Abstract: A radiation sensor for determining a direction, relative to the sensor, in which a radiation source is located. A plurality of elongated radiation detectors are located in a base plane of the sensor. In a plane, disposed before the base plane of the sensor, slits, associated with each radiation detector, are positioned at an angle with respect to direction of elongation of the associated radiation detector. The slits provide planes of radiation which intersect each elongated radiation detector. A coordinate of the intersection of the radiation with the detector is provided by output signals from the detector. The coordinates of the intersection of the radiation with the elongated detectors can determine the location of the radiation source when more than two radiation detectors (of which two are non-parallel) are utilized, or a direction of the radiation source when two non-parallel radiation detectors are utilized.