A very large area Micro Pixel Chamber

A Micro Pixel Chamber, called “ μ -PIC”, is a gaseous 2D imaging detector with a fine pixel electrode based on the Printed Circuit Board technology, and we developed it for the X/gamma-ray imaging and the tracking of the charged particles [A. Ochi, et al., Nucl. Instr. and Meth. A 478 (2002) 196; T. Nagayoshi, et al., Nucl. Instr. and Meth. A 525 (2004) 20.]. The previous μ -PIC has a fine position resolution, a high gas gain, a good gas gain uniformity and the stable operation. Although the detection area of the previous μ -PIC ( ∼ 10 × 10 cm 2 ) is not large enough for a variety of the application, for example an MeV gamma-ray Compton camera [T. Tanimori, et al., New Astron. Rev. 48 (2004) 263.] and dark matter search [T. Tanimori, et al., Phys. Lett. B 578 (2004) 241.]. Therefore, we developed a new μ -PIC having a ∼ 30 × 30 cm 2 detection area. The structure and the pitch of the electrode are same as those of the previous μ -PIC. There are 768 × 768 pixels in the whole area. This μ -PIC (TOSHIBA SN041129-1) is operated with a stable gas gain of ∼ 3500 and a maximum gain of ∼ 7000 at the center region, and the variety of the gain was 16.7% RMS. An X-ray image of the whole area was also taken by the irradiation of the X-rays from 109Cd (22 keV) to the whole detection area.