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Alkali - Halide Scintillators

The necessity to use NaI(Tl) crystals in sealed units is counterbalanced by the fact that they have the greatest light output among all the scintillators and a convenient emission range coinciding with a maximum efficiency of photomultipliers with bialkali photocatodes. Moreover, large-size NaI(Tl) crystals can be produced at a low cost.

CsI(Na) is a good alternative for NaI(Tl) in many standard applications because it has a high light output (85% of that of NaI(Tl)), the emission in a blue spectral region coinciding with the maximum sensitivity of the most popular PMT with bialkali photocatodes, and hygroscopicity substantially lower than that of NaI(Tl).

Since the maximum of emission spectrum is at 550 nm, photodiodes can be used to detect the emission. Because a scintillator-photodiode pair can be used, it is possible to reduce significantly the size of the detection system, to do without a high-voltage power supply, and to use the detection system in magnetic fields.

We offer a new scintillation material, CsI(CO3). The light output in gamma-excitation is 60% that of NaI(Tl). The decay time varies from 1.4 to 3.4 ms depending on the dopant concentration. These characteristics allow CsI(CO3) to be used in combination with other scintillators in phoswich detectors. CsI(CO3) has an afterglow of 0.05% after 5 microSec.

Undoped CsI
The decay time is ~10 ns. Undoped CsI can be effectively used for experiments in medium- and high-energy physics.

The absorption of thermal neutrons in Li-based crystals proceeds according to the following reaction:
6Li + n - > 4He + 3H + Q
Therefore, the thermal neutrons can be detected against the natural background using the amplitude discrimination. The lithium nuclei number per unit volume for LiF(W) is greater than that in LiI(Eu) by a factor of 3.3.

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Selector Guide for Alkali Halide Scintillators

MaterialImportant propertiesApplications comments
NaI(Tl)Very high light output, good energy resolutionGeneral scintillation counting, monitoring, health physics, environmental high temperature use
CsI(Tl)Non-hygroscopic, rugged, long wavelength emissionParticle - & high energy physics, general detection, photodiode readout, phoswiches
CsI(Na)High light output, ruggedGeophysical
CsI(pure)Fast, non-hygroscopic, radiation hardHigh energy physics (calorimetry)
CsI(CO3)Medium decay time, low afterglowGamma-detection, phoswiches
LiF(W)High neutron cross-sectionThermal neutron detection
LiI(Eu)High neutron cross-section, high light outputThermal neutron detection and spectroscopy

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Physical Properties of Alkali Halide Scintillators

Density [g/cm3]3.674.514.514.514.512.644.08
Melting point [K]9248948948948941133719
Thermal expansion coefficient [K-1]47.4x10649x10649x10649x10649x10637x10640x106
Cleavage plane<100>nonenonenonenone<100><100>
Hardness (Mho)2222232
Wavelength of emission maximum [nm]415420550310405430470
Refractive index at emission maximum1.851.841.791.951.841.41.96
Light output [% of NaI(Tl)](for gamma rays)10085455-6603.530-35
Primary decay time [microSec]0.230.6310.012401.4
Afterglow (after 6 microSec) [%]0.3-50.5-50.1-0.06--
Lower wavelength cutoff [nm]300300320260300-425

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