Experimental study of $\beta$ and $\beta \text{−}n$ decay of the neutron-rich $N=54$ isotone ${}^{87}\mathrm{As}$

The $\beta$-decay properties of neutron-rich ${}^{87}\mathrm{As}$ produced in the proton-induced fission of ${}^{238}\mathrm{U}$ were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The low-energy excited states in $N=53 {}^{87}\mathrm{Se}$ and $N=52 {}^{86}\mathrm{Se}$ were identified through $\beta \text{−}\gamma$ and $\beta$-delayed neutron-$\gamma$ decay of ${}^{87}\mathrm{As}$, respectively. The experimental systematics of low-energy levels of $N=53$ isotones, $Z=34 {}^{87}\mathrm{Se},$ and $Z=32 {}^{85}\mathrm{Ge}$, and along with an analysis of shell-model calculations, allow us to discuss the main features of excited states expected for the next $N=53$ isotone, ${}^{83}\mathrm{Zn}$.

Figure 1

Portions of the $\beta$-gated $\gamma$-ray spectrum from 0 to 800 keV (a) and from 800 to 1600 keV (b) obtained at mass $A=87$. The strongest transitions belonging to the $\beta \gamma$ and $\beta \text{−}n\gamma$ decay of ${}^{87}\mathrm{As}$ are labeled.

Figure 2

The $\beta$-gated $\gamma$-ray spectra in coincidence with the 92-keV (a,b) and 704-keV (c) transitions. The 92-keV $\gamma$ and 704-keV lines correspond to the $\beta \text{−}\gamma$ decay and $\beta \text{−}n\text{−}\gamma$ decay of ${}^{87}\mathrm{As}$, respectively.

Figure 3

Partial experimental decay scheme of ${}^{87}\mathrm{As}$. The $Q_{\beta }$ and $S_n$ energies are taken from Ref. [17]. See text for details.

Figure 4

Experimental and shell-model predictions of low energy excited states in even-$Z,N=53$ isotones. Data from the present work and from Refs. [7, 30]. All energies are in keV. See text for details.