC1)solution, 5M

● ‘lTA solution, 0.5M in xylene: Dissolve 28 g of 2- thenoyltrifluoroacetone (lTA) in 200 ml of pure xylene, filter, and dilute with xylene to 250 ml.

● Ferrous chloride (FeCIZ)

● EDTAsolution: Dissolve 37 g of discldiu.m ethylenediamine- tetraacetate (EDTA) in distilllsd water, adjust to pH 7 with ananonia solution, and dilllte to 100 ml.

Piwoduw

1. Weigh %300 mg of Pu ❑etal accur~.tely.

2. Add S ml of distilled water and then slowly add 0.5 ml of 1(M Hcl. When the reaction subsides, add 1 ml of ICR14HCl and 2 ❑l of 5M NH20H*HCIand warm the solution.

3. Dilute to 10 ml with distilled writer, mdd 2S0 mg of FeC12, allow 5 min for oxidation state djustmnt.

4. Transfer quantitatively to an extracticm vessel, and add 5 ❑l of O.SMTl’A. Stir for 10 minutes, allow the phases to separate, and remove the organic phase.

- 1s5 -

. . 5. Repeat the extraction with S ml of (),SMTTA.

15. Combine the organic phases in the extraction vessel, add 1 m.1of I.MHCI, and stir for 1 min (to remove entrained Pu. Remove the aqueous phase.

‘7. Add 5 ml of 10M HN03, and stir for I.(1nin t~ strip the Np.

13. Remove the aqueous phase into a clear,vessel, and repeat Steps 7 and 8.

!3. Evaporate the 10M HN03 to m3 ml and then add 5 ml c~f analytical-gradeconcentratedHN03.

10. Evaporate!to W1 ml, and repeat evaporation with twc}more 5-ml.portions of concentratedHN03.

1:1. Add 3 ml of analytical-gradeperchlcn’icacid (6C%) and more concentrated HNOS and evaporate to complete wet oxidation of organic matter.

1.2. Heat until solid perchlorates remain “but do not bake.

13. Dissolve the residue in 1 ml of warm 6M HC1 and 1 rnl of water.

15. Add 2 ml of 5M NH20H=HCl and evaporal:eslowly to ‘W.5 ml.

15. Add 0.5 ml of lM EDTA and 4 to 7 dro~~sof armnoniato adjust p}{to 5.5 to 6.5.

16. Dilute to 5.00 ml, and mix thoroughljr.Transfer 2.,00ml to a polarograph cell, and de-aerate with N2 (pre-saturated with water) for N3 min.

17. Record the Np peak at about -0.8 V al~ainstthe mercury- pool anode on the square wave polaro~:raph.

18. Add ‘vO.2 ml of a standard Np solution prepared in EDTA so that the original peak height is ~~pproximatelyfioubled. Deduce the Np concentrationof the o:?iginal solution from

- 156 - the increase in peak height, Interferencefrom the oxidation of chloride ions is decreased by adding EDTA to shift the half-wave potential of tho Np peak.

The precision is t2 and tlO% for concentrationsof S00 and 25 ppm, respectively.

- 157 - Procedure 6. Determination of Np in Sample Containing Ffssfon Products, U, and Other Actinfdes A. Schneiderlgk

Intro&Wion

This procedure describes an analytical. solvent extraction method for separating ~ from Pu, Am, Cm, lJ, TII, and fission products using tri-iso-octylamine (TIOA) and thenoyltrifluoroacetone

(TTA). Np is separated from Pu, Am, Cm, and fission products by extraction of Np(IV) into the amine from iiN03 containing a reducing agent. Further purification is obtained by stripping

Np from the amine with dilute HCl ani then extracting the Np into TTA.

Reagenta

● 5M HN03

. 3M [Ferrous Sulfamate], Fe[NH2SO:)2

● 5.5M [hydrazine], N2H4

. 10 Vol% tri-isooctylamine [TIOA) in xylene

● lM HCl

● 5M [hydroxylaminehydrochloride] (NHzOH=HC1)

● 0.5M TTA in xylene

Procedure

1. To a 5-ml extraction vial add 1.5 ml of 5M HN03 and a glass-covered magnetic stirring bar.

2. Pipet the sample (not to exceed 200 DE) into the HN03 and stir.

- 158 - 3. Add 3 drops 2M Fe(NH2S03]2 and 1 drop of 5.5M N2H4. Stir and allow to stand for .5 min at room temperature.

4. Add 1.0 ❑l of 10% TIOA in xy.lene and stir for 3 min to produce an emulsion. Allow the phases to separete. Separate the phases, and discard the aq~eous.

s. Transfer the organic phase from the original vial to a clean vial containing 1.5 ml of SM ~03, 3 drops of Fe@H2S03)2, and 1 drop of N:H4. Stir for two minutes, allow the phases to separate, and discard the aqueous phase.

6. Transfer exactly 0.7S ml of the organic phase to a clean vial containing 2.5 ml of IM HCl and 1.5 ml of xylene. Rinse the 0.75-ml pipet in t}e xylene phase of the new vial. Stir for 3 min and allow the phases to separate. Discard the organic phase.

7. Transfer exactly 2.0 ml of the aqueous HC1 phase to a clean vial. Add 3 drops of 5M NH20H”HC1and 3 drops of 2M Fe(NH2SOs]z. Stir and heat at 65°C for 3 min. Remove from the bath, and let stand for 3 min.

8. Add 1.0 ml of 0.5M ITA in xylene. Stir for 4 min to give a complete emulsion. Allow the phases to reparate. The organic phase contains the purified Np. This phase is ❑ounted for alpha counting for measurement of 2q7Np.

Notes

1. The presence of fluoride, sul~ate, tixalate, and phosphate lower the extraction coefficimt of Np(IV) into TIOA; Chloride ion does not interfere. The deleterious effect of these anions is circumventl:d by reducing the sample size or by adding Al ion.

- 159 - 2 !, For U-tree samples, the combined system yields 96 t2% recovery. For U-bearing samples, the!recoveries are dependent on the amount of U taken, ~’heextraction conditions are reproducible,and for control analyseis the recovery factors are included in l,he calculations,

3. In routine use, the combined e~tracti{m system achieves a separation from common fission prodticts (Cc, Ru, Nb, Zr, C% and Sr) of about 1 x 106 and :aPu separation factor of 5 to SO x 10s.

4. Control of the method for samples of lmknowr composition is maintained by spiking a portion of the sample solution with 237Np or 219Np and evaluating th~ recovery of the spike. An alpha pulse height analysis may be necessary if large amounts of Pu are initially present in the sample.

- 160 - Procedure 7. Determination of Np fn Samples of U ond Fission Products

W. J. Maeck G. l.. Booman, H. [. Elliott, and J. E. Rein’J’

Introduction

This procedure describes a method for separation and determination of Np in solutions of U and fission products using methyl isobutyl ketone and thenoyltrifluorom:etone (TTA) e,xtractants.

Np is oxidized to the hexavalent state and qllantitmtivelyextracted as a nitrate complex into methyl isobutyl ke:one from an acid- deficient A1[N03:)3 solution containing tetral]ropylammonium nitrate.

Np is stripped from the ketone with lM HCl c{mtaining reductants and then quantitatively extracted into 7TA-:qrlene to complete the separation.

Reagente

Al(N03]lJ salting solution: Dissol\’e 1050 g of A1(N03)3”9Hz0, add 13S ml of conccrltrated NH401{with mixing, and cool to SO°C. Md SO nii of 10% itetrapropylanmnonium hydroxide reagent, and stir the solution until ail solid is dissolked. Dilute the solution to one liter with water.

Reducing-strip solution: IM HI - C,,5M NH@H”HCl and ().25M FeCIZ solution.

0,>2SMKMn04

Methyl isobutyl ketone

(),5M‘lTAin xylene

Ethylenediamine

- 161 - Pmuedure

1,, Add 6 ad of A1(N03)s salting :}f~lution to a tube containing 0.1 ml of 0.2SM KMnOK. Then p:,pet 1 ml or loss of the sample into the tube and mix.

2. Add 3 ml of methyl isobutyl kel:one, and mix for 3 minutes.

3“ Centrifuge to separate the pha:~os.

4. Remove 2 ml of the organic ph~a:se, and transf(m to another tube containing 4 ml of the rmlucing strip solution. MiX for 10 ❑in and allow the phase~ to separate.

5,, Transfer 3 ml of the aqueous lp!lase tcl a 30-ml separator funnel; add 3 ml of 0.5M TTA, md stir vigorously for 10 min.

6. Let the phases separate, and discard the aqueous phase. Add 3 ml of reducing-stripsol~tion, and scrub far 5 minutes,

7. Remove an aliquot of the organic phase, and dry it on a counting plate under a heat lamp. Cover the residue with 2 to 3 drops of ethylenediamine,evaporate to dryness, ignite, and count.

1, Extraction from acid-deficient A1(IW3:1)3with methyl isobutyl ketone yields very good separation from Zr, and extraction with ‘lTA gives good separation from Pu and U. The extraction of U and Pu is cO.1 and 0.01%, respectively, Ru and Zr, the only 80-day cooled fission products that follow Np, are separated by >10”.

2. An alpha scintillation counter is used for gross counting, and a Frisch-grid chamber, 2S6-channel analyzer system is used for pulse height analysis.

- 162 - procedure 8. ExtractIon ChromatoqraDhic Semlratiorl of 23*ND From Fission and Activation P~]ducts in the “ Determination of Micro and S@nntc~gram Quantities of u H. Wehnar, S. A1-Nurab, ●nd H. Stoeppler2s2

Int2vduotion

This procedure describes extraction chr~tographic separa- tion Of ‘s’Np from fisAion and activation prtiucts after neutron irradiation. The system is Poropak-Q resin impregnated with lTA-xylene. It is suggested that radioactive samplles are more easily analyzed with extraction chromatography than with lTA extraction.

ReagentB

● Poropak-Q resin, 100 to 120 mesh

● 0.4PI ITA in xylene (~mall amount of n-pentane added)

● 2M W1

● lM FeC12

● 3M NHzOH”HC1

● 10M HIW3s

P2wmchlw?

1. Dissolve sample in 2M WI or convext to c~hloride with HCl .

2. Md 3 ml of freshly prepared lM FeC:lZ and 4 ❑l of 3M NH20HoHC1■ix, and let stand for 1!, min.

3. Transfer the adjusted solution to a column (S cm long and 0.6 cm I.D.) of Poropak Q impregnated with ‘lTA-xylene nt W1 ■l/(-2.min)C

- 163 - 4. When the feed has passed througlh the column, wlzsh with 2 ❑l of lM HCl and then a few dr~~ps of distilled water. Discard the effluents.

5. Pass S ml of 10M HNOSthrough tlw! column to strip the Np.

6. Count the HN03 solution containiltg the 23gNp immediately after separation with a 3 x 3 in NaI(TL) detector con- nected to a S12-channel pulse-he:!ght analyzer md evaluate the 0.106-MeV photopeak.

Not%e

1. The method was suggested for det[mnining low concentra- tions of U by irradiating a stan{lard sample of known U content at the same time as the Imknown and then deter- mining the 23gNp content of both samples. A sensitivity of 1 pg of U was determined for IL%1 hour irradiation, at a thermal neutron flux of 2 IC 10]3 n/cm2-sec with a cooling period of ‘K!Ohours. WilUh a longer imadiation, a detection limit of 0.S ug is sllggested.

- 164 - Procedure 9. Separation of U, Np, Pu, and Am by Reversed Phase Partition Chranatogruphy H. Eschrlch240

Introduction

This procedure describes extraction chromatographic separa- tion of U, Np, Pu, and Am. The system is Hyflo Super-Cel

(diatomaceous silica) impregnated with tributyl phosphate (TBP) and aqueous H?#lg solutions of the actinidos.

Reagente and MateriaL3

● Hyflo Super-Cel

● Purified tributyl phosphate (TBF)

● HN03

● Sodium bichromate solution [NazCrzOT]

● Dichloro-dimethylsilane

● Glass column

Rwceduw

1. Add Na2CrzOT to 1 to 2M HNOs containing the actinides, and heat at 75°C for five hours t~ yield hexavalent U,

Np, and Pu.

2. Wash the packed column with ‘v1O column volumes of NIM HNO~ at relatively high flow and pressure to remove any air and nonsorbed TBP.

3. Md the sample volume (not greater than 1/10 of the total column volume and containing a ma(imum c,f 1 mg TBP- extractable species per 100 mg of silaned Hyflo Super-Ccl) at a flow of 0.4 to 0.8 ❑l/(min-cn2).

- 16S - 4. Wash the columm with 1.7M H?U)3to remove (in order) Am(III), Cr(VI), and Pu(VI).

s. After Pu(VI) elution, switch to 1.7M HNOSI- O.lM NzH4 wash. (Np 1s reduced to Np[V) and elutes immediately, and U(VI) is remved.)

Nota

If U, Np, and Pu are present , no oxidation step is required.

The feed is adjusted 0.7M HNO, - 0.02M Fe(S03NH2):1 to yield Pu(III),

NP(IV), and UCVI), and the same composition wash !Jolution is used.

The order of elution is Pu(III), Np(IV), and U(VI).

- 166 - Procedure 10. An Analytical Method for *s’lip Usln9 AnIon Exchange F. P. Robertszlh

OutLine of Method

This method separates Np from Pu, U, Am, Cm, and fission products by anion exch~e in HNOSsolutions to permit 2Y7Np

estimation by gaama spectrometry. The sample is :;piked with 2ssNp

tracer to permit yield corrections and loaded onto a small colum of “Oowex” l-X4 (100 to 200 mesh) resin from 8M HIW13containing

Fe(NH2SO~)2 and sem.icarbazide. After washing with 30 to 40 column volumes of 4.5M HN03 containing Fe(NH2SOy)Z and semicarbazide, the

Np is eluted with dilute HNOs containing 0, 00SM Ce(SO~)z, Np recovery is @5# with a Pu decontamination factor of 5 x 10”.

Decontamination factors from U, Am, Cm, and gross fission products are all >104. Uranium at concentrations up to 180 g/1 in the feed does not interfere. The Pu decontamination factcm can be increased

10 to 100 by following the HNOgwash with 12M HC1. - O.lM NH*1.

Np is then eluted with 6.5M HCI - 0.004M HF. The ❑ethod is appli- cable to samples containing high salt COnCentratjLOnS.

Reagenta (C.P. C’hmn%a28)

● Concentrated HNOs

● w2M Fe(SOsNHz)z

s Semicarbazide

● 2agNp tracer

MtZte2%Uz8

● ?~~wextf 1.x4, 1oo-2OO mesh

● Glass column, 0.3 cm x 7 cm wit!l 10-ml reservoir

- 167 - ● Counting equip-n t

PJwf?ed3uw

1. Adjust an aliquot of sample to ‘@N HNOs Mith concentrated HFM33.

2. Add an equal volli .e of 8M HNOS - 0.02 Fe[NHzSOq)z - 0.2M semicarbazide and mix.

3. Add 23$Np tracer (’vIOSdis/min).

4. Pass the adjusted sample through the column at 3 to 6 drops/rein. s. Rinse the reservoir several times tiitha few drcps of. 8!4NNOs, pass through the column, md discard.

6. Pass 1S to 20 ml of 4.SM HNOS - O.IM semicarbazide - O.OIM [email protected])2 through the column at .5to 6 drops per minute (’Pufrnction).

7. Pass 2 ml of 8M HNOs rinse through the column.

8. Elute the Np with 2 ml of 0.005M ~f!(S04)2 in 0.25M WW3. Catch the eluate in a 2-ml volumet~’icflask.

9. Mount an aliquct of the Np product on a Pt disc for alpha counting and alpha energy analysis. (The yield is determined by comparative counting of the 0.23 MeV 239Np gansnafrom the disc with that of a standard 239Np disc.)

- 168 - Procedure 11. Separation of U, Np, and Pu Us-lngAnIon Exchan e F. Nelson, D, C, Michelson, ●nd J. H. Holloway ?2,

GutZine of Method

This ❑ethod utilizes anion exchange .n ml for separating

U, Np, and Pu from “~m-adsorbable” elements which include alkali metals, alkaline earths, trf.val-,~tactinides, rare earths, and a number of other elements such as Al, Sc, Y, Ac, ‘I’h, and Ni.

Sorption of the uranides by anion exchangers from HCl solutions can occur in either the +4 or +6 oxidation states but not in the +3 or +5 states. In this pr,>cedurm, U is sorbed as

+6, while Np and Pu are sorbed in the +4 oxidation state. Pu is selectively reduced to PuIIII) and elut:d, while UG+ and Np”+ remain sorbed. The latter are then eluted in separate portions with HCl - HF ❑ixtures.

Reagenta (C.P. ChmicaZe)

● 9M HCl

● 9M HCl - 0.05M NH~I

● 4M HCl - O.lMHF

● 0.5MHC1 - lMHF

Matefia2a

● “Dowex” 1-X1O, -400 ❑esh anion resin

● Column, 0.6 cm I.D. and 12 cm in length, with heating device.

● Resin bed, 0.28 cmz x 3 cm long.

● Plastic test tubes

- 169 -

.’. . e “Teflon” evaporatingdishes

e Pl!astictransfer pipettes

i%ooedure

:1,, Evaporate sample to near dryne!ss.

.‘).. Add 1 ml of 9M HCi - O.OSM HNCl~and heat for S min. Do not boil.

-.3 Heat column to 50° and maintain throughout elution.

4. Pretreat resin bed with 3 colum~ volumes of 9M HCI. Use air pressure to obtain flolwof (J.8cm3/min.

5. Pass sample through resin bed ac 0.8 c.mi’min.

6. Wash bed with 4 coiumn volumes of 9M E!Cl.

7“ Wash bed with 8 column volumes {~f9M HC1 - 0.05M NH41 (PLIfraction).

8. Washi bed with 4 column volumes clf4M HC1 - 0.1,?4HF (Np fraction].

9, Wash bcd with 3 column volumes cf 0.5M HCl - IM HF (U fraction].

10. Regenerate the column with 3 column volumes of 9M IiCl.

The total time for the column operation is about 80 min.

- 170 - Procedure 12. Separation of Zr, Np, and Nb Us”lngAnion Exchange J. H. Holloway and F. Nelson224

Outline of Method

This procedure is used to separate trace mounts of Np and

Nb from micro-amountsof Zr. It makes use of the fact that Zr(IV) in HCl - HF media at high HC1 concentrationsi:jessentiallynon- sorbabl.eby anion exchange resin under conditions where Np(VI) and

Nb(V) are strongly sorbed.

lkgenta

. 6MiHC1-lMHF-C12 @ 6~~HC~ - 1~1HF

o 0.5MHC1 - 1.OM tiF

o 4M HN03 - lM HC1 - 0.2M HF

Matetiah

e “Jlowex” 1-XIO, -400 mesh anicw resin

o Column, 0.9 cm I.D. x 12 cm ir length containing 2 ml of resin

e “Teflon” evaporating dishes

o Plastic transfer pipettes

o Plastic test tubes

a Chlorine gas

Prccedwe

1, Dissolve the sample, and evapcnate it to near dryness.

2, Add 1 ml of 6M HCI - lM HF - C12, and warm.

3, Transfer the sample to a plastic tube and bubble C12 gas through it for 53 min.

- 171 - 4. Chlorinate the resin, and add it to the column.

5. Wash the bed with 2 column volumes (’U ml) of 6M HCI - lMHF - Clz. Then pass the sample through the bed. (Control the flow with air pressure at W.8 cm/min. When the sample has passed, wash ~ith an additional 3.5 column volumes of 6M HCl - lM HF - Clz (Zr fraction).

6. Wash with 3 column volumes of O.SM HC1 - lM HF to elute Np.

7. Wash with 3 column volumes of 4M FNOS - lM HCl - 0.2M HF to elute Mb.

8. Regenerate with 3 column volumes of 6M HCl - IM HF - Clz.

The total time for the column operation is ‘k30min.

-. 172 - .

Procedure 13. Separation of Np and Pu by AnIon Exchange N. Jackson and J, F. Short34g

OAtZine of Method

This procedure describes separation of macro umo”unts of W

and Np. It is based on the fact that Pu(III) is not sorbed on

anion exchange resin, while Np(IV) is strongly sorbed at high

HC1 concentrations. The valence adjustment is done before sorp-

tion on the column by dissolving the hydroxides in a concentrated

HC1 solution that has been saturated with NHQI. The Np is removed

from the column with 2 M HC1. The separation is quantitative and

complete.

Bocedure

The purificationof 2.3 g of Np237 from approximately 50 mg

of PU239 was then undertaken. The Np and Pu were precipitated as

hydroxides, centrifuged,and dissolved in 210 ml of concentrated

HC1 saturated with NH41. The solution was allowed to stand for

30 min and poured onto a Deacidite FF*anion column 20 cm long and

2.5 cm diameter, while a flow rate of 1 ml/nin was maintained.

The first 200 ml of effluent were pale blue [PU(III)]. The column

was then washed with 100 ml of concentrated HCl, and wash was

collected separately. No activity was found in a drop collected

at the end of the washing,

The Np was eluted with 2M HC1. It was possible to follow the

dark green band of the Np down the column, and the first 4C pl of

eluate was included with the concentrated HCl wash. All the Np ●Deacidite is supplied by Permutit Co. Ltd., England.

- 173 - was, collected in the next SO ml of eluate. No activity w{asfound in any eluate after this stage. Some 6-Y :m:tivitywas detected on the glass wool at the top of the resin cf}lumnand was assumed to be 2’3Pa, the daughter of Np237.

- 174 - ,,.,

Procedure 14. !Separatfon of Np and Pu by (hltfon Exchange V. t). Zagrai ●nd L. i. Se14c1wMcov2’9

Outline of Method

Np(IV9 and Pu(III) ●re adsorbed on tho cation resin KUl or

KU2 from 0.2SM }Kl solution ●f~er reduction with SOz at boiling water :eqeratures. !#p is eluted with 0.0i91HF, and Pu stripped with 0.5M HF.

P2%w31iu2w

1. To 6 tc)8 al C 9.2SN HCl containl,rg Dg mounts c~f Np &nd Pu, add a’~t half of the resir in the hydrogen fom required to fill the pleyfg!ass cc)]- (1 IUSdiameter x !90 - high] and 1 to 2 ml of water.

2. Pass S(3Z gas through the solution tigorouBly for 1S to ,20rein,uhile the solutions heatinl on a boiling water bath.

3. Allou the solution to cool to room t~rature, mnd

ltransfer the resin to the CO]W with a pipette. Plug the top of the CO1- with cotton, s.nd pass the remaining solution throug% the CO1-.

4. Wash the resin with 10 ●l of 0.2S PI WI, follouedl by 10 Is!i of H20.

5* IEIute the Np into s Pt dish or a *’7eflon” beaker with 40 to 60B1 of 0.02M HF.

6. iElutethe Pu with 4 to S ●i of ().5#1HF.

- )75 - Procedure 15. Separation and Radfochemfcal Iletermfnatfon of U and the Transuranfu Elesmts Usfmg 8arfm Sulfate c. w. slll~23012*,125 Intrv&uth

Large trivalent and tetravalent ions ~re precipitated with

Ea!50t uhile mnomlent and diwlent cations are not precipitated.

This procedure outlines the separation of U and tronsuranium el-ts both from other elements ●nd froa emch other. The oxygenated cations of the hexavslent state ● re too large to fit into the iJa!Xl~ lattice and are not carried. The !kWt precipitate

Cm Ibe alpha c~~ted directly with 92% counting efficiency, or the radionuclidus can be electrodqxmited for ●lpb spectmametry.

Rmgmti d E@gment

Concentrated HIS06

C.!P. Kasm

C0ncontr8ted I’m)

ConC8ntrwed perchloric ●cid (HClO~)

C.P. KRO$

C.P. potassium dichremate (K2CrzO~l]

30t hydrogen p@roxido (H203)

Erletmeycr flask

Centrifuge and special tubes

Counting s~lies and qui~t

- 176 - Prood4r6t

1. Add 3 g of anhydrous KzSO~ 2 ml of concentrated HzSO*, 6 drops each of concentrated My mlkd HCICI~, and 2.00 ml of 0.45~ solution of 8aC1202H2C) (S /rng of em) to the

solution containing the elements to be precipitated in a 2S0-B1 Erlenmeyer flask md evapo]’ate until fumes of HzSO* appear. (If there is any quc!;tion about removal of organic Mtter$ ●dd IWO] and/or tlCiO~ and re-svaporate.

2. Heat the solution over s blast burncIr with swirling until the excess H2SOb and lKIOti are volatilized and a clear pyrosulfate melt is obtained.

.3. COIOI the aelt, add 2 al of concentrated H~SO*, and heat to boiling or until the pyrosulfate’ melt is dissolved. 00 not volatilize tsuch HzSO~.

‘4. Cool and add ~10 IDg of solid KICrzOT,, and mix to ensure cmplete cxidation of Np. Do not heat becBuse 1% Mill be oxidixed and the excess dichronate will he the]~nlly decomposed .

%. Cool to ‘v40*C ●nd add ~20 IR1 of water; boil for I minute.

t). Cool, centrifuge, ●nd Mash the precipitate; the %p and U are in the supemate.

7. Md 0.S ml of SO%H~02 and 2.00 ad] of 0.4S’i !laClz to the supernate, and evaporate until ftmes of H2!~Q appear to reduce any Pu that may have folloued the Np.

8. Heat the H~SOb to boiling, cool for ? minutes, and ●dd %10 q of KtCr20T to reoxidi:e the l~lJ.

9. Add ?0 ml of water ●nd boil for 1 wilwte; cool. centrifuge, and c~bine the supemate with that ~rom Step 6. la. Add 0.S ml of SO%tilOZ to reduce Np ~:o the quadrivalent state, and evaporate to 2S ml.

- 177 -, 11. Cool and add BaCIZ; then boil, centrifuj~e, wash, and mount the BaSO~ which contains the 2’7Np. TIN) U remains quantita- tively in the supernate.

Not88

1. Seweral other shorter procedures fo]: Np are given when Np is to be separated from one or tl~o other cations.

2. Details are given in the reference ~wticle for depositing the precipitate on a stainless steel disc that fits into

a specially designed centrifuge holhler andlalso into a specially designed counting holder,, An alternative pro- cedure uses electrodeposition of th~! radia’nuclides for alphs spectrometry.

- 178- 237~p Procedure 16. The Low-Level Radiochemica”l Determfnatiom of In Environmental Samples R. W. Taylor3S0

Intro&40t~on

Np, along with Pu and U,is removed frcm 8M HC1 by anion exchange to triisooctylamine (TIOA). Eac:h element can be indi- viduall}-removed from the TIOA. Pu is sl:ripped first with 8M

HCl - O.OSM NH*I. Np is removed next will 4M HCI - O.OSM HF, and U is removed last with O.SM HNO~.

Uost environmental saaples contain large quantities of Fe that will extract with the actinide elesmts into TIOA, Much of the Fe will bu stripped froa the TIOA al.cng with Np, but it is easily removed from 8 N HCl by isopropyl ether. If tho sample i!~ known to contain no Fe, the ether extraction step may be otsitted.

Final decontamination of Np is accomplished by solid ion emhange. ?@ is final 1y electrodepositet for rsdioassmy by alpha pulse height analysis.

When ths saaple contains large quantities of U, some of it may foliou the Np ●nd be elactrodepositccl on the plate. 2S’U and a 9TMp .Mve the same alpha energy (4. 7S MeIV) and cannot be distin- y~c~ by guished from one another. The Np can ba converted to neutron irradiation for verification of ~ “~. Also, whwn the Np activity is wry low, conversion to 2S’PtI will decreas~s the counting time. Tw-how irradiations ●t a flux cd’ 1 x 10*S n/(cm2-see) result in 8 2“pU activity level about 7 to 10 times greater thsn

- 179 “ the original activity due to Np.

R6!agt?nt’%

o HN03, 16M, lM

o HCl, 12M, 8M

e H202, 30%

c NMkOH, 1.SM f ● KOH, 12M

● 8M HC1 - O.OSM NHuI: This rm~gent must be prepared fresh just prior to use. Discard a:lyunusef reagent at the end of the day.

o 10% TIOA (triisooctylaminc): 10% vcilume/volumeTIOA in xylene. Clean the reagent b:y shaking in a separator funnel with half its volume OF 0.5M HN03. Repeat the HNOs wash, and wash finally with distilled water. Store the cleaned TIOA in a glass flask.

g 4M HCl - O.OSMHF

o Isopropyl ether

* “Dowex” 2-X8 anion exchange :rlasin, ~!Od to 400 ❑esh

PmudLir8

1“ Adjust the sample to be analy:z(sd to 8M HC1. Soluble saaples may be dissolved directly; irlsoluble materials may be leached with hot MM HCl; aqueous samples may be evaporated to near dryness and brought up in 8M W1. The sample should be adjusted 1:0a ccmvenient volume of from 200 to 400 ml.

2!. Add S m: of 303 }1202 to the !umple wnd heat nt about 80°C until effervescence ceaso:~. COCJIthe sample to about room temperature.

- 180 - 3. Transfer the sample to a 500-md separator funnel, Add an amount of 10* TIOA equal to one-fourth the amount of the original sa~le. Shake the funnel for one minute. Allow the phases to separate, and drain the bottom (aqueous) phase. Retain for other analyses.

4. Add 10 to 20 ml 8M HCI (according to volume c~foriginal sample) and shake one minute. Allow phases to separate, drain, and discard the aqueous.

5, To strip Pu from the TIOA, add to the separator funnel an amount of 8M HC1 - O.O”X NHu1 equal to one-half the voluune of TIOA. Shake one minute and then allow phases to separate. Drain the aqueous and retain fcm Pu analysis. Repeat the Pu strip ~ith a fresh Flortionof 8M w] - O.OSMNd~I. Combine t$e two strips, and save for Pu analysis.

6, To remove Np from the TIOA, ad(d to tho separatcry funnel an amount of 4M HCl - O.OSM HF equal to one-half the volume of TIOA and shake for o]ms minute. Allow the phases to separate, and drain tl~eaqloous which contains W* Repeat the strip with a f:rl!sh pmtion of 41.! HCl - O.OSM HF, and combine the two :s’:rips. U can now be stripped from the TIOA with 0.!51d HNOs.)

7. Add an equal amount of 12M HCl 1:0the combined strips, and transfer to a clean separatt~ryfumnel. Add 2S ml isopropyl ether and shake one m:lnute. (CAUTION: Vent the separator funnel frequentl:r while shaking.) Drain the aqueous, and retain. Disca]*d the ether in accordance with safety regulations. Repeal: the ether extraction with a fresh portion of ether.

8. Evaporate the aqueous phase frornl Step 7 to dryness. Place in a muffle furnace at 400*C fo]’ at least 4 hours. Wet oxidize the sample two or threo times with 3 or 4 ml

- 181 - 16M HWS and 30~ HzOZ. Md 2 or 3 ml 12M HCl and evaporate to dryness. Repeat the 12M lKl evaporation.

9. Dissolve the sample in 10 ■l of 8M HC1 and pass through a “Dowex” 2-X8, 200 to 400 mesh, anion exchange colm. The resin bed should be 50 m long and 6 m in diameter; it must be pro-conditioned with 5 ■l of &MlHC1. After the sa@e passes through the column, pass an additional

5 ❑l of 8M ICl through it. Elute the Np from the COIUWI with 10 ■l of O.lM HC1. Evaporate tD dryms.

10. Md 2 ml of 1(MIHNOSto the sample, md waporate to dryness. Repeat the W3 waporation. Add 2 ❑l IM HKls to the sa@e, and heat gently to ensure dissolution. Cool, ●nd transfer the sa~le to an dectrodeposition cell. Rinse the beaker twice with 2 ml of distilled water, and transfer the rinse to the cell. Add 2 ml of 1.SM NH@H to the cell, and add distilled water until the cell is full.

11. Electrodeposit the sample ●t 10 V and about 200 mamp for three hours. Maintain the pH of the solution between 1 and 3 during electrodeposition. A: the end of the electrodeposithn period, ●dd 1 ml o:? 12M B21Hand plate for 1 min. ~ty the cell , rinse with distilled water and remove the plate. Dry the plate and flame it.

12. Count the plate by ●lpha plse height analysis. If there is no U present ●ml if there i!; sufficient 2g7Mp present, radimssay carI be ●ccoqlishd directly. In the presence of U or when there is wry little 2% present, increased sensitivity can be) ●chieved by con- version of Z“Iq) to “% by neutron irradiation. The ●bsence of “% is verified by the initial count.

13. Irradlato the ~ aaqsle for approximately tm hours ●t ● flux of 1 x 1013 n/(cm2-see). A1lCIUtha plmte to

- 182 - cool long enough to pemit decay of induced Pt activities and to allow 23 ‘Np to decay to 2s ‘Pu. Recount the plate by alpha pulse height analysis. Correct the amount of ‘gepu now present by any originally present on the plate, if necessary. Calculate the amount of Np present before irradiation from the activation formula.

- 183 - Prowdure 17. Radiochemical Procedure for tle Separation of Trace Amounts of 2g9Np from Reactor Effluent Water R. W. Perklns1s5

Intmduotion

This procedure accommodates a relative:{ large volume of reactor effluent water, and emphasis is pla{csdon speed of separation and high radiochemical purity ratler than high yield.

%ocedure

1. Acid 20 mg of La carrier and S ml of concentrated HC1 to one gallon of reactor effluent water, and evaporate to %Sclml.

2. Cool the solution, dissolve 0.25 g >f [email protected]]2, and let stand for S min.

3. Transfer to a 100-ml plastic tube, ~dd 5 ml of concentrated

HF, stir, and let stand S min.

4. Centrifuge, and discard the liquid phase.

5. Dissolve the precipitate in 20 to S0 ml of 1?4HCl, and dilute to 75 ml with IM HC1.

6. Add 5 ml of concentrated HF, stir, and let stand for S min.

7. Centrifuge and discard the liquid phase.

8. Repeat Steps 5 through 7.

9. Transfer the precipitate to a 50-ml beaker containing 3 ml of concentrated HC104, and evaporate to dryness.

1.0. Dissolve!the residue in 20 ml of lM HC1 by boiling. Cool the solution and dissolve 0.2S g of Fe[NHzSOg]z.

Il. Transfer the solution to a 12S-Ialseparator funnel and mix, Add 20 ml of ‘ITAin benzene, and extract fcm 10 min. Discard the aqueous phase. - 184 .. 12. Wash the organic phase with three 20-ml portions of lM HCI for 5 min each. Discard the aqueous solutions.

13. 8ack-extract the 2S9NP with 10 ml of 8M HN03 for 10 min.

14. Place the aqueous in a SO-ml beaker containing 3 ml of concentrated HC104, and evaporate to dr:yness under a ,leat lamp.

15. Cool the beaker, add %5 ml of 8M HN03, and heat to boiling.

16. Dilute the solution to a measured volume and analyze by gaama counting.

Note

The analysis requires ti hours, and tle yield is ~90%.

- 18S - Procedure 18. Detennlnation of Np In Urine F. E. Butler3s J

Outline o~lfetbd

Urine is wet ashed with HN03 and H202 to destroy organic

matter. The salts are dissolved in BM HCI and extracted with

TIOA (tri-isooctylamine). The Np is then back extracted, and

the alpha activity is determined by direct plqnchetting and

counting on low background solid-state counters.

A variation of the procedure provides for sequential deter- mination of actinides in biological and en~’ironmental samples.

Pu, Np, and U are extracted from EN HC1 to TIOA. The residual

N HC1 containing Th, Am, Cm, Bk, Cf, and Es are extracted from i2M HNOS to DDCP [dibutyl N, N-diethylcarbamyl phosphonate). The actinidcs of interest are back-extracted sequentially for quanta- tive detezminations.

P2qmwztion ofthmpk

Urine collected in polyethylene bottles is transferred to an

Erlenmeyer flask with concentrated HNOI (201 n!l of acid per liter).

Acid is added to the urine in the polyethylene bottle to renwe the Np, which may be adsorbed on the walls of the container. The acidified sample is evaporated to dryness, ilnd the residue is wet ashed with HN03 and HzOZ. Nitrates are metilthesizedto chlorides by evaporation to prevent interference with Pu (liIj removal.

- J86 - Reqen ib and Equipment

The liquid anion exchanger, TIOA (BrainChemical Co.) is

diluted to 10 VOI % with xylene and washed with half its volume of O.lN HC1 before use.

The alpha-detection equ~pment are 211solid-state counters.

The counters arc equipped with detectors ::hathave an active area of 350 mmz and .me capable of accepting l-in. stainless steel planchets.

All other reagents used in the procecurc are prepa:redfrom analytical grade chemicals.

Firoccdure

1. Wet ash urine with HN03 and H202; then add 113ml of 8M HC1 to the white salts twice and evaporate the solution to dryness each time.

2. Dissolve the salts in freshly prepared 8M HC!,- 0.05M NH41 (50ml ofacid/250 ml of urine in sample), andheat to com- plete solution.

3. Transfer a 50-ml aliquot of the solution with 25 ml TIOA-xylene into a separator funnel and shake for 1 min. (For urine samples of 250 ml or lCSS, rinse the flask twice with 10 ml of 8F!HC1, and add the rinses to the funnel.)

4. Drain and store the aqueous [lower) ls)er for Pu, Th, #m, Cm, and Cf analysis.

5. Rinse the organic phase with 25 ml of EM HC1 - O.OSM NHkI at 80°C and shake for 1 min. Discard the rinse solution or com- bine with solution stored for other actinide analysis.

- 187 - 6. Add 25 ml of 4M HC1 - 0.02M HF tn the funnel and shake

vigorously for 10 sec. Drain the Np strip to n iOL1-mI breaker. Repeat a second time and combine the two 25-ml solutions. Discard the organic phase or strip with O.lM IIC1 for uranium analysis.

7, Evaporate the Np strip to dryness. Wet ash with tLYO1and 1[202. Rinse sides of breaker with 4M IL%03ond evaporate solution to dryness.

8. Add 1 ml 4M lINOIand transfer solution to stainless steel planchcts and evaporate to dryness under an infrared lamp. Complete transferwith 3 rinses of 4M I{NOJ.

9. Flame the dried planchet tc dull red, cool, nnd count on low- lCVC1 solid state alpha counters.

10. Calculation: Np activity on planchct is determined as follows:

total count - Bk d dis/(min-planchet)= ~t)(cout=r ~ff ~ - .

where: Bkgd. = counter background (3 to 10 counts/24 hr)

t = counting time in minutes

counter cff = counter efficiency as a fraction (normally0.30)

The sensitivityof this analysis is 0.02 ~ 0.01 dis/[min-samplel.

The recovery efficiency is determined by adding a known amount

of Np standard to an aliquot of urine sample and followingthe

same procedure for analysis.

- 188 - Procedur? 19. Detetmlnatlon of “’~:pby Ganma Ray Spectrometry W. O. Granade 352

Intrcdactiun

A gama spectromctric incthod was develoFed that allows for

the rapid determinationof Np in process solLtions containing

fission products. The method is unaffectedky highly salted,

corrosive,or organic mcdii3. 237Np is dctcrninedby ,iymma

spectrometryusing a thin lithium-driftedgermanium [Ge(Li)]semi-

conductor detector to resolve the 86.6-keV 237Np gamma ray.

The detector system consists of an Ortcc model 3113-10200,

low-energyphoton detector with cooled FIiTprzamp and a resolution

of 900-keV full width at half maximum [Fh’HM) ~t 86.&heV. ,!

4096-channelpulse height imaly~er is used for the accumulation

and storage of the gamma s;)ectra. The data are read onto magnetic

tape or printed out directly from a high-spee’jdigital printer.

Data reduction is performed using an IBM 360.:iystcmand FORTRAN

programs developed to calculate nuclide abundmccs from multi-

channel gamma ray spectra.:

%wcedwe

Calibration. 233Pa, the daughter of 237Np, has a 0,017

abundant gamma ray at 86.6-keV that interfereswith the measure- ment of the 237Np gamma my of the same encrg}”. 233Pa also has

u 0.34 abundant gamma ray at 311.9-keVthat i: not associatedwith

a 237Np gamma ray. In order to determine the 233Pa contribution

- 189 - to the 86.6-)ieV237Xp photopeak. a pure stancard solution of

233Pa is required. 233Pa is purified by passing an equilibrium

solution of ‘33Pa-237Npthrot’gha diatomaceoLsearth column which 233pan sorbs IIIC 233pa is cluted, and the ‘:7Np contaminant level

is determined by alpha counting ( 233Pa does not decay by alpha

emission). Aliquots of 213Pa are pipetted into a standard gamma

counting geometry. A series of counts of the 233Pa are made to

determine the ratio of gamma counts at the 8tl.6-keV peak to counts

at the 311.9-keV peak. The ratio is used to calculate the 213Pa contribution to the total counts detected at the 86.6-keV peak.

me efficiencyof the Gc(Li) detector for 86.G-heV gamma

rays is determinedby calibrationwith known gamma standards

between 43.5 and 511.6-kcV.

tkaly~i 3

Tnc standards and sample arc counted in a holder which ensures

a reproduciblegcomet~ at 2 cm. The deadtime correction (always

<20%) was found to be accurate to <1%. The gain setting of the amplifier is adjusted to provide a peak width of 7 to 10 channels

(FWUM)to allow reliable integrationof the photopeak area. For a Gaussian distribution,99% of a peak area is contained in 2,1 x

Fwllhl. Therefore a peak area of 24 channels is used with a gain setting giving 10 channels FWtB1.

The net counts per minute of 237Np is calculatedby subtracting

the Conqztonbackground and the 23spa contril,utionfrom the 86.6-keV

- 190 - total photopeak amm. The contributia of wdcrlying Co~con

bmckgromd is a~sumed to be linear over lhc peak area. An

average of the comts from 4 channels on each side of the peak

is used to determine the backgromd correction. For an analysis

above the determination limit (the relative standard deviation is

less than 101 of the measured value), the peak area ■inus the

backgrotmd should be greater thanz: 4 50 I + 1 . W. Sum {[ 12.5 1} me absolute disintegration per minute value of 7’7Np is obtaind by dividing the net counts per ❑inute hy rhc product of

the g- ray ahmhince (photon/disintegration) and the detector efficiency at B6.6-keV.

A coqarison of *“N,p results obtainsd by ga-a spcctromctfi and TTA extraction’ agreed ~ithin 5%. An aliquot of I.Ob x 10s alpha dis/(min-ml) 237Np standard solution was cxtractcd using

ITA. A standard geometry sa~le was =de from the lTA [organic] phase andone from the aqueous phase. TIM: resulting gama comt- ing shoued that 97% of the 237Np had been extracted into the lTA phase. Close agreement between the two mnthods demonstrated the reliability of the gs pulse height analysis. Samples can be counted in organic media with no adverse uffects. A lower limit of detection of 1 x 10” d/m/ml at a confidence level of 9S1 was detemined fmm a series of counts using a diluted standard 237Sp solution.

- 191 - F?u,%?rw?lm

* -. !4. A. Itakat and E. K. mkcs, c’. .%d~J@H@t. Cwm. +, 109

[1970).

.;. *. F. Ilidcr. Scieeai tii~:icul P?tiodr for Fwws I%vmea L.”mcrr:. IEAEC Rqort KAPL-890 ( 19S3).

- 192 - Procedure 20C Spectrophotometric Determqillation of Np R. G. Bryan and G. R. Watw’bury302

Outline of Method

Np is measured spectrophotometricall!r as the arsenazo Ill

complex after separation from Pu and impul-ity elements by liquid-

liquid extraction. U is removed first by extraction from 4M HC1

into triisooctyl amine (lIOA)-carbon tetr:~chloride,while Np(IV)

and Pu(III) are stabilized in their nonexl:ractable oxidation

states tJyFe(II] and ascorbic acid. Then Sp(IV) is extracted

from 8MHC1 into TIOA and back-extracted into O.lM I{Cl. The

?ip.arsenazo 111 complex is formed in 6.lM I!Cl, and the absorbance

is measured at a wavelength of 665 nm.

.7eag%~t8

o Arsenazo 111, 0.2$ [~,8-dihydrox:plapthal,ene -3, 6-disulfonic acid-2, 7-his (azo-2) -phenylarsonLc acid]. Dissolve 1 g of arsenazo 111 in S00 ml of wate:: containing two KOHpellets.

o Ascorbic acid, 5$. Dissolve 6 gr:~msof ascorbic acid in 120ml of 8t4W1.

c Carbon tatrachloride, (CClk) reaglmt grade.

o I!Cl, 12M, reagent grade.

o Np stock solution. Dissolve higlh purity Np metal in 12M HC1.

● Phosphoric acid, (HJPO*) 1S.9}1, rzagent grade.

● KOH, pellets, reagent grade.

- 193 - ● Reducing solution, 5% ascorbic acid and 0.5% Fe(II] ion in 4M HC1. Dissolve 2.5 It of ascorbic acid and 1.75 g of Fe(NH2S03)z in 50 ml of 4hl I{Cl.

● Tri(iso-octyl)amine-xylenc (TIOA in xylene), 5%. Dissolve 31 ml of TIOA in 500 ml of re~gent-grade xylene.

● Tri(iso-octyl)amine-carbontetrachloride (TIOA-CClb), 5%. Dissolve 31 ml of TIOA ir 500 ml of CC14.

Equipment

● Extractors (see figure in Reference 302).

● Laboratory glassware (beakers, pipet.s, syringes, and volumetric flasks).

● Spectrophotometer, Beckman model DU or equivalent, with ❑atched fused-silica cells having l-cm light paths.

Pretreatment The sample of metal or alloy is inspected, and extraneous material is remved. Cutting oil is remwed by washing with methyl chlorofom. For each Pu ❑etal sample, take two accurately weighed portions, each not greater than 200 mg and containing less than

60 ~g of Np. Make duplicate determinations on each sample, on a solution containing a known quantity of Np, and on the reagent blank solution.

- 194 - Procedure

1. Place each accurately weighed sample in a glass extractor and add 1.5 ml of 12M I{Cl. Mhen the sample has dissolved, add 1 ml of the reducing solution and 2.5 ml of water.

2, Prepare reagent blank solutions by adding 1 ml of reduc- ing solution and 4 ml of 4M HC1 to each of two extractors.

3. Prepare known Np solutions by adding an aliquot of standard Np solution that contains an amunt of Np approximately equal to that expected in the sample and

1 ml of reducing solution to each of two extractors. Dilute the solutions to 5 ml with 4M WI.

4. Add 5 ml of TIOA-CCl~ to each of the solutions prepared in previous steps, mix the phases for 2 rein, and then allow the phases to separate for 1 min.

5. Separate the TIOA-CCl~ layer and discard.

6. Repeat Steps 4 and 5.

7. Add 5 ❑l of 12M HC1 and 10 ml of TIOA-xylene to each extractor, ❑ix the phases for 3 min and allo~ the phases to separate for 1 min. Remove the aqueous phase con- taining the Pu.

8. Wash the inside of the extractor wit~h 53 ascorbic acid-al HC1, mix the phases for 2 min. and allow the phases to separate for 1 min. Rcmnm the aqueous phase.

9. Wash the inside of the extractor with RV IIC1. Mix the phases for 2 rein, and allow to separlatc for 1 min. Remove the aqueous phase.

10. Add 4 ml of O.lM HC1 to each extractor. Mix the phases for 3 tin, and allow to separate for 1 min.

- 195 - 11. Remove the aqueous phase into a 25-ml volumetric flask containing 0.6 ml of H3POb, 1 ml of 5% ascorbic acid- ~ I{Cl,and 12.7 ml of 12N HC1.

1~, Repeat Steps 10 and 11.

13. Add ~.5 ml of 0.23 Ar~ena~~ III ~o]ution to the vol~tric flask, and dilute to 25 ❑l with water. Stopper and mix the contents of the f’dsk.

14. Measure the absorbance of the solution in cells having l-cm light paths at a wavelength of 66S nm.

(As-Ah) (Wk, LIE ofN@ 15, ‘p’ ‘pm = (Ak-Ab) (sqle wt in grama Ab = absorbance of blank Ak = absorbance of known Np solution As = ahsorbancc of unknan saqIlc Wk = ug of Np in known NF solution

Uclative standard deviations range between 7.2 and 1.1S in measuring 8.S to 330 ppm of Np in 200 mg samples. Of 45 elements tested only Pd, Th, U, and Zr cause serious interference, but only if present in concentrations greater than 0.8%. However, initial extraction from 4N }ICIinto TIOA remves some U, and Th

is not significantly extracted from HC; solution. Also, lilPOh conplcxcs up to 1 mg of Zr without affecting the analysis. HF and IINOI cause low results unless remved by volatilization. The method tolerates the intense radioactiqrity fxom quantities of

*’aPu as Iargc as 100 mg.

- 196 - Procedure 21. Microvolumetrfc Complexonetrlc Method for Np with EDTA

A. P, Smirnov-Averin, G. S. Kovalenko, N. P. Ermoloev, and N. N, Krot:’26

Outline of Method

Np(IV] is titrated with a solution of EDTA at pH 1.3 to 2.0 with xylenol orange as indicator. The ;?eacticmc)fNp(IV) with

EDTA is stoichiometric, and the color changes from bright rose to light yellow at equal molar concent:riltions.The determination takes approximately two hours; the erro:-is tC1.03mg.

Reagenti and Equipmnr

o Hcl, reagent grade

o Test solution, 10 mg Mn2+ and ,50mg NH20H*MC1 per ml

e 30(%KOH

a 10% NaCl in 4M HC1

s 0.:1%xylenol orange

@ Centrifuge tubes

@ Micro or semimicroburet

Pswcedwe

1. Add 1 to 4 ml of Np solution and 2 ml of test solution containing 10 mg Mn2+ and !50mg of Ni120H*HClper ml into a centrifuge tube.

2. Dilute to 6 to 8 ml, and heat to 60°C; add 30% KOH with mixing until the pti>10.

3, Centrifuge the precipitate, and discard the solution.

4, Add 10% NaCl in 4M HC1 dropwise until the precipitate is dissolved.

- 197 - 5. Add 1 to 1.S ml of 4M HC1 COnta:Lning 50 ❑g of NIIZOH”HC1 per ml, and heat the solution for 20 min on a boiling water bath.

6. Cool the solution, dilute towldO ml with water, and add 1 to 2 drops of 0.1% xylenol or.mge.

7. Titrate with 2 x lLI-lM EI.)TAfrom a microburet until the color changes from rose to brig~t yellw.. lio tes

1, [ICI solutions are preferred in xder to reduce all the Np to the tetravalent state with NI[2011”IIC1. Ascorbic acid is not suitable, since its decomposition products interfere with the titration.

2. Doubly charged readily hydrolyzable ions (Mn2+, Ni2”, U3Z2+), which do not interfere with the titration, are used as carriers.

3. Np can bc determined with an error of tO.03 mg in the presence of large amounts of alkali, alkaline earth, and rare earths elements, Mn2*, Zn2+, Cd2+, Pb2+, Cr3+ (up to 20 mg), Ni2+, C02+ and lM322+. Anions which are separated by strong base precipitation include NO]-, (3{@0-, SOk2-, C@42-, Cr2072-, and EMA’-. Pu is reduced to Pu(III) and does not interfere up to 2 mg. 2rh+, fib+, and Fe3+ interfere because they arc cotitrated with Np(lV).

- 198 - Procedure 22. Photanetrlc Determination of lip as the Peroxide Canplex Yu. P. Novikov, S. A. Ivanova, E. V. Bezrogova, and A. A. Nemodruk3s3

Outline of Method

Np(V) forms an intensely colored complex in alkaline solutions

(pH >8) . The ratio ofNp(V) to Hz02 in the complex is 1:1; the molar absorptivities of the complex at 430 and 370 nm are 5010 t210 and 7950 t350, respectively. The method is highly selective for Np.

t?eagentaand Eq? - :ent

. NaOtl, Cl) grade

● 11202, CP grade

● Spectrophotometer and cells.

Pzwcedurw

1. Add the dilute acid (HN03, HCl, or IIC1(14) solution, %2.5 ml containing 5 to 50 Ug of Np into a test tube.

7 A. Adjust to Np(V) by adding 0.1 ml of 30% 11Z02, and keep in a boiling ~atcr bath for 10 min.

3. Cool the solution, and add 0.1 ml of 0..5}1 IIzOZ.

4. Neutralize to pl{ 1 to 3 with NaOi, nd add an extra 1 ml of 4N NaOH.

5. Dilute to exactly 4 ml with water, and mix thoroughly.

6. Measure the absorbance in a 1 cm cell iit 430 or 370 nm realtive to a blank.

7, Detenninc the Np content using a calibration curve,

- 199 - Note8

1. Np(V), but not Np(IV) or N:J(VI), gives a color reaction with 11:02.

2. The stability of th(? colored Np(li) peroxide complex increases as the pH is increased. In O.lM NaOl{ solution, the absorbance rem~ins unchanged for two hours.

3. Increasing the HZOZ concentratio~ to >? x 10-3M does not change the ?l~sorbance. At higher H202 concentrations, the time for constant absorbance increases.

4. When the solution contains U, 7 “to 10 mg of (lUi~)zHPOk is added before the NaOH. Greatm amounts of the phosphate reduce absorbance of the Np(V) complex. s. Fluoride reduces the absorbance of the Np(V) peroxide complex. Tartrate, carbonate, and sulfate ions to O.lM have no effect. When iron is present, Fe(OH).q precipitates and is removed by centrifugation, Up to 300-fold amounts of Fe do not interfere. Four-fold amounts of Pu do not interfere.

- 200 - procedure 23. Separation of Np for Spectrographic Analysis of Impurities J. A. Uheat232

Outline ofllethod

Np mmpounds are dissolved in concentrated HN03, and the

solution is heated to dryness. The residue is dissolved in

dilute HN09, and Np oxidation state adjustment is made with NzH4

and sulfamic acid. The hexanitrato anionic cornplcx of Np(IV) is

sorbed on strong base anion resin; the c~tionic impurities are

not sorbed by the resin. The cycle is rspeated, and the effluents

are evaporated and baked at 4110°C. The residue is dissolved in

6M HC1, and the cationic impurities are determned by emission spectroscopy.

Reagente and Equipment

● Double-distilled HNOg ● “Dowex” 1-4 100 mesh ● Hydrazine (N2H~] ● Sulfamic acid ● Cobalt solution ● Small glass column ● Spectrograph

Pxx%?dure

1. Dissolve SO mg of sample in concentrated HN03, and evaporate to dryness.

2. Dissolve solid residue in 2 ml of 0.35M HN03 and add one- fourth ml of llM aqueous solut.,on of N2H@. Wait at least 30 min for valance adj’x-:ment.

- 201 - 3. Add one-half ml of 3M sulfamic acid ,and 2.5 ml of 16M HN03, and mix the solution.

4. Pass the adjusted solution thrwgh a 3 ml bed of ILd-mesh “Dowex” l-X4 resin at <3 ml/(min-cm2j, and collect the effluent.

5. Hash the resin with w1O ml of N llN03, and combine the effluent with that from Step 2.

6. Elute Np from the resin with 0.35M N3, and condition the coluam with 8M HNOs for re~se.

7. Evaporate the sorption and wasl effluents to dryness, and repeat Steps 2 through 6. (99.96% of the Np was rermved with two cycles of anim exchange].

8. Evaporate the sorption and wasl effluents from Step 7 to dryness and bake at 400°C t~ expel hydrazine.

9. Dissolve the residue in 1 ml of aqua regia, and evaporate to dryness.

10. Dissolved the last residue in 1 ml of 6M HCI cont~ining 100 ug of Co, which serves as m internal standard.

11. Evaporate two hundred Bg of ths solution to dryness on top of a l/4-inch-diameter flat-top electrode.

12. Excite the sample for 30 sec b? a 10-amp dc arc using a large Littrow spectrograph in the 2500 to 3S00 A wavelength region. The slit width is 10 Urn, and a two- step neutral filter 100%/3S% i; inserted in the slit. SA-2 emulsion is used.

Because of the relatively large volume of reagents used, a reagent blank should be carried throu,~h the procedure. Doubly distilled tlNOJ was used.

- 202 - Recovery was 88 to 106% for all elements except Ni which was

65%.

The coefficient of variation for a single determination of

the several elements varies from 9 to 24% with an average of

17%. The precision is affected by large volumes of reagents and

inco~lete remval of cationic iupuritics from the resin column.

The method was applied to determination of Fe, Cr, Ni, Mn, Cu,

Al, andMg.

- 203 - Procedure 24. Photometric Determination of Np as the Xylenol Orange Complex

N. P. Ermoloev, G. S. t(ovalenko, N. N. Krot, and V. J. Blokhin30n

Outline of Metiwd

Np(IV) reacts in weakly acidic solution (pH %2) with xylenol orange to form a color complex with an absorbance maximum at 550 nm and molar extinction coefficient of 5.5 x 10b. Xylenol orange

is three times more sensitive than thorin but only one-half as sensitive as Arsenazo 111 as a reagent for Np[lV). The greatest advantage of xylenol orange coupared to thorin and Arsena:o 111 is the relatively minor interference of U.

Ff&aLJect8Umi Qaipme):t

tlc1

30”. ~al Test solution, 10 q M112’and 50 mg of XIIZOII”IIC1pcr ml 100 ❑g Sll@H”llCl per ❑l in 7S1IK1 31 xm~ai 0.0S3 xylcnol orange pll 3wtcr Spcctrophoto=tcr Centrifuge tdms

1. M solution containing S to 20 us of Sp to a centrifuge tube, and dilute to S to 8 ●l; then mdd S0% S3Wuncil @ >10.

:. Add 1 ml of test solution contrnlnlnr 10 mg of $hlJ* and

50 mK of .SHZCMI-IKI ine= the ccntrihl:c C*C.

-m4- 3. Mix and centrifuge the precipitate. Discard the liquid; then dissolve the precipitate in 2 ml c’f 7M HC1 contain- ing 100 mg NHzOtl”tlCl per ml.

4. Heat the solution to almst boiling on a water bath for 25 min to obtain Np[IV).

5. Dilute to %15 ml with water, add exactl,y 1 ml of 0.05% xylenol orange, and adjust to #l 2.0 to 2.2 with 2NI.Nl@ll.

6. Transfer the solution quantitatively to a 2S ml volmetric flask, and dilute to vol-e with water.

7. Mix and measure the optical density of the solution m an FE’K-M Instrument fitted with a green filter and using cells sith a path of 5 cm at 550 nm. The reference solution is the sam plland reagtnt coqositictn as the Sp solution.

;1012?8

1. the SF concentration is detcrminrd from a standard

cali~ration cume.

-.* The determination wq~ircs ‘-3 hours, and the error usually {s

3. ~p c= be detcmined by the abovr method in IKI, IMI, llCZlllOIo and NzSOb solutions an9J also I,a solutions

containing other anions that arm remowd by the strong

base precipitation: flmride and phosphate interfere.

-ms- Procedure 25. Analysis for Np by Controlled Potential Coulanetry R. W. Stro.matt’”

Intrv&ctwn

Controlled potential coulmetry is useful for detecting as little as 2 ug of Np, and 7 vg can be dett’nnined with 6% standard deviation. The general procedure is to first oxidize all the Np to Np[VI) with Ce(IV), then the Np(VI) and excess Ce(IV) are electrolytically reduced to Np(V) and Ce(l II). Finally the Np(V) is coulo-trically oxidized to Np(VI) to determine the concentration of Np.

RmgeRta and ~uipment

● lM H2S04 ● Mercury metal ● Mercuric sulfate ● Pure heli= gas Q Sodium silicate solution ● Controlled potential coulo~ter ● Titration cell (working electrode Pt gauze, isolated electrode Pt wirt and saturated calomel reference)

Plvra2df4n2

1. Add the Np sample and the titration medium into the cell, and adjust the hydrogen ion and sulfate ion concentrations

to %lN. (The hydrogen ion concer,t~tion is not critical between 0.4 to 2N but the electrc,de potential of the Np(V/VI) co~le is affected by the sulfate concentration).

2. Add Ce(lV) solution until there is an excess as evidenced by a persistent color.

-206- 3. De-aerate the solution with He for 5 min. [If during this time the excess Cc(IV) has rc.~ctcd, add additional Ce(IV)].

4. Apply the potential to reduce the \p(v1) and cxccss Ce[IV) to Np(V) and Cc(Ill) until chc current bccomcs constant.

5. Apply the potential to oxidize the Np(V) to Np(VI). The oxidation is continued until a constant current is obtained. Make several readings of the intcgrat~’d current, and extrapolate the integrated :urrent curve to zero time.

6. Prepare a blank solution containing the same amount of Ce(IV), and after S min of de-aeration perform reduction and oxidation titrations at the same potentials as used for the Np titration. After constant current is rcachcd for oxidation, read the integrate current several times and extrapolate to zero time.

7. Subtract the zero-time integrated current of the hliinti from that for the Np titration, ar.d calculztc tlm mount of Np based on the instrument calibration. (l”or Illg!lcst

accuracy, the Np lost in the de-mration and from migration

in the cell are taken into account.)

Noh?a

1. The ,Np(V]/[YI] couple can be titr;lted quantitatit-cly and

reversibly in 10101, IIC106, and 112!;Ob; hcnicrcrp more reproducible results arc obtmincd with 112SO~. Also, the potentials of the Pu(III)/(I\’) anlJ Sp(Vj/(\l) COIIIIICS arc separated better in ll@~.

- 207 - 2. Ce(IV] ion is used for oxidation because oxidation of ?Jp is rapid and quantitative, and Pu(IV) is not oxidized significantly in H2SOk.

3. Coulornetric titrations in solutions containing organic contaminants are often slow and yield low values.

4. The concentration of Np in the different oxidation states can be made using the Pt electrode cell. The ANP(J’1/(VI) couple Cm be titrat~!d without interference from oxidation of Np(IV). Np(VI) is determined by coulometric reduction to Np(V). The Np(V) is then oxidized coulcmetrically, and the difference between these two titrations is the Np(V) initially present. The total Np concentration is deter- ❑ined as previously discussed, and Np(lV) is calculated from the difference between the concentrations of Np(V) plus Np(VI) and the total Np. s. Propst 31’ has reported a coulometric method for Np utilizing a conducting glass ele:trode in a thin-layer electrochemical CC1l. Organic conta.mirlantsinterfered and were remved by a bisulfate fusion procedure.

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51. D. Cohen and A. J. Walter, J. Chem. Sot. 1964, 2696 (1964),

52. G. Koch (cd), Gmel;ne Handbuch der Ano~ani8chen Chemie, lknauraniums, Part C, The ConpoundeB Verlag Chemie - GMBH-Weinheim/Bergstrasse (1972).

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55. V. Emerson and K. Wilkinson, British Report AERE-M-1683 (196S).

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58. K. W. Bagnall and J. B. Laidler, J. C’hem. Sot. A1965,

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60. W. H. Zachariasen, J. Chem. Phya. 26, 2S4 (1968).

61. D. Brown, J. Hill, and C, E. F. Rickard, J, lChem. Sot. .42970, 476 (1970).

62. W. H. Zachariasen, Acts Cryst. 1, 26; (1948).

63. J. P. Marcon, C’onpt. Rend. C265, 235 (1967).

64. J. P. Marcon, CEA-R-3919 (1969).

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67. D. Cohen and J. C. Hindman, J. Amer. Chem. Sot. 74, 4682 (1952) .

68. L. B. Magnusson, J. C. t~indm~, and 1“. J. LaChapelle, “Chemistry of Neptunium(V), Formal Oxidation Potentials of Neptunium Couples,” in: G. T. Seaborg, J. J. Katz, and W. M. Manning (cd), The Tranauranium i%ments, p. 1059, National Nuclear Energy Series. Div. IV, Vol. 14B, McGraw-Hill co., New York (1949); J. R. Brandt and J. Ii. Cobble, lmrg. Chem. 9, 912 (1970).

69. A. J. Zielen and D. Cohen, d. Phy8. Chem. 74, 394 (1970).

70. G. A. Simakin and i. V. Matjascuk, Soviet fiadiochem. 11, 472 (1969) (English Translation).

71. J. C. Hindman, D. Cohenr and J. C. Sullivan, internaticnaZ Conference on the PeacefuZ UBes of Ammic Energy 7, 1st Geneva,345 (1956).

72. V. S. Koltunov, “Kinetics of the Redox Reactions of Uranium, Plutonium and Neptunium,” AtotiZdat [1965].

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74. J. J. Katz and G. T. Seaborg, The C7umi8t~ of the Actinide EZements, John Wiley, New York (1957).

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76. J. C. Sullivan, A. J. Zielen, and J. C. IIindman, J. Amer. C%@n. SOC. 83, 3373 (1961).

77. D. Cohen and B. Taylor, J. Ino~. NuzZ. Chcm. 22, 151 (1961).

78. A. J. Zielen, J. C. Sullivan , and D. Cohen, J. Inarg. NUC2. C’hem. 7, 378 (1958).

79. T. H. Siddall, III, J. Inorg. NucZ. Chem. 13, 151 (1960).

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A. D. Gel’man and M. P. !fefod’eva,P]vceeding% of the .$emnd AZ1-Uriion L’on,perence on Radiatiou Ch~!m”etry, p. 167 (1960].

82, V. F. Peretrukhin, N. N. Krot, 4. D. Glazunov, and H. D. Gel’man, Moklady An SSSR 17;{, 609 (1967).

83. A. [. Moskvin, Soviet Radiochem. 1S, 700 (1971).

84. J. C. Sullivan and J. C. Hindman, J. Pkj8 . L%em. H;;, 1332 (1959).

95, Kraus in: G, T. Seaborg and J. J. Katz, The :hemiat~ of the Ac~tinide L’Z.ewentsJ John Wiley, New York (19s!7),

86. G. H. Coleman, The ,?adiorhwri~try of ,’~utonims NAS-NS-3058, p. 16 (1965).

87. Y. A. Zolotov and 1. P. Alimarin, J. .“nc j. iVucl. Ckem. 2,5, 691 [1!363),

M. Sl$iIohand Y. Marcus , J. lnowg. NL.K’Z.Chem. 28, 2?25 (1966).

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R. W.,Stromatt. R. N. Peekema, and F. A. Scott, USAI;CReport tfW-S8212(19S8).

91. P. R. Danesi, R. Chiarizia, G. Scibona, and G. D’Alessandro, J. ‘TOP(J. Nucl. Chin. 33, 3s0-$ (1971).

92. S. Ahrland and L. Brandt, Acts Cfiern. S,xznd. ;?0, 328 (1966).

95. J. C. Sullivan and J. C. ilindman,J. ,4ver. Chew. SOC. 76, 5931 (19s4).

94 . hl. c. hfusi~as, .Ydiochirn. Act:z ?, 92 :1963).

95. P. 1. Kondratov and A. u. Gel’man, Radlokhimiya 2 (3), 52 (19W).

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98. C. Keller and S. H. Eberle, Radiouhin. Acts 4, 141 (1965].

99. T. Ishimori and E. Wluumma, Radiochlm. Acts 2, 6 (1962).

100. H. Irving and D. N. Edgington, J. Incrg. Nu?Z. Chem. 20, 321 (1961~.

11)1- A. I. Moskvin, soviet Radiouhem. 13 (4), 59B [19711 (English Translation).

102. 1. Gainar and K. W. Sykes, J. Chem. 50C. 1964, 44S2 (1964).

103. A. 1. Moskvin and M. P. Mefod’eva, RcdiokhLm@a 7, 411 (1965).

104. Yu. A. Zolotov, I. N. Marov, and A. I. Moskvin, Run8. J. Inorg. Chem. 6, S39 (1961) (English ~ranslation].

10s. M. P. Mefod’eva, Radiokhimiyu 2, 309 [1958).

106. C. Keller and S. H. Eberle, Radiochin. Acts 8, 65 (1967).

1070 S. H. Eberle and H. Schtifer, J. Inorg. NucZ. Chem. 31, 1523 (1969).

108. A. I. Mskvin, Souiet Radiooh6m. 13, 230 (1!371) (English Translation).

109. A. I. Moskvin, Soviet Radiochem. 13, S98 (1971) (English Translation).

110. A. I. Moskvin, 1. N. Marov, and Yu. A. Zolotov, Rune. J. Inorg. C?wn. 6, 926 (1961) (English ‘Translation).

111, C. Keller, J. Gross, and W. Bather, personal communication, quoted in Reference 8, p. 330.

112. A. 1. Wskvin, Sov”?t Radiochem. 13, 6S9 [1971).

113. S. H. Eberle and U. Wede, personal communication, quoted in Reference 8, p. 330.

114. N. S. A1-Niami, A. G. Wain, and A. C. McKai, J. Inorg. Jh?z. Chem. 28, 1047 (1970).

11s. S. Ahrland end L. Brandt, Acts Chem. Stand. 22, 106 (1968).

116. S. Ahrland and L. Brandt, Acts Chem. Stand. 22, 1S79 (1968).

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118. M. P. Mefod’eva, N. N. Krot, and A. l). Gel’man, Soviet Radiochem. 12, 210 (1970) (English Translation).

119. J. M. Nielsen and T. M. Beasley, USAEC Report HW-SA-3337 (1Y63) .

120. T. Y. Toribara, C. Predmore, and P. A. Hargrave, Talantu 10, 209 (1963).

121. L. B. Magnusson, S. G. Thompson, and G. T. %saborg, Phy8. Rev. 78, 363 (1950).

Ipo S. C. Foti and E. C. Freiling, TaZanta 11, 3,S5 (1964).

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124. C. W. Sill, HeaZth Ph@en 17, 89 (1969).

125. C. W. Sill in: Synpo#ium on Rapid Methods for Measuring Radioactivity in the EWironment, CONF-71O75 (197)),,

126. C. F. Metz and G. P.. Waterbury in: I. M. Kolthoff, P. J. Elving, and E. B. Sandell (cd), Treatiee on i4na@t&?aZ C%enr&Bt~, Vol. 9, Part II, Interscience, New York, (1962).

127. E. K. Hyde, International Conference cn PeacefuZ U8e8 Atm”c Bze~, -W Geneva 7, 281 (1955).

128. G. A. Burney, E. K. Dukes, and H. J. [~roh in: D. C. Stewart and H. A. Elion (cd), progre#aI in Nuciear her~, Series IX, Vol. 6, p. 194, Perg~n, Oxford (1960).

129. J. Ulstrup, At. Eh.g. Rev. 4= 36 (1966;.

130. V. P. Shvedov, S. G. Strizhov, and Chin Tsze-Khon, Radiokhinri~a 1, 622 (1959).

131. G. N. Yakovlev and D. S. Gorbenko-Genlanov, InternathnaZ Conference OR the PeaoejhZ U8e8 Atorril? hherg~, 18t Geneva, 7, 306 (1956), 132. G. A. Dupetit and A. H. W. Aten, Ji., Rad~ochim. Acts 1, 48 (1962).

1330 Thompson, L. O. Morgan, R. A. James, and I. Perlman S..0 G. . G. T. Seaborg, J. J. Katz, and W. M. Manning (cd), % ~auraniwn Ehmenta, National Nuclenr Energy Series, Div. IV, Vol. 14B, p. 1339, McGraw-Hill, New York (1949).

134. V. I. Kuznetsov and T. G. Akimova, .%zdiokhimi~a 2, 357 (1960).

135. B. P. Nikol’skii, M, V. Posvol’skii and G, S. Markov, At. kherg~ (USSR) 27, 566 (1969).

136. V. I. Kuznetsov and T. G. Akimova, Soviet At tie= 8, 135 (1961).

137. E. H. P. Cordfunke, J. Inorg. NuoZ. Chem. 24, 303 (1962).

138. T. K. Keenan, lno~. Chem. 4, 1500 [1965).

139. A. D. Gel’man and P. I. Kondratov, Radiokhimiga 2, 315 {1960).

140. G. A. Bumey and E. K. Dukes, ?%m@itation of Neptunium Perotide, DP-594 (1961).

141. K. W. Bagnall, A. M. Deane, T. L. Markin, P. S. Robinson and M. A. A. Stewart, J. C%em. Sot. 1961, 1611 (1961).

142. J. 1,. Ryan, J. Ph~a. Chem. 65, 1856 (1961)4.

143. J. L. Ryan, lno~. Chem. 2, 348 (1961).

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148. F. L. Moore, AnaZ. Chem. 29, 941 (1957).

149, R. A. Schneider and K. M. Harnm, USAEC Report NW-53368 (1961).

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154. 0.,C. f%rricos and J. A. T?waassea, KR-$S (1964].

1ss. R. W. Perkins, USAEC Report W-SOSl I (#934~).

1S6. U. Lindner, lEiAEC Report W&L- lJ~SB (196SjI.

1s7. II. P. NoIco*, USAEC Report 0$ ’-$86 [I$MJ).

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J59. 8. G. th~VC)’, ]i. G. Meal, A. G. $Whck, umd [. L. koul Qy, J. (Chan?.*. (1947), 1010.

160, R. $hibi:l utd N. Jelinuk, Chum. Lial:& 47 1326 (195S).

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16:! . U. N. Chgutova, 0. M. Petruhhin and YU. A. Zo]otow, Zh,, Ana2it. Nhk. 28, SS8 (1%3) (@$l SSim) .

16:;. L. # . kfOSCCV and B. V. Nomkhov , &u iet Rdicx?hm’!, 1s3, 293 (1%8) (English Translation).

1641. 1. f’. Alimarin, YU. A. Zolotov, ●nd E. S. lPalskin,, lk?k~. Akad. Nauk. SSSR 124, 328 (19S9) . 1?9. u. w. tisyakwo C. S. Gwwyw, 89M9G. S1 Yakowlew,a%qaratim of Trmsuraahm Elcwnts by SOlutkn Ex!:ractfowi in Alky] ?boaphorlc Acids, ” Pqter *iwn ●t Transolutoniun S~sitm, Arpwae NaCiomal La&mtory, May 196S. (Proc98din@ not PWbsisb?d). 180, E. C. Chudinov and G. N. Yakovlcv, Soviet Radiodem. 4, 443 (1962).

181,, G. M. Mason and D. F. Peppard. tfua2. Sin-. E%$. ?7$ 247 (1%3).

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186. Vu A. zolotov and !. P. Alimarin, J. irnorg. h%cl. Chem. 25, 719 (1%3).

187. .J. Kooi, Joint Establishment for Nuclear Energy Research, JENER-Pub-11 (19S6].

188<, (;. F. Best, E. Hesford, H. A. C. McKa:t, Memi.re8 pre8ent lea a * la Sd?etion de Chiurie Minewz ~, Sedd?tr, P&e, 1958, p. 3890 16th InternationalCongress of Pure and Applied Chemistry, Paris (19S7).

189,, D. E. Homer and C. F. Coleman, USAEC Report ORNL-2830 (19s,9).

190<, M. C. Kcder, J. C. Sheppard, and A. S. Wilson, t?. Inorg. Nxcl. Chem. 22, 327 (1960).

191, A. Chc~n6, ElAll. l~lforwr. Sci. Tech. (IDCLP;8) Jb. 66, S8 (1962).

192<, M. dc Trentinian and A. Chesnf, Coma. A. l’Er]ergie Atomique (Paris), Report 1426 (1960) .

193, F. L. Moore, NAS-NS-3101 (1960).

194. R. il. Schneider, Anal. Chem. 34, S22 (1962).

195. R. D. Britt, USAEC Report (1962].

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199. W. E. lteder, J. Ino~. Ml. C7umt. 24, S61 (1962).

200. V. M. Vdovenko, A. A. Lipovskii,, and S. A. Nik.ltina, Rdidd&@a 3, 3% (1961).

201. M. kller, Actiti# f?eu. 1, 71 (1967).

202. 1. A. Lebadev, B. F. ~asoedov, ~md P. N. Palei, J. Rr&oana2. @win. 5, 61 (1970] {English translation).

203. M. Taube, J. Ino~. Nucl. Char. 1S, 171 {1960),

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206. C. B. ~hlett, Inoqpnio Ion Ecakqer,a, Elsevier, Aasterdaa (1964).

207. W. Rieman and t+. F. Walton, lon Erchang13 iw Analytical chewtia~, Pergamon Press, New York (19’70).

208. D. L. Uassart, C’atiovAkc~e Tedm@ui?8 in Rczdioch&8t~, NAS-NS-3113 (1971).

209. J. Korkisch, Modern liethode fop tk Separation of Rarer Metal Ione, p. 28-97, Pergamon Press, New York (1969).

210. J. p. Faris and R. F. Buchanan in: D. (;.Stewart and H. A. Elion (cd), Pm@ese in Nuo?ear fiw~, Series IX, Vol. 6, p. 149, Pergamon Press, New York (1966).

211. J. Korkisch in: D. C. Stewart a]n(iH. A, Elion (cd), Progreis8 in Nuclear E?uqy, Series IX, Vol. 6, p. 3, Pergamon Press, Nm York (1966).

212. J. P. Faris and R. J. Buchanan, IJ;AEC Report, ANL-6811 (1964) . ~13* G. A. Burney, Ind. i?%g. Churn. A%la. Design l%vuhp. 3* 326 (1%4).

214. F. P. Roberts, USAEC Report IU-$9032 (19S9).

21s. F. P. Roberts and F. P. 8auer, LISAECReport HW-60SS2 ( 19s9).

21sa. G. H. Thompson and G. A. 8umey, USAEC Report DP-1333 (1973).

216. D. Cojeticanin and S. Ratkovic, d, Chmunatog. ~16, 326 (1970) .

217. Fujio Ichikawa, Bull Chain. S@. Japan 31, 7?8 (19S8].

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220. E. A. C. Crouch and G. B. Cook, d. lnoq~. ;hol. Chain. 2, 223 (19S6).

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226. 1. Markl and O. 8oble?er, Z. AnaZyt. Chm. 219, 160 (1966).

227, L. Wish and M. Rowall, USNRDL-TR-117 (19S6) .

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229. C. Cesarano and G. Pugnetti, RT-!C41-(63)-31 (1!363).

230. Y. Saito and T. Sekine, till. Chtan. Sot. Japan 30, 561 (:1957).

231. ‘~u. P,, Novikov, B. F. Myasoedov, and S. A. Ivanova, ,’. Anal. Chem. (USSR) 27, 47 (1972).

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233. F. U. Miles, Rluol. S@~ 9, 394 (1968).

234. J. C. Sullivan, D. Cohen, and J. C. Hindaan, J. Amr. Cb. Soo. 77, 620S (195S).

235. Y. A. Zolotov and D. Nish~v, Rtiw&iatq/ (USSR) 4, 217 (1962) (EnglishTranslation).

236. G. A. brlley andC. A. Prohaska, USAEC R~rt DP-741 (1962).

237. F. Nelson and D, C. Michelson, J. ~~~. 26, 414 (1966)

238. F. Nelson, T. Murase, and K. A. Kzaus, J. Chrcmnztog. 13, S03 (1964).

239. U. D. Zargrai and L. 1. Sel’Chenkcv, Rudwoheni8tq (USSR) 4, 161 (1962) (English Translation).

240. J. llubenak, M. S. Lew, and G. M. Matlack, Ana2. C’Mm. Actu 48, 233 (1969).

241. R. M. Harbour, W. H. Hale, G. A. Emney, andJ. T. Lowe, AticbYM~ Rev. 10, 379 (1972].

242. W. J. !4aeck, M. E. Kussy, and J. E. Rein, Anu2. Chem. 35, 2086 (1963).

243. A. I. Shafiev, Yu. V. Efrawv, V. H. Nikolmev, and G. N. Yakovlev, J. Rudwchm. (USSR) 13, 120 [1971).

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245. M. T. Ganzerli-Valentini, V. Maxi&,, S. Meloni, and A. Martinelli, Radwchem. Raiwancl. Lettere 7, 163 [1971).

246. M. T. Ganzerli-Valentini, V. Maxit., S. Meloni, A. Martinelli, and M. A. Rollier, J. Radwantz2. [%em. 11, 179 (1972).

247. T. Tsuboya, A. Kaya, and T. Hoshina, PNC-N-831-70-2, p. 70 [1970).

248. H. Eschrich, Kjeller Report KR-11 (1961).

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304. Yu. P. Novikov, B. V. Myasoedov, ,md M. N. Margorina, Radiochem. Radioam~Z. Letter8 10, 11 (1972).

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312. E. G. Chudinov, J. AnaZ. Chem. (lEl’??) 20, 880 (196S) (English Translation).

313. R. W. Stromatt, USAEC Report NW-59447 (19S9].

314. M. O. Fulda, USAECReport DP-673 (1962).

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316. W. L. Delvin and L. R. Duncan, USA.ECRepo:rt HW-SA-2635 (1962) .

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335. R. J. Kofoed, USAEC Report HN-SA-2530 (1962).

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339. R. E. Cofield, ffea2thPhytr.9, 283 [1963).

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344. Health Phy8, 3, 1-380 (1960).

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346. E. D. Clayton and S. R. Bierman, Actinide Rev., 1, 409 (1971).

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- 229 - ENI)

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