Figure 5. Results of imaging spectroscopy using a 137Cs radioisotope.
(a,b) An image for the whole energy band and energy spectra of gammas from 137Cs (0.86 MBq) source placed at a distance of 2 m from the ETCC with angular radii of 15° (blue), 30° (green), 60° (red), and 180° (black) between the extracted region and the source. A simulated energy spectrum is, for comparison, given in the inset in Panel (b) for events with recoil electrons hitting the backward detector. (c) A image of 137Cs (2.9 MBq) source at the off-axis with a polar angle of 20°. Red and black circles, each of which is 15° in radius, indicate source and background regions, respectively. (d) The spectrum after air-scattered gammas within the PSF(Θ ~ 15°) are removed, using the region symmetrical about the centre of the FoV (black circle in c) as the background region.