Ultra low background time projection alpha particle detector

The search for rare-events, such as double beta decay or dark matter detections, is primarily a fight to reduce the incidence of background events to sufficiently low levels so that the events of interest can be seen. Two major sources of background are trace amounts of radio-impurities found within the materials used to construct, support, and shield these experiments, and the contamination of these materials surfaces caused by exposure to atmospheric radon. Direct detection of alpha emission is necessary to accurately determine the levels of surface contamination on these ultra-pure materials, but currently available screening techniques do not have sufficient sensitivity to characterize these materials at the levels required. The DOE, which is a major supporter of rare-event search activities, therefore has an active interest in the development of ultra low activity materials. By extension, there is also an active interest in developing instrumentation for characterizing such ultra low activity materials, since it is impossible to improve something that cannot be measured. Approach: In this project we are proposing to develop an instrument to effectively characterize radiopure materials for surface alpha emission, an instrument whose lower detection limit will be over 100 times lower than that of the best commercially available instruments. XIA manufactures and sells the UltraLo-1800 alpha particle counter, which represents the current state-of-the-art in low background alpha particle detection. In the proposed approach, we will convert the UltraLo-1800 from an ionization chamber into a time projection chamber, which will allow us to push achievable background rates towards 1 alpha/day/m2, without shielding at the earth’s surface. This enhanced sensitivity will allow for the relatively rapid characterization of ultra-pure materials without having to conduct the measurement underground. Commercial Application & Benefits: If successful, this instrument’s direct benefit will be its support of a variety of rare-event experiments which seek to expand our understanding of the basic principles upon which the universe operates. Moreover, the enhancements made to the capabilities of the UltraLo-1800 will provide a significant performance advantage in other areas, including environmental remediation measurement of alpha radiation, and the semiconductor packing industry where controlling alpha activity from packaging materials is critical to increasing device reliability. Key Words: Low background, alpha particle detector, time projection chamber