We evaluate the ability of the Canberra Alpha Beta Environmental Continuous Air Monitor (ECAM) to detect and quantify airborne radiological contamination. The ECAM essentially consists of a passively-implanted planar silicon (PIPS) detector near a particulate filter through which outside air is pulled. Three years’ worth of background measurements on three different systems were assessed and calibrated to compensate for changing conditions and develop an average background response for the systems. The ECAM was also exposed to several radionuclides of interest, including ²³⁵U and ²³⁹Pu, to measure the response to alpha and beta particle sources. Both standard calibration sources and custom sources consisting of aqueous radioisotope solutions absorbed into clean filters. The ECAM responses to these sources were then scaled to quantities of interest and injected on the averaged background. Various alarm algorithms were evaluated on the source-injected spectra for minimum detectable air concentration for a given false alarm rate. Even in the worst case, the ECAM was able to detect radionuclides of interest at 10% of the Derived Response Level (DRL) for each isotope based on early-phase Protective Action Guides (PAG). Quantification of the radionuclides was also evaluated for the various algorithms, with mixed results, but overall clearly indicating the optimal algorithms for alpha and beta particle alarm and quantification. Finally, a limited evaluation of the beta particle detection efficiency points to a detection energy threshold of approximately 290 keV.

我们评估堪培拉Alpha Beta环境连续空气监测器（ECAM）检测和量化机载放射污染的能力。ECAM本质上由靠近微粒过滤器的被动植入式平面硅（PIPS）检测器组成，通过该检测器可以吸入外部空气。对三个不同系统进行了为期三年的本底测量，并进行了评估和校准，以补偿不断变化的条件并开发出系统的平均本底响应。ECAM还暴露在多种感兴趣的放射性核素下，包括²³⁵ U和²³⁹Pu，以测量对α和β粒子源的响应。标准校准源和定制源均由吸收到干净过滤器中的放射性同位素水溶液组成。然后将对这些来源的ECAM响应按比例缩放到感兴趣的数量，并在平均背景下注入。在给定的误报警率下，在源注入的光谱上评估了各种报警算法，以检测出最小的空气浓度。即使在最坏的情况下，ECAM仍能够根据早期保护行动指南（PAG），以每种同位素的10％的派生响应水平（DRL）检测感兴趣的放射性核素。还对各种算法对放射性核素的定量进行了评估，结果各有不同，但总体上清楚地表明了α和β粒子报警和定量的最佳算法。