Scintillation counter

Table of Contents

Introduction

The scintillation counter was one of the earliest devices used in the study of radioactivity.
With this simple instrument, it became possible to observe the scintillations (flashes or sparkles of light) produced by alpha particles or protons when they struck the screen.

The scintillation counter was re-established as a useful tool in nuclear physics by Curran and Baker in 1994. A photomultiplier tube was used to record the scintillations in place of a human eye. The first counter was used to detect α particles that were made to strike a layer of ZnS screen.

The application of this technique to other types of radiation was modified by Coltman but it didn’t prove to be successful. Until 1949, reliable results were obtained by Bell and Cassidy. The 𝝱 spectrum of Be10 was measured using the scintillation counter.

Principle

Various factors are involved in the construction of a scintillation counter that can be utilized for energy-measuring devices. The conditions necessary for such a counter are:

Uniformity of response – It requires particles produced by γ rays of equal energy of the same amplitude.
High energy efficiency – High energy efficiency is required to obtain the maximum signal from a given particle energy.
Proportionality – It is a desirable property since the scintillation counter needs to be calibrated.

Method or How it works

The initial stage

In this stage, the detection process is done by the interaction of incident radiation with the phosphor crystal. It basically deals with the blockage of the particles including alpha, and beta particles in the phosphor. This in turn helps in excitation in the fluorescence mechanism and a pulse of photons is produced in the crystal.
Thus, a ratio is obtained between the energy dissipated by the pulse and the particle in the phosphor. This ratio is known as energy conversion efficiency or light yield.
Its value is affected by both pulse height and uniformity.
For example, the most efficient phosphor is ZnS(Ag) which has a physical light yield of 30%. It requires only 10 ev in the phosphor to produce one photon of 3 eV.

Decay of the excitation state of photons

It generally means that the rate of production of photons is approximately exponential. It leads to the definition of a decay constant for each phosphor. The decay constant is the measure of the resolving time of the phosphor and sets the maximum counting rate.

The third stage

This stage is divided into two steps:

To get the light out of the phosphor
Collecting the light onto the photocathode surface.

To get the light out of the phosphor, transparency and refractive index play a key role in determining the size and uniformity of the pulse. Also, the intensity of light varies according to the depth measurement of the scintillation counter. The structure of the phosphor also affects the technical light yield as there will be a loss of light. Scattering will occur if the phosphor is in polycrystalline or in powdered form.

In addition to acting as a detector, the photomultiplier tube also contributes to a certain amount of pulse. It thus acts as a deciding factor while estimating signal to noise ratio of the counter.

Description of the equipment:

The Scintillation counter – When experiments were carried out on gamma rays, 931 A type of photomultipliers and naphthalene crystals were used. Due to the low efficiency of naphthalene crystals, good-quality crystals of anthracene finally came into existence.

Phosphor Crystals – Thallium-activated sodium iodide and anthracene were used as phosphors. They are used for the detection of alpha particles and are dependent on the optical clarity of their surfaces.

Photomultiplier Tubes – Photomultiplier tubes are a type of vacuum tube that is used to detect and amplify light signals.

Applications

Nuclear medicine: Scintillation counters are widely used in nuclear medicine for diagnostic imaging techniques like PET scans and SPECT scans.
Scintillation Counters have the ability to detect low levels of radiation. It thus makes them useful for environmental monitoring, particularly in areas with potential radioactive contamination.
Scintillation counters play an important role in detecting and identifying radioactive materials
Scintillation counting is often utilized in industrial settings for quality control purposes.
This device is also used to detect and measure ionizing radiation.

Advantages

High sensitivity: Scintillation counters are highly sensitive to small amounts of radiation, allowing for accurate detection of matter.
These devices can detect different types of ionizing radiation such as alpha, beta, gamma rays, and X-rays.
Scintillation counters have a fast response time compared to other detectors which adds to the extra advantage.

Disadvantages

High cost: Scintillation counters are expensive to purchase and maintain, making them less accessible to certain applications.
Scintillation counters are not able to detect very low levels of radiation

Q&A

1. What is a scintillation counter used for?

A scintillation counter is a device used to detect and measure ionizing radiation.

2. How does a scintillation detector work?

It works by converting the energy from incoming particles into flashes of light, which are then detected and measured.

3. What is the function of a scintillator?

With this simple instrument, it became possible to observe the scintillations produced by alpha particles or protons when they struck the screen.

4. What type of radiation is best detected by a scintillation counter?

A scintillation counter is best for detecting ionizing radiations. It includes alpha, beta, and gamma rays.

Summary

The scintillation counter was one of the earliest devices used in the study of radioactivity. It became possible to observe the scintillations produced by alpha particles or protons when they struck the screen.
The scintillation counter was re-established as a useful tool in nuclear physics by Curran and Baker in 1994.
A photomultiplier tube was used to record the scintillations in place of a human eye. The first counter was used to detect α particles that were made to strike a layer of ZnS screen
Scintillation counters are highly sensitive to small amounts of radiation, allowing for accurate detection of matter.
A scintillation counter is best for detecting ionizing radiations. It includes alpha, beta, and gamma rays.