Spectroscopy of $^{257,258}$Db in the vicinity of the N=152 deformed shell gap

Abstract : Investigations on the nuclear structure in the region around N = 152 deformed shell gap provide an understanding of the existence of superheavy elements (Z > 104). Recent experimental studies have lead to the determination of the size and the strength of this gap. Its influence was studied for nuclei like $^{255}_{103}$Lr$_{152}$ and $^{256}_{104}$Rf$_{152}$. Valuable information can be obtained by studying further the evolution of the N = 152 deformed shell gap. To this purpose, the isotopes of $^{257}_{105}$Db and $^{258}_{105}$Db were produced and are the subject of this work. Even though these two isotopes were previously studied, the currently available data are limited and the level schemes are still not fully determined. The $^{257}$Db was produced through the fusion-evaporation reaction $^{209}$Bi($^{50}$Ti,2n)$^{257}$Db at GANIL. The two previously observed long lived states of $^{257}$Db were confirmed in this experiment, as well as the two isomeric states of $^{253}$Lr. The $^{258}$Db was produced through the fusion-evaporation reaction $^{209}$Bi($^{50}$Ti,1n)$^{258}$Db at GSI. A strong indication of the existence of two states in $^{258}$Db with different half lives was observed. A new $\gamma$-ray transition of $^{250}$Md was identified and its placement in the partial level scheme is proposed. The $\alpha$ decay of $^{258}$Rf was also observed, suggesting a smaller branching ratio than previously reported.
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M. Vostinar. Spectroscopy of $^{257,258}$Db in the vicinity of the N=152 deformed shell gap. Nuclear Experiment [nucl-ex]. Université de Caen Normandie, 2015. English. ⟨tel-01242802⟩

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