Lanthanum Bromide Scintillator Practical Performance Evaluation

Since the introduction of lanthanum halide scintillation detector materials, efforts have been made to accurately characterize their performance. Basic traits such as energy response, resolution and efficiency have been determined. While these characteristics are of interest as general figures of merit, it is not obvious that they can be reliably equated to a particular level of performance in practical usage. This study attempts to provide application specific examples to gauge performance. Although such an approach entails a certain level of subjectivity, a consistent and sufficiently large sampling ensures that this inductive approach can be meaningfully interpreted. Furthermore, comparisons to sodium iodide and germanium detectors using the same metric provides reference benchmarks against more familiar performance. A standard application for portable scintillators is the identification of radionuclides for security purposes, as defined in ANSI N42.34. This standard provides a minimum set of nuclides required for identification. Sets of spectra from 28 of these nuclides, both singly and mixed, are created for LaBr3(Ce), NaI(Tl) and HPGe detectors. Since obtaining a full set of sources is difficult, the spectra are created by modeling in MCNP, matching the measured detector characteristics, and adding measured background spectra. Several of the nuclides have also been measured for comparison to provide a level of confidence that the modeled spectra sufficiently replicate actual measurements. All of the spectra are analyzed using the same algorithms to measure the ability to accurately identify the nuclides. Algorithm parameters are varied between analysis sets to sample for optimal settings, but are maintained constant throughout each analysis set. Results are tallied in terms of correct identifications and false identifications and presented in light of relative expectations given the measured traits. Analyses are conducted with accurate calibrations and no shielding, and with a gain shift and shielding.