Scintillator

A scintillator is a body whose molecules are excited by collisions during passage of high-energy photons or charged particles and release the excitation energy in the form of light (usually in the ultraviolet or visible region ) again. This process is known as scintillation (from the Latin scintillare: sparkle ',' flicker ').

Introduction

The effect is mainly used in scintillation counters to measure the energy and intensity of ionizing radiation. The energy deposited in the scintillator of each impulse action is obtained by measuring the amount of light (for example, a photomultiplier or a photodiode ), the intensity ( the flow of the particles or quantum ) from the number of scintillations per unit time.

Indirectly, free neutrons can be detected, namely the charged particles that move according to scattering processes due to the recoil by the scintillator or released during nuclear reactions of neutrons in the scintillator (see neutron detector ).

The word scintillator can call the relevant material or the finished piece of equipment.

There are organic and inorganic scintillators. They have different mechanisms of scintillation.

Inorganic scintillators

Inorganic scintillators are crystals, doped with activator centers. Ionizing radiation produces free electrons in the solid state, free of holes or electron -hole pairs ( excitons ). In the crystal lattice migrate such excited states, until they encounter a Aktivatorzentrum. The Aktivatorzentrum is now excited and decays with the emission of visible light (photons ) into the ground state. The Ionisationsverlust of the particles determines how many photons are generated in the crystal.

Thus the scintillator for its own light is permeable enough, he must generally be a single crystal.

Examples: bismuth germanate, lead tungstate, Lutetiumoxyorthosilicat, sodium iodide, zinc sulfide, cesium iodide

Organic scintillators

Organic scintillators can be crystals, liquids or polymeric solids. The mechanism of scintillation depends on the excitation of molecular conditions in a primary fluorescent material which emit UV radiation in the decomposition. A second fluorescent material, such as the " wavelength shifter " POPOP, the scintillator must be added because UV radiation in most transparent materials has a very short range. Recently, polyethylene was discovered as the primary fluorescent material in good yield in the visible wavelength range, which can expect a significant price reduction of organic scintillators.

For liquids as scintillators is to distinguish between

• Liquid scintillation, wherein the substance to be measured ( a low energy beta emitter ) is together with the scintillator, in a solution, and
• Liquid scintillators for measuring fast neutrons. Such a scintillator is enclosed in a sealed glass jar or metal vessel with glass windows, such as a solid scintillator used. These scintillators have the advantage that the problems stemming from gamma radiation pulses from the neutron pulses by electronic means ( pulse shape discrimination) can be distinguished.

Use

Scintillators are widely used in basic research, but also in areas such as radiation protection and radiation medicine. In particle physics, they are, for example - used in calorimeters - together with other materials such as wavelength shifters. With the increasingly higher energies and intensities of the particle thereby increase the demands on quality, complexity, and radiation resistance of the scintillator.