Structure, Directional-Correlation, and Doppler-Shift Lifetime Measurements inCu61viaNi58(He4,pγ)Reaction Spectrometry

Abstract

The level structure and the decay properties of the levels in ${}_{}{}^{61}{}_{}{}^{}\mathrm{Cu}$ up to 4082 keV of excitation have been carefully investigated via prompt $\gamma \gamma$ and $p\gamma$ coincidence experiments employing Ge(Li) $\gamma$-ray detectors and annular Si surface-barrier charged-particle detectors. From these experiments and from high-resolution singles energy and directional- correlation measurements an improved decay scheme has been obtained which includes 44 levels in ${}_{}{}^{61}{}_{}{}^{}\mathrm{Cu}$ and incorporates 120 $\gamma$ rays. New levels at 2584.5, 3739.4, 3942.4, and 4081.8 keV were postulated, while the $\gamma$ decay of several previously reported levels between 3277-3802 keV was not observed. The singles directional correlations from many transitions were used to obtain (i) reliable branching ratios for the more intense $\gamma$ rays and (ii) multipole mixing ratios $\delta \left(\frac{E2}{M1}\right)$ by employing both a ratio method and an independent analysis of the correlations via the compound statistical theory of nuclear reactions. Branching ratios for the weaker $\gamma$ rays were obtained from spectra taken at 55° to the beam direction. The lifetimes of 31 levels in ${}_{}{}^{61}{}_{}{}^{}\mathrm{Cu}$ were measured by the Doppler-shift attenuation method via the ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}({}_{}{}^4{}_{}{}^{}\mathrm{He},p\gamma )$ reaction at bombardment energies between 9.7 and 12.2 MeV. Lifetimes were extracted from singles spectra obtained at 0, 15, 30, 45, 70, 90, and 110° and from $p\gamma$ coincidence spectra obtained at 0° to the beam direction, by employing both a centroid shift analysis for the data from all angles and a line-shape fitting analysis for the data from angles ≤45°. The stopping power of Ni previously calibrated for Cu ions, was used for the line-shape analysis and for obtaining reliable $F\left(\tau \right)$ curves applicable to the present conditions of both the singles and the coincidence experiments. For a large number of transitions in ${}_{}{}^{61}{}_{}{}^{}\mathrm{Cu}$ values for $B\left(E2\right)$ and $B\left(M1\right)$ were obtained. The $B\left(E2\right)$ and $B\left(M1\right)$ values together with the $\delta \left(\frac{E2}{M1}\right)$ values and the branching ratios from the first 10 levels in ${}_{}{}^{61}{}_{}{}^{}\mathrm{Cu}$ are compared with recent detailed calculations for ${}_{}{}^{61}{}_{}{}^{}\mathrm{Cu}$ based on a unified model. Good general agreement is observed between experiment and theory for the $B\left(E2\right)$ values....