New techniques for isotope identification and separation of BigRIPS*

The RI beam factory (RIBF) accelerates primary beams from hydrogen to uranium to 345 MeV/u and produces RI beams by using the in-flight fragment separator BigRIPS. As RI beams get heavier or slower, the isotope separation and particle identification (PID) with BigRIPS become more difficult, since the charge state Q of the RI beams could be easily changed in materials and detectors used for the separation and PID. We have developed these RI beams to enable experiments in new regions in terms of energy and mass.

Experiments with slowed-down RI beams have been already conducted at the OEDO beamline constructed by CNS in cooperation with RIKEN. We introduce RIKEN's early development of beam tuning technology and new PID of secondary-reaction products at 50 MeV/u. The multi-sampling ionization chamber (MUSIC) was used to measure ΔE, E, and range for the first time. The energy measurement at the lower energy was the suggestive data for PID in the heavy regions in terms of the Q fluctuation in the detector.

To purity the heavy RI beam with the uranium primary beam, fission fragments must be considered. We found that the separation figure for each Q was powerful to consider the separation of the fission fragments from the heavy RI beam. The experiment to produce the ²⁰⁸Rn beam will be presented. The Z resolution of ²⁰⁸Rn and the energy measurement at the 50-MeV/u PID helped us to find that a poor Z resolution due to the Q fluctuation could be improved by a small difference of the cross section of the Q change. The MUSIC detector with the Xe-based gas was found to be promising for the Z identification, of which data will be presented by Yoshimoto et al. in a different workshop.