Neutron target research and development for BNCT: direct observation of proton induced blistering using light-polarization and reflectivity changes

The blistering problem due to high power proton irradiation is a crucial issue for any neutron generation target. When a proton beam irradiates a metal, the protons stopped inside capture free electrons in the metal to form a hydrogen gas. Eventually, blisters and/or flakes appear on the surface as the pressure of the hydrogen gas rises enough to cause ruptures. An experimental setup for observation of the metal surface that would have high sensitivity and high spatial resolution was proposed, designed and implemented. The system observes light-polarization and reflectivity and has successfully detected blistering surface dynamics.