We predict the existence of medium spin PDR and find experimental evidence in ⁸⁰Ge using β-decay of ⁸⁰Ga. This nucleus was produced in the photo-fission of ²³⁸U. A hybrid γ-ray spectrometer was developed using a plastic detector for β-tagging, HPGe detectors for low-energy γ rays detection and phoswich detectors of PARIS for high-energy γ rays. The low-high energy coincidence spectrum shows two peaks at 7181(53) and 7337(53) keV in the β-decay of the ^80mGa isomeric state only, in coincidence with the 2₁⁺ → 0⁺ transition of ⁸⁰Ge. Combined with decay information, electric dipole character (E1) were assigned to these γ rays which de-excite 7.84 MeV and 7.996 MeV states. Based on this fact and the comparison with theoretical calculations, we conclude that these enhanced E1 transitions are driven by neutron-skin oscillation of ⁸⁰Ge. The oscillation is triggered by a conversion of a deeply-bound neutron from the Z=N=28 proton-neutron saturated core into a proton in the Fermi surface. These results provide an evidence for a PDR state with spin different from 1⁻ and built on a low-energy excited state. Consequently, it extends the PDR’s boundary along spin dimension for the first time and provides experimental data for testing the validity of the Brink-Axel hypothesis in the PDR region.

Elastic scattering of fast neutrons at an incident energy of 30.8 MeV on a natural cerium target was measured during an experiment conducted at the Neutrons For Science facility at GANIL-SPIRAL2. This is the first measurement on cerium using incident neutron energy above 20 MeV. The differential cross-section up to 40 $$^\circ $$ ∘ in the centre-of-mass frame was extracted using the MONSTER liquid scintillator array for the scattered neutron detection. The experimental results are compared to global optical-model calculations, providing an overall very good agreement and a useful benchmark at intermediate energy.

In this paper we present results from two recent studies, both related to the emission of prompt fission γ rays. Firstly, we have analyzed data from the reaction 235U(n, f) induced by fast neutrons of average energy = 1.7 MeV. The deduced spectral characteristics are an average multiplicity = 7.11 ± 0.44 γ rays per fission and an average total γ-ray energy release in fission = 5.51 ± 0.46 MeV, corresponding to an average γ-ray energy = 0.77 ± 0.08 MeV. Secondly, we have addressed – and answered – the question how those characteristics in general depend on the width of the chosen prompt time window and the timing resolution, determined by the employed detectors and electronics. The conclusion is that once this is known, it is possible to compare results from different experiments in a more meaningful way.

In nuclear fission, the primary fragments deexcite through the emission of neutrons and $\ensuremath{\gamma}$ rays. This prompt emission conveys information about the initial angular momentum and excitation energy of the fragments at scission and is therefore important for improved understanding and modeling of the fission process. A long-standing question is how much the angular momentum $J$ of a fragment is changed after scission due to the evaporation of neutrons. Though few experimental data are available, the consensus has been that the neutrons carry only a small amount of $J$ on average (around $0.5\ensuremath{\hbar}$ per neutron), while the majority (typically $6\ensuremath{\hbar}--7\ensuremath{\hbar}$) is removed via $\ensuremath{\gamma}$-ray emission. This consensus was recently challenged [I. Stetcu et al., Phys. Rev. Lett. 127, 222502 (2021)], instead suggesting values $>1.2\ensuremath{\hbar}$ per neutron. Since the question of how much neutron emission impacts $J$ is important for understanding fission fragment deexcitation, we seek here to put experimental constraints on this value. An experiment was carried out with the nu-Ball2 Ge detector array to perform $\ensuremath{\gamma}$-ray spectroscopy of fission fragments produced in the $^{238}\mathrm{U}(n,\mathrm{f})$ reaction. A spectroscopic method [Y. Abdelrahman et al., Phys. Lett. B 199, 504 (1987)] was employed to determine average angular momenta after neutron emission for even-even fission fragments. By simultaneously selecting $\ensuremath{\gamma}$ rays from both a particular fission fragment and its partner fragment, the total number of neutrons emitted could be deduced in each event. The average fragment ${J}_{\text{e}}$ is extracted from measurements of the yrast feeding pattern of the selected fragment. Here we investigate the dependence of this observable on the number of neutrons emitted by studying 53 different fragment pairs. The uncertainty weighted dependences of the average change in entry-line spin with the total number of neutrons emitted are $(\ensuremath{-}0.03\ifmmode\pm\else\textpm\fi{}0.03)\ensuremath{\hbar}$ and $(\ensuremath{-}0.21\ifmmode\pm\else\textpm\fi{}0.04)\ensuremath{\hbar}$ for the light and heavy fragments, respectively. These results are interpreted in combination with other recent works in the literature.