Decay spectroscopy of neutron-rich nuclei produced in multinucleon transfer reactions at KISS

Multinucleon transfer (MNT) reactions have gained renewed interest in recent years as they provide a pathway to access neutron-rich nuclei that are difficult to produce by other methods such as complete fusion and fragmentation [1]. Because MNT reactions produce a wide variety of nuclides around both the projectile and target nuclei with wide angular and energy distributions, the development of experimental techniques to collect, separate, and identify the reaction products of interest is essential to perform their decay spectroscopy. In particular, exotic nuclei that are far from the projectile or target nuclei are produced very infrequently and may be buried among more abundant reaction products. Furthermore, for short-lived nuclei with lifetimes of less than a few minutes, rapid isolation becomes critical.

We are developing the KEK Isotope Separation System (KISS) focusing on the extraction of MNT reaction products at the RIBF facility of the RIKEN Nishina Center [2]. This is an argon-gas-cell-based laser ion source coupled with an isotope separation online system. All reaction products are efficiently collected and neutralized by argon gas, and nuclides of interest are element-selectively ionized by laser resonance method to be accelerated and mass-separated with a bipolar electromagnet for their high-purity decay spectroscopy. We have performed decay spectroscopy of neutron-rich nuclei of refractory elements near the N = 126 region. Recently, we extracted the neutron-rich actinide nuclei produced by MNT reactions with ²³⁸U beams to extend our spectroscopic studies to the neutron-rich actinide region.

In this presentation, we will report the experimental methods and results of KISS, including the perspective of decay spectroscopy on the upgrade plan KISS-II.



References

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

[2] Y. Hirayama et al., Nucl. Instrum. Meth. B 353, 4 (2015).