Basic nuclear physics with thermal neutrons: cold fragmentation and odd-even effects in fission

Recent experimental results and their interpretation on mass, charge and energy distribution of fragments from the thermal neutron induced fission of 229Th, 232U, 233U, 235U and 239Pu are reviewed with special emphasis on cold fragmentation and odd-even effects in the charge yields and kinetic energies. It is shown that cold fragmentation, with all of the available energy being converted into kinetic energy of the fragments, obtains for specific combinations of fragments only. The odd-even effect in the charge yields depends sensitively on the fissility of the compound nucleus. This is taken as indication that pairs are broken in the descent from saddle to scission. Internal excitation energies at the scission are deduced and shown to be low. (author)