Signal Processing and Its Effect on Scanning Efficiencies for a Field Instrument for Detecting Low-energy Radiation

Abstract

Signal processing within a radiation detector affects detection efficiency. Currently, organizations such as private industry, the U.S. Navy, Army, and Air Force are coupling some detector systems with data collection devices to survey large land areas for radioactive contamination. As detector technology has advanced and analog data collection has turned to digital, signal processing is becoming prevalent in some instruments. Using a NIST traceable (241)Am source, detection efficiency for a field instrument for detecting low-energy radiation (FIDLER) was examined for both a static and scanning mode. Experimental results were compared to Monte Carlo-generated efficiencies. Stationary data compared nicely to the theoretical results. Conversely, scanning detection efficiencies were considerably different from their theoretical counterparts. As speed increased, differences in detection efficiency approached two orders of magnitude. To account for these differences, a quasi time-dependent Monte Carlo simulation was created mimicking the signal processing undertaken by the FIDLER detection system. By including signal processing, experimental results fell within the bounds of the Monte Carlo-generated efficiencies, thus demonstrating the negative effects of such processing on detection efficiencies.

Validating a Methodology That Associates Minimum Detectable Activity with Detector Velocity

“…The Multi-Agency Radiation Survey and Site Investigation (MARSSIM) manual discusses how speed could affect detection results in remediation but provides no guidance on how to correct for it (US NRC 2000). Marianno identified the phenomenon when evaluating the performance of a field instrument for the detection of low-energy radiation to locate plutonium point source contamination during a mobile survey (Marianno et al 2000; Marianno 2015). Hart expanded upon Marianno’s work to establish correction factors for detectors based on speed but did not explore the explicit relationship between speed and minimum detectable activity (Hart et al 2003).…”