Measurements of neutron- and photon-production cross sections from heavy-ion reactions on tissue equivalent elements

In the heavy-ion radiotherapy, considerable discussion has been attracted regarding the potential for second cancer induction by secondary neutrons produced from the primary heavy-ion fragmentation. It is important to measure energy-angle double-differential cross sections of neutron- and photon productions in heavy-ion nuclear reactions. is essential to estimate neutron doses and the photon contribution. Since it is notoriously hard to measure the spectral cross sections of neutrons in an energy range of around 1 MeV where the relative biological effectiveness (RBE) value reaches at its maximum. In the first year of the project, test experiments were carried out at the synchrotron Heavy Ion Medical Accelerator in Chiba (HIMAC) of National Institute of Radiological Sciences (NIRS), Japan. The ¹⁶O beam of 290 MeV/u bombarded a carbon target. In neutron measurements were used liquid scintillator detectors of 5'' and 2''. Resultant spectral cross sections of neutrons were compared with Monte-Carlo simulation codes, PHITS-QMD. Thanks to the careful energy calibration procedure, we succeeded to lower the energy threshold down to 0.6 MeV. The present results are in reasonable agreements with PHITS. Since our goal in technical aspects has been fulfilled, measurements will be continued for other reactions. (author)