An electron beam scanner includes a stationary source producing an electron beam and a detector positioned to partially circumscribe a scan field, the detector divided into a pair of detector rings arranged adjacent to one another and separated by a gap extending at least partially about a circumference of the detector. The electron beam scanner also includes a target arranged concentric with the detector and located opposite the detector across the scan field, the target having end portions circumferentially overlapping the detector and radially aligned with the gap between the detector rings, such that when the electron beam impinges on the target the target transmits radiation through the gap across the scan field to an associated section of the detector.