Sodium Iodide (Tl) Scintillator Crystal

Sodium Iodide (Tl) - NaI(Tl) - is a well established and the most extensively used scintillator. It is used for detecting gamma rays of low and intermediate energies. It has a high level of optical output and relatively inexpensive. It is available in both single crystal and polycrystalline formats.

NaI(Tl) scintillators:

Are one of the ‘brightest’ scintillators available
Have good density and a high Z
Have an optical output well match to the maximum sensitivity of commonly available PMTs
Have good ‘rad hard’ properties
Do not glow in the UV
Have an optical output largely independent of temperature

NaI(Tl) scintillators - issues to be aware of:

Highly hygroscopic with encapsulation needed

NaI(Tl) scintillators are useful in applications such as:

Time-of-Flight measurements
Positron lifetime studies
Positron Emission Tomography (PET)
Specialist applications in nuclear and high energy physics

NaI(Tl) Scintillation Crystals - Optical Properties

Property	Units	Value
Wavelength (Max. Emission)	nm	415
Wavelength Range	nm	325 - 550
Decay Times	ns	230
Light Yield	photons/keV	55
Photoelectron Yield	% of NaI(Tl)	100
Radiation Length	cm	2.6
Optical Transmission	µm	0.15 - 12.5
Transmittance	%	>90 (0.35 - 9µm)
Refractive Index		1.85 (@415nm)
Reflection Loss/Surface	%	6.8

NaI(Tl) Scintillation Crystals - Mechanical Properties

Property	Units	Value
Chemical Formula		NaI(Tl)
Density	g/cm³	3.67
Atomic Number (Effective)		56
Melting Point	ºK	924
Thermal Expansion Coeff.	C⁻¹	47.4 x 10⁻⁶
Cleavage Plane		<100>
Hardness	Mho	2
Hygroscopic		Yes
Solubility	g/100gH₂0	TBA (23ºC)