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.

[A] - [F]

 
Alpha: Alpha radiation is a heavy, very short range particle, and is actually an ejected helium nucleus.  Alpha radiation is not able to penetrate human skin.  Examples of some alpha emitters are: radium, radon, uranium, thorium.
 
Backscatter Detection:
Electron backscatter - A method to investigate crystallographic properties of a sample in an SEM by placing a stationary beam on the sample and record the patterns of backscattered electrons emitted from that area.  The recording is done by making the electron pattern visible on a fluorescent screen and record the image with a TV camera.
Neutron Backscatter – A method used for oil exploration by logging the relative hydrogen bulk density of the material down a drilled well.  The technique works by ejecting high energy neutrons from the source to react with the immediate surrounding.  The moderated neutrons (called slow neutrons or thermal neutrons) are scattered back towards the detector and counted.  Materials rich in hydrogen produce high count rates while materials with little hydrogen concentration give low count rates.  The results are typically plotted versus distance.
X-ray backscatter – A method used for discrimination of organic or "low Z" (i.e., low atomic number) materials such as explosives, drugs, cigarettes, and people, especially when hidden within a complex environment.
 
Beta: Beta radiation is a light, short range particle, and actually an ejected electron. Beta radiation may travel several feet in air and is moderately penetrating.  Examples of some pure beta emitters: strontium-90, carbon-14, and tritium.
 
CCD - Charge Coupled Device: A 2D imaging device made up of rows and columns of pixels.  Charge is generated within the active area of each pixel when light is incident.  Every pixel’s charge is then transferred through to an output node to be converted to a voltage, buffered and sent off chip as an analogue signal.  Further electronic circuits are then needed to process this signal so that the image can be read by a computer.
 
CMOS – Complementary Metal Oxide Semiconductor: A 2D imaging device made up of rows and columns of pixels.  Each pixel has it’s own photon to charge to voltage converter.  CMOS devices require less current and typically have on-chip digitising circuits so that the output is in digital form directly, or with the aid of only a few extra components, readable by a computer.
 
CsI:Tl: Caesium Iodide doped with Thallium is a high efficiency x-ray scintillator favoured for its columnar growth structure when deposited by evaporation.  The columnar structure reduces scatter from exiting photons by light guiding within the columns.
 
CT - Computed Tomography: This is an x-ray scanner that takes successive images of an object from different angles and uses a computer to build these images into cross-sectional images of the object.  Computed Tomography is a specialized X-ray imaging technique.  It may be performed "plain" or after the injection of a "Contrast Agent".  This technique eliminates the problem of conventional X-rays, where all the shadows overlap.
 
CTF – Contrast Transfer Function: A mathematical function that expresses the ability of an optical or electronic device to transfer signals as a function of the spatial or temporal frequency of the signal.  The CTF is the ratio of percentage Contrast of a square wave signal leaving to that entering the object over the range of frequencies of interest.  The CTF is usually presented as a graph of Contrast versus frequency (line pairs per mm – lp/mm).
The resolution measurement system at AST uses a square wave ‘Line pair’ lead phantom as the basis of square wave input signal, and measures the peak contrast in the resulting x-ray image. This measurement is performed from 2 lp/mm to 10 lp/mm and the peak contrast value is averaged over many images.
 
Fluoroscopy: Fluoroscopy is a technique for continuous or intermittent x-ray monitoring.  X-ray images may be viewed directly without taking and developing x-ray photographs.  This allows observation of certain dynamic body processes and is useful in certain surgical and diagnostic procedures.  The radiologist moves the screen up and down the patient's body and observes what is happening within selected parts of the body.
 
FOP – Fibre Optic Plate: This is a matrix of optical fibres bonded together to form a coherent fiber optic plate that precisely transmits an image from its input surface to its output surface.

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