The scintillation counter consists of two components, such as a scintillator (phosphorus) and a photoelectronic type multiplier. In the basic configuration, manufacturers added to this counter a source for electrical power and radio equipment that provides amplification and registration of PMT pulses. Quite often, the combination of all elements of this system is carried out using an optical system - a light guide. Further in the article, we will consider the principle of operation of a scintillation counter.
Features of work
The device of a scintillation counter is rather complicated, so this topic needs to be given more attention. The essence of the operation of this apparatus is as follows.
A charged particle enters the device, as a result of which all molecules are excited. These objects settle down after a certain period of time, and in this process they release the so-called photons. This whole process is necessary for the flash of light to occur. Certain photons pass to the photocathode. This process is necessary for the appearance of photoelectrons.
Photoelectrons are focused and delivered tooriginal electrode. This action occurs due to the work of the so-called PMT. In the subsequent action, the number of these same electrons increases several times, which is facilitated by electron emission. The result is tension. Further, it only increases its immediate effect. The duration of the pulse and its amplitude at the output are determined by the characteristic properties.
What is used instead of phosphorus?
In this device, a replacement for such an element as phosphorus was invented. Generally, manufacturers use:
- organic-type crystals;
- liquid scintillators, which must also be organic type;
- solid scintillators that are made of plastic;
- gas scintillators.
Looking at the data on phosphorus substitution, you can see that manufacturers in most cases use only organic substances.
Main Feature
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 very duration of the scintillation.
In the process of passing various charged particles through the scintillator, a certain number of photons are produced, which carry here or another energy. A rather large part of the produced photons will be absorbed and destroyed in the tank itself. Instead of photonswhich have been absorbed, other kinds of particles will be produced, which will represent energy of a somewhat lesser nature. As a result of all this action, photons will appear, the properties of which are characteristic exclusively for the scintillator.
Light output
Next, consider the scintillation counter and the principle of its operation. Now let's pay attention to the light output. This process is also called conversion-type efficiency. The output of light is the so-called ratio of the energy that comes out to the amount of energy of the charged particle lost in the scintillator.
In this action, the average number of photons goes exclusively outside. This is also called the energy of the average nature of the photons. Each of the particles present in the device does not bring out the monoenergetics, but only the spectrum as a continuous band. After all, it is he who is characteristic of this type of work.
It is necessary to pay attention to the most important thing, because this spectrum of photons independently leaves the scintillator known to us. It is important that it coincide or at least partially overlap with the spectral characteristic of the PMT. This overlap of scintillator elements with a different characteristic is determined solely by the coefficient agreed upon by the manufacturers.
In this coefficient, the spectrum of the outer type or the spectrum of our photons goes into the external environment of this device. Today there is such a thing as "scintillation efficiency". It is a comparison of the device withother 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. This indicator also takes into account the sensitivity of the device to photons.
- The effectiveness of this work, as a rule, is evaluated by comparing with the scintillation efficiency of the scintillator, which is taken as a standard.
Various scintillation changes
The principle of operation of a scintillation counter also consists of the following no less important aspect. Scintillation can be subjected to certain changes. They are calculated according to a special law.
In it, I0 indicates the maximum intensity of the scintillation we are considering. As for the indicator t0- it is a constant value and it denotes the time of the so-called attenuation. This decay shows the time during which the intensity decreases in its value by certain (e) times.
It is also necessary to pay attention to the number of so-called photons. It is denoted by the letter n in our law.
Where is the total number of photons emitted during the scintillation process. These photons are emitted at a certain time and registered in the instrument.
Phosphorus work processes
As we wrote earlier, scintillation countersact on the basis of the work 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 kind is fluorescence.
- The second kind is phosphorescence.
These two species differ primarily in time. When the so-called flashing occurs in conjunction with another process or during a period of time on the order of 10-8 sec, this is the first kind of process. As for the second type, here the time interval is somewhat longer than the previous type. This discrepancy in time arises because this interval corresponds to the life of an atom in a restless state.
In total, the duration of the first process does not depend at all on the index of restlessness of this or that atom, but as for the output of this process, it is the excitability of this element that affects it. It is also worth noting the fact that in the case of the restlessness of certain crystals, the rate of the so-called exit is somewhat less than with photoexcitation.
What is phosphorescence?
The advantages of the scintillation counter include the phosphorescence process. Under this concept, most people understand only luminescence. Therefore, we will 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 crystal phosphors arises from the recombination of electrons and holes that have arisen during excitation. In certainphosphorus objects, it is absolutely impossible to slow down the process, since electrons and their holes fall into so-called traps. From these very traps, they can be released on their own, but for this they, like other substances, need to receive an additional supply of energy.
In this regard, the duration of the process also depends on a particular temperature. If other molecules of an organic nature also take part in the process, then the process of phosphorescence occurs only if they are in a metastable state. And these molecules cannot go into a normal state. Only in this case can we see the dependence of this process on the speed and on the temperature itself.
Features of counters
Has a scintillation counter advantages and disadvantages, which we will consider in this section. First of all, we will describe the advantages of the device, because there are quite a lot of them.
Specialists highlight a rather high rate of temporary ability. In time, one pulse emitted by this device does not exceed ten seconds. But this is the case if certain devices are used. This counter has this indicator several times less than its other analogues with an independent discharge. This greatly contributes to its use, because the counting speed increases several times.
The next positive quality of these types of counters is a rather small indicator of a late impulse. But such a process is carried out only after the particles have passed the registration period. it's the sameallows you to directly save 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.
Production of devices
Who invented the scintillation counter? This was done by the German physicist Kalman Hartmut Paul in 1947, and in 1948 the scientist invented neutron radiography. The principle of operation of the scintillation counter allows it to be produced in a fairly large size. This contributes to the fact that it is possible to carry out the so-called hermetic analysis of a rather large energy flux, which includes ultraviolet rays.
It is also possible to introduce certain substances into the device, with which neutrons can interact quite well. Which, of course, has its immediate positive qualities in the manufacture and future use of a counter of this nature.
Design type
Particles of the scintillation counter ensure its high-quality performance. Consumers have the following requirements for the operation of the device:
- on the so-called photocathode is the best indicator of light collection;
- on this photocathode there is an exceptionally uniform type of light distribution;
- unnecessary particles in the device are darkened;
- magnetic fields have absolutely no effect on the entire carrier process;
- coefficient inin this case is stable.
Disadvantages scintillation counter has the most minimal. When carrying out work, it is imperative to ensure that the amplitude of the signal types of pulses corresponds to other types of amplitudes.
Counter packaging
The scintillation counter is often packaged in a metal container with glass on one side. In addition, a layer of special material is placed between the container itself and the scintillator, which prevents ultraviolet rays and heat from entering. Plastic scintillators do not need to be packed in sealed containers, however, all solid scintillators must have an exit window at one end. It is very important to pay attention to the packaging of this appliance.
Meter Benefits
The advantages of the 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 instrument's capabilities include a wide range of services.
- The ability to distinguish between certain particles uses only information about their energy.
It is due to the above indicators that this type of meter outperformed all its competitors and rightfully became the best device of its kind.
It is also worth noting that its disadvantages include sensitive perceptionchanges in a particular temperature, as well as environmental conditions.
