Long-term empirical radiation detector calibration for airborne geophysical surveying

This study investigates the long-term calibration and validation of the Aerial Measuring System (AMS) fixed and rotary-wing aerial gamma-ray survey platforms. Each of the five aircraft are equipped with an array of 2.08 L NaI(Tl) scintillator detectors that are empirically calibrated using the large area calibration pads located in Grand Junction, Co. Two spectral extraction methods, the International Atomic Energy Agency (IAEA) published window method and the Gaussian method, are compared using calibration pad data. Aerial surveys conducted at Lake Mohave and Government Wash are also analyzed, with good agreement between the IAEA and Gaussian methods and ground truth measurements within two standard deviations. The study's findings showcase the stability and reliability of the AMS system for naturally occurring radioactive material (NORM) mapping for use in applications such as geologic mapping, environmental monitoring, and exploration as well as highlight the feasibility of the Gaussian based approach which has some advantages over the IAEA window method in that the Gaussian extractions may avoid some of the isotopic and altitude dependence of the terms in the IAEA window method.