barium-133, and cerium-144 were adsorbed on a cation column. Figure 2 shows the cation exchange separation of a mixture. The sodium and ammonipm chloride elutions did not interfere with the recovery of the cerium and alkaline earths. There was a slight increase in the cerium-144 tail and about 0.2% eluted with the calcium 45. Since cerium is the lightest of the rare earths, the procedure was investigated with lutecium, the heaviest, to determine if any would be eluted with the sodium and ammonium chloride solutions. None of the lutecium-177 was eluted.
Figure 2.
DETERMINATION OF FISSION PRODUCT CESIUM
Column 6 cm. X 0.2 sq. cm.) volume/3 mln.
Three samples of uranium-235 were irradiatcd with thermal neutrons in the Materials Testing Reactor at Arco, Idaho. The uranium was enclosed in aluminum foil to prevent the escape of the gaseous precursdrs of the cesium radionuclides from the surface. The aluminum and uranium were dissolved in hydrochloric and nitric acids. Aliquots of this solution were analyzed for cesium by the quantitative radiochemical procedure (3-6). The results are given in Table I1 as gamma counts per minute per fission (fissions determined from molybdenum-99 analyses). Since all the samples were analyzed only a few days after irradiation, the 13-day cesium-136 was a significant fraction of the total cesium gamma-ray activity. The first and third cesium fractions were allowed to
Table I. Yields of Sodium-22 and Cesium-1 37 from Dowex 50 Cation Column
Mixture 1 2 3 4 5 6
Elution from Dowex 50-X8 flow rate column
Na” (%) 99.3 100.6 99.7 99.8 101 .o 101.2 Av. 100.3 f .9
* 1.0
Table 11. Cesium Activities from Neutron-Irradiated Uranium-235 y C.P.M./Fissiona X 10-e Sample, CS’J’ CS’M Ut86
1
decay for 10 half lives of cesium-136. The residual activity (assumed to be cesium-137) was subtracted from the original total to give the cesium-136 which is given in Table 11. The cesium-137 was also determined in a 256-channel gamma analyzer immediately after separation by summing up the pulses in the high energy gamma ray peak. The analyzer was crosscalibrated with the scintillation well counter so that the cesium-137 activity is given in the first column as determined by the g a m m a spectrometer, but in terms of the scintillation counter. A comparison of the first two columns shows very’ little difference in the spectrometer method from the decay method which takes considerable time depending on the age of the sample.
Cs*” (%)
100.2 100.0 100.0 100.9 99.1 100.2 100.1
2
y Spec. 1.41 1.42 1.40 1.39
Decay 1.37 1.38
y
3
8
1.41 1.42 1.40 i 1.41 f .03 .02 Fissions baaed on Mom.
Decay 2.48 2.47
y
2.46 2.48 2.47
*
.@2
LITERATURE CITED
(1) Bonner, 0. D., J . Phye. Chcm. 59, 719 (1955). (2) Bonner, 0. D., Juniper, C . F., Rogera, 0.C.,la., 62,260 (1958). (3) Wish, Leon, ANAL. CHBM.31, 326 (1959). (4 Zbid.,32, 920 (1980). Zbid., 33,53 (1961). RBCBIVED for review January 19, 1961. Accepted March 13, 1981.
Radiochemical Determination of Total Rare Earths by Liquid-Liquid Extraction J. J. McCOWN and R. P. LARSEN Chemical Engineering Division, Argonne National Laboratory, 9700 South Cass Ave., Argonne, 111.
b A rapid and quantitative radiochemical method for the determination of rare earth activities produced in nuclear fission is based on the extractability of the rare earths with bis(2ethylhexy1)orthophosphoric acid. The extraction procedure affords excellent separations from the other fission elements as well as a considerable saving in time and effort.
P
for the radiochemical determination of rare earth activities in fission product mixtures depend either on precipitation, or a combination of precipitation and ion exchange, for separating the rare UBLISHED PROCEDURES
earths from other fission products. Those methods utilizing only precipitation (1, 4, 10) are designed to determine the total rare earth activity present in a sample, whereas the methods involving an ion exchange separation procedure (8, 3, 7) generally separate the individual rare earth activitiea one from another. In every instance four or more precipitation steps are required for separation purposes and these are followed by a final oxalate precipitation to determine a chemical yield factor. Such methods require 2 or more hours to complete duplicate analyses. Solvent extraction methods for rare earth separation as reviewed by West (9) are generally used in separating
individual rare earths from ores and sands. Tracer studies (6, 8) have shown that both tributyl phosphate and dibutyl phosphate extractions can be used in separating the yttrium group of rare earths from the lanthanum group. Theae solvent systems have definite possibilities in radiochemical analysis applications but there is no evidence that any investigation has been made. Peppard et al. (6)demonstrated the effectiveness of the hydrochloric acidbis(2-ethylhexyl)orthophosphoric acid (HDEHP) extraction system for separating yttrium-90 and lanthanum140 from their parent radio nuclides, strontium-90 and barium-140. In the VOL. 33, NO. 8,
JULY 1961
1003
system 0.05M hydrochloric acid-1.5Al HDEHP in toluene, partition ratios for yttrium and lanthanum were 10' and 60,respectively, and for strontium and barium were 0.06 and 0.03, respectively. The usefulness of the hydrochloric acid-HDEHP system for separating rare earths from all other important fission products has now been demonstrated and a radiochemical procedure has been devised. With all the precipitation separations eliminated, analysis time has been reduced to 30 minutes; no determination of chemical yield is required. The rare earths are extracted from a dilute hydrochloric acid solution, scrubbed with more of the same dilute acid, and stripped with a concentrated acid solution. The beta and/or gamma activity assays are made on an aliquot of the aqueous strip. EXPERIMENTAL
1.5M bis (2-ethyl hexyl)orthophosphoric acid (HDEHP) in toluene. Mix 50 ml. of HDEHP (Virginia-Carolina Chemical Corp.) with M) ml. of toluene. No special purification is necessary. Procedure. Dilute the sample solution t o contain a total activity of about 108 c.p.m. per ml. in 0.5M hydrochloric or nitric acid. Pipet a 100-fi1. aliquot of the dilution into 5 ml. of water in a separatory funnel. Add an equal volume of 1.5M HDEHP in toluene and agitate for 2 minutes. Discard the aqueous phase and scrub Reagents.
Table I. Separation of Ceriurn(lll) from Other Fission Products with Bis(2-ethylhexyl)orthophosphoric Acid
Amt. Extracted, Element % Ce(II1) >99
