Nuclear-charge distribution in fission: Cumulative yields of short-lived krypton and xenon isotopes from thermal-neutron fission of 235U

Abstract

Experiments are described in which use was made of the very large emanating powers of barium stearate and uranyl stearate for determination of cumulative yields for a number of krypton and xenon isotopes formed in the thermal-neutron fission of 235U. The results, expressed as the fraction of the total chain yield, are: 89Kr, 0·960 ± 0·004, 90Kr, 0·86 ± 0·02; 91Kr, 0·59 ± 0·01; 92Kr, 0·31 ± 0·01; 139Xe, 0·82 ± 0·02; 140Xe, 0·59 ± 0·01; 141Xe, 0·21 ± 0·02; 143Xe, (8·5 ± 0·5) × 10 −3; 144Xe, (1·1 ± 0·1) × 10 −3. These data along with previously reported independent-yield data are used for construction of an empirical curve of the most probable primary charge ( Z P ) vs. mass number. In the regions where shell edges are absent the curve is about equidistant for complementary mass numbers from the most stable charge ( Z A ) lines for light and heavy fragments as proposed in the postulate of equal-charge displacement; in the regions where shell edges are present the Z P curve makes a smooth continuous transition. The Z P curve tends to approach and remain close to the 50-proton shell edge. It is proposed and some evidence is presented that the charge distribution curve (for a given mass number) is distorted for uranium fission in the regions near Z = 50 and Z = 42 because the 50-42 proton split is favoured, at least partly at the expense of the 51-41 and 49–53 proton splits.