FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

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archivability of film or its ability to retain the original film record, is
very questionable.
10. SAFETY OF PERSONNEL
Radiation safety must also be considered when comparing different systems.
Currently, the total time of radiation exposure is calculated and safety
areas are delimited so that personnel will not be overexposed. The total
time of exposure at a given radiographie station on the laybarge during one
day usually will not exceed two hours if 180 joints per day (4 minute cycle
time) is assumed. This also assumes a 20 second exposure. Radiation safety
zones are determined by marking off an area outside of which exposure will be
limited to two milliroentgen per hour (2mR).
11. REAL TIME RADIOGRAPHY
11.1 System Description
Real time radiography is the non-destructive examination procedure which
collects radiation that penetrates a specimen, converts the radiation to an
electronic image, and then visibly displays the image. The technology of
real time radiography poses three problems:
1• the physics of image formation,
2. the computer management of information, and
3. the application of the complete system to its environment.
11.2 Physics of Image Formation
The formation of real time radiographs follows the same principle as the
formation of conventional film radiographs. Sources utilized for real time
radiography are identical to those utilized in conventional film radiography.
The quantity of radiation energies absorbed by the specimen results in the
contrast density differences that form the image. Radiation sources have the
same influence in the quality of real time image produced as they do in the
quality of film image produced. Focal spot size and energy output directly
influence geometric unsharpness and contrast sensitivity, respectively.
The physics of producing a real time image is more complicated than producing
a film radiographie image. X- or gamma radiation must be converted into a
useable electronic image. Conversion of the radiation to an electronic image
begins when x- or gamma radiation interacts with special phosphors, metals,
or crystalline structures sometimes called scintillators. Scintillators
convert x- or gamma rays into luminescence or electron charges that can be
readily made into a visible image. Common equipment which convert x- or
gamma ray energies into analog information are intensifiers, linear arrays,
and charged coupling devices (CCD). New technologies are aiding in the
development of miniaturized and solid state detecting components. Regardless
of the converter, this analog information must be digitally addressed so that
the computer can create and retain an image. The computer image is called a
digital image because the computer has assigned numerical values to the
densities (brightness) and locations of each picture element (pixel).