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The Compton camera can provide 3-D images of radioactive material distribution based on a single measurement at a fixed position. The Compton camera also can image several different kinds of radioactive materials simultaneously, by means of the "multitracing" capability. In the present study, this multitracing capability was tested for a double-scattering-type Compton camera, or Double-Scattering Compton Imager (DOCI), which utilizes two double-sided silicon strip detectors (DSSDs) and one NaI(Tl) scintillation detector. Our experimental result shows that the 137 Cs and 60 Co gamma sources can be clearly distinguished in 2-D and 3-D Compton images, and that there is no significant interference between the two gamma sources. The imaging resolutions were determined to be 6.2 and 4.7 mm FWHM for the 137 Cs (662 keV) and 60 Co (1332 keV) point sources at 4 cm, respectively. The angular resolutions, determined from the angular resolution measure (ARM) distributions, were 7.3 and 6.5 for the source energies of 662 and 1332 keV, respectively. The DOCI remains under development; its imaging resolution will be further improved with the incorporation of more sophisticated detectors and the related electronics, including a faster scintillation detector (LYSO) and higher-spatial-resolution position-sensitive detectors.

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