Sodium Iodide

Of all available scintillators, NaI(Tl) is the most extensively used. The material has an unequalled high light output and an excellent match of the emission spectrum to the sensitivity of photomultiplier tubes, resulting in very good energy resolution detectors.


  • Material – NaI(Tl)
  • Density (g/cm3) – 3.67
  • Emission Maximum (nm) – 415
  • Thermal expansion coefficient (c-1) – 47.4 x 10-6
  • Decay Constant – 0,23 µs
  • Refractive Index – 1.85
  • Conversion Efficiency – 100
  • Light yield (photons/KeVγ) – 38
  • Hygroscopic – Yes
Very high light output, good energy resolution
General scintillation counting, Medical, Security, Industrial, Environmental monitoring, Oil & gas - core logging, Nuclear physics
  • Medical – SPECT (gamma camera), whole body counting, radioimmunoassay (RIA)
  • Security – Thermal neutron activation
  • Industrial – Thickness or density gauging, coal / mineral assy
  • Oil and gas exploration – well logging
  • Environmental monitoring
  • Aerial survey
  • Nuclear physics

NaI(Tl) crystals are widely used for radiation detection: in nuclear medicine, for environmental monitoring, in nuclear physics, aerial survey, well logging and in many other applications including low background applications.

NaI(Tl) produces one of the highest signals in a PMT per amount of radiation absorbed. Under optimum conditions, an average of 1x 104 photoelectrons are produced per MeV γ-rays.

NaI(Tl) exhibits several decay time constant components. The primary single exponential decay constant is 250ns at room temperature.

NaI(Tl) is susceptible to radiation damage, i.e. prolonged exposure to intense radiation degrades the scintillation performance. Radiation damage has been observed above levels of 1 Gray (102 rad). The crystal should not be exposed to ultraviolet radiation from fluorescent lamps or sunlight.

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