Spontaneous fission properties of 103259Lr.

Abstract

We have measured the mass and kinetic-energy distributions of fragments from the spontaneous fission of $^{259}\mathrm{Lr}$. The $^{259}\mathrm{Lr}$ was produced via the $^{248}\mathrm{Cm}$ ${(}^{15}$N,4n) reaction with a production cross section of 100 nb using 81-MeV projectiles. The kinetic energies and times of the alpha particles and coincident fission fragments were measured using our rotating wheel system. From these data the half-life, mass, and kinetic-energy distributions were derived. The total kinetic-energy (TKE) distribution appears to consist of a single component with a most probable pre-neutron-emission TKE of 215\ifmmode\pm\else\textpm\fi{}3 MeV. The mass distribution is predominantly symmetric with a full width at half maximum of about 20 mass numbers. These results are consistent with trends observed for other trans-berkelium spontaneously fissioning isotopes. We determined the half-life to be 6.14\ifmmode\pm\else\textpm\fi{}0.36 s by measuring its alpha decay and the observed spontaneous fission half-life was consistent with that value. An energy of 8.439\ifmmode\pm\else\textpm\fi{}0.010 MeV was measured for the main alpha transition of $^{259}\mathrm{Lr}$. We measured a spontaneous fission to alpha-decay ratio of 0.25\ifmmode\pm\else\textpm\fi{}0.03 which results in a partial half-life for spontaneous fission of 31\ifmmode\pm\else\textpm\fi{}4 s, if there are no other appreciable modes of decay.