Abstract
The performance of Radio-Isotope Identification (RIID) algorithms using NaI-based γ spectroscopy is increasingly important. For example, sensors at locations that screen for illicit nuclear material rely on isotope identification using NaI detectors to distinguish innocent nuisance alarms, arising from naturally occurring radioactive material, from alarms arising from threat isotopes. Recent data collections for RIID testing consist of repeat measurements for each of several measurement scenarios to test RIID algorithms. It is anticipated that vendors can modify their algorithms on the basis of performance on chosen measurement scenarios and then test modified algorithms on data for other measurement scenarios. It is therefore timely to review the current status of RIID algorithms on NaI detectors. This review describes γ spectra from NaI detectors, measurement issues and challenges, current RIID algorithms, data preprocessing steps, the role and current quality of synthetic spectra, and opportunities for improvements.
Highlights
Radioactive isotopes produce characteristic γ−rays of various energies and intensities that are measured by γ spectrometers
This review describes γ spectra from NaI detectors, measurement issues and challenges, current Radio-Isotope Identification (RIID) algorithms, data preprocessing steps, the role and current quality of synthetic spectra, and opportunities for improvements
Securing national borders against terrorist threats such as dirty bombs regularly makes the news [1], as sensors at various locations screen for illicit nuclear material. Many of these sensors rely on Radio-Isotope Identification (RIID) algorithms using γ spectroscopy to distinguish innocent nuisance alarms arising from naturally occurring radioactive material (NORM)
Summary
Radioactive isotopes produce characteristic γ−rays of various energies and intensities that are measured by γ spectrometers. Securing national borders against terrorist threats such as dirty bombs regularly makes the news [1], as sensors at various locations screen for illicit nuclear material Many of these sensors rely on Radio-Isotope Identification (RIID) algorithms using γ spectroscopy to distinguish innocent nuisance alarms arising from naturally occurring radioactive material (NORM). PMTs consist of a glass vacuum tube that contains a photocathode material that produces photoelectric effect electrons, plus several dynodes and an anode that together amplify the signal from an incident γ by approximately a factor of 106 Due to this amplification and largely due to the fact that a random number of initial electrons is created by each “detected” γ-ray leads to pulse broadening, or “Gaussian energy broadening.”. Due to this amplification and largely due to the fact that a random number of initial electrons is created by each “detected” γ-ray leads to pulse broadening, or “Gaussian energy broadening.” Many peaks in NaI spectra are approximately Gaussian in shape [7], so peak fitting methods often assume a symmetric, Gaussian shape around the peak centroid
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