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

This paper describes two Si micromachined structures for sensing beta-particles. The basic device (the micro-detector) includes a square silicon cathode surrounded by a concentric anode, and is formed by stacks of glass and Si wafers. Incident beta-particles ionize the gas encapsulated between the electrodes, resulting in an avalanche current pulse or ‘count’. It is shown experimentally that devices with 8 × 8 mm2 footprint can detect radiation in the proximity of sealed sources, such as 90Sr and 204Tl with 0.1–1.0 μCi strengths. The sensitivity (cpm mRad−1 h) of the micromachined device is comparable to that of commercial radiation detectors, but substantially superior when normalized to the detector volume, which is about 0.06% of the conventional detectors. An extension of the basic device, the stacked micro-detector, consists of a two-tiered arrangement of cavities separated by a thin glass intercavity attenuator that is intended to provide controlled energy absorption. Higher energy particles are detected in both cavities, while lower energy particles are detected in the first cavity and subsequently absorbed by the intercavity attenuator. This can provide initial assessment of the incident radiation without adding significant complexity to the system. Preliminary experimental validation is performed by comparing the device response to 204Tl and 90Sr. (Some figures in this article are in colour only in the electronic version)