Categories
Chemistry

Detection of Radiation

Diffusion Cloud Chamber

The Diffusion Cloud Chamber is used to view high energy alpha particles, lower energy beta particles, and electrons produced by gamma rays interacting with gas molecules. The Chamber allows for the viewing of cosmic rays without the need for dry ice or external illumination. Historically the Cloud Chamber was the first particle detector for making ionizing particles visible. Its working principle is based on supersaturated vapour. This vapour shows tracks of condensated alcohol while being penetrated by ionizing particles. Vapour clouds build up along the particle tracks, which are sometimes thin and long, sometimes thick and round or bulbous. They may appear gradually or pop up all of a sudden or move very fast like a projectile splintering into all directions.

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Geiger – Muller Counter

The Geiger-Muller counter is a particle detector designed to detect ionizing radiation, such as alpha and beta as well as gamma radiation (although with significantly lower sensitivity than other types of detectors). It was invented by the German physicist Hans Geiger (co-discoverer of the atom nucleus) and later improved by his student Walther Muller, therefore the name Geiger-Muller counter. It is probably one of the most famous radiation detectors, mostly due to its simplicity and the distinctive audible clicks produced with the detection of individual particles.

Alternatively, except for its use in the detection of ionizing radiation, the Geiger counter is also used as a random number generator.

The main element of a Geiger counter is the Geiger-Muller tube, which is basically a chamber filled with inert gas or a mix of organic vapor and halogens. The tube contains two electrodes, the anode and the cathode, which are usually coated with graphite. The anode is represented by a wire in the center of the cylindrical chamber while the cathode forms the lateral area. One end of the cylinder, through which the radiation enters the chamber, is sealed by a mica window.

As ionizing radiation coming from the surrounding medium passes through the mica window and enters the Geiger-Muller tube, it ionizes the gas inside, transforming it into positively charged ions and electrons. The electrons eventually migrate towards the anode of the tube detector, while the positively charged ions accelerate towards the cathode. As the positive ions move towards the cathode, they collide with the remaining inert gas thus producing more ions through an avalanche effect. When this happens an electrical current is established between the two electrodes. The current is amplified and the resulting flow of electrons can be used to produce sound, light flashes or meter readings.

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Scintillation Counter

Certain minerals, such as zinc sulphide fluoresce or glow when exposed to radiation. The glow is made up of tiny flashes of light or scintillation and these may be seen under a microscope or counted with suitable device.

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