Precision measurements of proton emission from the ground states of ${}^{156}\mathrm{Ta}$ and ${}^{160}\mathrm{Re}$

The decays of the $\pi d_{3/2}$ ground states of ${}^{156}\mathrm{Ta}$ and ${}^{160}\mathrm{Re}$ have been studied in detail using the GREAT spectrometer. More than 7000 ${}^{160}\mathrm{Re}$ nuclei were produced in reactions of 290- and 300-MeV ${}^{58}\mathrm{Ni}$ ions with an isotopically enriched ${}^{106}\mathrm{Cd}$ target and separated in flight using the RITU separator. The proton and $\alpha$ decays of the $\pi d_{3/2}$ level were confirmed and the half-life and branching ratios of this state were determined with improved precision to be $t_{1/2}=611\pm 7$ $\mu$s and $b_{\mathrm{p}}=89\pm 1\%$ and $b_{\alpha }=11\pm 1\%$, respectively. The $\alpha$-decay branch populated the ground state of ${}^{156}\mathrm{Ta}$, allowing improved values for the proton-decay energy and half-life to be obtained ($E_p=1011\pm 5$ keV; $t_{1/2}=106\pm 4$ ms). The $\beta$ decay of this level was identified for the first time and a branching ratio of $b_{\beta }=29\pm 3\%$ was deduced. The spectroscopic factors deduced from these measurements are compared with predictions.

Figure 1

Decay scheme of the $\pi d_{3/2}$ state in ${}^{160}\mathrm{Re}$. Decay energies in keV, half-lives in ms, and branching ratios are taken from the present work and Ref. [8]. The tentative spin and parity assignments for ${}^{160}\mathrm{Re}$ and ${}^{156}\mathrm{Ta}$ are given in parentheses. The dashed lines indicate unknown $\beta$ decays that were searched for in this work. Of these, only the $\beta$ decay of the $\pi d_{3/2}$ state in ${}^{156}\mathrm{Ta}$ feeding the ground state of ${}^{156}\mathrm{Hf}$ could be identified. Note that the $\beta$ decays of ${}^{156}\mathrm{Ta}$ may feed the $\alpha$-emitting isomers in ${}^{156}\mathrm{Hf}$ via intermediate states.

Figure 2

(a) Energy spectrum of ${}^{160}\mathrm{Re}$ proton decays following a recoil implantation within 3 ms and correlated within 22 ms with a subsequent $\alpha$ decay of ${}^{159}\mathrm{W}$ in the same DSSD pixel. The inset shows the high-energy region of this spectrum with an expanded vertical scale. No peak is visible that could correspond to the proton decay of the $\pi h_{11/2}$ state in ${}^{160}\mathrm{Re}$. (b) Energy spectrum of decays of the $\pi d_{3/2}$ state in ${}^{156}\mathrm{Ta}$ observed up to 320 ms after $\alpha$ decays of the $\pi d_{3/2}$ state in ${}^{160}\mathrm{Re}$ that occur within 3 ms of the implantation of an ion into the same pixel. The inset shows the high-energy region of this spectrum, revealing the ground-state $\alpha$-decay peak of ${}^{156}\mathrm{Hf}$, the $\beta$-decay daughter of ${}^{156}\mathrm{Ta}$.

Figure 3

(a) Energy spectrum of decays occurring within 3 ms of a recoil implantation and followed within 320 ms by the proton decay of the $\pi d_{3/2}$ state of ${}^{156}\mathrm{Ta}$. (b) As (a), except the energy region selected for the second decay is above the proton peak. This spectrum shows the background peaks that arise from correlations with escaping $\alpha$ particles when selecting proton decays.