Constraining the Synthesis of the Lightest p Nucleus 74Se

Abstract

We provide the first experimental cross section of the $^{73}\text{As}(p,γ)^{74}\text{Se}$ reaction to constrain one of the main destruction mechanisms of the p nucleus $^{74}\text{Se}$ in explosive stellar environments. The measurement was done using a radioactive $^{73}\text{As}$ beam at effective center-of-mass energies of 2.9 and 2.3 MeV/nucleon. Along with the total cross-section measurement, statistical properties of the $^{74}\text{Se}$ compound nucleus were extracted, constraining the reaction cross section in the upper Gamow window of the $γ$ process. The impact of the experimentally constrained reaction rate on $^{74}\text{Se}$ production in Type II supernovae was investigated through Monte Carlo one-zone network simulations. The results indicate that the overproduction of $^{74}$Se by Type II supernova models cannot be resolved by nuclear physics alone and point toward the need for a more detailed understanding of the astrophysical conditions of relevance for the $γ$ process.

Figures (4)

• Figure 1: Doppler-corrected TAS spectra showing the background subtraction for the sum peak for the $^{73}\text{As}(p,\gamma)^{74}\text{Se}$ reaction at beam energy of 3.7 MeV/nucleon. The black histogram corresponds to the gas cell filled with hydrogen gas, the orange histogram corresponds to the empty gas cell scaled, and the blue histogram is the fully subtracted sum peak with the band indicating the statistical uncertainty of the background subtraction.
• Figure 2: The measured cross section of the $^{73}\text{As}(p,\gamma)^{74}\text{Se}$ reaction (black dots) compared with standard Non-Smoker theoretical calculations nonsmoker, represented by a red dashed line, and default Talys 1.96 calculations talys, depicted in blue lines. The color coding of the Talys calculations reflects the ability of each model combination to simultaneously describe the experimental spectra and the calculated cross section. More details in text.
• Figure 3: The $\chi^2$ minimization fits of the SoS spectrum for the $^{73}\text{As}(p,\gamma)^{74}\text{Se}$ reaction at a beam energy of 3.7 MeV/nucleon. The black line represents the experimental spectrum, and the various blue lines correspond to the simulated spectra for the combinations of the NLD and $\gamma$SF models from Talys 1.96. The varying shades of blue in each line reflect different scores, where darker tones represent a better description of the experimental spectrum.
• Figure 4: Final $^{74}\text{Se}$ mass fraction produced during a 20 $M_\odot$ CCSN as a function of time calculated using NuGrid ppn one-zone simulations herwig_2008_nugridPignatari_herwig_2012_nugrid (see text for details). The blue band corresponds to the 95th percentile of the MC sampled $^{73}\text{As}(p,\gamma)^{74}\text{Se}$ reaction rates with the median prediction shown in a darker blue line. The red dashed line corresponds to the default JINA-REACLIB reaction rate Cyburt_2010_reaclib and the orange dotted lines to the minimum and maximum reaction rates from Talys 1.96. The inset shows the final $^{74}\text{Se}$ mass fraction distribution obtained in the MC simulations relative to JINA-REACLIB.