The 18th International Symposium on Origin of Matter and Evolution of Galaxies (OMEG18)

Direct mass measurements for nuclear astrophysics and prospects toward the $N = 126$ r-process region

Oct 20, 2026, 5:50 PM

20m

Headquarters Building 2F (RIKEN)

Oral Presentation Scientific Session

Speaker

Shun Iimura

Description

Nuclear masses of unstable nuclei are essential inputs for understanding nuclear structure far from stability and astrophysical nucleosynthesis. For neutron-rich nuclei, neutron separation energies are among the key nuclear inputs that shape the r-process path and element abundance peaks. However, experimental data remain limited for heavy neutron-rich isotopes relevant to the r-process. At RIKEN RIBF, the recent development of a high-intensity $^{208}$Pb primary beam, together with BigRIPS and ZeroDegree Spectrometer, has opened new opportunities to access heavy exotic nuclei near the predicted r-process path$^{[1]}$.
For astrophysical applications, mass uncertainties of <100 keV are often required to constrain separation energies and nucleosynthesis calculations. To achieve this precision, short-lived RIs are produced and separated by BigRIPS and ZeroDegree Spectrometer, stopped and extracted with a radio-frequency carpet-type helium gas cell, cooled in an ion trap, and injected into a multi-reflection time-of-flight mass spectrograph. With a measurement time of a few tens of milliseconds and relative mass precision of $\delta m/m < 10^{-7}$, MRTOF mass spectrometry is well suited for direct mass measurements$^{[2]}$.
In this contribution, we summarize recent mass measurements performed at RIBF. The results will be discussed in terms of separation-energy systematics, shell evolution$^{[3-6]}$, and implications for explosive nucleosynthesis$^{[7]}$. We will also present plans to extend MRTOF mass measurements toward neutron-rich nuclei around $N = 126$, enabled by recent heavy-RI beam developments at RIBF, and discuss challenges toward the third r-process abundance peak around $A = 195$.
[1] N. Fukuda $\textit{et al.}$, Prog. Theor. Exp. Phys. $\textbf{2026}$, 061D01 (2026).
[2] M. Rosenbusch $\textit{et al.}$, Nucl. Instrum. Methods Phys. Res. A $\textbf{1047}$, 167824 (2023).
[3] S. Iimura $\textit{et al.}$, Phys. Rev. Lett. $\textbf{130}$, 012501 (2023).
[4] D. S. Hou $\textit{et al.}$, Phys. Rev. C $\textbf{108}$, 054312 (2023).
[5] W. Xian $\textit{et al.}$, Phys. Rev. C $\textbf{109}$, 035804 (2024).
[6] W. Xian $\textit{et al.}$, Front. Phys. $\textbf{13}$, 1644477 (2025).
[7] S. Kimura $\textit{et al.}$, Phys. Rev. Lett. $\textbf{135}$, 152701 (2025).