Analysis of gamma-ray spectra from an aircraft-mounted array of high-resolution sensors

Abstract

Gamma-ray spectra have been collected using the Environmental Radionuclide Sensor System.². Twenty aircraft-mounted, high-purity germanium sensors are utilized to collect high-resolution environmental spectra. Since time-over-target is limited for aerial surveys, one must often attempt to glean the maximum quantity of information from low-count spectra. The spectral data are collected in a time-stamped-list-mode, which time tags every gamma-ray. This allows a gamma-ray spectrum to be built without dilution for only the time-over-target. The analysis package utilizes photopeaks from natural background isotopes to autocalibrate and gain shift the individual spectra into a composite spectrum. The analysis software utilizes several unique techniques to robustly analyze low-count spectra. It carefully determines the spectral baseline, finds all the peaks which differ from the baseline by more than 4-standard deviations, uses a binary-search technique to fit Gaussian peaks, and utilizes a large library to identify peaks (including minor and escape peaks). Although in an aerial survey, the source geometry is often unknown or difficult to model, the software attempts to assign consistent source strengths to radionuclides. *** DIRECT SUPPORT *** A00E1009 00008