Study of event reconstruction algorithm for a large-scale Si/CdTe multilayer Compton camera

The SGD is a Soft Gamma-ray Detector on board the ASTRO-H satellite and is a Narrow FOV Compton Camera. The key technology utilized to realize this concept is a “large-scale” Si/CdTe multilayer Compton camera. Although we need an algorithm that can reconstruct the gamma-ray event correctly with this detector, such algorithms have not been well established so far. We have developed a new event reconstruction algorithm for the “large-scale” Si/CdTe semiconductor Compton camera of the SGD. This algorithm is based on parameterizations that indirectly represent the probability of each sequence and can be applied uniformly to any patterns of signals that might occur in this Compton camera. With this algorithm and SGD background rejection concept, the S/N ratio is increased by a factor of 2.5. Detection efficiency is improved by a factor of 4 compared with the simplest algorithm. We have high (~ 70% @ 500 keV) correctness in the order determination with the algorithm.