$\beta$ decay of ${}^{132}\mathrm{In}$ and spectroscopy of ${}^{132}\mathrm{Sn}$ and ${}^{131}\mathrm{Sb}$ with the GRIFFIN spectrometer

Spectroscopy of doubly magic ${}_{50}^{132}{\mathrm{Sn}}_{82}$ has been performed with the GRIFFIN spectrometer at TRIUMF-ISAC following the $\beta$ decay of ${}_{49}^{132}{\mathrm{In}}_{83}$. The analysis has allowed for the placement of a total of 70 transitions and 29 excited states in ${}^{132}\mathrm{Sn}$. Detailed spectroscopy has also been performed on ${}^{131}\mathrm{Sb}$, resulting from the $\beta$ decay of ${}^{131}\mathrm{Sn}$, produced from the $\beta$-delayed neutron decay of ${}^{132}\mathrm{In}$. Measurement of $\gamma$ rays in both ${}^{131}\mathrm{Sn}$ and ${}^{131}\mathrm{Sb}$ has led to the determination of the $\beta$-delayed neutron emission probability $P_n$ from ${}^{132}\mathrm{In}$. This is the first time that $P_n$ has been measured for this nucleus by using $\gamma$ spectroscopy, and the new value of 12.3(4)% is consistent with the most recent $\beta -n$ counting experiment. Additionally, $\gamma -\gamma$ angular correlations have been performed in ${}^{132}\mathrm{Sn}$, supporting the spin assignments of several excited states. Novel ab initio calculations are presented which describe several of the excited states, and these are compared with the experimental spectrum.

Figure 1

A sample of the $\gamma$ spectrum gated on the 1226-keV $(11/2^{+})\to (7/2^{+})$ transition in ${}^{131}\mathrm{Sb}$, clearly demonstrating the sensitivity of the experiment to the $\beta$-delayed neutron decay of ${}^{132}\mathrm{In}$. The strong 450-keV transition feeds the 1226-keV level.

Figure 2

A level scheme showing the transitions observed in ${}^{131}\mathrm{Sb}$ following the $\beta$ decay of the high-spin $11/2^{-}$ isomer in ${}^{131}\mathrm{Sn}$. The widths of the arrows are proportional to the observed $\gamma$-ray intensity. Energies are given in keV. Level energies are taken from the ENSDF [40].

Figure 3

A sample of the $\beta -\gamma$ spectrum gated on the 375-keV $4^{+}\to 2^{+}$ transition in ${}^{132}\mathrm{Sn}$. The black squares highlight some of the coincident peaks which could be identified and placed in the level scheme.

Figure 4

A level scheme showing the transitions observed in ${}^{132}\mathrm{Sn}$ following the ${\beta }^{-}$ of ${}^{132}\mathrm{In}$. The widths of the arrows are proportional to the observed $\gamma$-ray intensity. Energies are given in keV. The two parts of the level scheme are not drawn to scale to each other.

Figure 5

The lifetime measurement for the decay of the $\left(7^{-}\right)$ ground state in ${}^{132}\mathrm{In}$. Shown is a background-subtracted sum of gates on transitions at 300, 375, 2269, 2380, 4041, 4352, and 4416 keV in ${}^{132}\mathrm{Sn}$, plotted as a function of the time since the beam was blocked. The best-fit curve is shown in red, which gives a half-life of 194(4) ms.

Figure 6

The best-fit angular correlation for the 479–4352-keV $4^{-}\to 3^{-}\to 0^{+}$ cascade in ${}^{132}\mathrm{Sn}$. The experimental data points are shown in black, and the simulated curve is shown in red. The fit corresponds to an $E2/M1$ mixing ratio of 0.02(2) for the 479-keV $4^{-}\to 3^{-}$ transition.

Figure 7

A sample of the low-lying excited states in ${}^{132}\mathrm{Sn}$ from experiment (left) and calculated with the VS-IMSRG (right). Positive-parity states are shown in red, and negative-parity states in blue. The calculated levels are shown up to 8 MeV and are connected to experimental levels by dashed lines where the levels can be directly matched. The experimental and calculated ground-state (g.s.) energies are also listed below the graph.