Radiation detection techniques in today’s world have important applications ranging from health. Nuclear, environmental industries just to mention a few. In Radiometric geophysics the detection of radiation may be used to explore distribution of radioelements that may assist with exploring important deposits such as uranium. There are many modern techniques due to rapid advancement of technology. However the principle behind these techniques remains common. Today I have written this post to you just to give an idea on only two (2) techniques frequently employed in radiometric geophysics. Thank you for continuing to read this post!
What is Geiger Muller (GM) Tube?
It is a device used to detect radiation particles and rays such as alpha, beta particles and gamma rays by applying ionization effects produced in the tube.
The tube consists of two metal electrodes at which one is a thin wire which is positively charged (act as Anode), while the other is a cylinder shaped around the wire which is negatively charged (act as cathode). The space between them is filled with a gas, usually argon or other inert gases (halogens) such as Neon. A high voltage of about 400 - 900 volts is applied across these two electrodes.
When radiation passes into the tube, through a mica window it interacts with the gas filled inside the tube and an ionization effect occurs which produces ion pair (Positively charged and electrons). Each ion is attracted towards an electrode of its respective opposite charge, such as electrons are attracted towards anode while positively charged ions are attracted towards cathode.
Because the electric field is so strong due high Potential difference at electrodes, the electrons are accelerated to high energies and liberate other electrons in collisions with gas atoms. An electron conduction through gas grows, resulting in ionization of most of the gas in the tube, and in such a way a current pulse develops when a threshold level is reached and can be detected and counted by external electronics.
See the diagram below for more understanding
Application of Geiger Muller Tube
i/ It acts as a radiation Particles Counter: You may use it to count the individual particles of radiation entering the detector at a time as a counter per unit time, hence the name Geiger Muller Counter.
ii/ It used to measure radiation strength: If the average magnitude of current across is measured.
Despite being employed frequently, Geiger Muller Counter can’t give an identity of type of radiation either its alpha, beta or gamma rays!
Scintillation Counter.
As the name describes, a scintillator is the material that emits light energy when hitted by energetic radiation and particles.
It simply works by the principle of photoelectric effect that an electron is excited when a material is illuminated by energetic radiation such as X-rays, gamma rays. Materials such as Sodium Iodide (NaI), Stilbite have this property
The incident light excites the electrons into their higher energy levels, when they turn back to their ground (lower) energy level it emits light which is proportional to the energy of incident light. Then this light strikes the Photomultiplier tube (PMT), and becomes converted into an electrical signal which is then analyzed by a detector.
Fig: Showing simple schematic flow of scintillation counter
There are many types of scintillator Crystal materials that are used for different purpose of radiation detection as shown in the figure below
Gamma Ray Spectrometer (GRS)
It is a scintillometer that is designed to distinguish gamma rays according to their energy level. Because gamma rays from different natural elements have different energy levels.
The intensity of the light emitted induces a voltage whose amplitude is directly proportional to the original gamma Ray energy.
This can occur when the gamma rays lose all their energy at once by photo conversion. Light is received by a photoMultiplier Tube (PMT) and converts light into a voltage.
The sky has no limit, this is just the basics. Enjoy your time!
Follow this blog on Telegram group
0 Comments