Speaker
Description
The nuclear properties such as lifetimes and masses of the neutron-rich nuclei are important parameters to investigate the astrophysical rapid neutron capture process (r-process). However, the difficulty in the production of those neutron-rich nuclei, especially at the waiting points on the neutron closed shell $N = 126$ and beyond, makes their experimental studies difficult. Therefore, the theoretical nuclear models play crucial roles in the simulation of the r-process nucleosynthesis. The experimental studies of those nuclear properties and nuclear structures provide significant inputs to those theoretical models to improve their predictability for the neutron-rich nuclei relevant to the formation of the r-abundance peak around $A = 195$ and actinide elements such as uranium and thorium.
We are developing KEK Isotope Separation System (KISS) at RIKEN RIBF facility to produce and separate those nuclei for their spectroscopic studies [1-3]. The multi-nucleon transfer (MNT) reactions between the $^{136}$Xe beam and the $^{198}$Pt target are employed to produce the nuclei around $N = 126$ [4-5]. The KISS consists of an argon-gas-cell-based laser ion source and an isotope separation on-line system, which allow to provide the mass and atomic number selectivity. The detector systems consisting of a multi-segmented gas counter [6-7] combined with high-purity germanium detectors and a Multi-Reflection Time-Of-Flight Mass Spectrograph (MRTOF-MS) make it possible to perform their beta-gamma spectroscopy, mass spectroscopy, and laser spectroscopy. Recently, we have also successfully measured masses in the actinide region using the MNT reactions between the $^{238}$U beam and the $^{198}$Pt target.
In this presentation, we will report the present status of the KISS including the recent experimental results of nuclear spectroscopy and the future plan.
[1] Y. Hirayama et al., Nucl. Instrum. and Methods B 353 (2015) 4.
[2] Y. Hirayama et al., Nucl. Instrum. and Methods B 376 (2016) 52.
[3] Y. Hirayama et al., Nucl. Instrum. and Methods B 463 (2020) 425.
[4] Y.H. Kim et al., EPJ Web of conferences 66 (2014) 03044.
[5] Y.X. Watanabe et al., Phys. Rev. Lett. 115 (2015) 172503.
[6] M. Mukai et al., Nulc. Instrum. and Methods A 884 (2018) 1.
[7] Y. Hirayama et al., Nucl. Instrum. and Methods A 997 (2021) 165152.
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