Spectroscopy of Neutron Induced Reactions with the $\nu $-ball Spectrometer

The $\nu$-ball is a high-efficiency hybrid spectrometer which consists of both germanium (Ge) detectors and associated anti-Compton BGO shields, coupled to lanthanum bromide (LaBr$_3$) detectors. The hybrid configuration provides a combination of both excellent energy and timing resolutions. The $\nu$-ball geometry allows the coupling with the LICORNE directional neutron source at the ALTO facility of the IPN, Orsay. This opens the possibility to perform precise spectroscopy of neutron induced reactions and was used for two experiments during the recent experimental campaign. These two experiments are described here: 1. Spectroscopy of the neutron-rich fission fragments produced in the $^{238}$U($n, f$) and $^{232}$Th($n, f$) reactions; 2. Spectroscopy above the shape isomer in $^{238}$U. The $^{238}$U($n, f$) and $^{232}$Th($n, f$) reactions produce hundreds of neutron-rich nuclei on which gamma-ray spectroscopy can be performed. The main goal of the experiment aiming to populate the shape isomer in $^{238}$U is the measurement of the gamma-ray and fission decay branches as well as determination of level scheme in the super-deformed minimum. The shape isomer is populated by $^{238}$U($n, n'$) reaction, which gives a very advantageous population cross section over other reactions. More detailed descriptions of these two $\nu$-ball experiments will be presented here.