Helium gas cell with RF wire carpets for KEK Isotope Separation System

We have developed radio-frequency (RF) wire carpets and installed them in a cryogenic helium gas cell to increase the extraction yields of target-like fragments (TLFs) produced in multi-nucleon transfer (MNT) reactions at the KEK Isotope Separation System (KISS). KISS is an on-line isotope separator based on a gas cell system, and has been implemented for nuclear spectroscopy of isotopes approaching the N = 126 neutron shell closure below lead and neutron-rich actinides. We optimized the design of the RF wire carpet for efficient ion transport of TLFs from the simulations. We then performed experiments both off-line using rubidium ions from an alkali thermal ion-source in the gas cell, and on-line using TLFs produced by a 136Xe beam impinging upon a 198Pt target system, to confirm the performance expected of the design. We confirmed an increase in the extraction yields of more than an order of magnitude when using the cryogenic He gas cell with RF wire carpets as compared to our typical argon gas cell system with laser resonant ionization. The techniques and knowledge acquired in the development of these RF wire carpets will be applied to new RF wire carpets for use in a large-volume helium gas cell which will be installed at an upgraded KISS facility in the near future.