Measurements of longitudinal gamma ray distribution using a multichannel fiber-optic Cerenkov radiation sensor

Cerenkov radiation occurs when charged particles are moving faster than the speed of light in a transparent dielectric medium. In optical fibers, Cerenkov radiation can also be generated due to the fiber's dielectric components. Accordingly, the radiation-induced light signals can be obtained using the optical fibers without any scintillating material. In this study, we fabricated a multichannel, fiber-optic Cerenkov radiation sensor (FOCRS) system using silica optical fibers (SOFs), plastic optical fibers (POFs), an optical spectrometer, multi-anode photomultiplier tubes (MA-PMTs) and a scanning system to measure the light intensities of Cerenkov radiation induced by gamma rays. To evaluate the fading effects in optical fibers, the spectra of Cerenkov radiation generated in the SOFs and POFs were measured based on the irradiation time by using an optical spectrometer. In addition, we measured the longitudinal distribution of gamma rays emitted from the cylindrical type Co-60 source by using MA-PMTs. The result was also compared with the distribution of the electron flux calculated by using the Monte Carlo N-particle transport code (MCNPX).