The invention relates to a radiation detector (100′) and a method for detecting radiation, particularly for detecting X-rays (X) in a CT imaging apparatus (1000′). According to a preferred embodiment, the radiation detector (100′) comprises a conversion element (110) for converting incident radiation (X) into electrical signals which are read out and processed by a readout circuit (120). A heating device comprising the heat source (135′) of a Peltier element is provided with which the conversion element (110) can controllably be heated in order to reduce negative effects, e.g. of polarization, on image accuracy, wherein the heat sink (137′) of the Peltier element is oriented towards the readout circuit.