Se beams to inform weak r-process nucleosynthesis*

The mass-80 peak of the r-process abundance pattern is believed to be the product of a possible weak r-process that could occur in hot (~1 GK) environments such as core-collapse supernovae. Surman et al. assessed that neutron capture rates on unstable ^81,83Se isotopes had a significant effect on the calculated weak r-process abundance pattern [1]. However, for stable ⁸²Se there are limited (n,γ) data and the evaluated cross sections are inconsistent. To inform the contributions to the (n,γ) cross section from both direct and compound-nucleus processes, the (d,pγ) reaction with 8.4 MeV/u ⁸²Se beams and a 320 μg/cm² CD₂ target was measured at ATLAS. GODDESS was deployed to detect gamma rays in GRETINA in coincidence with reaction protons in ORRUBA. Beam-like recoils were analyzed in an ionization chamber. Spectroscopic factors have been extracted for the 1/2⁺ (540 keV) and 5/2⁺ (582 keV) exited states in ⁸³Se, which were then used to deduce the direct neutron-capture cross section. The resolving power of coincident charged particle and gamma-ray spectroscopy facilitated extending the spectroscopy of excited states in ⁸³Se.  Preliminary results for ⁸³Se excitations and the deduced (n,γ) cross sections will be presented. 

[1] R. Surman et al., AIP Advances 4, 041008 (2014)