An object of the present invention is to reduce false detection due to charge sharing. According to one embodiment, a radiation detector includes a plurality of main electrodes, sub-electrodes, and a determination unit. The plurality of main electrodes detect electrons from the semiconductor element according to the incidence of radiation. The sub-electrodes are arranged between the plurality of main electrodes, detect electrons corresponding to the incidence of radiation from the semiconductor element, and have a smaller dimension in the arrangement direction than the main electrodes. The determination unit makes a determination regarding charge sharing based on the outputs of the main electrode and the sub-electrode. [Selection diagram] FIG.【課題】チャージシェアリングによる誤検出を低減させること。【解決手段】実施形態の放射線検出器は、複数の主電極と、サブ電極と、判定部とを備える。複数の主電極は、放射線の入射に応じた電子を半導体素子から検出する。サブ電極は、複数の主電極の間に配列され、放射線の入射に応じた電子を半導体素子から検出し、主電極よりも配列方向の寸法が小さい。判定部は、主電極とサブ電極との出力に基づいて、チャージシェアリングに関する判定を行なう。【選択図】図４
