Experimental constraints on $γ$-ray strength function of $^{72}$Ga from $^{72}\mathrm{Ga(n,γ)^{72}Ga}$ capture data and reevaluation of Maxwellian-averaged cross sections of $^{71}$Ga

TL;DR

The paper addresses constraining the $^{72}$Ga $\gamma$-ray strength function from $^{71}$Ga$(n,\gamma)^{72}$Ga capture data and uses this to reevaluate the MACS of $^{71}$Ga. It employs a Hauser–Feshbach statistical-model framework with a fixed neutron optical-model potential and $^{72}$Ga NLD constrained by recent experimental data, testing several $\gamma$SF models and finding the Gogny D1M HFB+QRPA description with a low-energy upbend to be superior. The best-fit parameters—and the finding that the E1 channel dominates the capture cross section with a substantial low-energy upbend—are quantified, with uncertainties primarily driven by the NLD. The resultant MACS at $kT=30$ keV is $115.35^{+11.92}_{-10.44}$ mb, broadly consistent with prior studies, supporting robust reaction-rate inputs for s-process modeling. Overall, the work demonstrates how combining microscopic $\gamma$SF modeling with experimental capture data can meaningfully constrain reaction rates for medium-mass, neutron-rich nuclei.

Abstract

The $γ$-ray strength function of medium-mass neutron rich nuclei $^{72}$Ga has been extracted from the statistical Hauser-Feshbach analysis of the available capture data of $^{71}\mathrm{Ga}(n,γ){}^{72}\mathrm{Ga}$ over the 0.01 - 3 MeV energy range with the required nuclear level density (NLD) of the $^{72}$Ga constraint from the work of R. Santra et al.,[\href{https://doi.org/10.1103/PhysRevC.107.064611}{Physical Review C 107, 064611 (2023)}]. The Gogny D1M model for the E1 and M1 strength functions, including low-energy upbends of $^{72}$Ga nuclei, is experimentally constrained in the present work. Subsequently, the Maxwellian-averaged cross section(MACS) of $^{71}\mathrm{Ga}$ has been reevaluated based on the present $γ$-ray strength function. It is found that the present MACS value at \(kT = 30\) keV is 115.35$^{+11.92}_{-10.44}$ mb, which is consistent with previous work.

Figures (6)

• Figure 1: The statistical model Calculation with Gogny D1M HFB+QRPA model $\gamma$SF for the $^{71}$Ga$(n,\gamma)$$^{72}$Ga capture cross-section and compare with available experimental data.The blue and red solid lines represent the capture cross-sections with the default Gogny model and with adjustments to $\gamma$SF parameters. The dashed blue and black lines are the E1 and M1 $\gamma$SF contribution in capture cross-sections.
• Figure 2: Correlation matrix of the best fitted parameters.
• Figure 3: The variations of upbend contribution of E1 $\gamma$SF with neutron energy.
• Figure 4: (a) The extracted $\gamma$SF with considering only (n, $\gamma$) capture data uncertainty.(b) The extracted $\gamma$SF with considering only the uncertainty in NLD of $^{72}$Ga. (c) The $\gamma$SF considering both uncertainties.
• Figure 5: The present $\gamma$SF of $^{72}$Ga compare with $^{73,74}$Ge ren2016$\gamma$SF which available in literature.