Sodium iodide - Nal Tl

This is the most commonly used scintillator material. It is cheap and readily available. Detectors up to 0.75 m diameter have been produced. More typically, the 76 mm diameter by 76 mm high cylindrical sodium iodide detector was for many years the standard gamma-ray spectrometer 

Data are taken from the Haishaw QS Scintillation Detector Catalogue (March 1992) and Saint-Gobain Ceramics and Plastics Inc. Internet sources. 

I Fraction of light emitted more than 6 ms after the initial fluorescence, s Hygroscopic Y, yes N, no S, slightly. 

Notwithstanding its excellent performance compared to other materials, Nal(TI) does has several drawbacks. It is brittle, sensitive to thermal gradients and thermal shock. It is hygroscopic and must be encapsulated at all times. It also exhibits the long afterglow referred to above. At low count rates, this is not necessarily a problem, in that pulses due to the phosphorescence can be eliminated electronically, but at high count rate they tend to pile up and limit high count rate performance. 

Potassium is chemically similar to sodium and is a very likely impurity in sodium salts. Because a small proportion of natural potassium is the radioactive it is 

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Alpha-particle detector Beta-particle detector Gamma-ray detector proportional counters silicon (Si) diode with spectrometer proportional counters Geiger-Muller counters liquid scintillation (LS) counters thallium-activated sodium iodide (Nal(Tl) detector with spectrometer germanium (Ge) detector with spectrometer... 

One effective medium in common use for gamma-ray measurements is thallium-activated sodium iodide [Nal(Tl)]. The relatively high-Z iodine atom provides a high attenuation coefficient for interacting with energetic gamma radiation. It... 

A similar comparison between germanium and sodium iodide (Nal(Tl)) is even more stark. For sodium iodide, both a higher Fano factor and a larger 8 combine to give, at... 

Scintillation methods offer the possibility of high-efficiency detectors with a more rapid time response than the BF3 counter. As mentioned in the previous section, the basis of the scintillation detector is the conversion, in a suitable crystal, such as thallium-activated sodium iodide, Nal(Tl), of the kinetic energy of the charged particle to light, which can be amplified by a photomultiplier tube to provide an electrical pulse. Again, the neutron has to interact to produce either a charged particle or a 7 ray, the latter of which may in turn interact to produce ionizing particles. 

Large-area planar sodium iodide (Nal(Tl)) detectors, which are used routinely in gamma cameras for imaging of single-photon tracers, have seen a revival in... 

The crystal scintillator is usually made from cleaved, optically clear sodium iodide (Nal) activated with 1% of Tl. The crystals are hydroscopic and thus, they are usually sealed in a vacuum tight enclosure with a thin Be window in the front (x-rays entry window) and high quality optical glass in the back (blue light photons exit window). The crystal is usually mounted on the photomultiplier tube using a viscous fluid that minimizes the refraction of blue light on the interface between the crystal and the photomultiplier. 

SODIUM IODIDE (Nal) The most common material used in a scintillation detector for measuring gamma-rays. Often shown with its usual added trace of thallium as Nal (Tl). 

ZnS(Ag) is a traditional phosphor for a-detection while anthracene and stilbene can be used for /3-particle detection. For y-rays, sodium iodide with a small amount of thallium impurity, Nal(Tl), is the most common phosphor. CsI(Tl) is another often used scintillator because it can be formed to special shapes, e.g. thin sheets, much easier than Nal(Tl). Plastics with incorporated organic scintillators are often used in nuclear physics experiments because they produce short light pulses and can be made in various shapes. 

The whole-body counter is equipped with six sodium iodide doped with thallium (Nal(Tl)) detectors, combined in two triangular arrays. The upper array consists of three detectors that scan above and the lower array of three detectors that scan below the subject. The upper array is on a moveable arm that can be raised from the bed surface to the roof of the counting chamber. The lower array is in a fixed geometry 12 cm below the bed. 

The most commonly used commercial scintillation detector has a thallium-doped sodium iodide crystal, Nal(Tl), as the scintillating material. A single crystal of Nal containing a small amount of T1 in the crystal lattice is coupled to a PMT, shown in Fig. 8.25. When an X-ray photon enters the crystal, it causes the interaction... 

As it happens, the band gap of sodium iodide is large and photons emitted by de-excitation of electrons directly from the conduction band would be far outside of the visible range. This makes detection of the light difficult. Not only that, the bulk of the material absorbs the emitted photons before they reach the photomultiplier. Both problems are solved by using an activator. In the case of Nal, this would be thallium and for Csl it is thallium or sodium. The shorthand descriptions for these activated scintillators are Nal(Tl), CsI(Tl) and CsI(Na). 

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