Beta-Decay Half-Lives and Neutron-Emission Probabilities of Very Neutron-Rich Y to Tc Isotopes.

Abstract

Neutron-rich ${}_{39}$Y to ${}_{43}$Tc isotopes have been produced by fission of uranium with a 50 MeV ${\mathrm{H}}_{2}^{+}$ beam. Beta-decay half-lives, delayed neutron-emission probabilities, and production yields have been measured and compared with theory. Beta decay of 4 new isotopes is reported, and the $\ensuremath{\beta}$-delayed neutron-emission mode has been discovered for 12 isotopes of the elements niobium and technetium. The results compared to quasiparticle random phase approximation predictions indicate the increasing importance of fast $\ensuremath{\beta}$ transitions to high-lying states of nuclei with large neutron excess.