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This paper reports on a multichannel radiation detection platform enabled with nanoparticles that is capable of detecting and discriminating all types of radiation emitted from fissionable bomb making materials. Typical Geiger counters are limited to detecting only beta and gamma radiation. The micro-Geiger counter reported here detects all species of radiation including beta particles, gamma/X rays, alpha particles, and neutrons. The multispecies detecting micro-Geiger counter contains a hermetically sealed and electrically biased fill gas. Impinging radiation interacts with tailored nanoparticles to release secondary charged particles that ionize the fill gas. The ionized particles collect on respectively biased electrodes resulting in a characteristic electrical pulse. Pulse height spectroscopy and radiation energy binning techniques can then be used to analyze the pulses to determine the specific radiation isotope. The ideal voltage range of operation for energy discrimination was found to be in the proportional region at 1000 Vdc. In this region, specific pulse heights for different radiation species resulted. The amplification region strength which determines the device sensitivity to radiation energy can be tuned with the electrode separation distance. An electrode separation of 0.8 mm produced a count rate of 530 cpm for a 90Sr beta source when compared to an off-the-shelf Geiger counter which produced 1500 cpm. Count rates as high as 15 300 were observed for the same radiation source with electrodes spaced closer than 0.5 mm. By using a novel microinjection ceramic molding and silver paste metallizing process, the batch fabrication of essentially disposable devices can be achieved.
Date of Publication: Oct. 2009