1. Gamma spectroscopy measurement can quantitatively determine the content of uranium, thorium, and potassium in rocks (minerals, building materials) based on the original composition of these three nuclides γ Differences in spectra. γ The high-energy region of the instrument (greater than 500 KeV) can clearly distinguish the original γ The main characteristic peak of radiation (omnipotent peak). The Y-rays produced by the decay of different radioactive isotopes have different characteristic energies, such as 1.461 MeV for potassium, 2.614 MeV for thorium, and 1.764 MeV for radium. Therefore, qualitative and quantitative calculations of nuclides can be carried out using differences in nuclide energy and Y-ray intensity.



2. Implemented using Nal (T1)+photomultiplier tube combination detector γ X-ray spectroscopy measurement



The scintillation detector combined with Nal (T1) and photomultiplier tube has a short resolution time and is suitable for γ The detection efficiency of radiation and the ability to measure the energy of radiation are currently widely used detectors. The scintillation detector utilizes γ The principle of fluorescence effect generated by the interaction between radiation and Nal (T1) for detection



Theoretical basis analysis of low background measuring instruments (Figure 1)



3 γ Radiation. Nal (T1) crystal is a highly efficient scintillator, and its luminescence intensity exhibits a good linear relationship with the energy of photons over a large range. Therefore, based on the light height or the amplitude and number of voltage pulses output by the photomultiplier tube, it can be determined γ The energy of radiation and γ The intensity of radiation.



4. Nal (T1) has achieved γ The conversion process from radiation to high-energy photons requires the detection of photons, especially low light levels. An ideal detector is a photomultiplier tube, which converts photons into pulsed electrical signals. Then, a special nuclear electronics circuit amplifies, shapes, analyzes the pulse amplitude of the electrical signal, and forms the spectral lines of the radiation (recording the intensity of the radiation according to different energy distributions, with energy on the horizontal axis and intensity on the vertical axis).