Astrophysical significance of the isomer $^{119m}$Ag demonstrated through direct mass measurement

Abstract

The abundance of elements heavier than iron produced via the astrophysical rapid-neutron capture process depends sensitively on the atomic mass of the involved nuclei as well as the behavior of a few special types of nuclear isomers called astromers. High-precision mass measurements of $^{119}$Cd, $^{119}$Ag and their respective isomeric states have been performed with the Phase Imaging-Ion Cyclotron Resonance (PI-ICR) method with a precision of $δm/m \approx 10^{-8}$ using the Canadian Penning Trap (CPT). The ground state mass excess, as well as the excitation energy, agrees with recent Penning Trap measurements from JYFLTRAP. Network calculations using these new measurements revealed that, contrary to previous expectations, $^{119m}$Ag behaves as an astromer which significantly affects the population of $^{119}$Ag.

Figures (6)

• Figure 1: Typical 2D histogram of ion hits on the PS-MCP after a final measurement phase. This image is from a measurement of the ground state of $^{119}$Ag with $t_{acc}$=710.324 ms. During this particular run, the PS-MCP would typically record a single ion per trap ejection, and the spots shown in this plot are those where fewer than 3 ions hit the PS-MCP in a single trap ejection. The ground state and isomer states of Ag are clearly separated.
• Figure 2: Data (in blue) and sinusoidal fit (in red) of the $^{119}$Ag$^+$ ground state measurement, using the model in Orford2020. The dark gray line represents the true cyclotron frequency, and the lighter gray band is the statistical uncertainty.
• Figure 3: Mass excesses of the ground state and isomeric states of $^{119}$Cd and $^{119}$Ag as compared to the AME2020 value. JYFLTRAP measurements for Cd and Ag are from Jaries2023 and deGroote2024, respectively.
• Figure 4: Isomer excitation energies for $^{119}$Cd and $^{119}$Ag, relative to their respective ground states, as determined by this work, NUBASE 2020, and recent publications.
• Figure 5: Reaction rates used in the presented calculations as function of thermalization temperature. Shown are the rate of thermal excitation of the ground state $\Lambda_{1,2}$ (solid red), the effective de-excitation rate from the isomeric state $\Lambda_{2,1}$ (dotted green), as well as the respective $\beta$-decay rates of the ground state ($\Lambda_{1 \beta}$, dashed red), and isomer state ($\Lambda_{2 \beta}$, dashed green). The vertical dashed line at 18.7 keV indicates the temperature below which thermal equilibrium between the two states breaks.