The weakening of the N=28 shell gap, the erosion of energy level associated N=28 magic number has been suggested from several spectroscopic experimental data for nuclei around this number. We measure nuclear electromagnetic moments which are very important in investigating the nuclear structure to investigate the weakening of nuclear shell gap. The nuclear electromagnetic moments are measured from spin polarized rare isotope beams(RIBs) at heavy ion accelerator facility. These spin polarized RIBs are produced via projectile fragmentation reaction. beta nuclear magnetic resonance(beta-NMR) method has been conventionally used to measure the nuclear electromagnetic moments. However, information on the resonance region of nuclei being investingated in a prerequisite in this method and there are cases where this region cannot be detected or observed due to the shorter spin relaxation time compared with the lifetime. To cope up with this problem, adiabatic field rotation(AFR) method has been used as an alternative at RIKEN. With AFR method, spin polarization is measured through a change in beta-ray asymmetry without information on the resonance of nuclei. We tested the current AFR system using 40S and prepared nuclear electromagnetic moment measurement experiment for 41,43,45S with spin polarized beams at RIKEN Radioactive Isotope Beam Factory(RIBF). We obtained 0.0132 ± 0.0121 % of spin polarization. We aim to increase Figure of Merit(FOM) for the AFR system. To improve the system, we have designed a new magnet, which is larger and is expected to be stronger than present one:1)the expected field in central area is 4.70 kG. In addition, we have designed new plastic scintillators, which are longer and are expected to detect more beta-rays than current one: the expected solid angle is 0.714 sr which is larger than 0.411 sr of the current scintillator. The magnetic field was measured to be 4.95 kG at center of the stopper region and 4.75 kG at center of the magnet cavity. Hense we expect increased spin polarization. In the near future, we will test the new AFR system after we recieive the plastic scintillators then we will measure the ground state nuclear magnetic moments of 41,43,45S with the new AFR system, and spin polarized beams at RIKEN RIBF.
Thesis Advisor: Prof. Wooyoung Kim