3: Basic Principles Flashcards
Mask, collimators, diaphragms and lead backing are used for what in radiography?
Reducing scatter
Close contact between the film and metal intensity by screens is essential to obtain what?
Sharp images
A thin sheet of lead or lead sandwiched between sheets of tin is placed between the film and object being radiographer. What kind of effect does this provide?
Intensifying
What is one of the main advantages of gamma rays over X-rays for radiography?
No electric supply needed
What is depleted uranium used in industrial radiography for?
Shielding in isotope cameras
The quality of radiation refers to what?
Penetrating ability of x or gamma rays
When using a 400 kV X-ray machine, what range of steel thickness could you radiograph with?
19-76 mm
With 1000 keV, what range of steel thickness could you inspect?
25-127 mm
What keV or less may scatter in air path?
15 keV or less
When inspecting a thin foil up to 3 mm of steel, what range of keV should you be using?
5-50 keV
With 50-150 keV, what thickness of steel can you inspect?
3-19 mm
With 100-200 keV, what range of steel could you inspect?
6-50 mm
With 2000-6000 keV, what thickness of steel can you inspect?
50-203 mm
When you have steel that’s between 75-457 mm, what voltage should you be using?
15-24 MeV
Blurring of an image due to subject moved is called what?
Motion unsharpness
If a radiograph is produced with too short a SFD and yet processed to give good density, what imperfection is it likely to have?
Lack of sharpness
Collimators should be selected by…
Their size, shape and ability to limit beam to only the area being radiographed
The elimination of unwanted portions of the d or gamma ray beam at its source by use of shielding is called what?
Collimation
What is the purpose of masking a specimen with lead is to what?
Reduce undercut caused by scattered radiation
An exposure device housing a radio isotope for industrial radiography can be called a what?
Camera
What is computed radiography?
A flexible phosphorus imaging plate - that absorbs radiation energy which is stored and won’t be released until stimulated - used with a laser scanning device.
How does computed radiography work?
The laser scan stimulates the phosphorus which causes the stored charges to emit blue light which is collected by a photomultiplier tube, converted to electrical signals that are digitized
What is the process called in computed radiography?
Photo-stimulated luminescence
How do digital detectors work?
Radiation energy is captured by an absorbing material (such as caesium iodide), which coverts radiation into visible light, then absorbed by a low-noise photodiode array which converts light into an electric charge.
