the invention provides a switchable photomultiplier switchable between a detecting state and a non - detecting state including a cathode upon which incident radiation is arranged to impinge . the photomultiplier also includes a series of dynodes arranged to amplify a current created at the cathode upon detection of photoradiation . the invention also provides a detection system arranged to detect radiation - emitting material in an object . the system includes a detector switchable between a detecting state in which the detector is arranged to detect radiation and a non - detecting state in which the detector is arranged to not detect radiation . the system further includes a controller arranged to control switching of the detector between the states such that the detector is switched to the non - detecting state while an external radiation source is irradiating the object .