scintillation spectrometer[‚sint·əl′ā·shən spek′träm·əd·ər]
a device based on a scintillation counter and used for measuring such characteristics of nuclear radiations and elementary particles as radiation intensity, particle energy, and the lifetime of unstable nuclei and particles.
The possibility of measuring energy by means of a scintillation spectrometer is associated with the dependence of the intensity of the luminescence of a scintillator (the luminescence yield) on the energy lost in the scintillator by a particle. For strongly ionizing particles, such as alpha particles and fission fragments, and for low-energy particles, for which ℰ ≤ 1 million electron volts (MeV), inert gases and crystals of sodium iodide activated by thallium have the best spectrometric characteristics. In the case of thallium-activated sodium iodide, the luminescence yield is linearly dependent on particle energy for electrons with energy ℰ ≤ 1 kiloelectron volt and for protons with energy ℰ ≤ 0.4 MeV.
Thallium-activated sodium iodide is also the most suitable scintillator for the study of gamma quanta and high-energy electrons, since it has a high density (3.67 g/cm3) and a high effective atomic number. A high luminescence yield and good transmission permit a scintillation spectrometer to have good energy resolution. For a crystal 50 cm thick, the resolution Δℰ is given by the equation where ℰ is in gigaelectron volts (GeV). In the case of electrons and gamma quanta with energy ℰ ~ 1 GeV, Δℰ reaches 1 percent.
In high-energy physics, giant sectional complete-absorption scintillation spectrometers are sometimes used for the measurement of the energy of an incoming particle with ℰ ~ 10–100 GeV. The weight of the scintillator in such spectrometers reaches tens or hundreds of tons. Measurement of the total energy released in a nuclear cascade permits the energy of an incoming particle to be determined with an accuracy of up to ± 10 percent.
Because of their high efficiency in recording various particles and radiations and their rapid response, scintillation spectrometers are widely used in nuclear spectroscopy and the spectroscopy of high-energy particles. At low energies (≤1 MeV), the energy resolution of scintillation spectrometers is inferior to that of proportional counters and semiconductor detectors.
V. S. KAFTANOV