Multi-tracing capability of double-scattering Compton imager using NaI(Tl) scintillator absorber

Abstract

The conventional imaging technique using a mechanical collimator does not provide good imaging resolution for high-energy gamma-ray sources because high-energy gamma-rays tend to penetrate the collimation system and, thus, deteriorate the imaging quality. In addition, the conventional technique is not suitable for three-dimensional imaging of a large object such as freight container or vehicle. On the other hand, the imaging resolution of a Compton camera is improved with the increase of the gamma-ray energy, and the 3-D location of the multiple radioisotopes, especially interested in the medical or security inspection applications, can be simultaneously determined by a single measurement with a Compton camera at a fixed position. In the present study, the multi-tracing capability of the Compton camera was demonstrated with a novel type Compton camera, named double-scattering Compton imager (DOCI). The DOCI consists of three radiation detectors, two double-sided silicon strip detectors (DSSDs) as scatterer detectors and a scintillation detector as absorber detector. The DSSDs were used to determine the track of the scattered photons between these two detectors. A 3″ × 3″ NaI(Tl) scintillation detector was placed right behind the second scatterer detector to determine the energy of the double-scattered photons for energy gating, which is used to reject random-coincidence events. The NaI(Tl) scintillation detector is considered as a proper absorber detector, when compared with a semiconductor detector, for its high detection efficiency, adequate energy resolution, robustness, and room-temperature operation capability. Figure 1 shows a reconstructed Compton image for two point-like gamma sources, 60Co and 137Cs, obtained by the DOCI.