Device for locating and imaging gamma or X-radiation sources, comprising: (a) a detection assembly comprising at least two gamma or X-radiation detectors sensitive to position, as well as a coded mask made of a radiation opaque material; and (b) electronic means for processing the electrical pulses provided by said detectors, so as to locate the source and form a bi- or tri- dimensional image thereof. The device is characterized in that the electronic means are suitable for reconstructing a bi- or tri- dimensional image of an X or gamma radiation source by applying a data processing method which combines the principles of Compton imaging and coded-mask imaging.