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RADIOCHEMICAL STUDY OF THE SEPARATION OF LANTHANUM FROM BARIUM BY CATION EXCHANGER Genetic Study of B U ' ~ ~ - L ~ and ' * a La1* Reservoir PAUL KRUGER1 and CHARLES D. CORYELL Massachusetts Institute of Technology, Cambridge, Massachusetts
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experiment described in this paper is designed for a laboratory course in radiochemistry or in advanced physical chemistry. Theuse of ion-exchange chromatography ss a chemical tool is demonstrated. The experiment can he used t o illustrate the genetic relationship between radioactive nuclides and effective use of discrimination in counting. The experiment consists of the separation of the 40-hr. La'40daughter fromits 12.8-day Ba140parent by chromatographic elution from an ion-exchange resin column. The radiations from the two separated fractions are measured to show the decay of the 40-hr. LaHoin the lanthanum fraction and the growth of 40-hr. La140in the barium fraction. From two to three hours are required for the experiment. Further information can be obtained by making subsequent elutions at weekly intervals. The elaboration of ion-exchange separation techniques for similar elements has played an important role in the development of modern radiochemistry (1, 8, 3). The place of such techniques in a course in radiochemistry or nuclear chemistry has been discussed elsewhere (4). The experiment outlined here has added interest because it deals with the decay chain Ba140-La140-the subject of study that led to the discovery of nuclear fission by Hahn and Strassmann (6)-and it is a prominent and very useful fission product (6,7). The 12.8-day Ba140is readily available from cyclotronproduced fission2 or from the Isotopes Division of the U. S. Atomic Energy Commission or other national producers. I t decays (7, 8) by the emission of 6 rays (60 per cent a t 1.0 m. e. v. and 40 per cent a t 0.5 m. e. v.), and yraysof medium energy (0.5 m. e. v.) are associated with the low-energy (3 rays. The 40-hr.La14' decays by the emission of harder (3 rays of several energies, and several 7 rays, the most prominent being an intense component of 1.60 m. e. v. A thin-window Geiger-Miiller counter is slightly more sensitive to the (3 rays of La1", hut use of Nuolear Science and Engineering Corpora1 Present address: tion, Post Office Box 10901, Pittsburgh, Pennsylvania. 'The separation of Bar" from uranium and the other fission products (neutrons or charged particles impinging on uranium targets) is described by L. E. Glendenin (lo) for carrier-free samples, and (11) for samples with small amounts of camer.
sufficient absorber to cut out all (3 rays leads to 14-fold greater sensitivity for the y rays of La140(9). THEORY
The genetic relationship between two radioactive nuclides can be determined by observing the gross decay and growth behavior of the nuclides after chemical separation. The daughter nuclide always decays with its characteristic half-life. The behavior of the purified parent nuclide depends on the relativehalf-lives of parent and daughter (6,s). If the half-life of the parent is greater than that of the daughter, there is an increase of activity in the parent fraction. Transient equilibrium results vhen the decay of the daughter is balanced by its growth from the parent. Both activities then decay with the parent's half-life. If the parent is shorterlived than the daughter, the sample decays and no equilibrium is attained. The general equation which describes the growth and decay of a radioactive daughter nuclide from an initially pure parent is given as:
where Ad is the activity of the daughter a t time t, APois the initial activity of the parent, and Xd and A, are the decay constants of the daughter and parent respectively. If the parent is longer-lived than the daughter (X,
