Abstract
The neutron capture cross section of 185Re was measured in the astrophysically important energy region. Measurements were made using a neutron beam from a 7Li(p,n)7Be neutron source with energies ranging from 3 to 90 keV. Two different experimental techniques, time-of-flight (TOF) and activation methods, were employed. In the TOF experiments, the total neutron capture cross section of 185Re was determined by the pulse-height weighting technique. In the activation method, the partial capture cross section leading to the ground state of 186Re was measured by detecting decay γ-rays from neutron activated samples. The present cross section values were compared with evaluated cross section data and previous measurements. The difference between the TOF and activation results was smaller than experimental uncertainties. This suggests that the production cross section of isomer states of 186Re is very small.
Highlights
A Re/Os nucleo-cosmochronometer has been proposed to date a rapid neutron-capture process (r-process) in nucleosynthesis [1]
We experimentally determined the total capture cross section of 185Re by the time-of-flight (TOF) method, and the partial capture cross section leading to the ground state of 186Re by the activation method
The rhenium sample was sandwiched between two gold samples with the same diameter and placed at a distance of 2 cm from the 7Li(p, n)7Be neutron source for irradiation
Summary
A Re/Os nucleo-cosmochronometer has been proposed to date a rapid neutron-capture process (r-process) in nucleosynthesis [1]. Rhenium-187 is primarily considered a pure r-process nuclide and has a long half-life of 43.5 Gyr. the 187Re/187Os abundance ratio changing with the 187Re half-life can be a good chronometer for the r-process. Slow neutron-capture process (sprocess) through an isomer state of 186Re (T1/2 = 0.2 Myr) may contaminate the 187Re/187Os abundance ratio [2]. It is necessary to evaluate a contribution from 186mRe created from the 185Re(n, γ)186mRe reaction. We experimentally determined the total capture cross section of 185Re by the time-of-flight (TOF) method, and the partial capture cross section leading to the ground state of 186Re by the activation method. The production cross section of the isomer state of 186Re is discussed from a difference between the two different technique measurements
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