Excited states in ${}^{82}\mathrm{As}$ studied in the decay of ${}^{82}\mathrm{Ge}$

The excited states of odd-odd ${}^{82}\mathrm{As}$ are studied in the $\beta$ decay of ${}^{82}\mathrm{Ge}$. An isotopically pure beam of ${}^{83}\mathrm{Ga}$ was produced at the Holifield Radioactive Ion Beam Facility using a resonance ionization laser ion source and high-resolution electromagnetic separation. The atoms of ${}^{82}\mathrm{Ge}$ are created after $\beta$-delayed neutron emission in the decay of ${}^{83}\mathrm{Ga}$. The number of ${}^{82}\mathrm{Ge}$ atoms is found by normalization to the 1348-keV $\gamma$ ray. Detailed analysis of the decay scheme is compared with shell-model calculations with several commonly used $fpg$ shell interactions.

Figure 1

(a) Total $\beta$-gated $\gamma$ spectrum obtained in the experiment. Transitions identified by dotted lines and energies were assigned to the decay of ${}^{82}\mathrm{Ge}$. Other transitions are marked by parent decay: open circles (${}^{83}\mathrm{Ga}$ $\beta 0n$), filled circles (${}^{83}\mathrm{Ga}$ $\beta n$), squares (${}^{83}\mathrm{Ge}$), open triangles (${}^{82}{\mathrm{As}}^m$), half-filled triangles (${}^{82}{\mathrm{As}}^{gs}$), filled triangles (both ${}^{82}{\mathrm{As}}^{gs,m}$), pentagons (${}^{83}\mathrm{As}$), or question mark if unassigned. The letter $n$ indicates that the $\gamma$ ray is emitted in the neutron reaction on natural germanium isotopes ($A=70$, 72–74, 76). The crosses indicate a background transition. (b) $\gamma$-singles spectra obtained in tape-cycling mode (upper curve, black), and in saturation mode (lower curve, red). The most prominent common background lines are marked with crosses.

Figure 2

The grow-in/decay-out pattern of selected $\gamma$ transitions. The lines show the solutions of the Bateman equation for the first (dashed), second (solid and dotted), and third (dashed-dotted) isotopes in the radioactive chain. The curves were calculated using known half-lives of the isotopes and absolute $\gamma$-ray normalization; the only fitted parameter was the implantation rate of ${}^{83}\mathrm{Ga}$ ions.

Figure 3

Proposed $\beta$-decay scheme of ${}^{82}\mathrm{Ge}$. Intensities of $\gamma$ transitions (in parentheses) are given per 100 parent decays. Notice that 14.6% of $\beta$ feeding is unplaced in the decay scheme. This value is included in the $log\left(ft\right)$ calculations.

Figure 4

Background-subtracted $\gamma \text{−}\gamma$ coincidence spectra gated on the following transitions: 92 keV (a), 427 keV (b), and 952 keV (c). The peaks marked with a star ($☆$) are artifacts due to the background- subtraction procedure.

Figure 5

Comparison of the experimental level schemes of ${}^{82}\mathrm{As}$ obtained in the $\beta$ decay (this work) and in ${}^{82}\mathrm{Se}{\left(t{,}^3\mathrm{He}\right)}^{82}\mathrm{As}$ [18]. In the latter case the thicknesses of the levels reflects the experimental uncertainties (10–20 keV).

Figure 6

Comparison of the ${}^{82}\mathrm{As}$ level scheme from the present work and results of the shell-model calculations with different interactions (see text for more details). The tentative $6^{-}$ state at 340 keV is from [18].