KISS gas cell system for the nuclear spectroscopy of multinucleon transfer reaction products*

We have developed the KEK Isotope Separation System (KISS) [1,2] at RIKEN to study heavy element synthesis in the universe. KISS presently consists of an argon gas cell based laser ion source (atomic number selection) followed by isotope separation on-line (mass number selection). KISS has successfully provided pure low-energy beams of neutron-rich isotopes near N = 126 in the platinum region and near N = 152 in the uranium region produced by multi-nucleon transfer reactions [3], which were studied by their nuclear spectroscopy such as b-decay spectroscopy, mass measurements, and laser spectroscopy.

To extend the studies to more neutron-rich regions, we plan to upgrade the KISS facility to KISS-II [4] whereby we replace the present argon gas cell with a next-generation, large-volume, cryogenic helium gas catcher utilizing an advanced RF wire carpet. The RF wire carpet structure features a 4-phase RF traveling wave technique [5] which enables efficient transport of the desired radioactive ions under a strong plasma of He²⁺ and e^— induced by ionizing interactions with the primary and secondary beams. The helium gas catcher can offer faster, more efficient, and element-independent extraction of ions. In advance of the development of the large-volume He gas catcher, we have started to test the RF wire carpet structure installed in a small-volume cryogenic helium gas catcher at KISS. We could successfully extract radioactive ions from the gas catcher and identify them by using the MRTOF-MS.

In this presentation, we will report the activities by using the argon gas cell system at KISS, and present the development of the small-volume cryogenic helium gas catcher and the upgrade plan.

[1] Y. Hirayama et al., Nucl. Instr. and Meth. B 353, 4 (2015).

[2] Y. Hirayama et al., Nucl. Instr. and Meth. B 412, 11 (2017).

[3] Y.X. Watanabe et al., Phys. Rev. Lett. 115, 172503 (2015).

[4] T. Aoki et al., https://arxiv.org/abs/2209.12649v2.

[5] K.R Lund et al., Nucl. Instru. and Meth. B 463, 378 (2020).