New results on a gaseous detector using Medipix2 and Micromegas

A prototype time projection chamber (TPC) has been built (GridPix) consisting of a Medipix2 pixel CMOS readout circuit as a direct anode and a Micromegas grid 50μm above the chip. With this new TPC it is possible to detect single electrons from tracks made by minimum ionizing particles. It is also shown that GridPix can withstand high counting rates and high intensity radiation environments, better than traditional wire chambers. Up to 0.9MHz/mm2 of 8 keV X-rays at a gain of 104 the chamber shows no deviation from the current-rate proportionality. GridPix is estimated to be roughly a factor of 400 times more radiation tolerant compared to traditional wire chambers.