"NO-NUKE: Researchers show solid-state Geiger counter costing $10"
Professor Douglas McGregor at Kansas State University discusses his gallium arsenide diodes that are being used to build real-time nuclear-radiation detectors that promise to be as small and cheap as today's non-real-time "dosimeter" badges. The button-size single-chip detectors will give on-the-spot readings of radiation levels, as Geiger counters do, but without the Geiger counters' expense and heft. In the current version, a round gallium arsenide sensor chip outputs a pulse for every 13th radioactive particle it encounters. A model on the drawing board would sense every fifth thermal neutron and cost roughly $10.

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Story in EE Times: http://www.eet.com/at/news/OEG20021125S0055