Measurement of the Ge70(n,γ) cross section up to 300 keV at the CERN n_TOF facility

Abstract

Neutron capture data on intermediate mass nuclei are of key importance to nucleosynthesis in the weak component of the slow neutron capture processes, which occurs in massive stars. The (n, γ) cross section on 70 Ge, which is mainly produced in the s process, was measured at the neutron time-of-flight facility n_TOF at CERN. Resonance capture kernels were determined up to 40 keV neutron energy and average cross sections up to 300 keV. Stellar cross sections were calculated from kT = 5 keV to kT = 100 keV and are in very good agreement with a previous measurement by Walter and Beer (1985) and recent evaluations. Average cross sections are in agreement with Walter and Beer (1985) over most of the neutron energy range covered, while they are systematically smaller for neutron energies above 150 keV. We have calculated isotopic abundances produced in s-process environments in a 25 solar mass star for two initial metallicities (below solar and close to solar). While the low metallicity model reproduces best the solar system germanium isotopic abundances, the close to solar model shows a good global match to solar system abundances in the range of mass numbers A = 60-80.

Measurements of the 107 Ag neutron capture cross sections with pulse height weighting technique at the CSNS Back-n facility

“…The neutron capture cross sections between 1 eV and 60 eV were analyzed using the R-matrix SAMMY code [48] which takes into account all experimental effects, such as multiple interaction events (multiple scattering), self shielding, the broadening of resonances due to thermal motion (doppler broadening) and the resolution of the experimental setup. In addition, the full sample composition, including impurities, was taken into account [49] in simulation. There are some individual resonance parameters, such as resonance spin 𝐽 , neutron and radiative partial decay widths Γ n and Γ γ , which can be determined in fitting data.…”

n_TOF: Measurements of Key Reactions of Interest to AGB Stars

“…To date, at n_TOF, we have studied 4 of the 33 s-only isotopes along the s-process path: 58 Ni [46], 70 Ge [64], 154 Gd [65] and 186 Os [66,67]. Moreover, we plan to measure 94,96 Mo(n,γ) in the near future.…”

The status and future of direct nuclear reaction measurements for stellar burning

“…The TAC system offers the advantage of Q-value separation to separate capture on different isotopes or materials in the sample. Together, resonance analysis and cross section measurements have come from the n TOF neutron capture program on a wide range of isotopes for nuclear astrophysics, 70 Ge [252] and 171 Tm [253].…”