Energy, depth calibration, and imaging capability of Nuclear Compton Telescope

The Nuclear Compton Telescope (NCT) is a balloon-borne soft gamma ray (0.2–10 MeV) telescope designed to study astrophysical sources of nuclear line emission and polarization. The heart of NCT is an array of 12 cross-strip germanium detectors, designed to provide 3D positions for each photon interaction with full 3D position resolution to < 2 mm3. Tracking individual interactions enables Compton imaging, effectively reduces background, and enables the measurement of polarization. The keys to Compton imaging with NCT's detectors are determining the energy deposited in the detector at each strip and tracking the gamma-ray photon interaction within the detector. The 3D positions are provided by the orthogonal X and Y strips, and by determining the interaction depth using the charge collection time difference (CTD) between the anode and cathode. Our preliminary calibrations of the energy and the 3D position of interactions have been completed as well as the verifications of imaging capabilities. Here we will present the techniques and results.