Abstract
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 148Sm and 150Sm 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: 147Nd (10.98 d half-life), 147Pm (2.62 yr) and 148Pm (5.37 d). This paper reports on the activation measurement of 147Pm, 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 147Pm, 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 148Pm 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.
Highlights
Introduction and motivationMost of the elements in our universe are produced in a nucleosynthesis process in the stars that consists of a chain of neutron capture reactions and β-decays
Regarding the partial contributions to the overall systematic uncertainty, the dominant components are the 4.3% of the 147Pm target mass, the 2%, 4% and 9% in the calculated number of 198Au, 148mPm and 148gPm nuclei, the 3% in the correction related to the different beam intensity intersecting the Pm and the monitor Au target and, in the case of capture to 148mPm, the 3% related to the amount of 148mPm in the target before the irradiation at LiLiT
These partial cross sections are significantly different (−15% and +41%) from the only other experimental values available
Summary
Most of the elements in our universe are produced in a nucleosynthesis process in the stars that consists of a chain of neutron capture reactions and β-decays. In previous work related to the branching in the region A = 147/148, Reifarth et al [21] estimated a value of 4.9(5) × 108 cm−3 for the neutron density in the He-burning shell of low-mass AGB stars from their measured values of the 147Pm(n, γ )148g,mPm reactions cross sections, which was the only measurement to date. This measurement was made with only 28.7 ng of 147Pm which required using a close geometry detection set-up and measuring decay cascades instead of individual γ -rays.
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