Significance: A significant amount of radical related luminescence is observed from the titanium dioxide (TiO₂) plate during irradiation of alpha particles although alpha particles do not emit Cerenkov-light.

Aim: TiO₂ is a promising material for application to photodynamic therapy in combination with positron radionuclides that emit Cerenkov light. However, it is not clear that radicals are produced by the irradiation of alpha particles, since although Cerenkov light is required to produce radicals, alpha particles do not produce Cerenkov light.

Approach: To clarify this point, the author irradiates alpha particles to a TiO₂ plate and measured the produced luminescence of the plate, which indicates the radical production in TiO₂.

Results: A significant amount of luminescence was observed from the TiO₂ plate during irradiation of alpha particles. The spectrum of luminescence from the TiO₂ plate during this irradiation was the same as that emitted by ultraviolet (UV) light irradiated luminescence, which actually showed radical production in a TiO₂ plate. This luminescence was not attributed to the UV light from the air scintillation by alpha particles but to the direct irradiation of alpha particles to the TiO₂ plate.

Conclusions: A significant amount of luminescence from TiO₂ plate was detected during irradiation of alpha particles. The luminescence is thought to be emitted from the radicals produced by the direct alpha particle irradiation to the TiO₂ plate.