Quantitative Radiochemical Analysis by Ion Exchange Calcium, Strontium, a n d Barium LEON WISH U. S. Naval Radiological Defense Laboratory, Sun Francisco 24, Calif. b An ion exchange procedure has been developed for the separation of calcium, strontium, and barium from the rare earths and from each other. This is similar to the method of Baerg and Bartholomew. By lowering the cross linkage of the column resin to 870 and changing the concentration and pH, it was possible to accomplish ihe analytical separation at room temperature. Column runs wiih cerium144, calcium-45, strontium-85, and barium-1 33 tracers showed that the recoveries were quantitative. No significant cross contaminaiion could b e detected by y-ray spectrometer measurements. The determination of barium and strontium was then included in the sequential radiochemical analytical scheme for mixed fission product and actinide elements.
T
HE separation of cerium, barium, strontium, and lanthanum from uranium-235 thermal neutron fission prodiict mixtures using hot (87' C.) ammoiiiuni a-hydroxyisobutyrate elution from 12% cross-linked Dowex 50, cation resin has been reported by Baerg and Bartholomew ( 1 ) . However, while investigating lanthanide and actinide separations, Smith and Hoffman (6) found that by reducing the resin cross linkage to 47, comparable results were obtained with the same eluting agents a t room temperature and a t 87" C., thereby eliminating the need for specialized equipment and techniques. Also, as these authors pointed out, the use of hot columns for a large number of samples becomes extremely awkward. 'Therefore, an investigation was made t o determine whether the separation of calcium, strontium, and barium would be feasible a t room temperature. In addition, more data on the quantitativeness of the recoveries were desirable in order to include the separation in the sequential carrier-free analytical procedure for fission product and actinide elements as previously described (7. 8).
EXPERIMENTAL
Barium-133, calcium-45, and cerium144 were obtained from Oak Ridge Xational Laboratory, and strontium-85 from the Nuclear Science and Engineer-
ing Corp. The first two were of high specific activity and the last two were carrier-free. All activities were measured in a y-ray scintillation counter having a 3 X 3 inch sodium iodidethallium crystal with a ll/r-inch dianieter well 21/4inches deep. The calcium45, which is a p-ray emitter, gives rise to a small percentage of bremsstrahlung which can be measured in the well counter. However, the sample contained about 25y0 y-ray contamination which was removed by adsorbing the calcium on Dowex 50 from 0.5X hydrochloric acid. The contaminant, which was identified as scandium-46, did not adsorb on the resin and, after washing, more than 997, had passed through the column. The calcium was then eluted with 6 S hydrochloric acid. After the purification was repeated, the y-ray impurity could not be detected in a y-ray pulse height analyzer. Approximately 5 to 10 pc. of calcium-45 gives rise t o sufficient bremsstrahlung for measurement in a y-ray counter. The resin column was 0.2 sq. cm. by 6 em. and the flow was maintained by a
'C 2
h1 8 34' 303
50
Figure 1. Dowex 50 ion exchange separation of barium, strontium, calcium, and cerium A. 6.
87' C., 16% cross linkage Room temperature, 8 %cross linkage
vacuum arrangement as previously described (7). Since the vacuum system was subject to large fluctuations, an apparatus was designed to keep the flow rate constant (3). A solenoid valve was inserted in the line and by means of an electronic relay system increased the vacuum slightly whenever the interval between drops fell below a preset level. I n this way the drop rate was automatically kept within 10% of that desired. The elution fractions were collected in 50-ml. Lusteroid tubes, which were then transferred directly to the well counter for activity measurement. For cerium144 i t was necessary to wait 3 hours to allow the 17.5-minute praseodymium daughter t o reach equilibrium with its parent. The purity of all the fractions was checked on a 256-channel y-ray spectrometer. SEPARATIONS A N D RECOVERIES FROM SYNTHETIC MIXTURES
The 4, 8, 12, and 16% cross-linked Dowex 50 resins mere tested a t room temperature; the 8% resins gave the most satisfactory separations. Figure 1 shows the elution curve of a mixture of cerium-144, calcium-45, strontium85, and barium-133 a t 87' C. and a t room temperature, the former being obtained with a 167, cross-linked resin. The cerium-calcium separation is more complete a t the higher temperature. A very small part (
