AN ENERGY-DEPENDENT CALCULATION OF ISOMER RATIOS OF 134CS PRODUCED IN FISSION OF 239PU BY MEDIUM-ENERGY PROTONS

The isomer ratios of 134Cs, produced in the fission of 239Pu induced by protons of energies 30-85 MeV, have been measured experimentally. Calculations based on a statistical theory of the spin distribution of the primary fragments have been made for these isomer ratios. Competition between fission and neutron emission has been taken into account in the calculation. The calculated isomer ratios have been weighted with the relative formation probabilities of the pertinent fragments resulting from different fissioning nuclei. Values of √J2, the root-mean-square angular momentum, which gave the best fit between the calculated and experimental isomer ratios, varied from 11h{stroke} at 30 MeV to about 16h{stroke} at 60-85 MeV. These large values of √J2, which cannot be accounted for by the initial angular momentum of the fissioning nucleus, indicate that angular momentum must be induced in the fission process. Moreover, these results also show that a fraction of the angular momentum of the fissioning nucleus appears as the intrinsic spin of the fragments. © 1969.