Statistical gamma-ray decay studies at iThemba LABS

Abstract. A program to study the γ -ray decay from the region of high-level density has been established at iThemba LABS, where a high-resolution gamma-ray detector array is used in conjunction with silicon particle-telescopes. Results from two recent projects are presented: 1) The 74Ge(α, α γ ) reaction was used to investigate the Pygmy Dipole Resonance. The results were compared to (γ,γ ) data and indicate that the dipole states split into mixed isospin and relatively pure isovector excitations. 2) Data from the 95Mo(d,p) reaction were used to develop a novel method for the determination of spins for low-lying discrete levels utilizing statistical γ -ray decay in the vicinity of the neutron separation energy. These results provide insight into the competition of (γ ,n) and (γ,γ ) reactions and highlights the need to correct for angular momentum barrier effect

Nuclear level densities and γ\gamma-ray strength functions of 87Kr^{87}\mathrm{Kr} -- First application of the Oslo Method in inverse kinematics

The $\gamma$-ray strength function ($\gamma$SF) and nuclear level density (NLD) have been extracted for the first time from inverse kinematic reactions with the Oslo Method. This novel technique allows measurements of these properties across a wide range of previously inaccessible nuclei. Proton-$\gamma$ coincidence events from the $\mathrm{d}(^{86}\mathrm{Kr}, \mathrm{p}\gamma)^{87}\mathrm{Kr}$ reaction were measured at iThemba LABS and the $\gamma$SF and NLD in $^{87}\mathrm{Kr}$ obtained. The low-energy region of the $\gamma$SF is compared to Shell Model calculations which suggest this region to be dominated by M1 strength. The $\gamma$SF and NLD are used as input parameters to Hauser-Feshbach calculations to constrain $(\mathrm{n},\gamma)$ cross sections of nuclei using the TALYS reaction code. These results are compared to $^{86}\mathrm{Kr}(n,\gamma)$ data from direct measurements

First application of the Oslo method in inverse kinematics

International audienceThe $\gamma$-ray strength function ($\gamma$SF) and nuclear level density (NLD) have been extracted for the first time from inverse kinematic reactions with the Oslo method. This novel technique allows measurements of these properties across a wide range of previously inaccessible nuclei. Proton–$\gamma$ coincidence events from the $\mathrm {d}(^{86}\mathrm {Kr}, \mathrm {p}\gamma )^{87}\mathrm {Kr}$ reaction were measured at iThemba LABS and the $\gamma$SF and NLD in $^{87}\mathrm {Kr}$ was obtained. The low-energy region of the $\gamma$SF is compared to shell-model calculations, which suggest this region to be dominated by M1 strength. The $\gamma$SF and NLD are used as input parameters to Hauser–Feshbach calculations to constrain $(\mathrm {n},\gamma )$ cross sections of nuclei using the TALYS reaction code. These results are compared to $^{86}\mathrm {Kr}(n,\gamma )$ data from direct measurements

Signature splitting of the g7/2[404]7/2+{g}_{7/2}[404]{7/2}^{+} bands in 131Ba^{131}\mathrm{Ba} and 133Ce^{133}\mathrm{Ce}

International audienceExcited states in Ba131 and Ce133 were studied using in-beam γ-ray spectroscopy through the Sn122(C13,4n)Ba131 and Te125(C12,4n)Ce133 reactions, respectively. A strongly coupled band, associated with the νg7/2[404]7/2+ configuration, was identified in Ba131 and Ce133. It is the first time to observe the νg7/2[404]7/2+ bands in the N=75 isotones. The signature partners exhibit considerable energy splitting in comparison with those in the πg7/2[404]7/2+ bands in the odd-A Ta and Re isotopes. Extensive cranked shell model and quasiparticle-plus-triaxial-rotor model calculations reveal the origin of the signature splitting, which depends not only on the triaxiality, but also on the configuration mixing with nearby low-j orbitals