Penning-trap-assisted study of excitations in ${}^{88}\mathrm{Br}$ populated in $\beta$ decay of ${}^{88}\mathrm{Se}$

Excited levels of ${}^{88}\mathrm{Br}$ populated in the $\beta$ decay of ${}^{88}\mathrm{Se}$ have been studied by means of $\beta \gamma$ and $\gamma \gamma$ spectroscopy methods. Neutron-rich parent ${}^{88}\mathrm{Se}$ nuclei were produced with proton-induced fission of ${}^{238}\mathrm{U}$ using the Ion Guide Isotope Separator On-Line (IGISOL) method and separated from contaminants using a dipole magnet and the coupled JYFLTRAP Penning trap at the Accelerator Laboratory of the University of Jyväskylä. The level scheme of ${}^{88}\mathrm{Br}$ has been constructed and $logft$ values of levels were determined. The ground-state spin of ${}^{88}\mathrm{Br}$ is now firmly determined to be $1^{-}$. Low-energy levels in ${}^{88}\mathrm{Br}$ were interpreted as members of the $\pi p_{3/2}{\left(\nu d_{5/2}\right)}^3, \pi p_{3/2}^{-1}{\left(\nu d_{5/2}\right)}^3, \pi f_{5/2}^{-1}{\left(\nu d_{5/2}\right)}^3$, and $\pi g_{9/2}\nu g_{7/2}$ multiplets. The shell-model calculations performed in this work reproduce well the experimental results.

Figure 1

Ion counts registered in the experiment using the MCP detector placed after the Penning trap. The well resolved singly charged ions from the IGISOL isobaric beam of mass $A=88$ are marked with their element symbol.

Figure 2

Schematic view of the experimental setup. The monoisotopic ion samples released from JYFLTRAP (A) are implanted in the middle of a spectroscopic array consisting of a $\beta$ counter (B) and seven Ge detectors (C). The moving tape collector device (D) is operating the implantation tape and removing unwanted long-lived decay products from the center of the setup.

Figure 3

A $\beta$-gated, singles $\gamma$-ray spectrum obtained in the present experiment. Energies of $\gamma$ lines are labeled in keV. A nonlinear, constant-peak-width energy calibration was applied to enhance the low-energy part of the spectrum, where the density of lines is high.

Figure 4

A $\beta$-decay scheme of ${}^{88}\mathrm{Se}$, as observed in the present work. $T_{1/2}$ and $Q_{\beta }$ values are taken from [14].

Figure 5

Examples of $\beta$- and $\gamma$-gated spectra, obtained in this work. Peaks are labeled in keV. The arrow in panel (a) marks the position of the 272.8-keV energy.

Figure 6

Scheme of the idea of direct $\beta$ feeding in $\beta$ decay proposed by Lin et al. [16].

Figure 7

Comparison of excited levels in ${}^{88}\mathrm{Br}$, observed in this work, to the present shell-model calculations. Calculations are normalized to the experiment at the $1_1^{-}$ level. The experimental levels with spin 4 and 5 are taken from Ref. [2].