RIKEN radioactive beam facility and polarized radioactive beams

• Published in: Progress in particle and nuclear physics Vol. 46; no. 1; pp. 321 - 333
• Main Author: Asahi, K.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 2001
• ISSN: 0146-6410; 1873-2224
• DOI: 10.1016/S0146-6410(01)00139-9

The radioactive beam facility at RIKEN, presently consisting of K=540 cyclotron and projectile fragment separator RIPS, has been in operation for about a decade, in which a number of experiments with beams of light neutron-rich nuclei have been conducted. Recently, the construction of new accelerators has been initiated to form a new facility upgraded in energy and intensity, called the RI Beam Factory. In this paper we briefly describe the present and future facilities at RIKEN, and then discuss the physics results obtained up to now. In particular, we focus on results obtained with beams of spin-polarized radioactive nuclei. The polarized radioactive beams are produced in the projectile fragmentation reaction induced by intermediate-energy heavy ion beams, and used for the measurement of magnetic dipole and electric quadrupole moments of nuclei in the regions far from stability. Analyses of the observed magnetic moments in terms of shell models show intriguing results which imply that some of the basic nuclear properties, such as the order in energy of the single-particle orbits, the pairing energy between the excess neutrons, the effective g s -factor for a halo nucleon, and the E2 effective charges tend to alter as the degree of neutron excess increases.