Charge Distribution in the Fission ofTh232

Abstract

p, ny)"5th reaction, implies the spin sequence for the (wg», )(vd, ») ' multiplet to be 6', 5', 4', 3', 7', 2' for the corresponding states at energies 0-, 43-, 142-, 180-, (233-), 630-MeV, respectively. Because these spin assignments depend on the structure of the states as previously identified, ' the assignments cannot be viewed as most definite. Except for the 7' 233~5-keV state, the level energies were obtained from the y measurements to within uncertainties of 1 to 2 keV. The above spin assignments are in accord with the tentative spin assignments made by Comfort et al. 'The results also agree with those predicted by the Pandya transformation from the known (wgz, )(vd",) multiplet in~Nb. The 2 and 3 states associated with the (wp",}(vd", ) ' configuration are expected at a low excitation energy in Nb. The present y measurements suggest that the state at 506 keV is 2 and the 687-keV state is 3; however, more experiments, such as an internal-conversion measurement, are needed to verify that the 687-506-keV dipole transition is an M1 transition and that the 506-180-keV y transition is El.Independent-fission yields of Nba~~, Nbse, Tce~, Rh~, Ag In 5~, Cs~, and Cs 3~~, and fission yields of four mass chains in the symmetric region A =111-115have been determined in the fission of Th232 induced by 14.8-MeV neutrons. Various postulates of charge distribution were tested to correlate the experimental data. It was found that the equalcharge-displacement hypothesis agreed well for the fission products produced by the asymmetric mode of fission, and the constant-charge-ratio postulate showed the best correlation for the fission products produced by the symmetric mode of fission. Evidence for 40and 50-proton shell effects on the fission yields has been found in this work.