21-29 July 2022
US/Pacific timezone

The Stellar $^{72}\mathrm{Ge}(n,\gamma)$ Cross Section for weak s-process: A First Measurement at n_TOF

26 Jul 2022, 06:24
Folsom ()



Mirco Dietz the n_TOF Collaboation


The slow neutron capture process (s-process) is responsible for producing about half of the elemental abundances heavier than iron in the universe. Neutron capture cross sections on stable isotopes are a key nuclear physics input for s-process studies. The $^{72}\mathrm{Ge}(n,\gamma)$ Maxwellian-Averaged Cross Section (MACS) has an important influence on production of isotopes between Ge and Zr in the weak s-process in massive stars [1] and so far only theoretical estimations are available [2].

An experiment was carried out at the neutron time-of-flight facility n$\_$TOF [3] at CERN to measure the $^{72}\mathrm{Ge}(n,\gamma)$ reaction for the first time at stellar neutron energies. At n$\_$TOF, the neutron beam covers a large energy range (few meV to several GeV). The capture measurement was performed using an enriched $^{72}\mathrm{GeO}_2$ sample at a flight path length of $184\,$m, which provided high neutron energy resolution. The prompt gamma rays produced after neutron capture were detected with a set of liquid scintillation detectors (C$_6$D$_6$). The neutron capture yield is derived from the counting spectra taking into account the neutron flux and the gamma-ray detection efficiency using the Pulse Height Weighting Technique [4].

Over $70$ new neutron resonances were identified, providing an improved resolved reaction cross section to calculate experimental MACS values for the first time. Furthermore, averaged resonance parameters such as $\langle \Gamma_\gamma \rangle$ and $D_0$ were derived from the resonance data. In summary, the experiment, data analysis and the new MACS results will be presented including their impact on stellar nucleosynthesis, which was investigated with $\mathsf{mppnp}$ [5] using a $25$ solar mass model.

[1] M. Pignatari et al., The Astroph. J. 33, 1557-1577 (2010).; [2] I. Dillmann et al., Nuclear Data Sheets 120, 171-174 (2014); (http://www.kadonis.org).; [3] C. Guerrero et al., Eur. Phys. J. A 49, 27 (2013).; [4] U. Abbondanno et al., Nucl. Instr. Meth. Phys. Res. A 521, 454-467 (2004).; [5] M. Pignatari et al., The Astroph. J.,Suppl. Ser. 225, 24 (2016).

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