$\beta$ decay of ${}^{127}\mathrm{Cd}$ and excited states in ${}^{127}\mathrm{In}$

A dedicated spectroscopic study of the $\beta$ decay of ${}^{127}\mathrm{Cd}$ was conducted at the IGISOL facility at the University of Jyväskylä. Following high-resolution mass separation in a Penning trap, $\beta \text{−}\gamma \text{−}\gamma$ coincidences were used to considerably extend the decay scheme of ${}^{127}\mathrm{In}$. The $\beta$-decaying $3/2^{+}$ and $11/2^{-}$ states in ${}^{127}\mathrm{Cd}$ have been identified with the ${}^{127}\mathrm{Cd}$ ground state and the 283-keV isomer. Their respective half-lives have been measured to $0.45{(}_8^{12})\mathrm{s}$ and 0.36(4) s. The experimentally observed $\beta$ feeding to excited states of ${}^{127}\mathrm{In}$ and the decay scheme of ${}^{127}\mathrm{In}$ are discussed in conjunction with large-scale shell-model calculations.

Figure 1

Sketch of the experimental setup starting with the cooled and bunched beam from the RFQ cooler and buncher [22]. Using the purification trap [6] ${}^{127}\mathrm{Cd}$ ions were separated from neighboring isobars, transferred to the TASISpec decay station [7], and deposited on an aluminum catcher foil. The measurement trap was employed for separating ground and isomeric state of ${}^{125,127}\mathrm{Cd}$. Dimensions are not to scale.

Figure 2

Observed $\gamma$-ray spectrum of the ${}^{127}\mathrm{Cd}\beta$ decay in prompt coincidence with a $\beta$ particle. Known transitions emitted following the $\beta$ decay of daughter nuclei are labeled with the following symbols: * for transitions in ${}^{127}\mathrm{Sn},\#$ for transitions in ${}^{127}\mathrm{Sb}$, and + for transitions in ${}^{127}\mathrm{Te}$. Single- and double-escape peaks are denoted by SE and DE, and the corresponding annihilation peak at $511\mathrm{keV}$ is marked with $\left(e^{+}{e}^{-}\right)$. The bin width is $1\mathrm{keV}$ for $E_{\gamma }\le 1600\mathrm{keV}$ and $2\mathrm{keV}$ for $E_{\gamma }>1600\mathrm{keV}$. Energy labels are in keV.

Figure 3

Observed $\gamma$-ray spectrum for the first $70\mathrm{ms}$ after a trap-release signal where all $\gamma$ rays detected later than $70\mathrm{ms}$ after the last trap-release signal were subtracted, i.e., highlighting $\gamma$-ray transitions following the first $\beta$-decay step of ${}^{127}\mathrm{Cd}$. Energy labels are in keV. See text for details.

Figure 4

Decay scheme of ${}^{127}\mathrm{In}$ following the $\beta$ decay of ${}^{127}\mathrm{Cd}$. Panel (a) shows the model based on shell-model calculations and panel (b) shows results observed experimentally. Energy labels are in keV, and tentative levels and transitions are dashed. In panel (a), the predicted main branches of Gamow-Teller (GT) $\beta$-decay feeding from ${}^{127}\mathrm{Cd}$ are indicated for the $3/2^{+}$ ground state on the left-hand side and for the $11/2^{-}$ isomer on the right-hand side. This includes the excitation energies of the experimental levels associated with the main GT feeding. The $\gamma$-ray decay pattern in panel (a) is derived from experimental excitation energies but calculated transition strengths. Unobserved $\gamma$-ray transitions with predicted yields above the observational limit are labeled with their energy in keV. More details and the relevant discussion are provided in Sec. 4c. Detailed numerical results are given in Table 4.

Figure 5

Observed $\gamma$-ray spectra in prompt coincidence with (a) the 1282-keV transition, (b) the 376-keV transition, (c) the 1067-keV transition, and (d) the 1856-keV transition. Peaks marked with (CP) arise from Compton scattered $\gamma$ rays of the intense 491-keV transition in ${}^{127}\mathrm{Sb}$, the 1235-keV transition in ${}^{127}\mathrm{In}$, or the 1597-keV transition in ${}^{127}\mathrm{Sn}$. In case of the spectrum shown in panel (a), for instance, the peak at $\sim 315$ keV stems from 1597-keV $\gamma$ rays which first deposited $1282\mathrm{keV}\left(315\mathrm{keV}\right)$ in one HPGe detector via Compton scattering and the remaining energy of $315\mathrm{keV}\left(1282\mathrm{keV}\right)$ in another HPGe detector. Energy labels are in keV.

Figure 6

Observed $\gamma$-ray spectra in prompt coincidence with (a) the 1202.3-keV transition, (b) the 523.5-keV transition, (c) the 388.1-keV transition, and (d) the 1686.7-keV transition. Peaks marked with CP are due to Compton scattered $\gamma$ rays as explained in Fig. 5. Energy labels are in keV.

Figure 7

Comparison of experimental (exp) and calculated (jj45 and NA-14) level energies for the $A=125$, 127, and 129 isotopes of Cd (top row) and In (bottom row). Isomeric states are marked by thick horizontal lines. The energy of the excited $(3/2^{+})$ state in ${}^{129}\mathrm{Cd}$ (dashed) is experimentally not yet determined. Thin dashed lines connect observed and predicted energy levels. With the exception of the jj45 prediction of ${}^{125}\mathrm{Cd}$, the $3/2^{+}\left({}^{125,127}\mathrm{Cd}\right)$, the $11/2^{-}\left({}^{129}\mathrm{Cd}\right)$, and $9/2^{+}$ (all three In isotopes) ground states served for normalization. See text for more details.

Figure 8

Results of shell-model calculations for the Gamow-Teller strength distribution, B(GT), for the decay of the $11/2^{-}$ (a) and the $3/2^{+}$ (b) states in ${}^{127}\mathrm{Cd}$ to excited states in ${}^{127}\mathrm{In}$. The experimental GT strengths are shown as black dots.