Research of the neutron damage and measurement of the energy distribution of gamma ray under the carbon-ion beam therapy

Measurement of the energy distribution of gamma ray under the Carbon-Ion Beam Therapy environment was carried out in order to measure the background for positron annihilation gamma ray peak in the use of in-beam monitoring. In this fiscal year, we studied the effect of the thermal neutron in the irradiation room against a CdTe semiconductor detector. Carbon-ion beam was irradiated on a water phantom and the energy spectrum of gamma ray was measured. The 559 keV gamma ray peak which is emitted from the neutron absorption reaction of ¹³³Cd are observed in the spectrum. For the case using the boron-paraffin block, the peak is clearly disappeared and the continuous component of the spectrum under the 511 keV annihilation peak decreased and the S/N ratio was refined. Neutron damage of the detector was not observed after the 20 hours use in the 10⁸ pps beam environment. (author)