Photon emission induced by fusion neutrons on optical window materials

In situ 14 MeV neutron, 60Co gamma-ray and ion beam irradiation experiments were performed to analyze photons emitted from sapphire and quartz. Wavelength spectrum of photons emitted from sapphire during 14 MeV neutron irradiation had luminescence peaks around 330, 410 and 690 nm, and the spectrum from quartz had luminescence peaks around 450 and 650 nm. These spectra were compared with those measured for gamma-ray and ion beam irradiations. The luminescence intensity was proportional to the 14 MeV neutron flux. As for window materials at low damage levels, it has been found from the comparison of the spectra that there is no large difference in the luminescence mechanism between 14 MeV neutron, gamma-ray and ion beam. However, the number of photons per unit absorbed energy for 14 MeV neutrons in the visible range was one order smaller than that for 60Co gamma-rays. The data on the luminescence of window materials for 14 MeV neutron and gamma-ray irradiations should be useful for the design of D-T fusion plasma diagnostic system. (orig.)