Preparation and Half Life of Carrier-Free Yttrium-90 MURRELL L. SALUTSKY and H. W. KIRBY M o u n d Laboratory, Monsanto Chemical Co., Miamisburg, O h i o
A rapid method was needed for obtaining a continual supply of carrier-free yttrium-90. The lack of agreement among the reported half-life values indicated that a precise determination of the half life of yttrium90 would be desirable. Carrier-free yttrium-90 was “milked” periodically from a purified strontium-90 sample by precipitation of the strontium-90 with strontium nitrate carrier in 80% nitric acid. The half life, determined by beta counting, was found to be 64.029 =k 0.024 hours. By use of the recommended procedure high purity yttrium-90 with yields of 95% is available when needed for an indefinite period of time.
REAGENTS
Ten millicuries of strontium-yttrium-90 equilibrium mixture as the chlorides in dilute hydrochloric acid solution were obtained from the Radioisotopes Division of Oak Ridge National Laboratory. The isotopes were reported to be carrier-free. Strontium89 (less than 0.1%) was the only radioactive impurity reported to be present. Spectrographic analysis indicated that trace amounts of the following elements were present: boron, chromium, nickel, lead, aluminum, iron, magnesium, calcium, and strontium. The red fuming nitric acid was Baker and Adamson reagent grade and assayed 93.1% nitric acid and 7.05% nitrogen trioxide. The concentrated (70%) nitric acid, strontium nitrate, potassium dichromate, and potassium cyanate were analytical reagent grade. RECOMMENDED PROCEDURE
R
ADIOCHEMICSL methods are particularly useful in the determination of yttrium in fractionation and coprecipitation studies (29) because many of the physical methods used in rare earth analyses-e.g., absorption spectroscopy, magnetic susceptibility, etc.-are not applicable. Yttrium-90 is a suitable nuclide for these tracer experiments because it has a convenient half life of about 64 hours, is a pure beta emitter which decays to a stable isotope (zirconium-SO), and since a continual supply of yttrium-90 can be obtained by “milking” it a t desired intervals from its long-lived parent, strontium-90 (19.9-year half life) (19). Although carrier-free yttrium-90 has been separated from strontium-90 by radiocolloidal formation of the yttrium in basic solutions (2, 15, 27, SO), by ion exchange (34), by electrochromatographic methods ( 3 , 25), by solvent extraction ( 4 ) , by mass spectroscopy ( 9 ) , and by vacuum evaporation (31), the authors have found that carrier-free yttrium-90 can be separated rapidly with a high yield and purity by precipitation of the strontium-90 ~ i t hinert strontium nitrate carrier in 80% nitric acid. The procedure, which is based on an analytical method developed by Killard and Goodspeed ( 3 6 ) , is similar to that previously reported ( 2 3 ) for the separation of carrier-free lanthanum-140 from barium-140. Modifications of the Willard and Goodspeed method have been used by other investigators (5, 6, 16, 35) to separate strontium and barium activities from fission product mixtures. Sottorf (17) used the fuming nitric acid procedure to separate yttrium-90 with yttrium carrier from strontium-90. The lack of agreement among the reported half-life values shown in Table I indicated that a precise determination of the half life mould be desirable. Bccordingly, such a determination was made on a highlv purified sample of yttrium-90.
Purification of Strontium-90. Dissolve the desired quantity of strontium-yttrium-90 and 0.75 gram of strontium nitrate carrier in 2 ml. of water. Add dropwise 2 ml. of concentrated nitric acid and evaporate with stirring until the volume of the mixture is approximately 2 ml. Cool in an ice bath and add 3 ml. of red fuming nitric acid. Digest a t 0” C. for 15 minutes with stirring. Filter the strontium nitrate and wash three times with 1-ml. portions of 807, nitric acid. Discard the filtrate and washings.
Table I. Date 1936 1937 1937 1938 1938 1940 1941 1946 1946 1948 1949 1949 1951 1951 1953 1954 a
Survey of Reported Half-Life Values for Yttrium -90 Source
References
y ( n ,Y ) Nb(n,a) Zr(n,p) l‘(n,-t)
Y(n,r) Fission products Fission products Not reported Fission products 1Sr(2,n,/3) Fission products Zr(n,p) Fission products
Half Life, Hr. 70 5 7 . 6 ( 2 . 4 days) 60.5 k 2 . 0 66 66 i 3 G6 k 2
60 61 i 1 72 60 108 (days)a 62 >60 65 65 64.60 f 0.43
Probably incorrect mass assignment.
Dissolve the strontium nitrate in 2 ml. of water, and add 20 mg. of barium nitrate and 50 mg. of potassium dichromate. Adjust the acidity of the solution by the dropwise addition of dilute nitric acid and ammonium hydroxide until a slight precipitate of barium chromate just redissolves in 1 drop of dilute nitric acid. Add 0.5 ml. of glacial acetic acid. Dilute the solution to 5 ml. with water. Add 50 mg. of potassium cyanate. Heat to about 60’ C. and stir for 30 minutes. Cool and filter, but do not wash the barium chromate. Discard the precipitate. Add 20 mg. of barium nitrate to the filtrate, readjust the acidity with dilute nitric acid and ammonium hydroxide, and carry out a second barium chromate precipitation by the described procedure. No additional potassium dichromate need be added to the filtrate for the second precipitation, as a considerable excess was used in the first precipitation. Add 2 ml. of concentrated nitric acid to the filtrate from the second barium chromate precipitation and precipitate the strontium nitrate by evaporating the solution to 2 ml. Cool the mixture in an ice bath, filter, and wash the strontium nitrate with a few milliliters of cold concentrated (70y0) nitric acid until the washings are free of the orange dichromate color. Discard the filtrate and washings. Set aside the strontium nitrate containing the purified strontium-90 for about 2 weeks to permit the growth of yttrium-90. I n the preceding step, strontium nitrate was precipitated from 70 rather than 80% nitric acid because red fuming nitric acid was observed to reduce chromate ion to an insoluble brown oxide.
EXPERIMEh-TAL
I n the recommended procedure the strontium-90 parent is first purified. This is accomplished by a nitrate precipitation in 80% nitric acid with inert strontium carrier followed by two homogeneous chromate precipitations ( 2 4 ) with barium carrier. The strontium is finally recovered from the chromate filtrate by precipitation of strontium nitrate in 70% nitric acid. The strontium-90 need be purified only once, after which yttrium-90 can be “milked” when needed for,an indefinite period of time. The nitrate precipitation in 80% nitric acid removes all possible contaminants with the exception of isotopes of strontium, barium, radium, and lead (36). The chromate precipitations remove barium, radium, and lead. Strontium-89, which may still be present as an impurity, does not interfere since it decays to a stable isotope, yttrium-89. The purified strontium is reconverted to the nitrate and set aside to allow for the regrowth of yttrium-90. The yttrium-90 is then separated from strontium-90 by reprecipitation of the strontium nitrate in 80% nitric acid. Carrier-free yttrium-90 is recovered from the filtrate. 567
568
I
Separation of Yttrium-90. Bfter fresh yttrium-90 has g r o m in, dissolve the strontium nitrate in 2 ml. of water. Reprecipitate the strontium nitrate from 80Yc nitric acid as in the strontium-90 urification. Filter the strontium nitrate, but do not wash it. %vaporate the filtrate to dryness in a small beaker (20 or 30 ml.). 1
DAYS Figure 1. Decay of yttrium-90 Sample A B C D
E
Mean
TI/?, Hr.
P.E.
64.1060 63.9699 64.0483 63.9211 64.1418 64.029
0.0494 0.0425 0.0294 0.0443 0.0578 0.018 (int.) 0.024 (ext.)
Dissolve the slight residue in dilute nitric acid and dilute the solution t o the desired volume. Save the strontium nitrate for future milkings. The separation can be carried out in small beakers using small sintered-glass funnels for the filtrations or, more conveniently, in a modified filter-beaker described in an earlier paper ( 2 3 ) . The filter-beakers are particularly euitable since the strontium-90 is confined and need never be removed. I n either case, it is suggested that reagents be added a-ith medicine droppers, stirring effected with a magnetic stirrer, and heat supplied by an infrared lamp. One millicurie is a convenient quantity of strontium-yttrium90 to use, although larger quantities may be used with suitable shielding. At least 2 weeks should be allowed bet-iveen successive milkings.
be substantially in accord with published values (11). Strontium-90 was not detected. The telescoping technique, by means of which a radioactive material can be counted for many half lives without loss of counting precision, is illustrated in Figure 1. Five samples of yttrium90 of ascending magnitude were prepared for beta counting. Sample A, which originally contained 0.33 microcurie of yttrium90, was counted daily beginning 1 day after purification. By the 23rd day, it had decayed to less than 1000 counts per micute, the arbitrary lower limit. Aleanwhile, Sample B, which originally contained 5 microcuries of yttrium-90, had decayed to less than 350,000 counts per minute, the upper limit of the counter. I t was counted daily from the 12th to the 30th day after purification. Samples C, D, and E, containing 62, 179, and 350 microcuries of yttrium-90, respectively, were treated in the same manner. Thus, while no one sample was counted for more than 8 half lives, their composite decay spanned a period of 18.4 half lives. Instrumentation, counting techniques, and mathematical treatment %ere identical with those previously described ( 1 4 ) . Corrections were made for residual strontium-90 in all samples in which the contamination contributed more than 1 count per minute. The half life of each sample was determined, and the five half-life values were examined for consistency. No systematic deviation was observed. The mean half life, obtained by weighing the five determinations inversely as the squares of their probable errors, rTas 64.029 i 0.024 hours (external probable error). DISCUSSION
The purity of the carrier-free yttrium-90 prepared by the recommended procedure was determined by following its decay. The yttrium-90 showed no significant deviation from a half life of 64.029 hours for at least 26 days, as s h o m in Figure 2. After this length of time less than 0.2y0 of the original yttrium-90 remained.
7.5h
6.51
HALF LIFE
Table I shows the need for a precise determination of the half life of yttrium-90. The reported half-life values are listed by date. Yttrium-90 was prepared by a variety of methods: neutron bombardment of yttrium, niobium, zirconium, and strontium; deuteron bombardment of yttrium; and separation from fission products. The half-life values vary from 57.6 to 72 hours with most of the values falling between GO and 66 hours. The 108-day half life is probably the result of an incorrect mass assignment. The yttrium-90 used for the half-life determination was first separated and purified by the recommended procedure. A sample was taken for the determination of the yttrium-90 yield and of the quantitativeness of precipitation of strontium nitrate in 80% nitric acid. To the remainder was added inert strontium, and the strontium nitrate precipitation in 80% nitric acid was repeated. The filtrate was evaporated to dryness, and the residue was dissolved in dilute nitric acid. The yttrium-90 preparation, as calculated from the data on the yield and quantitativeness of precipitation, contained approximately 90% of the original yttrium-90, lo-7yc of the original strontium-90, and 20 y of inert strontium. The residual strontium-90 was also determined by counting after the yttrium-90 had decayed to radioactive equilibrium. A sample of the yttrium-90 solution was mounted for betaray-spectrometer analysis. The beta spectrum was found to
ANALYTICAL CHEMISTRY
5
d 4.5-
0
a 0
-
-I
I
0
Figure 2.
IO
20 30 DAYS Decay of yttrium-90
Prepared by recommended procedure
A yield of 96yc was obtained when the separation was carried out in a filter-beaker. If small beakers and sintered-glass funnels are used, the yield is lower (25) due to a greater retention of filtrate on the strontium nitrate crystals. Although washing the crystals in 80% nitric acid would increase the yield, it vould also increase slightly the amount of strontium-90 im-
V O L U M E 2 7 , NO. 4, A P R I L 1 9 5 5 purity. Therefore, the strontium nitrate crystals should not be washed. The quantitativeness of precipitation of strontium nitrate in 80% nitric acid was determined by analyzing the filtrates for strontium-90 b y the method of differential decay (IS),and by allowing the yttrium-90 t o decay t o equilibrium and counting the residual strontium-yttrium-90 activity. The average strontium concentration in the 80% nitric acid filtrates was 0.004 mg. of strontium per ml. Since the total volume was 5 ml., and about 300 mg. of strontium carrier was used, the amount of Btrontium-90 remaining in the filtrate as a radioactive impurity in the yttrium-90 was about 0.007%. T h e quantitativeness value for strontium nitrate precipitation in 80% nitric acid eolution is approximately the same as that previously found ( 6 3 ) for barium nitrate (0.05 millimole of strontium nitrate per ml. as compared to 0.07 millimole of barium nitrate per ml.). ACKNOWLEDGMENT
T h e authors wish to express their indebtedness to L. N. Russell and G. R. Grove for their analysis of the beta spectrum of the material used in the half-life determination. LITERATURE CITED
Bothe, W.,2. Saturforsch., 1, 173 (1946). Bradon, C. H., Slack, L., and Shull, F. B., Phys. Rev., 75, 1964 (1949). Chem. Eng. X e w s , 30, 4244 (1952). Chetham-Strode, 8.,Jr., and Kinderman, E. 31., Phys. Rea., 93, 1029 (1954). Glendenin, L. E., “Determination of Strontium and Barium Activities in Fission,” NatZ. Nuclear Energy Ser., IV-9, pp. 1460-4, RIcGraw-Hill Book Co., Kew York, 1951. Glendenin, L. E., “Preparation of Carrier-Free Strontium and Barium Tracers by Use of Lead Nitrate and Lead Chromate Precipitations,” .Vatl. Nuclear Energy Ser., IV-9,pp. 1466-9, 3IcGraw-Hill Book Co., New York, 1951. Goeckermann, R. H., and Perlman, I., Phys. Reu., 7 6 , 628 (1949). Grummitt, W.E., and Wilkinson, G., Sature, 158, 163 (1946). Hayden, R. J.,Phys. Rea., 74, 650 (1948). Hevesy, G., and Levi, H., KQZ. Danske T’idenskab. Selskab, Math.-fys. Medd., 14, S o . 5 (1936). Hollander, J. AI., Perlman, I., and Seaborg, G. T., Recs. M o d . Phys., 25, 469 (1953).
569 Katcoff, S., “Thermal-Neutron Absorption Cross Sections of Unstable Kuclei V. 53d Srs9,’’~Vutl. A’uclear Energy Ser., IV-9, pp. 1405-9, RlcGraw-Hill Book Co., Kern, York, 1951. Kirby, H. W., ANAL.CHEM.,24, 1678 (1952). Kirby, H. W., and Salutsky, M. L., Phys. Rev., 93,1051 (1954). Kurbatov, J. D., and Kurbatov, RI. H., J . Phys. Chem., 46, 441 (1942). Lieber, C., nraturwissenschaften,27, 421 (1939). Nottorf, R. W., ”Identification of SrQOand Y90 in Uranium Fission,” NaTatl. A’uclear Energy Ser., IV-9,pp. 682-6, McGrawHill Book Co., New York, 1951. Pool, M. L., Cork, J. M., and Thornton, R. L., Phys. Rev., 52, 239 (1937). Powers, R. I., and Voigt, A. F., Ibid., 79, 178 (1950). Sagane, R., Kojima, S., RIiyamoto, G.. and Ikawa, Rl., Ibid., 54, 542 (1938). Ibid., p. 970. Ibid., 57, 1179 (1940). Salutsky, 31. L., and Kirby, H. W.,ANAL. CHEM.,26, 1140 (1954). Salutsky, 11.L., Stites, J. G., and llartin, A . W., Ibid., 25, 1677 (1953). Sato, T. R., Sorris, W. P., and Strain, H. H., Ibid., 26, 267 (1954). Schott, G. L., and lleinke, W.W.,Phys. Rev., 89, 1156 (1953). Schweitzer, G. K., Stein, B. R., and Jackson, W. If.,J . Am. Chem. Soc., 75, 793 (1953). Segre, E., and Wiegand, C. E., Phys. Reu., 75,39 (1949). Shaver, K., Division of Physical and Inorganic Chemistry, 125th Meeting, ACS, Kansas City, N o . , March 1954. Shern-in, C. W., Phys. Rev., 73, 1173 (1948). Sherwin, C. IT., Rev. Sei. Instr., 22, 339 (1951). Sinma, K., and Yamasaki, F., Phys. Rea., 59, 402 (1941). Stewart, D. W., Lawson, J. L., and Cork, J. ll.,Ibid., 52, 901 (1937). Tompkina, E. R., Khym, J. X., and Cohn, W. E., J . Am. Chem. Soc., 69,2769 (1947). Tompkins, P. C., Wish, L., and Khym, J. X., “Some Unit Onerations for Prenaration of Carrier-Free Strontium.” SatZ. -=-YiLclear Energy Ser., IV-9, pp. 1470-81, RIcGraw-Hill Book Co., Sew York, 1951. Willard, H. H., and Goodspeed, E. W,, IND.ESG.CHEM.,ANAL. ED.,8, 414 (1936). RECEIVED for review May 12, 1954. Accepted Xovember 22, 1954. Presented before t h e Division of Analytical Chemistry a t t h e 126th Meeting of t h e AYERICANCHEMICAL S o c m r u , New York, N . T. Abstracted from Mound Laboratory Reports hILRI-937, February 1, 1954, b y H . W. Kirby a n d SI. L . Salutsky, and MLM-938, February 1 , 1954, b y hI. L. Salutsky and H. W . Kirby. Mound Laboratory is operated b y I l o n s a n t o Chemical Co. for t h e U. 8. Atomic Energy Commission under Contract Number AT-33-1Gen-53.
CRYSTALLOGRAPHIC DATA
93. Hexahyd ro-I ,3,5-t rinit roso-S-t riazine (1,3,5-Trinitroso-l,3,5-triazacyclohexane) Contributed b y RALPH J. HINCH, JR., Arrnour Research Foundation of Illinois Institute of Technology, Chicago 16, 111.
OS-N
P H 2 \
N--SO I
I CH?
CH?
\d I SO
Structural Formula of Hexahydro-1,3,5trinitroso-s-triazine
EXCELLEXT crystals of hexahydro-1,3,5-trinitroso-s-triazine I
can be obtained by recrystallization on a macro scale from isopropyl alcohol, amyl alcohol, or benzyl alcohol. T h e best
crystals for optical and x-ray analysis are obtained from benzyl alcohol (Figure 1). Figure 2 represents an orthographic projection of a typical hexahydro-1,3,5-trinitroso-s-triazineI tablet obtained by slow recrystallization from benzyl alcohol at room temperature. CRYSTAL MORPHOLOGY Crystal System. Monoclinic. Form and Habit. Yeedles and tablets elongated parallel to b lying on the orthopinacoid { 100 I, up_per positive orthodome (3011 , or lower positive orthodome (201 } and showing the ba9aI pinacoid { 001 } and clinodome (011} . -1xialRatio. a : b : c = 2.050:1:1.460.Interfacial A4ngies(polar). 100 201 = 360; 001 A 201 = 560 35’; 011 011 = 690 14’. Beta Angle. 92” 35’(reflection goniometry).
