The Figure (Gamma spectrum mono energetic source.png) in the section Interaction of ๐›พ-radiation and matter describes the shape of an E๐›พ-spectrum, resulting from a mono-energetic source. In nature, however, ๐›พ-photons with different energies are emitted and the ๐›พ-energy spectrum will be more complex than the one described in Figure 3.2. When photons from a source with different energies hit a ๐›พ-ray detector, the measured spectrum will be composed of a number photo-peaks and different Compton continua. Since the natural decay series of 40K, 232Th and 238U emit ๐›พ-rays with different energies, a ๐›พ-ray spectrum of natural sediment will contain various photo-peaks.

Typical response curves for natural radionuclides

Depending on the resolution of the detector system, the information in those ๐›พ-ray spectra can be translated in the activity concentrations of the different radionuclides either by photo-peak analysis or full spectrum analysis (FSA).