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Scintillation Counter


An instrument that measures ionizing radiation is the scintillation counter. A scintillator generates photons when the radiation hits the counter. Then, a PMT (photomultiplier tube) converts electronic and electrical signals to process the signal further.

A scintillator counter consists of the following instruments-
1. Scintillator – generates photons when the incident radiation hits the counter.
2. Sensitive photodetector – to convert signals for further processing
3. Charge-coupled device (CCD) – converts light to electrical and electronic signals for amplification.

Scintillation counters are excessively used in radiation protection, various physics research, and radioactive materials. These studies can result in good quantum efficiency. In addition, scintillation counters can measure both the intensity and energy of an incident radiated light.

How does the scintillation counter work?

The scintillation counter detects gamma rays along with the presence of a particle. It can measure the energy loss or energy gain in the radiation. The medium can be solid, liquid, or gas. It comprises transparent crystalline materials, like liquids, plastics, glasses, etc.

While passing through a scintillator, a charged particle loses its energy. Thus, it creates a trail of excited atoms and molecules. The scintillator is allowed to pass through rapid electronic energy that bursts its material to the luminescence characteristics. The scintillator responds when a particle stops the output. It measures the energy loss of a particle when a particle ultimately moves through it. This quantity is proportional to the energy collected by the ionizing particle. These collected particles are directed to a photocathode photomultiplier tube that emits at most one electron for every photon coming towards it due to the photoelectric effect.

These electrons are accelerated and focussed by the electrical potential to make them strike at the first diode of the tube. This impact of accelerated electrons releases several secondary electrons that are accelerated further to strike ample diodes. At each stage, the potential increases, resulting in the generation of an accelerating field.

This accelerating field is a measurable pulse that arrives at the photocathode and carries energy-related information of the original incident radiation. The scintillator counter also determines the intensity of the pulse when the numbers increase, increasing the radiation. In some experiments, the number of pulses is not counted. Instead, the average of the anodic current is measured to find the intensity of the radiation.

The scintillator must be shielded with opaque foil so that external photons do not swamp any events caused by the ionization of the incident radiation.

Detector efficiencies

  • Gamma - The quantum efficiency of a gamma-ray detector (per unit volume) depends upon the density of electrons in the detector, and certain scintillating materials, such as sodium iodide and bismuth germanate, achieve high electron densities as a result of the high atomic numbers of some of the elements of which they are composed. However, detectors based on semiconductors, notably hyper pure germanium, have better intrinsic energy resolution than scintillators and are preferred where feasible for gamma-ray spectrometry.
  • Neutron - In the case of neutron detectors, high efficiency is gained through scintillating materials rich in hydrogen that scatter neutrons efficiently. Liquid scintillation counters are an efficient and practical means of quantifying beta radiation.

Applications of scintillation counter

1. The scintillation counter is used in radiation survey meters, radioactive contamination, the safety of the nuclear plant,            radiometric assay, and medical imaging to measure radiation.
2. Several scintillation counters are attached to helicopters and trucks to prevent hazards that may happen accidentally due        to radioactive wastes or nuclear bombs.
3. Scintillation counters are designed for freight terminals, border security, scrap metal yards, contamination monitoring of      nuclear waste, and weighbridge applications.
4. They are also used in pharmaceutical industries to extract protein and perform academic research.
5. They are used in cancer research, cellular research, in-vivo and ELISA studies, and other screening technologies.
6. The scintillation counter exists in all the stages – solid, liquid, and gas—the liquid scintillation counter measures beta            emission from the nuclides in the nuclear power plant or any research.

Frequently asked questions on a scintillation counter

Ques 1: What is meant by scintillation efficiency?
Ans: Scintillation efficiency is the ratio of the energy of scintillation light to the energy collected in the ionizing particle.

Ques 2: For what purpose a scintillation counter is used?
Ans: A scintillation counter is used for detecting and measuring ionizing radiation. They are also used to study radiation in nuclear power plants and academic research.

Ques 3: Why is liquid scintillation used?
Ans: Radioactivity is best detected by the liquid scintillation counter. The analytical method is used to measure radioactivity when the photons are emitted once the incident light hits the counter.

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