Fragment-mass and kinetic-energy distributions from the spontaneous fission ofNo252

Abstract

Pre-neutron-emission fragment-mass and total-kinetic-energy distributions and the mass-energy correlations in the spontaneous-fission decay of 2.30-sec ${}_{}{}^{252}{}_{}{}^{}\mathrm{No}$ have been deduced from measured energies of coincident fragment pairs using silicon surface-barrier detectors. The ${}_{}{}^{252}{}_{}{}^{}\mathrm{No}$ for these measurements was produced in the ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}({}_{}{}^{15}{}_{}{}^{}\mathrm{N}, 4n)$ reaction and deposited on 40-μg ${\mathrm{cm}}^{-2\mathrm{}}$ carbon foils using a He-jet technique. From an analysis of 154 correlated fission events, the average pre-neutron-emission total-kinetic energy, $〈\mathrm{TKE}〉$, was found to be 202.4±1.2 MeV. The mass distribution is decidedly asymmetric, similar to that observed for ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ spontaneous fission, although a maximum in the $〈\mathrm{TKE}〉$ curve as a function of fragment mass occurs for near-symmetric mass divisions as it does for the heavier isotopes of fermium. The measured spontaneous-fission-decay branching fraction for ${}_{}{}^{252}{}_{}{}^{}\mathrm{No}$ is 26.9±1.9% and the measured total half-life is 2.30±0.22 sec. The measured and deduced fission charàcteristics for ${}_{}{}^{252}{}_{}{}^{}\mathrm{No}$ are compared with those for the Cm, Cf, and Fm nuclides as well as with recent theoretical predictions.