Spectroscopic studies of neutron-rich ${}^{129}\mathrm{In}$ and its $\beta$-decay daughter, ${}^{129}\mathrm{Sn}$, using the GRIFFIN spectrometer

The $\beta$ decay of neutron-rich ${}^{129}\mathrm{In}$ into ${}^{129}\mathrm{Sn}$ was studied using the GRIFFIN spectrometer at the ISAC facility at TRIUMF. The study observed the half-lives of the ground state and each of the $\beta$-decaying isomers. The level scheme of ${}^{129}\mathrm{Sn}$ has been expanded with thirty-one new $\gamma$-ray transitions and nine new excited levels, leading to a reevaluation of the $\beta$ branching ratios and level spin assignments. The observation of the $\beta$ decay of the ($29/2^{+}$) 1911-keV isomeric state in ${}^{129}\mathrm{In}$ is reported for the first time, with a branching ratio of 2.0(5)$\%$.

Figure 1

$\beta$-gated $\gamma$-ray spectrum, in addback mode, showing various known transitions in ${}^{129}\mathrm{Sn}$ (red squares). Transitions in ${}^{129}\mathrm{Sb}$ ($\beta$ decay daughter of ${}^{129}\mathrm{Sn}$; green circles) and ${}^{128}\mathrm{Sn}$ ($\beta n$ daughter of ${}^{129}\mathrm{In}$; blue triangles) are also observed.

Figure 2

A $\gamma$-ray spectrum, in addback mode, showing evidence for the 1071-keV $\gamma$ ray, depopulating the 2118-keV state, in coincidence with the 1047-keV $\gamma$ ray, depopulating the 1047-keV state of ${}^{129}\mathrm{Sn}$. The 1071-keV transition lies on the shoulder of a much more intense transition at 1075-keV, necessitating gating from below to obtain its relative intensity. The inset shows the gate on 1047 keV used to produce the spectrum.

Figure 3

A $\gamma$-ray spectrum, in addback mode, showing evidence for the 1271-keV $\gamma$ ray, depopulating the new state at 2326-keV, in coincidence with the 1054-keV $\gamma$ ray, depopulating the 1054-keV state in ${}^{129}\mathrm{Sn}$. Although weak, this transition is visible in the ungated $\gamma$-ray spectrum, but it is much more clear in the 1054-keV coincidence spectrum. This coincidence also confirms its placement in the level scheme. The transition at 1257 keV is also newly observed, while those at 1289 and 1302 keV are known in ${}^{129}\mathrm{Sn}$. The inset shows the gate on 1054 keV used to produce the spectrum.

Figure 4

A spectrum of total counts as a function of cycle time, representing 39 transitions associated with the ${}^{129}\mathrm{In}$ ground-state decay into states in ${}^{129}\mathrm{Sn}$. The fit, seen in red, returned a value of $t_{1/2}=0.60\left(1\right)$ s. The reduced ${\chi }^2$ for this fit is 1.3.

Figure 5

The level scheme of ${}^{129}\mathrm{Sn}$, populated through the $\beta$ decay of the ground state of ${}^{129}\mathrm{In}$, showing the high-lying states (top) and the low-lying states (bottom). The color (red) represents new transitions and levels found in this work. For the case of the 1614-keV state, the colored ($7/2^{+}$) spin indicates a new spin assignment to a previously observed level. The half-lives of the ground state and the ${}^{129}\mathrm{Sn}^{m1}35$-keV isomer are 2.23(4) min and 6.9(1) min, respectively, as given by Timar, Elekes, and Singh [31]. Information about $\gamma$-ray intensity and their uncertainties can be found in Table 1.

Figure 6

The level scheme of ${}^{129}\mathrm{Sn}$, populated through the $\beta$-decay of the ($1/2^{-}$) 459-keV isomer of ${}^{129}\mathrm{In}$. The color (red) represents new transitions and levels found in this work. The half-life of the ${}^{129}\mathrm{Sn}$ ground state is 2.23(4) min, as given by Timar, Elekes, and Singh [31]. Information about $\gamma$-ray intensity and their uncertainties can be found in Table 1.

Figure 7

A spectrum of total counts as a function of cycle time, representing twelve transitions associated with the decay of ${}^{129}\mathrm{In}^{m1}$ into states in ${}^{129}\mathrm{Sn}$. The fit, seen in red, returned a value of $t_{1/2}=1.16\left(1\right)$ s. The reduced ${\chi }^2$ for this fit is 1.2.

Figure 8

A spectrum of total counts as a function of cycle time, representing four transitions associated with ${}^{129}\mathrm{In}^{m2}$ decay into states in ${}^{129}\mathrm{Sn}$. The fit, seen in red, returned a value of $t_{1/2}=0.65\left(1\right)$ s. The reduced ${\chi }^2$ for this fit is 2.2.

Figure 9

The level scheme of ${}^{129}\mathrm{Sn}$, populated through the $\beta$ decay of the ($23/2^{-}$) ${}^{129}\mathrm{In}$. The color (red) represents new transitions and levels found in this work. The half-life of the ${}^{129}\mathrm{Sn}$ ground state is 2.23(4) min, as given by Timar, Elekes, and Singh [31]. Information about $\gamma$-ray intensity and their uncertainties can be found in Table 1. The dashed lines presented two known states, at 1762 and 1803 keV, whose energies can only be inferred in this work from feeding from above.

Figure 10

A spectrum of total counts as a function of cycle time for the 281-keV transition. The fit, in red, returned a value of $t_{1/2}=0.085$(15) s, which is in good agreement with the half-life of the 1911-keV ${}^{129}\mathrm{In}^{m3}$, quoted at 0.110(15) s [31]. The fit returned a reduced ${\chi }^2$ of 1.1. The fit included a component associated with the $\beta$ decay of the ${}^{129}\mathrm{In}^{\text{g.s.}}$ since the energy of the 281-keV internal transition in ${}^{129}\mathrm{In}$ is unresolved from two transitions in ${}^{129}\mathrm{Sn}$ at 278 and 280 keV (see text for details).

Figure 11

Partial level scheme showing the decay of the ($29/2^{+}$) 1911-keV ${}^{129}\mathrm{In}^{m3}$ isomer into the ($27/2^{-}$) 2552-keV state in ${}^{129}\mathrm{Sn}$. The intensity of the 146-keV transition was obtained in coincidence with the 604-keV transition.

Figure 12

A spectrum showing the 146-keV transition in the 604-keV gate. Note the red lines in the inset denote the placement of the gate.