• Density and atomic number (Z)
• Light output (wavelength + intensity)
• Decay time (duration of the scintillation light pulse)
• Mechanical and optical properties
• Cost

See this article for details – https://www.berkeleynucleonics.com/july-27th-2022-cerium-bromide-and-sodium-iodide-detectors

There is a great variety of choices to consider. Selecting the right material, geometry, readout and electronics are only a start. See https://www.berkeleynucleonics.com/february-11th-2022-customizing-your-scintillation-detector for further reading.

A scintillator is a material that exhibits scintillation, which refers to the emission of light when the material interacts with ionizing radiation. Scintillators are widely used in various fields, including radiation detection, medical imaging, and high-energy physics. Different types of scintillators exist, and some common examples include NaI (sodium iodide), LaBr (lanthanum bromide), CeBr (cerium bromide), and CsI (cesium iodide). These scintillators have distinct properties and are utilized in specific applications. Each of these scintillators has its advantages and suitability for specific applications, depending on factors such as energy resolution, light output, decay time, and cost. Researchers and engineers select the most appropriate scintillator based on the requirements of their particular application.

To detect fast changes in transmitted intensity of X-Ray beams, such as in CT scanners or luggage X-ray detectors, crystals are required exhibiting low afterglow. Afterglow is defined as the fraction of scintillation light still present for a certain time after the X-Ray excitation stops. Afterglow originates within a millisecond and can last hours in long decay time components. Afterglow in most halide scintillation crystals can be as high as a 5-10 percent after 3 ms. The long duration afterglow in e.g. CsI(Tl) can be a problem for many applications. Afterglow in halides is believed to be intrinsic and correlated to certain lattice defects. BGO, CeBr3, and Cadmium Tungstate (CdWO4) crystals are examples of low afterglow scintillation materials.

Radiation damage is defined as the change in scintillation characteristics caused by prolonged exposure to intense radiation. This damage manifests itself by a decrease of the optical transmission of a crystal which causes a decrease in pulse height and deterioration of the energy resolution of the detector. Radiation damage other than radio-activation is usually partially reversible; i.e. the absorption bands often disappear slowly in time; some damage can be annealed thermally.

In general, doped alkali halide scintillators such as NaI(Tl) and CsI(Tl) are rather susceptible to radiation damage. All known scintillation materials show more or less damage when exposing them to large radiation doses. The effects usually can only be observed clearly with thick (> 5 cm) crystals. A material is usually called radiation hard if no measurable effects occur at a dose of 10.000 Gray. Examples of radiation hard materials are CeBr3 and YAP:Ce.

Scintillation light pulses (flashes) are usually characterized by a fast increase of the intensity in time (pulse rise time) followed by an exponential decrease. The decay time of a scintillator is defined by the time after which the intensity of the light pulse has returned to 1/e of its maximum value. Most scintillators are characterized by more than one decay time and usually, the effective average decay time is mentioned. The decay time is of importance for fast counting and/or timing applications.

To detect y-rays efficiently, a material with a high density and high effective Z (number of protons per atom) is required. Inorganic scintillation crystals meet the requirements of stopping power and optical transparency. Their densities ranging from roughly 3 to 9 g/cm3 makes them very suitable to absorb penetrating radiation (γ-rays). Materials with high Z-values are used for γ-ray spectroscopy at high energies (> 1 MeV).

Because photoelectron statistics (or electron-hole pair statistics) play a key role in the accurate determination of the energy of the radiation, the use of scintillation materials with a high light output is preferred for all spectroscopic applications. The scintillator emission wavelength should be matched to the sensitivity of the light detection device that is used (PM, SiPm or photodiode).

Neutrons do not produce ionization directly in scintillation crystals but can be detected through their interaction with the nuclei of a suitable element. In a 6LiI(Eu) scintillation crystal, for example, neutrons interact with 6Li nuclei to produce an alpha particle and a triton (tritium nucleus), which both produce scintillation light that can be detected. Another Li-containing scintillator is CLYC.

Also enriched 6Li containing glass can be used, doped with Ce as an activator. Alternatively, Boron or Gadolinium containing inorganic scintillators can be used but these scintillators are not common. One alternative technique is to construct a large area thermal neutron detector using 6LiF/ZnS(Ag)screens. These can then be read out via green wavelength shifters by PMTs or SiPMs.

Each scintillation material has a characteristic emission spectrum, with wavelength and intensity. The shape of this emission spectrum is sometimes dependent on the type of excitation (photons/particles).

Emission spectra of NaI(Tl), CsI(Tl) and CeBr3, scaled on maximum emission intensity.
Also a typical quantum efficiency curve of a bialkali photocathode and a Silicon Photomultiplier (SiPm) are shown above.

This emission spectrum is of importance when choosing the optimum readout device (PMT / photodiode/SiPm) and the required window material. The graph above shows the emission spectrum of some common scintillation materials.

See this article: https://www.berkeleynucleonics.com/december-3th-2020-history-neutron-detection