PROBLEM TO BE SOLVED: To provide a detection method and device for grasping a radiation energy distribution so as to acquire information about, in particular, imaging of the X-ray or beam hardening in a CT in a short time under conditions where radiation mainly including an X-ray enters to a radiation detector in a burst mode.SOLUTION: The detection method according to the present invention is configured to: arrange in series a Cerenkov counter different in an energy threshold value when Cerenkov radiation occurs with respect to an incident direction of a charge particle, which is radiation, or an electromagnetic wave to be converted to the charge particle; and estimate an energy distribution of the radiation by conversion of radiation intensity existing within a prescribed range of an energy threshold value from optical intensity to be measured by an optical detector in each Cerenkov counter. The energy threshold value can be controlled by a refractive index of a Cerenkov radiating body included in the Ceren
