βdecay of theπf5/2ground state ofCu77studied with225 MeV and0.2 MeV purified radioactive beams

Abstract

Isobarically purified beams of $^{77}\mathrm{Cu}$ with energies of $225$ and $0.2$ MeV were used at the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory to study $\ensuremath{\beta}$ decay into states in $^{77}\mathrm{Zn}$. Data taken at $225$ MeV allowed the determination of absolute branching ratios relative to the decay of $^{77}\mathrm{Cu}$ for this $\ensuremath{\beta}$ decay as well as its daughters. From these we obtained a refined $\ensuremath{\beta}$-delayed neutron emission probability of $30.3(22)%$ and a probability that the decay proceeds through $^{77}\mathrm{Zn}$${}^{g}$ of $49.1(26)%$. A total of $64 \ensuremath{\gamma}$ rays were placed in a level scheme for $^{77}\mathrm{Zn}$ containing $35$ excited states including one state above the neutron separation energy, whereas two $\ensuremath{\gamma}$ rays were observed for the $\ensuremath{\beta}$$n$ branch to states in $^{76}\mathrm{Zn}$. The growth and decay curves of some prominent $\ensuremath{\gamma}$ rays indicate a single $\ensuremath{\beta}$-decaying state with a half-life of $480(9) $ms. The decay pattern for $^{77}\mathrm{Cu}$, with observed feeding of $8(3)%$ to $7/{2}^{+} $$^{77}\mathrm{Zn}$${}^{g}$ and $6(3)%$ to $1/{2}^{\ensuremath{-}} $$^{77}\mathrm{Zn}$${}^{m}$, in contrast to the large feeding observed for decay of $\ensuremath{\pi}{p}_{3/2}$ $^{73}\mathrm{Cu}$${}^{g}$ to $1/{2}^{\ensuremath{-}} $$^{73}\mathrm{Zn}$${}^{g}$, strongly suggests a $\ensuremath{\pi}{f}_{5/2}$ ground state for the studied $^{77}\mathrm{Cu}$ activity.