Radiochemical studies of the fission of heavy elements by fast neutrons

Abstract

The relative yields of 8 mass chains both in the fission of Th(^232) y 3- and 14-Mev. neutrons have been easured radiochemically. The measured relative yields ere corrected to total chain yields by applying the equal charge displacement hypothesis. The relative yields were converted to absolute yields by imposing the condition that the sum of all the fission products must be 200%. Use has been made of the measured relative yields of near complementary fragments to determine the number of secondary neutrons emitted by a few fragment pairs. The number of secondary neutrons emitted by mass number 145 and its complementary fragment in 14-Mev neutron fission was found to be 4.04 and by mass number 132 and its complementary fragment in 3-Mev neutron fission to be 2.30.The mass, yield curves obtained in the present investigations showed the predominance of asymmetric fission at the lower excitation energy. The maxima of the peaks for 14-Mev fission were at mass numbers 91.00 and 137.96, while those for 3-Mev neutron fission were at mass numbers 91.55 and 139.28. An explanation of the relative change of the peak maxima at different energies has been put forward.