Properties of $\gamma$-decaying isomers in the ${}^{100}\mathrm{Sn}$ region populated in fragmentation of a ${}^{124}\mathrm{Xe}$ beam

A systematic study was performed of microsecond $\gamma$-decaying isomers around ${}^{100}\mathrm{Sn}$ produced in a fragmentation reaction of a ${}^{124}\mathrm{Xe}$ beam at 345 MeV/u at the Radioactive Ion Beam Factory of the RIKEN Nishina Center in Saitama, Japan. Half-lives of isomeric states in that region were remeasured allowing us to improve the currently available experimental information. Reduced transition probabilities were deduced and compared to shell-model calculations in various model spaces. The recently reported low-energy transitions in ${}^{92}\mathrm{Rh}$ and ${}^{96}\mathrm{Ag}$ were remeasured with improved precision. Additionally, experimental information on isomeric ratios, including five new ones, were extracted and compared to a previous experimental study and the sharp cutoff model of fragmentation reaction.

Figure 1

Particle identification plot of secondary ions produced in this experiment and implanted in the active stopper detector at the end of the ZeroDegree spectrometer (see text for details). Events from the identification of ${}^{100}\mathrm{Sn}$ isotopes are highlighted as a reference.

Figure 2

Time spectra and decay curves used to obtain the half-lives of $\gamma$-decaying isomers. The decay curves are fitted using a single exponential function (red) together with a constant or time-dependent background term (black). The on-peak gated time distributions are plotted in blue and the respective background counts are given as histograms in black. Each figure is labeled with the isotope, isomeric spin, parity, and its respective half-life.

Figure 3

Reduced transition probabilities for isomeric $\gamma$-ray transitions. Comparison between experimental and calculated transition strengths. See Table 1 for the description of the labels (a) and (b).

Figure 4

Time-delayed projected $\gamma$-ray energy between $400\le T_{\mathrm{DGF}}\le 1200\mathrm{ns}$. The inset shows the time spectrum and decay curve of the 55-keV transition. Note that this time spectrum was generated by increasing the upper time limit to $T_{\mathrm{DGF}}\le 3500\mathrm{ns}$.

Figure 5

(a) Partial $\gamma$-ray spectrum of ${}^{96}\mathrm{Ag}$ showing time-delayed $\gamma$-ray energies between 800 and 3400 ns. The inset shows the time distribution of the 44-keV transition in ${}^{96}\mathrm{Ag}$ obtained with a time window of $800\mathrm{ns}\le T_{\mathrm{DGF}}\le 20\mu \mathrm{s}$. (b) Projection of the $\gamma -\gamma$ matrix gated on 44 keV. The labeled peaks belong to transitions in ${}^{96}\mathrm{Ag}$ following the decay of the $\left({15}^{+}\right)$ isomer.

Figure 6

Isomeric ratios: comparison between experimental and theoretical values expressed as the ratio $R_{\mathrm{expt}}/R_{\mathrm{theor}}$. If not denoted otherwise, the theoretical isomeric ratios were calculated using $\nu =0.5$. For isomers with $J_m<J_{gs}$ the theoretical value was obtained using Eq. (10). Figure adapted from Ref. [42] and new experimental values are labeled with the respective isotope. In the case of ${}^{96}\mathrm{Cd}$ only one of the ratios, i.e., for the alternative assignment $\left({13}^{-}\right)$, has been plotted. For details see text and Table 2.