$\beta \text{−}\gamma$ spectroscopy of the ${}^{195}\mathrm{Os}$ nucleus

The $\beta \text{−}\gamma$ spectroscopy of ${}^{195}\mathrm{Os}$ nucleus was performed at the KEK isotope separation system (KISS). The radioactive isotope of ${}^{195}\mathrm{Os}$ was produced by the multinucleon transfer reactions of ${}^{136}\mathrm{Xe}$ beams and ${}^{198}\mathrm{Pt}$ target. The isotope of interest was separated and extracted by using KISS, which is an argon-gas-cell based laser ion source with a mass separator. Those extracted isotopes are implanted into an aluminized mylar tape, which is surrounded by the multisegmented proportional gas counter (MSPGC) and four clover-type high-purity germanium (HPGe) detectors for the $\beta \text{−}\gamma$ spectroscopy. 27 $\gamma$-ray peaks were observed in coincidence with internal conversion electrons and x rays detected by the MSPGC. 21 of them were identified as $\beta$-delayed $\gamma$ rays of the ${}^{195}\mathrm{Os}$ ground state, where the energies of 19 $\gamma$-ray peaks agree with the literature values of transitions observed in ${}^{195}\mathrm{Ir}(n,\gamma )$ reactions and two $\gamma$-ray peaks were newly found. The $\beta$-decay branching ratios of the ${}^{195}\mathrm{Os}$ ground state were deduced. The obtained log-$ft$ values range from $5.99\left(4\right)$ to $7.56\left(22\right)$, indicating all $\beta$-decay channels are the first forbidden transitions. It suggests that the spin-parity of the ${}^{195}\mathrm{Os}$ ground state is $3/2^{-}$, which is consistent with the systematical expectation. The $\beta$-decay half-life of the ${}^{195}\mathrm{Os}$ ground state was evaluated to be 6.5(4) min, which agrees well to the previously known value 6.5(11) min.

Figure 1

$\gamma$-ray energy spectra measured in coincidence with the MSPGC hit patterns “$M=1$” (dotted line) and “$M=2$” (solid line).

Figure 2

Time spectrum for the 286-keV $\gamma$ transition with the MSPGC hit pattern “$M\ge 1$”. Dotted line indicates fitted line of growth and decay of ${}^{195}\mathrm{Os}$ activity. Reduced $\chi$ square is 1.10.

Figure 3

$\gamma \text{−}\gamma$ coincidence spectra gating on (a) 305-, (b) 234-, (c) 164-, and (d) 776-keV $\gamma$ rays.

Figure 4

Energy levels and spin-parity values of ${}^{195}\mathrm{Ir}$ [18] with observed $\beta$-delayed $\gamma$ transitions of the ${}^{195}\mathrm{Os}$ ground state. Thick arrows indicate newly observed 305- and 776-keV $\gamma$ transitions. Thin arrows indicate previously reported transitions [18]. All transition energies above arrows were taken from the measurements in this work.

Figure 5

Time spectrum for the number of events detected by the MSPGC with the hit pattern “$M=2$”. Thick solid line indicates the fitting result, which consists of four contributions from ${}^{195\mathrm{m}}\mathrm{Os}$ decays (thick dashed line), ${}^{195\mathrm{g}}\mathrm{Os}$ decays (thin solid line), ${}^{195\mathrm{g}}\mathrm{Ir}$ decays (thin dashed line), and the constant background (thick dotted line).

Figure 6

Comparison of half-lives of Os isotopes among experimental data [19, 23, 24, 25, 26] and theoretical predictions [4, 5, 27].