ar X iv : a st ro - p h / 04 12 04 7 v 1 2 D ec 2 00 4 Development of an advanced Compton camera with gaseous TPC and scintillator

A prototype of the MeV gamma-ray imaging camera based on the full reconstruction of the Compton process has been developed. This camera consists of a micro-TPC that is a gaseous Time Projection Chamber (TPC) and scintillation cameras. With the information of the recoil electrons and the scattered gamma-rays, this camera detects the energy and incident direction of each incident gamma-ray. We developed a prototype of the MeV gamma-ray camera with a micro-TPC and a NaI(Tl) scintillator, and succeeded in reconstructing the gamma-rays from 0.3 MeV to 1.3 MeV. Measured angular resolutions of ARM (Angular Resolution Measure) and SPD (Scatter Plane Deviation) for 356 keV gamma-rays were 18 • and 35 • , respectively. In spite of the significance of the MeV gamma-ray imaging in Astronomy and Medical imaging, the quality of MeV gamma-ray images obtained with existing cameras, such as a position-sensitive detector with a collimator [1] and classical Comp-ton imaging [2], are not adequate yet. The deterioration of the images is attributed to the large background made by the scatterings in the colli-mator and other materials nearby and the ghost images intrinsic to the classical Compton method. Therefore we need a new method which can reconstruct the incident direction completely for a single photon and can reject the background in order to obtain clearer MeV and sub-MeV gamma-ray images. We are developing a detector based on a new method: the advanced Compton imaging [3]. Fig. 1 shows the schematic view of our detector. Our detector consists of a micro-TPC, which is a three dimensional tracker of charged particles, and a surrounding position-sensitive scintillator. When the incident gamma-rays Compton-scatter in the micro-TPC [4], the recoil electrons are detected by the micro-TPC and the scattered gamma-rays are absorbed in the scintillator. The difference with classical Compton imaging is the 3D tracking of the recoil electrons. With the information of the recoil electron and the scattered gamma-ray, the