Lithium scintillator detectors

A flow-through scintillation detector equipped with a lithium glass solid scintillator flow cell is used to detect the eluted "Tc. The glass scintillator enables an absolute detection efficiency of 55% and is stable in the 8 mol/l nitric acid medium for pertechnetate elution. 

The purified pertechnetate eluted from the column was detected and quantified with a flow through scintillation detector using a lithium glass solid scintillator. This scintillator material exhibited excellent stability in the strong nitric acid solutions used for pertechnetate elution. 

For a similar Ge lithium-drifted detector, the energy required for ionization is 2.96 eV. This is much less than the energy required for ionization in a proportional counter or a Nal(Tl) scintillation detector. 

The efficiency of the detector may be improved by increasing the isotopic ratio of the Li, which is present as only 7.4% in natural lithium. Owing to its sensitivity to y radiation, a scintillation detector is not generally suitable where a strong background of high-energy y rays is present. 

Figure 8.28 shows how the X-rays fall on the solid or liquid sample which then emits X-ray fluorescence in the region 0.2-20 A. The fluorescence is dispersed by a flat crystal, often of lithium fluoride, which acts as a diffraction grating (rather like the quartz crystal in the X-ray monochromator in Figure 8.3). The fluorescence may be detected by a scintillation counter, a semiconductor detector or a gas flow proportional detector in which the X-rays ionize a gas such as argon and the resulting ions are counted.

As discussed above, the measurement of characteristic y rays is very similar to the methods used in EDXRF. Early studies used a scintillation counter, typically a crystal of sodium iodide containing a small amount of thallium (Tite 1972). y ray absorption by these counters produces visible light, which is converted into an electrical pulse using a photosensitive detector. More recently semiconductor detectors have been used, either a lithium drifted germanium crystal, or, more typically, a pure ( intrinsic )... 

Detectors include (1) Geiger-Mueller tube, (2) ionization chambers, (3) scintillation counters, (4) proportional counter, (5) electron-multiplier tubes, and (G) nondispersive detectors using cooled lithium-drifted Si detectors, See Fig. 3... 

Solid scintillators include materials such as sodium iodide, lithium iodide, anthracene, naphthalene and loaded polymers. Sodium iodide detectors are by far the most important, and subsequent discussions will be restricted to... 

The semi-conductor transducer (scintillation counter). Each X-ray photon increases the conductivity of the active zone (the junction) of a lithium-doped silicon diode (one electron for around 3.6 eV). The background noise is reduced if the sensor is maintained at low temperature (cooled by liquid nitrogen or a Peltier device). The entry surface is protected by a beryllium film of a few pm (transparent for Z > 11) (Figure 12.8). In one or other cases the impulse furnished by the detector allows to go back to the energy of the incident photon. 

Cherepy NJ, Sanner RD, Beck PR, Swanberg EL, Tillotson TM, Payne SA et al (2015) Bismuth- and lithium-loaded plastic scintillators for gamma and neutron detection. Nucl Instmm Methods Phys Res Sect A Accelerators Spectrometers Detectors Assoc Equip... 

Scintillators which have hydrogen as a constituent, such as organic liquids for example, may be used for fast neutron detection, since the protons produced by fast neutron collisions create the ionization required to operate the detector. In order to adapt a sodium iodide scintillator for the detection of slow neutrons, a small concentration of boron may be distributed in the crystal, giving a particles on neutron capture as discussed above. Alternatively, it is possible to add a neutron absorber which emits 7 rays following the (n, y) capture reaction. Another possibility is the use of lithium iodide (Lil) which, in addition to its own suitability as a scintillator, interacts with neutrons through the reaction... 

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