The s -process in the Nd-Pm-Sm region: Neutron activation of $^{147}$Pm
Résumé
The Nd-Pm-Sm branching is of interest for the study of the s -process, related to the production of heavy elements in stars. As 148 Sm and 150 Sm are s -only isotopes, the understanding of the branching allows constraining the s -process neutron density. In this context the key physics input needed is the cross section of the three unstable nuclides in the region: 147 Nd (10.98 d half-life), 147 Pm (2.62 yr) and 148 Pm (5.37 d). This paper reports on the activation measurement of 147 Pm, the longest-lived of the three nuclides. The cross section measurement has been carried out by activation at the SARAF LiLiT facility using a 56(2) μg target. Compared to the single previous measurement of 147 Pm, the measurement presented herein benefits from a target 2000 times more massive. The resulting Maxwellian Averaged Cross Section (MACS) to the ground and metastable states in 148 Pm are 469(50) mb and 357(27) mb. These values are 41% higher (to the ground state) and 15% lower (to the metastable state) than the values reported so far, leading however to a total cross section of 826(107) mb consistent within uncertainties with the previous result and hence leaving unchanged the previous calculation of the s -process neutron density.