ANALYSIS OF GAMMA-RAY SPECTRA FROM AN AIRCRAFT-MOUNTED ARRAY OF HIGH-RESOLUTION SENSORS

Gamma-ray spectra have been collected using the Environmental Radionuc lide 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 sp ectra. The spectral data are collected in a time-stamped-list-mode, wh ich time tags every gamma-ray. This allows a gamma-ray spectrum to be built without dilution for only the time-over-target. The analysis pac kage utilizes photopeaks from natural background isotopes to autocalib rate and gain shift the individual spectra into a composite spectrum. The analysis software utilizes several unique techniques to robustly a nalyze low-count spectra Tt carefully determines the spectral baseline , finds all the peaks which differ from the baseline by more than 4-st andard deviations, uses a binary-search technique to fit Gaussian peak s, and utilizes a large library to identify peaks (including minor and escape peaks). Although in an aerial survey, the source geometry is o ften unknown or difficult to model, the software attempts to assign co nsistent source strengths to radionuclides.