Decay Scheme and Gamma-Gamma Angular Correlations inNi60Following the Decay of 23-MinCu60

Abstract

A new decay scheme is given for ${\mathrm{Cu}}^{60}$ which agrees with the main features of previous schemes. However, evidence was found for previously unreported feedings to levels at 4.08, 3.73, 3.39, 3.27, and 3.19 MeV. Analysis of single-crystal $\gamma$-ray spectra and spectra in coincidence with 1.33-MeV radiation and with annihilation radiation revealed, in addition to previously established $\gamma$ rays, new weaker $\gamma$ rays whose energies are 0.47, 0.50, 0.64, 0.95, 1.03, (1.10), 1.86, 1.94, 2.06, 2.40, 2.74, 3.19, and 3.27 MeV. No 3.52-MeV $\gamma$ ray was found. The half-life for ${\mathrm{Cu}}^{60}$ was measured to be 22.9±0.1 min. Angular-correlation measurements for $\gamma$ rays of 0.83, 0.95, 1.03, and 1.79 MeV in coincidence with 1.33-MeV radiation have been made. Spin-2 assignments resulted for levels at 2.16 and 3.12 MeV. $\frac{E2\mathrm{}}{M1\mathrm{}}$ mixing ratios $\delta =-1.2\mathrm{}\pm 0.3 \mathrm{and} 0.21\pm 0.04$ were found for ${2_i}^{+}\to {2_1}^{+}$ transitions of 0.83 and 1.79 MeV, respectively. A spin-0 assignment for the 2.29-MeV level was made. The present $\gamma -\gamma$ angular-correlation results are compared with results of a previous $\gamma -\gamma$ angular-correlation study and with results of a ${\mathrm{Ni}}^{60}(p, p^{\prime }\gamma )$ $\gamma$-ray angular-distribution study. In the case of the $\frac{E2\mathrm{}}{M1\mathrm{}}$ mixing ratio for the 0.83-MeV $\gamma$ ray arising from the 2.16-MeV level, the present value for $\delta$ is close to the value obtained from the ($p, p^{\prime }\gamma$) study, and disagrees with the previous radioactivity work. The negative sign of $\delta$ for this $2_2^{+}$→$2_1^{+}$ transition is discussed in the light of new theoretical estimates by Greiner. The relationship of the present experiment to other recent work is discussed.