Full-spectrum analysis of natural gamma-ray spectra.

In this paper, a new system to measure natural gamma-radiation in situ will be presented. This system combines a high-efficiency BGO scintillation detector with full-spectrum data analysis (FSA). This technique uses the (nearly) full spectral shape and the so-called 'standard spectra' to calculate the activity concentrations of 40K, 232Th and 238U present in a geological matrix (sediment, rock, etc.). We describe the FSA and the determination of the standard spectra. Standard spectra are constructed for various geometries and a comparison in intensity and shape will be made. The performance of such a system has been compared to a more traditional system, consisting of a NaI detector in combination with the 'windows' analysis. For count rates typically encountered in field experiments, the same accuracy is obtained 10-20 times faster using the new system. This allows for shorter integration times and hence shorter measurements or a better spatial resolution. The applicability of such a system will be illustrated via an example of an airborne experiment in which the new system produced results comparable to those of much larger traditional systems. This paper will conclude with a discussion of the current status of the system and an outlook for future research.