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Sodium iodide

Sodium iodide
CAS number 7681-82-5
RTECS number WB6475000
Molecular formula NaI
Molar mass 149.89 g/mol
Appearance White solid.
Density 3.67 g/cm³, solid
Melting point


Boiling point


Solubility in water 184 g/100 ml (25°C)
EU classification Irritant (I).
NFPA 704
R-phrases R36, R38, R42, R43,
S-phrases S26, S36, S37, S39
Flash point Non-flammable.
Related Compounds
Other anions Sodium fluoride
Sodium chloride
Sodium bromide
Other cations Lithium iodide
Potassium iodide
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Sodium iodide is a white, crystalline salt with chemical formula NaI used in radiation detection, treatment of iodine deficiency, and as a reactant in the Finkelstein reaction.

Solubility of NaI in various solvents
(g NaI / 100g of solvent at 25°C)
H2O 184
Liquid ammonia 162
Liquid sulfur dioxide 15
Methanol 62.5 - 83.0
Formic acid 61.8
Acetonitrile 24.9
Acetone 28.0
Formamide 57 - 85
Acetamide 32.3
Dimethylformamide 3.7 - 6.4


Sodium iodide is commonly used to treat and prevent iodine deficiency.

Sodium iodide is used in polymerase chain reactions, and also (as an acetone solution) in the Finkelstein reaction, for conversion of an alkyl chloride into an alkyl iodide. This relies on the insolubility of sodium chloride in acetone to drive the reaction.

R-Cl + NaI → R-I + NaCl

Solid crystals of sodium iodide can be used to detect radiation (e.g. radiation from uranium)—a solid crystal of sodium iodide creates a pulse of light when radiation interacts with it.[2]

Sodium iodide crystals doped with thallium, NaI(Tl), when subjected to ionising radiation, emit photons (scintillate) and are used in scintillation detectors, traditionally in nuclear medicine, geophysics, nuclear physics, environmental measurements, etc. NaI(Tl) is the most widely used scintillation material and has the highest light output. The crystals are usually coupled with a photomultiplier tube, in a hermetically sealed assembly, as sodium iodide is hygroscopic. Fine tuning of some parameters (radiation hardness, afterglow, transparency) can be achieved by varying the conditions of the crystal growth. Crystals with higher level of doping are used in X-ray detectors with high spectrometric quality. Sodium iodide can be used both as single crystals and as polycrystals for this purpose.

Notes, references

  1. ^ Burgess, J. "Metal Ions in Solution" (Ellis Horwood, New York, 1978) ISBN 0-85312-027-7
  2. ^ DIY Nuke Detector Patrols SF Bay

See also

  • Scintillation counter
  • Gamma spectroscopy
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Sodium_iodide". A list of authors is available in Wikipedia.
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