Abstract: A radiation scanning system having a radiation detector which receives radiation from a focussing system after reflection from first and second scanners which are rotatable about parallel axes, and in which the first scanner is annular having its reflective surfaces on its outer periphery, the rotational axis of the second scanner being displaced by a distance which is less than the radius of the second scanner from the plane containing the rotational axis of the first scanner and the axis of the radiation focussing system.

Abstract: In a radiation scanning system, scanning is achieved by rotation of two drums about parallel axes. The first drum is rotated at an angular speed s.sub.1 and has n.sub.1 reflective surfaces at a distance r.sub.1 from a first axis of rotation. The second drum is rotated at an angular speed s.sub.2 and has n.sub.2 reflective surfaces at a distance r.sub.2 from a second axis of rotation. The axes are separated by a distance d. A detector is located a distance a from the first axis. The following conditions hold:2 a(n.sub.1 /n.sub.2 -1).sup.2 + 2 d(n.sub.1 /n.sub.2).sup.2 +r.sub.2 (n.sub.1 /n.sub.2).sup.2 =r.sub.1 (2n.sub.1 /n.sub.2 -1).sup.2 , (i)n.sub.1 s.sub.1 =n.sub.2 s.sub.2.

Abstract: Apparatus for use in a radiation scanning system comprising a radiation detector and an optical system arranged to scan radiation from a field of view across the radiation detector. The optical system includes two sets of planar reflective surfaces, one set being movable relative to the other, and a rotary assembly carrying one of the sets and rotatable about an axis of rotation. The detector is arranged relative to the optical system such that the radiation enters the detector after sequential reflection from reflective surfaces of the two sets, and the surfaces which effect the sequential reflection being separated by a predetermined amount and being located with respect to the axis of rotation such that the angle of incidence of radiation at the detector is independent of the position of the radiation in the field of view.