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Impact of experimental mass of $^{70}$Kr on the $^{68}$Se waiting-point in $rp$-process

Min Zhang, Yudong Luo, Akira Dohi, Xing Xu, Xinliang Yan, Toshitaka Kajino, Yuhu Zhang, Meng Wang

TL;DR

This study links a precise experimental mass measurement of $^{70}$Kr, obtained with $B\rho$-defined isochronous mass spectrometry, to the astrophysical rp-process waiting point at $^{68}$Se in Type-I X-ray bursts. By feeding the new mass into a local network calculation and a one-zone XRB model, it shows that the more bound $^{70}$Kr increases the bypass via sequential $2p$-capture, shortening the effective lifetime of $^{68}$Se and enhancing rp-process heating. The result is a modest rise (~$10\%$) in the burst luminosity around $t\sim100$ s and a more pronounced SnSbTe signature in the final ashes, with the magnitude of the effect tied to the $^{70}$Kr mass uncertainty. This work demonstrates the critical role of precise nuclear masses in shaping XRB light curves and nucleosynthesis, motivating further mass measurements in the $A\approx70$ region.

Abstract

The recent mass measurement of $^{70}$Kr using the $Bρ$-defined isochronous mass spectrometry yields a mass excess of $-41320(140)$ keV, indicating a 220-keV increase in binding energy compared to the AME2020 prediction. We utilize this experimental mass -- the last piece of information needed -- to model the potential waiting point $^{68}$Se in $rp$-process and quantitatively constrain the sequential $p$-capture reaction flow bypassing this waiting point. Our investigation shows that the more tightly bound nature of $^{70}$Kr enhances this reaction flow up to a factor of four. This enhancement reduces the effective half-life of $^{68}$Se. {A} one-zone X-ray burst model calculations reveal that the higher flow of $^{70}$Kr has distinct effects on the tail structure of light curve and the final SnSbTe abundances in the ashes due to a stronger $rp$-process heating.

Impact of experimental mass of $^{70}$Kr on the $^{68}$Se waiting-point in $rp$-process

TL;DR

This study links a precise experimental mass measurement of Kr, obtained with -defined isochronous mass spectrometry, to the astrophysical rp-process waiting point at Se in Type-I X-ray bursts. By feeding the new mass into a local network calculation and a one-zone XRB model, it shows that the more bound Kr increases the bypass via sequential -capture, shortening the effective lifetime of Se and enhancing rp-process heating. The result is a modest rise (~) in the burst luminosity around s and a more pronounced SnSbTe signature in the final ashes, with the magnitude of the effect tied to the Kr mass uncertainty. This work demonstrates the critical role of precise nuclear masses in shaping XRB light curves and nucleosynthesis, motivating further mass measurements in the region.

Abstract

The recent mass measurement of Kr using the -defined isochronous mass spectrometry yields a mass excess of keV, indicating a 220-keV increase in binding energy compared to the AME2020 prediction. We utilize this experimental mass -- the last piece of information needed -- to model the potential waiting point Se in -process and quantitatively constrain the sequential -capture reaction flow bypassing this waiting point. Our investigation shows that the more tightly bound nature of Kr enhances this reaction flow up to a factor of four. This enhancement reduces the effective half-life of Se. {A} one-zone X-ray burst model calculations reveal that the higher flow of Kr has distinct effects on the tail structure of light curve and the final SnSbTe abundances in the ashes due to a stronger -process heating.

Paper Structure

This paper contains 4 sections, 5 figures, 1 table.

Table of Contents

  1. Introduction
  2. Calculation of effective half-life
  3. XRB model calculation
  4. Summary

Figures (5)

  • Figure 1: The $rp$-process path passing through the $^{68}$Se waiting point.
  • Figure 2: The effective lifetime of ${^{68} \rm Se}$ in the stellar environment as a function of temperature for typical $rp$-process conditions:$\rho=10^6 \rm\ g/cm^{3}$ and $Y_p=0.7$. The blue shaded region is the result using AME2020 mass and the corresponding 1$\sigma$ mass error. The red area is the range of lifetimes using the new mass measurement ($B\rho$-IMS) and the corresponding 1$\sigma$ uncertainties obtained in this work.
  • Figure 3: Top: The density and temperature trajectories from our one-zone XRB model. We take $^{70}$Kr mass mean value from AME2020 database and the $B\rho$-IMS, respectively. For the calculation, $P_{\rm ign}=10^{23.03}\ \rm dyn/cm^{2}$ and ratio of the H and He mass fraction was set to be $X/Y=3$. Bottom: The ratio of densities and temperatures between AME2020 and $B\rho$-IMS.
  • Figure 4: X-ray luminosity as a function of time using $^{70}$Kr mass from AME2020 (blue dotted line) and new mass (with 1$\sigma$ uncertainty) measured by $B\rho$-IMS (red solid line with shadow). The bottom panel shows the ratio of these luminosities.
  • Figure 5: Comparison of the final mass fraction in ashes from AME2020 (blue dotted line) and new mass (with 1 $\sigma$ uncertainty) measured by $B\rho$-IMS (red solid line). The bottom panel shows the ratio of these final abundances.