PROJECT TITLE :

A Gamma Radiation Detector With Orthogonally Arrayed Micromachined Electrodes

ABSTRACT:

Microfabricated radiation detectors can be used to produce 1st alert info concerning presence of harmful radiation. This paper describes a micromachined gamma detector that operates in the Geiger-Muller (G-M) regime. Gamma rays eject photoelectrons from the cathode material through the photoelectric impact and/or Compton scattering, which in turn ionize the Ar fill-gas providing a current pulse. The detector utilizes cathode stacks that are micromachined from stainless steel #304 foil. Micromachined glass fingers with skinny-film anode metal traces are positioned transversely through aligned perforations in the stacked cathodes. This orthogonal array of anodes and cathodes effectively distinguishes electron avalanche regions from drift regions despite the miniaturization, thereby reducing the probability of spurious discharges. Overall, the detector diameter and height are nine and 2.5 mm, respectively. Detector performance is characterized using a 99-μCi 137Cs supply placed at a distance of three cm from the detector. In an integration time of ten min at an applied voltage of 630 V, a supply:background ratio of eighty nine:1 is achieved-a fivefold improvement over the previously reported micromachined devices operating in the G-M regime. This design conjointly reduces the typical charge per discharge to 6.half-dozen pC, permitting the estimated dead time between detection events to be ~one μs.