A study of the low-energy transitions arising from the prompt de-excitation of fission fragments

Abstract

A four-dimensional experiment has been performed in which the energies of coincident complementary fragment pairs, internal conversion electrons, and K X-rays emitted as a result of the spontaneous fission of 252Cf were recorded event by event using a multiparameter analyser. The fission fragment energies were used for mass identification and the X-ray energies supplied precise atomic number identification. The analysis of the conversion electron spectra has resulted in the assignment of numerous transitions to new isotopes, the determination of many transition half-lives, and the procurement of limited information concerning multipolarities. It was concluded, based on the X-ray and conversion electron data, that most of the large number of observed low-energy transitions associated with heavy fragments are attributable to odd-mass or doubly odd nuclei and that surprisingly little contribution to the low-energy spectra is associated with doubly even nuclei in the rare-earth region. Low-energy transitions in doubly even nuclei were found to be more prevalent among the light fragments. Data are presented supporting the assignment of a high intensity 241 keV transition as the 2 + to 0 + transition in 110Ru. An examination of this transition in terms of the energy predicted on the basis of rotational behaviour and with regard to the systematics of neighboring doubly even Ru isotopes reveals evidence which strongly suggests that 110Ru belongs to a new region of stable deformation.