Scintillation Counter

What is a Scintillation Counter?

The flash of light which is produced by a transparent material due to the passage of a subatomic particle (electron, ion, alpha particle, or photon) is called scintillation. The scintillation counter is a device that is used to detect radiation by means of a scintillation effect. It is also known as a scintillation detector. Scintillation is a major part of a scintillation detector. A scintillation detector usually consists of the following components:

  • Scintillator: A scintillator is a device that emits light when a high energy particle hits it. The energy of the emitted pulse of light is directly proportional to the particle that hits the scintillator. This makes it an efficient energy-dispersive radiation detector much used in spectroscopy. The generation of photons occurs in the scintillator as a response to the incident radiation.

  • Photodetector: A photodetector converts light to an electrical signal in order to process the signal. A photomultiplier tube (PMT), a photodiode or a charged coupled device (CCD) is generally used as a photodetector.

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Scintillation Counter How it Works

Let us try to understand the principle of scintillation counter through the following points.

  • When ionizing incident radiation enters the scintillator, it interacts with the material of the scintillator due to which the electrons enter an excited state.

  • Charged particles follow the path of the particle itself.

  • The energy of gamma radiation (uncharged) is converted to a high energy electron either through the photoelectric effect, Compton scattering, or pair-production effect.

  • The excited atoms of the scintillator material gradually undergo de-excitation and emit photons in the visible range of light. This emission is directly proportional to the energy of the incident ionizing particle. The material shines or flows brightly due to fluorescence.

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  • Three types of phosphors are used namely:

  • Inorganic crystals,

  • Plastic phosphors,

  • Organic crystals.

  • The pulse of light emitted by the scintillator hits the photocathode of the photomultiplier and releases at most one photoelectron for each photon.

  • These electrons are accelerated through electrostatic means by applying a voltage potential, and are targeted to hit the first dynode, by having enough energy to produce further electrons.

  • These released electrons are called secondary electrons. They strike the second dynode, thereby releasing further electrons. This process occurs in a photomultiplier tube.

  • Each subsequent impact on the dynode releases further electrons, and hence a current amplifying effect occurs on the dynodes. Each subsequent dynode is at a higher potential than the previous one, and so helps in enhancing the acceleration.

  • Likewise, the primary signal is multiplied throughout 10 to 12 stages.

  • At the final dynode, highly sufficient numbers of electrons are present to produce a pulse of high magnitude to develop amplification. This pulse carries information about the energy of the incident ionizing particle. The number of pulses per unit time gives the significance of the intensity of radiation.

Types of Scintillation Counter

There are basically two types of scintillators used in nuclear and particle physics. They are plastic or organic scintillators and crystalline or inorganic scintillators.

  1. Organic Scintillators

Organic scintillators are the organic materials that provide photons in the visible part of the spectrum after a charged particle is passed through it. The scintillation mechanism of organic material is different from that of inorganic material. The fluorescence or scintillation in organic materials is produced due to the transition of the energy levels of a single molecule. The fluorescence in organic materials can be observed independently in any of the physical states viz: vapor, liquid, and solid.

  1. Inorganic Scintillators

Inorganic scintillators are the crystals made in high-temperature furnaces. They include lithium iodide (LiI), cesium iodide (CsI), sodium iodide (NaI) and zinc sulfide (ZnS). NaI(TI) (thallium-doped sodium iodide) are highly used inorganic scintillation materials. The iodide, present in sodium iodide provides the necessary stopping power (because it has high Z = 53). The process of scintillation in inorganic materials is normally slower than that of organic materials. The inorganic scintillators have very high efficiency to detect the gamma rays and are also capable of handling high rates of counts.

FAQ (Frequently Asked Questions)

1. Applications of Scintillation Counter.

Ans- Following are the application of scintillation counter:

  1. Scintillation Counters are used in many processes like radioactive contamination, radiometric assay, radiation survey meters, medical imaging, and nuclear plant safety.

  2. There are several scintillation counters which are mounted on helicopters and on pickup trucks to measure the rapid response of the particles in case any security situation or emergency arises because of radioactive wastes.

  3. Special scintillation counters are designed for weighbridge applications, scrap metal yards, freight terminals, contamination monitoring of nuclear waste, and border security.

  4. Scintillation counters are used for protein interaction and detection, pharmaceutical, and academic research.

  5. Liquid scintillation counter is a special type of scintillation counter which is used to measure the beta emission from the nuclides.

  6. It is used in various screening technologies like Vivo and ELISA and also in alternative technologies, epigenetics, and cancer research, and in cellular research.

2. What is Liquid Scintillation Counter?

Ans- Liquid scintillation is the processes in which the radioactive activity of a sample material is measured by mixing the active material with a liquid scintillator. Here, the photons that are emitted are counted as the scintillation reaction proceeds to take place. It is usually used to detect the alpha and beta particles.

3. What are the Advantages of Scintillation Counter?

Ans- These are some of the major scintillation counter advantages.

  1. It has a very fast counting rate.

  2. It is used to detect x-rays.

  3. It is more sensitive to Geiger Muller counters.

  4. The scintillation counters can detect the lower levels of radiation.

4. What Causes Scintillation?

Ans- Scintillation is the process of producing a flash of light when high energy ionized radiation strikes a scintillation surface or materials. Scintillation occurs because, when an energetic particle hits a material, it imparts energy to the electron and the electron goes to an excited state. This electron, when it loses its excited state, releases photons as a flash of light thus causing scintillation to occur.