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 NaI(Tl) scintillators | |||
| Identifiers | |||
|---|---|---|---|
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3D model (JSmol) | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider |
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| ECHA InfoCard | 100.028.800 | ||
| RTECS number |
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| UNII | |||
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| Properties | |||
| NaI | |||
| Molar mass | 149.894 g/mol[1] | ||
| Appearance | white solid deliquescent[1] | ||
| Odor | odorless | ||
| Density | 3.67 g cm−3[1] | ||
| Melting point | 661 °C (1,222 °F; 934 K)[1] | ||
| Boiling point | 1,304 °C (2,379 °F; 1,577 K)[1] | ||
| 1587 g/L (0 °C) 1842 g/L (25 °C) 2278 g/L (50 °C) 2940 g/L (70 °C) 3020 g/L (100 °C)[2][3] | |||
| Solubility | ethanol, acetone[1] | ||
| Band gap | 5.89 eV[4][5] | ||
| −57×10−6 cm3 mol−1[6] | |||
Refractive index (nD) | 1.93 (300 nm) 1.774 (589 nm) 1.71 (10 μm)[7] | ||
| Structure[8] | |||
| Halite,cF8 | |||
| Fm3m, No. 225 | |||
a = 0.6462 nm | |||
Formula units (Z) | 4 | ||
| Octahedral | |||
| Thermochemistry[9] | |||
| 52.1 J mol−1 K−1 | |||
Std molar entropy(S⦵298) | 98.5 J mol−1 K−1 | ||
Std enthalpy of formation(ΔfH⦵298) | −287.8 kJ mol−1 | ||
Gibbs free energy(ΔfG⦵) | −286.1 kJ mol−1 | ||
| Hazards | |||
| Occupational safety and health (OHS/OSH): | |||
Main hazards | Irritant, can harm the unborn child | ||
| GHS labelling: | |||
  | |||
| Danger | |||
| H315,H319,H400 | |||
| P273,P305+P351+P338[10] | |||
| NFPA 704 (fire diamond) | |||
| Flash point | Non-flammable | ||
| Safety data sheet (SDS) | [1] | ||
| Related compounds | |||
Otheranions | Sodium fluoride Sodium chloride Sodium bromide Sodium astatide | ||
Othercations | Lithium iodide Potassium iodide Rubidium iodide Caesium iodide Francium iodide | ||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Sodium iodide (chemical formulaNaI) is anionic compound formed from thechemical reaction ofsodium metal andiodine. Under standard conditions, it is a white, water-solublesolid comprising a 1:1 mix of sodiumcations (Na+) andiodideanions (I−) in acrystal lattice. It is used mainly as a nutritional supplement and inorganic chemistry. It is produced industrially as thesalt formed when acidic iodides react withsodium hydroxide.[11] It is achaotropic salt.
Sodium iodide, as well aspotassium iodide, is commonly used to treat and preventiodine deficiency. Iodized table salt contains 10 ppmiodide.[11]
Sodium iodide is used for conversion ofalkyl chlorides intoalkyl iodides. This method, theFinkelstein reaction,[13] relies on the insolubility ofsodium chloride inacetone to drive the reaction:[14]
Some radioactive iodide salts of sodium, including Na125I and Na131I, haveradiopharmaceutical uses forthyroid cancer andhyperthyroidism or asradioactive tracer in imaging (seeIsotopes of iodine > Radioiodines I-123, I-124, I-125, and I-131 in medicine and biology).
Sodium iodideactivated withthallium, NaI(Tl), when subjected toionizing radiation, emitsphotons (i.e.,scintillate) and is used inscintillation detectors, traditionally innuclear medicine,geophysics,nuclear physics, and environmental measurements. NaI(Tl) is the most widely used scintillation material. The crystals are usually coupled with aphotomultiplier tube, in ahermetically sealed assembly, as sodium iodide ishygroscopic. Fine-tuning of some parameters (i.e.,radiation hardness,afterglow,transparency) can be achieved by varying the conditions of thecrystal growth. Crystals with a higher level ofdoping are used inX-ray detectors with high spectrometric quality. Sodium iodide can be used both assingle crystals and aspolycrystals for this purpose. The wavelength of maximum emission is 415 nm.[15]
António Egas Moniz searched for aradiocontrast agent forcerebral angiography.[16] After experiments onrabbits anddogs he settled upon sodium iodide as the best medium.[16]
Sodium iodide exhibits high solubility in some organic solvents, unlike sodium chloride or even bromide:
| Solvent | Solubility of NaI (g NaI/kg of solvent at 25 °C)[17] |
|---|---|
| H2O | 1842 |
| Liquid ammonia | 1620 |
| Liquid sulfur dioxide | 150 |
| Methanol | 625–830 |
| Formic acid | 618 |
| Acetonitrile | 249 |
| Acetone | 504[18] |
| Formamide | 570–850 |
| Acetamide | 323 (41.5 °C) |
| Dimethylformamide | 37–64 |
| Dichloromethane | 0.09[19] |
Iodides (including sodium iodide) are detectably oxidized by atmosphericoxygen (O2) to moleculariodine (I2). I2 and I− complex to form thetriiodide complex, which has a yellow color, unlike the white color of sodium iodide. Water accelerates the oxidation process, and iodide can also produce I2 by photooxidation, therefore for maximum stability sodium iodide should be stored under dark, low temperature, low humidity conditions.
