Scintillation Process and Light Detectors

Abstract

Scintillation detectors convert energy from the incident radiation into visible or near visible light. The light is guided out of the sensitive volume and appropriately detected with photosensors. This chapter describes first the physics mechanism of luminescence and the materials most commonly used before dealing with the transport of light, the wavelength shifting and photoelectric light detection. A section on bolometers, which are sensitive thermal light detectors, ends the chapter.

Glossary

Birk’s law Empirical relationship between the light output (L.O.) and the energy deposited in a scintillator

$$\begin{aligned} \frac{\mathrm{\text {d}\,L.O.}}{\text {d}x} = \frac{A \text {d}E/\text {d}x}{1+C \text {d}E/\text {d}x}, \end{aligned}$$

(9.13)

where x is the path length, A is the scintillation efficiency and C is an experimental constant that depends on the scintillating material

Bolometers Thermal detectors that absorb photons transforming their energy into heat

Dynode Part of a photomultiplier acting as a secondary emission electrode, i.e. increasing the number of photoelectrons moving through the device

Fluorescence Fast emission of light by a substance following the deposition of the energy from an incident radiation. It is a type of luminescence

Inorganic scintillator Crystals that produce luminescence when struck by radiation, such as sodium iodide (NaI), cesium iodide (CsI), barium fluoride (BaF$_2$), often with a small amount of activator impurities

Light guide Plexiglass used to transport the light emitted from a scintillator onto a photosensor

Light response The amount of light emitted from a scintillator following the deposition of the energy from an incident radiation

Light yield Ratio between the energy absorbed from the incident radiation and the energy of the luminescence produced

Organic scintillator Aromatic hydrocarbon compounds, such as Naphthalene (C$_{10}$H$_8$), Antracene (C$_{14}$H$_{10}$), Stilbene (C$_{14}$H$_{12}$), producing luminescence when struck by radiation

Phosphorescence Emission of photons sometime after the primary luminescence component, due to electrons being trapped into energy levels which forbid direct de-excitation

Photocathode Part of a photomultiplier which emits electrons via the photoelectric effect

Photomultiplier (PMT) Electron tubes converting light into a measurable current

Plastic scintillator A substance composed of a plastic solvent, most commonly polyvinyl toluene (PVT), doped with one of the organic scintillators

Quantum efficiency Efficiency of photon to electron conversion of a photocathode, i.e. the ratio between the number of electrons produced and the number of photons incident onto a photosensitive material

Scintillator Material emitting light, at visible or near visible frequencies, when struck by radiation

Time response Time interval between the deposition of energy and the emission of luminescence by a scintillator substance

Wavelength shifter Fluorescent material absorbing light at a given frequency and re-emitting at a lower frequency.