Detection of luminescence from Vitamin B2 plate during alpha particle irradiation

Vitamin B2 (V-B2) is a material that converts shorter-wavelength light such as ultraviolet (UV) light to longer-wavelength light. However, it is not clear whether longer-wavelength light is produced by the irradiation of alpha particles. Because UV light such as Cherenkov light is required to produce longer-wavelength light for V-B2 and alpha particles do not produce Cherenkov light in a material, no light is expected to be emitted in V-B2 by the irradiation of alpha particles. However, we irradiated alpha particles to a V-B2 plate and measured the produced light in the plate. During irradiation of alpha particles, a significant amount of longer-wavelength light was observed from the V-B2 plate. The luminescence intensity of the V-B2 plate during irradiation of alpha particles was ∼1/6 of that of the plastic scintillator. The spectrum of luminescence from the V-B2 plate during this irradiation was the same as that emitted by the irradiation of ultraviolet (UV) light, which possibly indicates UV or shorter-wavelength light production in the V-B2 plate by the irradiation of alpha particles. This longer-wavelength light is not attributed to the UV light from the air scintillation by the alpha particles but to the direct irradiation of alpha particles to the V-B2 plate. From these results, we conclude that the luminescence of the V-B2 plate was the scintillation by the irradiation of alpha particles, or other phenomenon that was; UV as well as shorter-wavelength visible light was produced in the V-B2 plate by the irradiation of alpha particles and that the longer-wavelength light was produced from this light. The UV light was produced from the light generated by the dipole interaction of moving secondary electrons with V-B2 or binder molecules and then converted to the longer-wavelength light with a slower decay of the V-B2 in the plate that had high intensity due to the decreased simultaneity of the light emission.