Microgeiger: A Micromachined Gas-Based Beta Radiation Detector

Abstract

This paper reports a micromachined Geiger counter fabricated from a glass-Si-glass stack of wafers. As a beta particle passes through, a bias applied between two enclosed electrodes generates electron cascades in the gas between them. This results in a current pulse or "count". A single die of 2 cm 2 had 6 independent chambers ranging in size from 8X 8 mm to 1X 3 mm. He, Ne, and a He/air mixture, which have different voltage bias requirements, are separately evaluated as background gases. Counting rates are lower in a Ne background gas than in He, but Ne is more suitable for packaging. In tests the device was found to detect incident beta particles from a Uranium-238 source. Counting rates of up to 22 counts/min were measured. As with conventional Geiger counters, the rates varied inversely with distance from the source. The microGeiger was tested with pure He and Ne background gas with 90 Sr, 60 Co, and 204 Tl, all beta emitting isotopes. Rates up to 24 counts/min. were measured.

A bulk silicon micromachined structure for gas microdischarge-based detection of beta-particles

“…The basic micro-detector structure consists of a square chamber with a central cathode and a peripheral anode (figure 1(a)). The region proximal to the cathode has a 2 Portions of this work have been reported in conference abstract form in [20]. 3 Portions of this work have been reported in conference abstract form in [21].…”