Ultra-Low Background Alpha Activity Counter

76318-Naturally occurring alpha¿particle emitters disrupt both sensitive nuclear physics measurements (such as in rare particle detectors, where they raise background rates) and the operation of high density digital electronics chips (where they introduce soft errors in memory or processing steps). Therefore, ultra-low alpha¿particle emitting materials are critical to future development in both these areas. A major problem hindering the development of these materials is the lack of suitable instrumentation to characterize them. The critical issue is that the materials used in the alpha¿particle counters also contain these same natural alpha¿emitters, and their presence sets background levels that prevent the counter from measuring materials with significantly lower activity than the counter itself. It is difficult and expensive to construct counters of ultra-low activity materials, which are unfortunately prone to contamination. This project will employ digital signal processing and pulse shape discrimination to determine whether counted alpha¿particles were emitted from the sample or from counter construction materials. By reducing detector noise, optimizing pulse shape recognition algorithms, and optimizing detector geometry it should be possible to achieve rejection ratios of 10,000-to-1 between counter-source and sample-source alpha¿particles. In Phase I, the geometry and instrumentation of an existing detector will be modified to demonstrate that electronic noise levels can be reduced by an order of magnitude. Using the modified detector, data will then be collected to demonstrate the aforementioned rejection ratios. Commercial Applications and Other Benefits as described by the awardee: Potential commercial applications include: (1) support for government research programs, such as rare particle detection, that require ultra-low background materials; (2) instruments for monitoring environmental pollution, where there is interest in measuring the alpha activity of very low level samples; and (3) the semiconductor industry, which has targeted requirements for ultra-low alpha activity level materials for next generation, package-free mounting schemes ¿ because alpha¿particles introduce ¿soft errors¿ into both large memories and processors.