This glossary is a list of some of the technical terms used on this website.  Please contact us if there are other words or phrases you would like us to add.

[G] - [N]

 
Gamma radiation: Gamma radiation is very long range, penetrating electromagnetic radiation. A source of this is technetium-99m which is used in nuclear medicine. Gamma rays interact with material by colliding with the electrons in the shells of atoms. They lose their energy slowly in material, being able to travel significant distances before stopping. Depending on their initial energy, gamma rays can travel from 1 to hundreds of meters in air and can easily go right through people.
 
Gel documentation: This is the capture and storage of Gel analysis data.  Electrophoresis is an extremely common technique in molecular biology, used routinely to analyse DNA preparations in order to check quantity, size, structure and constitution of prepared samples.  After separation on a gel (usually agarose), DNA is normally visualised under UV light after treatment with a fluorescent stain.  Whatever the sample or method of visualisation, it is often required to keep a record of the analysis for future reference and analysis.  This can be achieved with instant photography to produce a “hard copy” print of the illuminated gel and its visible bands.
 
Gel Electrophoresis: Gel electrophoresis is a method that separates macromolecules-either nucleic acids or proteins-on the basis of size, electric charge, and other physical properties.  A gel is a colloid in a solid form.  Gel electrophoresis refers to the technique in which molecules are forced across a span of gel, motivated by an electric field.  Activated electrodes at either end of the gel provide the driving force.  A molecule properties determine how rapidly an electric field can move the molecule through a gelatinous medium.  The number and position of bands formed on each lane of gel is the actual genetic "fingerprint" of that DNA sample.
 
Image Quality: Image quality is made up of many perceived factors such as contrast, resolution, mottle, noise etc. As a result there is no simple absolute measure of Image quality, but rather a user/application specific judgement.
 
Infrared Imaging: Imaging of wavelengths longer than those of the visible spectrum.
 
Intra-oral Digital X-ray Imaging: Imaging from within the mouth.  A compact digital imaging device held within the mouth enables dentists to look at specific areas whilst minimising dose to the patient.
 
Laser Alignment/Detection: Laser detection cards are a phosphor based product that are commonly used to visualise the size, shape and position of infra-red or ultraviolet light from a laser source.  However, these devices are also useful for imaging visible laser light that becomes invisible to the laser user when safety goggles are worn.  The laser card converts the laser light into a wavelength that can be seen through safety goggles.
 
Line-Pair: A line-pair is 1 cycle of an attenuating mark followed by a non-attenuating mark with equal spacing which produces a square wave.  1 lp/mm would then be a 500 micron attenuation followed by a 500 micron transmission.
 
MTF – Modulation Transfer Function: A mathematical function that expresses the ability of an optical or electronic device to transfer signals faithfully as a function of the spatial or temporal frequency of the signal.  The MTF is the ratio of percentage modulation of a sinusoidal signal leaving to that entering the device over the range of frequencies of interest.  The MTF is usually presented as a graph of MTF versus frequency (line pairs).  For a square wave signal, the function is known as the CTF.
 
NDT - Non-Destructive Testing: NDT includes those test methods used to examine an object, material or system without impairing its future usefulness.  Non-destructive testing methods include: Penetrant testing systems, radiographic / X-ray imaging, ultrasonic, and other specialized techniques.  Example: Analysis of tyres, castings, welds etc for voids and flaws using x-ray.
 
Neutrons: Neutrons have no electrical charge.  They have nearly the same mass as a proton (a hydrogen atom nucleus).  The source of neutrons is primarily nuclear reactions, such as fission, but they may also be produced from the decay of radioactive nuclides. Because of their lack of charge, neutrons are difficult to stop and have high penetrating power. Neutrons are attenuated (reduced in energy and numbers) by three major interactions, elastic scatter, inelastic scatter and absorption.
Elastic scatter, a neutron collides with a nucleus and bounces off.  This reaction transmits some of the kinetic energy of the neutron to the nucleus of the atom, resulting in the neutron being slowed, and the atom receives some kinetic energy (motion).  As the mass of the nucleus approaches the mass of the neutron, this reaction becomes more effective in slowing the neutron.  Hydrogenous materials therefore attenuate neutrons most effectively.
Inelastic scatter reaction, the same neutron/nucleus collision occurs as in elastic scatter. However, in this reaction, the nucleus receives some internal energy as well as kinetic energy. This slows the neutron, but leaves the nucleus in an excited state. When the nucleus decays to its original energy level, it normally emits a gamma ray.
Absorption reaction, the neutron is actually absorbed into the nucleus of an atom. The neutron is captured, but the atom is left in an excited state.
 
Neutron Imaging/Detection: Plastics and water-based substances have a much higher Neutron attenuation coefficient than metals.  Therefore whilst X-rays are attenuated more effectively by heavier materials like metals, neutrons make it possible to image some light materials such as hydrogenous substances with high contrast.

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