High-Precision Mass Measurements of Proton-Rich Rh, Pd, Cd isotopes in the vicinity of 100Sn and Impact on X-Ray Burst and Supernova Nucleosynthesis

Abstract

Using the ZeroDegree multi-reflection time-of-flight mass spectrograph of the CRISMASS project at RIKEN Radioactive Isotope Beam Factory, we performed high-precision mass measurements of proton-rich nuclei near the doubly magic nucleus 100Sn, achieving uncertainties on the order of 10 keV. The masses of 91Rh, 92Pd, and 96Cd were determined for the first time with high precision, and the accuracy of several additional masses was substantially improved. Incorporating the new data into X-ray burst simulations significantly reduces the abundance uncertainties in the $A$ = 90-100 region, shifting the reaction flow toward $A$ = 90 production and suppressing the synthesis of heavier nuclei. Further investigation of the $νp$-process indicates that 99Rh plays a significant role in the reaction flow within the mass region studied. These high-precision mass measurements refine the mass surface near 100Sn and provide critical constraints on models of proton-rich nucleosynthesis.

Figures (4)

• Figure 1: Schematic reaction flows of $rp$ -(a) and $\nu p$ (b)-processes. Nuclides included in the updated $rp$ and $\nu p$ -process calculations are indicated by the blue boxes, while stable nuclides are shown as the black squares. The thick (thin) arrows indicate the main (secondary) reaction flow branches.
• Figure 2: TOF spectra coverted to the mass excess scale for the isobaric chains with $\textsl{A}$ = (a) 91, (b) 92, and (c) 96, measured with the MRTOF-MS. The spectra include the contributions from proton-rich nuclei of interest as well as contaminant species. For $^{16}$O$^{32}$S in (c), the mass excess shown corresponds to twice its actual value. Prominent peaks corresponding to the identified nuclides are labeled. The most intense peaks in each spectrum ($^{91}$Ru, $^{92}$Ru, and $^{96}$Pd) were used to determine the peak-shape parameters employed in the fitting procedure.
• Figure 3: Comparison of the final abundance in ashes from AME2020 (blue line with shadow) and new masses (with 1$\sigma$ uncertainty) measured by the MRTOF (red line with shadow). The bottom panel shows the ratio of these final abundances.
• Figure 4: X-ray luminosity as a function of time using AME2020 masses (blue line with shadow) and new masses (red line with shadow, 1$\sigma$ uncertainty). The bottom panel shows the ratio of luminosity.