Elsevier Science 1 Journal logo A novel design of the MeV gamma-ray imaging detector with Micro-TPC R.Orito * ,H.Kubo,K.Miuchi,T.Nagayoshi,A.Takada,T.Tanimori,M.Ueno Department of Physics,Graduate School of Science,Kyoto University,Sakyo-ku,Kyoto 606-8502,Japan Elsevier use only: Received date here; revised date here; accepted date here Abstract A new type of MeV gamma-ray imaging detector in the energy band from 0.2 to 30 MeV, based on a gaseous time projection chamber with Micro Pixel Chamber (Micro-TPC), is proposed. This detector consists of a gas chamber and a scintillation camera. The Micro Pixel Chamber (µ-PIC) has pixel type anodes and cathodes with 400 µm pitch, which enables it to measure the fine tracks of electrons or positrons in Compton scattering or pair creation. The scintillation camera measures the positions and energies of Compton-scattered gamma-rays, electrons and positrons by pair creation. Using information from both the gas chamber and scintillation camera, the incident gamma-rays can be reconstructed event by event with high angular resolution. Simulation of the detector performance and the status of the prototype are reported. © 2001 Elsevier Science. All rights reserved Keywords: MeV gamma-rays;imaging;Compton;TPC ——— 1. Introduction The most classical MeV gamma-ray imaging detector is a phoswich detector with a lead collimator, such as OSSE[1]. The design is simple but the field of view is narrow because of the collimator. COMPTEL[2], another type of the MeV gamma-ray detector based on the double Compton method doesn’t need a collimator. In this detector, the incident gamma-ray can be reconstructed only on the direction cone, since the direction of the recoil electron by Compton scattering can’t be measured. The MeV gamma-ray detectors based on the multiple Compton scatterings method[3] with layers of semiconductor detectors are recently studied. In these detectors, it is also difficult to measure the direction of low energy recoil electron because of the large angle deflection by multiple scattering in the solid detector. Since multiple scattering is smaller in the gas phase than that in the solid, the angular resolution * Corresponding author.e-mail:orito@cr.scphys.kyoto-u.ac.jp