A scintillation counter consists of two such components as a scintillator (phosphorus) and a photoelectronic type multiplier. In the basic configuration, manufacturers added a source for electric power and radio equipment to this counter, which provides amplification and registration of PMT pulses. Quite often, a combination of all the elements of a given system is carried out using an optical system - a light guide. Further in the article, we consider the principle of operation of the scintillation counter.
Features of work
The scintillation counter device is rather complicated, therefore, this topic needs to be paid more attention. The essence of this unit is as follows.
A charged particle enters the device; as a result, all molecules are excited. These objects after a certain period of time calm down, and in this process they release the so-called photons. This whole process is necessary for a flash of light to occur . Certain photons pass to the photocathode. This process is necessary for the appearance of photoelectrons.
The photoelectrons are focused and fed to the original electrode. This action occurs due to the operation of the so-called PMT. In the subsequent action, the number of these same electrons increases several times, which is facilitated by electron emission. As a result, voltage appears. Further, it only increases its direct effect. The pulse duration and its amplitude at the exit are determined by characteristic properties.
What is used instead of phosphorus?
In this apparatus, the replacement of such an element as phosphorus was invented. Typically, manufacturers use:
- organic crystals;
- liquid scintillators, which must also be of organic type;
- solid scintillators that are made of plastic;
- scintillators from gas.
Looking at the phosphorus substitution data, one can see that in most cases manufacturers use exclusively organic substances.
The main characteristic
It's time to talk about the main characteristic of scintillation counters. First of all, it is necessary to note the light output, radiation, its so-called spectral composition and the duration of scintillation itself.
During the passage through the scintillator of various charged particles, a certain number of photons are produced, which carry here or some other energy. A rather large part of the produced photons will be absorbed and destroyed in the tank itself. Instead of the photons that were absorbed, other types of particles will be produced that will represent energy of a slightly smaller nature. As a result of all this action, photons will appear, the properties of which are characteristic exclusively for the scintillator.
Light output
Next, we consider the scintillation counter and the principle of its action. Now pay attention to the exit of light. This process is also called conversion type efficiency. The output of light is the so-called ratio of energy that goes out to the amount of energy of a charged particle lost in the scintillator.
In this action, the average number of photons goes exclusively outside. This is also called mid-energy photon energy. Each of the particles present in the device does not bring out monoenergy, but only a spectrum with a continuous strip. After all, it is he who is characteristic of this type of work.
It is necessary to pay attention to the most important, because this spectrum of photons independently leaves the scintillator known to us. It is important that it coincides or at least partially overlaps with the spectral characteristic of the PMT. This overlap of scintillator elements with a different characteristic is determined solely due to a coefficient agreed by the manufacturers.
In this coefficient, the spectrum of the external type or the spectrum of our photons enters the external environment of this device. Today there is such a thing as "scintillation efficiency." It is a comparison of the device with other PMT data.
This concept combines several aspects:
- Efficiency takes into account the number of our photons emitted by the scintillator per unit of absorbed energy. Also, this indicator takes into account the sensitivity of the device to photons.
- The effectiveness of this work, as a rule, is estimated by comparing with the scintillation efficiency of the scintillator, which is taken as a standard.
Various scintillation changes
The principle of operation of the scintillation counter also consists of the following no less important aspect. Scintillation can be subjected to one or another change. They are calculated according to a special law.
In it, I 0 denotes the maximum intensity indicator of the scintillation under consideration. As for the indicator t 0 , this is a constant value and it means the time of the so-called damping. This attenuation shows the time during which the intensity decreases in its indicator by a certain (e) times.
It is also necessary to pay attention to the number of so-called photons. It in our law is denoted by the letter n.
Where
- the total number of photons emitted during the scintillation process. These photons are emitted at a specific time and are recorded in the device.
Phosphorus processes
As we wrote earlier, scintillation counters operate on the basis of the operation of such an element as phosphorus. In this element, the process of so-called luminescence is carried out. And it is divided into several types:
- The first type is fluorescence.
- The second type is phosphorescence.
These two species differ primarily due to time. When the so-called highlighting occurs in fusion with another process or over a period of time of the order of 10 -8 sec, this is the first type of process. As for the second type, then the time interval is slightly larger than the previous type. This time difference arises for the reason that this interval corresponds to the life of an atom in an unstable state.
In total, the duration of the first process does not depend at all on the indicator of anxiety of one or another atom, but as for the output of this process, it is precisely the excitability of this element that affects it. It is also worth noting the fact that in the case of the uneasiness of certain crystals, the speed of the so-called exit is somewhat lower than with photoexcitation.
What is phosphorescence?
The advantages of a scintillation counter include the phosphorescence process. Under this concept, most people understand only luminescence. Therefore, we consider these features based on this process. This process is the so-called continuation of the process after the completion of a particular type of work. Phosphorescence of crystallophosphors occurs upon the recombination of electrons and holes arising upon excitation. In certain phosphorus objects, it is completely impossible to slow down the process, since electrons and their holes fall into so-called traps. From these same traps, they can be freed independently, but for this they, like other substances, need to get an additional supply of energy.
In this regard, the duration of the process also depends on a particular temperature. If other organic molecules take part in the process, the phosphorescence process occurs only if they are in a metastable state. But these molecules cannot go into a normal state. Only in this case can we see the dependence of this process on speed and on temperature itself.
Counter Features
It has a scintillation counter of advantages and disadvantages, which we will consider in this section. First of all, we describe the advantages of the device, because there are a lot of them.
Experts identify a fairly high rate of temporary ability. In time, one pulse that this device emits does not exceed ten seconds. But this is if certain devices are used. This counter has this indicator several times less than its other counterparts with a discharge of an independent nature. This greatly contributes to its application, because the counting speed increases several times.
The next positive quality of these types of counters is a rather small indicator of a late pulse. But such a process is carried out only after the particles pass the registration period. It also allows you to save directly the time of the pulse of this type of device.
Also, scintillation counters have a fairly high level of registration of certain particles, which include neurons and their rays. In order to increase the level of registration, it is imperative that these particles react with the so-called detectors.
Manufacture of devices
Who invented the scintillation counter? The German physicist Kalman Hartmut Paul did this in 1947, and in 1948, the scientist invented neutron radiography. The principle of operation of the scintillation counter allows you to produce a rather large size. This contributes to the fact that it is possible to carry out the so-called hermetic analysis of a fairly large flow of energy, which include ultraviolet rays.
You can also introduce certain substances with which neutrons can interact quite well with the device. Which, of course, has its immediate positive qualities in the manufacture and future use of this type of meter.
Type of construction
Particles of the scintillation counter ensure its high-quality operation. Consumers have the following requirements for the operation of the device:
- the so-called photocathode is the best indicator of the collection of light;
- this photocathode is used to distribute light of an exceptionally uniform type;
- unnecessary particles in the device are darkened;
- magnetic fields have absolutely no effect on the entire carrying process;
- the coefficient in this case is stable.
Disadvantages scintillation counter has the most minimal. When working, it is imperative to ensure that the amplitude of the signal types of pulses corresponds to other types of amplitudes.
Counter packaging
Often the scintillation counter is packed in a metal container, in which there is glass on one side. In addition, a layer of a special material is placed between the container and the scintillator itself , which prevents the ultraviolet rays and heat from entering. Plastic scintillators do not need to be packaged in sealed containers, but all solid scintillators must have an exit window at one end. It is very important to pay attention to the packaging of this device.
Counter Benefits
The advantages of a scintillation counter are as follows:
- The sensitivity of this device is always at the highest level, and its direct effectiveness directly depends on this.
- The capabilities of the device include a wide range of services.
- The ability to distinguish between particles use only information about their energy.
It is due to the above indicators that this type of meter has bypassed all its competitors and has rightfully become the best device of its kind.
It is also worth noting that its disadvantages include a sensitive perception of changes in a particular temperature, as well as environmental conditions.