Isotopic mass dispersion discontinuity in various fission processes and its interpretation as a neutron shell effect

Abstract

The isotopic dispersions have been calculated for fission processes listed in the Introduction below by using recommended fission yield data. Those dispersions in which the neutron numbers of isotopes lying in the vicinity of the most probable mass fit a strong shell have been found to be pronouncedly discontinuous; the discontinuity is proved to occur exactly at the most probable mass. The influence of neutron shells on mass dispersion with special reference to discontinuity is discussed on the basis of shell correction versus deformation and neutron number reported by Wilkins, Steinberg, and Chasman. In discontinuous dispersions on the narrower branch lie the isotopes fitting the strong spherical and deformed neutron shells. Apart from recommended data, the relative isotopic fragment yields predicted by the Wilkins-Steinberg model for the complementary pairs z = 50-42, 51-41, 54-38, and 56-36, in thermal-neutron fission of /sup 235/U have also been used to calculate the corresponding dispersions. These have been found to be in good agreement with those calculated from recommended data, and discontinuities were observed, in general, wherever expected.