Gamma Decay ofSe73m,gandSe81m,gIsomeric Pairs

Abstract

The gamma decay of the isomeric pairs (42-min ${\mathrm{Se}}^{73m}$ 7-h ${\mathrm{Se}}^{73g}$), and (57-min ${\mathrm{Se}}^{81m}$, 18.6-min ${\mathrm{Se}}^{81g}$) was investigated with Ge(Li) and NaI(Tl) detectors by means of singles, coincidence, and sum-peak coincidence spectrometry. The half-lives of ${\mathrm{Se}}^{73g}$ and ${\mathrm{Se}}^{81m}$ were determined to be 7.0±0.1 h and 56.6±0.6 min, respectively. The gamma energies from 7-h ${\mathrm{Se}}^{73g}$ were determined to be 66.9±0.5 and 360.4±0.5 keV. A new gamma of 75.7±0.5 keV was found in 42-min ${\mathrm{Se}}^{73m}$ decay and is placed as the ground-state transition from a 76-keV level (½-, $\frac{3}{2}-$) in ${\mathrm{As}}^{73}$. The absence of a 42-min component in the intensity of the 67-keV gamma indicates that the 67-keV ($\frac{5}{2}-$) first excited state of ${\mathrm{As}}^{73}$ is not fed from 42-min ${\mathrm{Se}}^{73m}$ either directly or through the 76-keV state. The energies and relative intensities of seven gammas in ${\mathrm{Se}}^{81m,g}$ equilibrium decay have been measured: 102.7±0.5 (100) (isomeric transition), 275.8±0.5 (10.2), 289.9±0.5 (8.7), 539.0±0.5 (0.8), 553.0±0.5 (1.5), 566.1±0.5 (2.9), and 829.0±0.5 (4.9) keV. A new level at 539.0 keV is proposed tentatively in ${\mathrm{Br}}^{81}$ with a possible spin parity of $\frac{5}{2}-$ or $\frac{7}{2}-$. Decay schemes are proposed for ${\mathrm{Se}}^{73m,g}$ and ${\mathrm{Se}}^{81m,g}$ which are consistent with all available data.