Scintillation detectors are one of the types of measuring equipment designed to detect elementary particles. Their feature is that reading occurs through the use of light-sensitive systems. For the first time these instruments were used in 1944 to measure the radiation of uranium. There are several types of detectors depending on the type of working agent.
Destination
Scintillation detectors are widely used for the following purposes:
- registration of radiation pollution of the environment;
- analysis of radioactive materials and other physical and chemical studies;
- use as an element to launch more complex detector systems;
- spectrometric study of substances;
- signaling component in radiation protection systems (for example, dosimetric equipment designed to notify about the entry of a ship into a zone of radioactive contamination).
Counters can produce both quality registrationradiation and measure its energy.
Detectors arrangement
The basic structure of a scintillation radiation detector is shown in the figure below.
The main elements of the equipment are as follows:
- photomultiplier;
- scintillator designed to convert the excitation of the crystal lattice into visible light and transmit it to the optical converter;
- optical contact between the first two devices;
- voltage stabilizer;
- electronic system for recording electrical impulses.
Types
There is the following classification of the main types of scintillation detectors according to the type of substance that fluoresces when exposed to radiation:
- Inorganic alkali halide meters. They are used to register alpha, beta, gamma and neutron radiation. Several types of single crystals are produced in industry: sodium iodide, cesium, potassium and lithium, zinc sulfide, alkaline earth metal tungstates. They are activated with special impurities.
- Organic single crystals and transparent solutions. The first group includes: anthracene, tolan, trans-stilbene, naphthalene and other compounds, the second group includes terphenyl, mixtures of anthracene with naphthalene, solid solutions in plastics. They are used for time measurements and for detecting fast neutrons. Activating additives in organic scintillators are notcontribute.
- Gas medium (He, Ar, Kr, Xe). Such detectors are mainly used to detect fission fragments of heavy nuclei. The wavelength of the radiation is in the ultraviolet spectrum, so they require appropriate photodiodes.
For scintillation neutron detectors with a kinetic energy up to 100 keV, zinc sulfide crystals activated with a boron isotope with a mass number of 10 and 6Li are used. When registering alpha particles, zinc sulfide is applied in a thin layer on a transparent substrate.
Among organic compounds, scintillation plastics are the most widely used. They are solutions of luminescent substances in high-molecular plastics. Most often, scintillation plastics are made on the basis of polystyrene. Thin plates are used to register alpha and beta radiation, and thick plates are used for gamma and X-rays. They are produced in the form of transparent polished cylinders. Compared to other types of scintillators, plastic scintillators have several advantages:
- short flash time;
- resistance to mechanical damage, moisture;
- constancy of characteristics at high doses of radiation exposure;
- low cost;
- easy to make;
- high registration efficiency.
Photomultipliers
The main functional component of this equipment is a photomultiplier. It is a system of electrodes mountedin a glass tube. To protect against external magnetic fields, it is placed in a metal casing made of a material with high magnetic permeability. This shields electromagnetic interference.
In the photomultiplier, the light flash is converted into an electrical impulse, and the electric current is also amplified as a result of the secondary emission of electrons. The amount of current depends on the number of dynodes. The focusing of electrons occurs due to the electrostatic field, which depends on the shape of the electrodes and the potential between them. The knocked out charged particles are accelerated in the interelectrode space and, hitting the next dynode, cause another emission. Due to this, the number of electrons increases several times.
Scintillation detector: how it works
Counters work like this:
- Charged particle enters the working substance of the scintillator.
- Ionization and excitation of crystal, solution or gas molecules occurs.
- Molecules emit photons and after millionths of a second they return to equilibrium.
- In the photomultiplier, the flash of light is "amplified" and hits the anode.
- The anode circuit amplifies and measures the electric current.
The principle of operation of the scintillation detector is based on the phenomenon of luminescence. The main characteristic of these devices is the conversion efficiency - the ratio of the energy of a flash of light to the energy lost by a particle in the active substance of the scintillator.
Pros and cons
The benefits of scintillation radiation detectors include:
- high detection efficiency, especially for high energy shortwave gamma rays;
- good temporal resolution, that is, the ability to give a separate image of two objects (it reaches 10-10 s);
- simultaneous measurement of the energy of detected particles;
- possibility of manufacturing counters of various shapes, simplicity of technical solution.
The disadvantages of these counters is the low sensitivity to particles with low energy. When they are used as part of spectrometers, the processing of the obtained data becomes much more complicated, since the spectrum has a complex form.
