Abstract
Although light emission from an acrylic block during irradiation of carbon ions at lower energy than the Cerenkov-light threshold was found recently, the origins and fractions of the light in the images have not yet been clarified. Since light spectra may provide information to estimate the origins and fractions of the light emission, we conducted optical imaging of an acrylic block during irradiation of carbon ions using a charge-coupled device (CCD) camera with optical filters. We measured the light images of the acrylic block with optical filters of different wavelengths using an ultraviolet (UV)-sensitive CCD camera during carbon-ion irradiation with slightly higher energy to produce secondary electrons to emit Cerenkov light (241 MeV/u). From the images, we derived depth profiles with different wavelengths and calculated the spectra of the emitted light from the acrylic block. The depth profiles showed higher intensity due to Cerenkov light at the shallow area distributed in the images of longer wavelengths. By calculating between the depth profiles of different wavelengths, we could derive the depth profiles for possible origins of the produced light: luminescence, Cerenkov light, and scintillation of the acrylic block. Using the derived fractions of these components, we could estimate their depth profiles at different wavelengths.