For hadron and heavy ion accelerators, the Institute of Physical and Chemical Research (RIKEN) is now constructing a radioactive beam factory using heavy ion beams from a separate sector cyclotron.
For medical use, a heavy ion synchrotron, HIMAC, has been operated at the National Institute of Radiological Sciences (NIRS) and a similar synchrotron has just been constructed at the Cancer Research Center of Hyogo Regional Government. Proton therapy machines are now under construction at three other institutes.
Very recently, the Japanese government approved construction of a high-intensity proton accelerator complex of 3 GeV to provide an intense neutron source and 50 GeV for nuclear/elementary physics. This is a joint project of KEK and the Japan Atomic Energy Research Institute (JAERI).
For radiation safety at these high-energy accelerator facilities, shielding design is essential and the following items are necessary: source term estimation, bulk shielding calculations, residual radioactivity evaluation, skyshine, and streaming problems. Among these items, data on the source term and residual radioactivity are especially needed for heavy ion projectiles.
Our group (Tohoku University, KEK, RIKEN, and NIRS) has been doing a systematic study of secondary neutrons and residual activity produced by high-energy heavy ions using the HIMAC and RIKEN accelerators. We have also done neutron deep-penetration experiments for bulk shielding by using newly developed high-energy neutron spectrometers. Analytical formulas have been presented to estimate source neutrons produced by heavy ions and their transport through the bulk shield, skyshine, and streaming. The fragment mass distribution of residual radioactivity has been discussed with the projectile dependency. The KEK group has performed measurements on radioactivity produced in underground water and soil.