Compton gamma-ray imager using electron tracking gaseous TPC and scintillation camera

An MeV gamma-ray imaging detector for astrophysics, which enables us to reconstruct gamma-rays event by event by tracking both a Compton recoil electron and a scattered gamma-ray, has been developed. This detection method is powerful for background rejection. The prototype detector is a hybrid of a gaseous time projection chamber (micro-TPC) with 10 × 10 × 8 cm³ volume with a micro pixel chamber (μ-PIC) readout, and an enclosing NaI(Tl) Anger camera with 10 × 10 × 2.5 cm³ size read by 25 single anode PMTs of 3/4" diameters. The obtained angular resolutions (FWHM) of the prototype detector are 18° and 35° for single photon with 356 keV for an angular resolution measure and a scatter plane deviation, respectively. In order to improve the resolutions the following improvements have been done. At first, an intermediate gas multiplier, conductive capillary plate, has been placed in front of the μ-PIC. Secondly, for improving the position resolution of scattered gamma-rays, an 8 × 8 array of CsI(Tl) pixels with each volume 6 × 6 × 20 mm³ readout by an 8 × 8 multi-anodes PMT has been developed.