A radiation detector includes a scintillator crystal 2 in the form of a slab mounted to be rotated by a drive 4 in a housing 8. A photon detector 6 detects photons emitted by the crystal 2. The crystal 2 is rotated to a number of measurement angles and the radiation emitted by a radiation source determined by counting the photons detected by the photon detector. This is used to determine the direction towards the radiation source.
