Cross-section measurement of the ${}^{82}\mathrm{Kr}(p,\gamma ){}^{83}\mathrm{Rb}$ reaction in inverse kinematics

The total cross section of the ${}^{82}\mathrm{Kr}{(p,\gamma )}^{83}\mathrm{Rb}$ reaction was measured for the first time at effective center-of-mass energies between 2.4 and 3.0 MeV, within the relevant Gamow window for the astrophysical $\gamma$ process. The experiment took place at the National Superconducting Cyclotron Laboratory at Michigan State University using the ReA facility. A ${}^{82}\mathrm{Kr}$ beam was directed onto a hydrogen gas cell located at the center of the Summing NaI(Tl) (SuN) detector. The obtained spectra were analyzed using the $\gamma$-summing technique and the extracted cross section was compared to standard statistical model calculations using the non-smoker and talys codes. The comparison indicates that standard statistical model calculations tend to overproduce the cross section of the ${}^{82}\mathrm{Kr}(p,\gamma$)${}^{83}\mathrm{Rb}$ reaction relative to the experimentally measured values. Furthermore, the experimental data were used to provide additional constraints on the nuclear level density and the $\gamma$-ray strength function used in the statistical model calculations.

Figure 1

Doppler-corrected TAS spectra showing the background subtraction for the sum peak for the ${}^{82}\mathrm{Kr}{(p,\gamma )}^{83}\mathrm{Rb}$ reaction at the initial beam energy 3.7 MeV/nucleon. The black histogram corresponds to the gas cell filled with hydrogen gas, the red histogram corresponds to the empty gas cell scaled to the beam current, and the blue histogram is the fully subtracted sum peak that was used for the remaining analysis.

Figure 2

The ${\chi }^2$ minimization fits for the SoS (a), TAS (b), and multiplicity (c) for the ${}^{82}\mathrm{Kr}{(p,\gamma )}^{83}\mathrm{Rb}$ reaction at an initial beam energy of 3.7 MeV/nucleon. The black lines are the experimental spectra and the green bands indicate the simulated spectra for the combinations of the NLD and $\gamma \mathrm{SF}$ models chosen, taking into account all possible contributing $E_x$ of the ${}^{83}\mathrm{Rb}$ CN. In panel (a), the red and blue lines are the simulated spectra for the default initial parameters of the BSFG model and CT model NLD from Ref. [37] and $\gamma \mathrm{SF}$ from Ref. [38].

Figure 3

The measured cross section of the ${}^{82}\mathrm{Kr}{(p,\gamma )}^{83}\mathrm{Rb}$ reaction (black dots) compared with standard non-smoker theoretical calculations [28] (blue solid line) and default talys 1.96 calculations [43] (orange band). Standard statistical model calculations with the default models tend to overproduce the cross section relative to the experimentally measured values. A more consistent theoretical description of the experimental results is obtained in Sec. 5.

Figure 4

Decomposition plot of the $S$ factor for proton capture on ${}^{82}\mathrm{Kr}$. The dashed lines correspond to a standard talys calculation. The solid lines use an optimized set of parameters. See text for more details on the optimized parameters. The ${}^{79}\mathrm{Br}$ production by the ${}^{82}\mathrm{Kr}$($p,\alpha$)${}^{79}\mathrm{Br}$ reaction is below the scale of the figure.

Figure 5

Same as Fig. 3 with the addition of the green band, which corresponds to optimized talys calculations using the parameters for modeling the NLD and the $\gamma \mathrm{SF}$ of the ${}^{83}\mathrm{Rb}$ nucleus from Table 2, as well as a “jlm-type” potential and a strong WFC, as described in Sec. 5.