Investigation of high-spin states in ${}^{53}\mathrm{Fe}$

The fusion-evaporation reactions ${}^{28}\mathrm{Si}({}^{32}\mathrm{S},1\alpha 2p1n){}^{53}\mathrm{Fe}$ at 125 MeV and ${}^{24}\mathrm{Mg}({}^{32}\mathrm{S},2p1n){}^{53}\mathrm{Fe}$ at a 95-MeV beam energy were used to investigate excited states in ${}^{53}\mathrm{Fe}$. The combination of the Gammasphere Ge detector array and ancillary devices led to the construction of an extensive level scheme comprising some 90 transitions connecting 40 states. The lifetime of the yrast $25/2^{-}$ state and upper limits for the lifetimes of a number of additional states were determined using the Cologne plunger device coupled to the GASP γ-ray spectrometer. The experimental results are compared to large-scale shell-model calculations using different sets of two-body matrix elements. In particular, predictions on electromagnetic decay properties such as lifetimes, branching ratios, and mixing ratios are studied in detail.

Figure 1

The proposed level scheme of ${}^{53}\mathrm{Fe}$. The top panel (a) provides the “low-spin” regime, which was in part known from previous studies [3], whereas the bottom panel (b) focuses on the “high-spin” part, which is built on the 3041-keV $19/2^{-}$ spin gap isomer. Energy lables are in kilo-electron-volts. The thickness of the arrows corresponds to the relative intensities of the transitions. Tentative transitions are dashed.

Figure 2

γ-ray spectrum in coincidence with one α particle, two protons, and one neutron from the two Gammasphere experiments. Small contaminations from ${}^{52}\mathrm{Mn}$, ${}^{54,55}$Fe, and ${}^{56}\mathrm{Co}$ were carefully substracted (see text for details). The most intense transitions are labeled with their energies in kilo-electron-volts.

Figure 3

γ-ray spectra in coincidence with one α particle, two protons, and one neutron from the two Gammasphere experiments. Panel (a) is in coincidence with the 1134-keV $9/2^{-}\to \hspace{1em}5/2^{-}$ transition decaying from the 2558-keV level, panel (b) is in coincidence with the 2445-keV doublet decaying from the 3774- and 4785-keV levels, respectively, and panel (c) is in coincidence with the intense 287-keV $15/2^{-}\to \hspace{1em}13/2^{-}$ yrast transition. These three spectra provide examples for the data quality of the low-spin part of the level scheme of ${}^{53}\mathrm{Fe}$ shown in Fig. 1a. Panels (d) and (e) are in coincidence with the 963-keV $25/2^{-}\to \hspace{1em}21/2^{-}$ yrast transition and the high-energy 4362-keV $27/2\to \hspace{1em}25/2^{-}$ transition, respectively. They illustrate the newly established high-spin part of the level scheme of ${}^{53}\mathrm{Fe}$ displayed in Fig. 1b. The energy labels next to the peaks are in kilo-electron-volts.

Figure 4

Decay curve of the unshifted component of the 963-keV transition in ${}^{53}\mathrm{Fe}$ for 13 effective flight distances measured in coincidence with the shifted component of the 1771-keV transition.

Figure 5

Experimental and calculated excitation energies for the observed yrast sequence between $I^{\pi }=7/2^{-}$ and $I^{\pi }=29/2^{-}$ states. For all calculated states the binding energy shift (cf. Table ) has been added to the excitation energies.