Fission of <math><mmultiscripts><mi>Fr</mi><mprescripts/><none/><mn>215</mn></mmultiscripts></math> studied with <math><mi>γ</mi></math> spectroscopic methods

International audienceBackground: Asymmetric fission is known to occur in two regions, the actinides and sublead, and is dependent on the fissioning system excitation energy. Experimental evidence in the sublead region show that this mode is surprisingly persistent with increasing energy and its origin is not fully understood.Purpose: To experimentally study the fusion-fission reaction of Fr215 at moderate excitation energy and determine previously unknown independent fission yields and other properties.Method: The compound nucleus was formed in the reaction O18+Au197. The prompt γ rays emitted during the reaction were measured with the high efficiency and high granularity ν-ball-2 spectrometer. Independent fission yields of even-even nuclei were determined by detecting triple-gamma cascades in the fission fragments.Results: The observed yields, although dominated by a symmetric peak, show maxima for heavy fragment of Z≈54–56, which is consistent with the known results in the actinide region but unexpected for the nuclide of interest, and at the studied excitation energy.Conclusions: The mode of asymmetric fission is present even at relatively high excitation energies in the system studied. This observation matches experimental findings in the sublead region, contrary to the actinides, and so far there is no well-developed explanation of this phenomenon

Study of N=50N=50 gap evolution around Z=32Z=32: new structure information for 82{}^{82}Ge

International audienceMedium spin states of light N = 50 isotones have been populated using fast neutron-induced fission of ${}^{232}$Th. Online prompt $\gamma$ spectroscopy has been performed using the hybrid $\gamma$ spectrometer $\nu \text {-}$Ball coupled to the LICORNE directional neutron source at the ALTO facility of IJCLab. Medium spin states of the neutron-rich nucleus ${}^{82}$Ge have been investigated using $\gamma$-$\gamma$ and $\gamma$-$\gamma$-$\gamma$ coincidence data to exploit the resolving power of $\nu \text {-}$Ball. Two new transitions were assigned to this nucleus and a new level was placed in the level scheme. We tentatively assigned to this new state a ($7^{+}$) spin-parity, which is interpreted as a new $N=50$ core breaking state. This provides further insight into the energy evolution of the $N=50$ shell gap toward ${}^{78}$Ni