Operation and performance of microhexcavity pixel detector in gas discharge and avalanche mode

The Microhexcavity Panel ( muHex) is a novel gaseous micropattern particle detector comprised of a dense array of close-packed hexagonal pixels, each operating as an independent detection unit for ionizing radiation. It is a second generation detector derived from plasma panel detectors and microcavity detectors. The muHex is under development to be deployed as a scalable, fast timing (ns) and hermetically sealed gaseous tracking detector with high rate ( > 100 KHz/cm^2 ) capability. The devices reported here were fabricated as 16 x 16 pixel arrays of 2 mm edge-to-edge, 1 mm deep hexagonal cells embedded in a thin, 1.4 mm glass-ceramic wafer. Cell walls are metalized cathodes, connected to high voltage bus lines through conductive vias. Anodes are small, 457 micron diameter metal discs screen printed on the upper substrate. The detectors are filled with an operating gas to near 1 atm and then closed with a shut-off valve. They have been operated in both avalanche mode and gas discharge devices, producing mV to volt level signals with about 1 to 3 ns rise times. Operation in discharge mode is enabled by high impedance quench resistors on the high voltage bus at each pixel site. Results indicate that each individual pixel behaves as an isolated detection unit with high single pixel intrinsic efficiency to both beta's from radioactive sources and to cosmic ray muons. Continuous avalanche mode operation over several days at hit rates over 300 KHz/cm^2 with no gas flow have been observed. Measurements of pixel isolation, timing response, efficiency, hit rate and rate stability are reported.