Research with fast radioactive isotope beams at RIKEN

Abstract

The RIKEN RI Beam Factory (RIBF) provides intense radioactive isotope (RI) beams with energies around 200 MeV/nucleon in a wide range of unstable nuclei. Part of the facility started routine operation in 1987 and, in 1990, RI beams from this part became available, with energies of a few tens of MeV/nucleon and the world's highest intensities at the time for many light exotic nuclei. To exploit the research opportunities available with such fast RI beams, various experimental devices have been constructed and several new methods have been developed. A number of modern aspects of nuclear structure, such as the neutron halo and the disappearance/appearance of magic numbers, have been investigated. Several attempts to approach astrophysical nuclear processes involving short-lived nuclei have been made. The present RIBF facility was completed in 2006. It far exceeds other existing facilities in the world in its RI beam production capability. A variety of research programs have been started, and several groundbreaking results have already been obtained.

Progress in nuclear astrophysics of east and southeast Asia

“…In nuclear physics, extensive studies of neutron halo, which was first discovered by a Japanese group [5,6] under INS-LBL (Institute for Nuclear Study -Lawrence Berkeley Laboratory) collaboration, were made at the accelerator facility of RIKEN. Search for new super-heavy elements which led later to the discovery of Nihonium with atomic number Z=113 [7,8], discovery of appearance and disappearance of new and known magic numbers [3,9], and measurement of the half lives of r-process nuclei [10][11][12], respectively, were carried out in this institute. The INS of The University of Tokyo made continuous efforts in developing accelerator technology that would be realized later in HIMAC (Heavy Ion Medical Accelerator in Chiba) and J-PARC (Japan Proton Accelerator Research Complex).…”

“…While there has been no accelerator producing RI beams in Korea, the Korean nuclear astrophysics community explored many indirect studies of important reactions in astrophysics. Some examples are 17 F(p,γ ) 18 Ne [44,45], 19 Ne(p,γ ) 20 Na [46], 7 Be(p,γ ) 8 B [43], 3 H(p,γ ) 4 He [47], 3 H(p,n) 3 He [48], 13 N(p,γ ) 14 20 Ne [51], and 22 Na(p,γ ) 23 Mg [52], which are related to astrophysical processes including the primordial BBN, the pp chain, the hot CNO cycle, and the breakout reaction to the rp-process.…”

“…Most paths involve unstable nuclei, many of which are either difficult to be studied due to their short lifetimes and low beam intensities, or have not yet been discovered.. Two hundred twenty-six new isotopes (red boxes) have been synthesized and 84 nuclear masses (blue boxes) have been measured at Asian facilities and adopted in the Atomic Mass Evaluation by 2020 [1,2]. The nuclei shown in purple-red and light blue indicate those with production rates higher than 1 particle per day, given a primary-beam intensity of 1 particle μA at RIBF [3]. Isotopes in the yellow region are predicted based on the KTUY mass formula [4] but not synthesized yet.…”

Towards a novel laser-driven method of exotic nuclei extraction−acceleration for fundamental physics and technology

“…7 and RIKEN's RIBF 8 , respectively. In the ISOL method, unsuitable for measurements of nuclei with life-times less than few hundred milliseconds, the isotope extraction strongly depends on the target chemical properties of the isotope source, and in some cases the extraction efficiency is less than a percent 9 .…”

Reaching the Limits of Nuclear Existence

“…The extra stability of neutron-rich fluorine and neon relative to oxygen has also been attributed to the emergence of the island of inversion (Z ¼ 10-12, N ¼ 20-22, and their neighbors), where the ground states gain energy by strong deformation due to spontaneous symmetry breaking [23][24][25]. An interesting suggestion has been made by Tanihata [26], where the neutron dripline is related to closing (sub)shell orbitals, as in 8 He with N ¼ 6 that closes the 1p 3=2 orbital, and 22 C, 23 N, and 24 O with N ¼ 16 that closes the 2s 1=2 orbital.…”