Varian Linatron High-Energy X-ray Applications 2007

Optical disks are classified as non-volatile because they can
be written to once, read as many times as desired and
cannot be erased. Therefore, optical disks are the digital
equivalent to standard film. Additionally, optical disks have
a very high capacity. Present optical disks can store up to
8000 images per disk pack. Since disk packs are removable,
virtually unlimited storage is possible.
Hard disk storage is usually an intermediate digital storage
before transferring the images to optical disk, magnetic
tape or floppy diskette. This is because the hard disk has a
definite limit on storage capacity. Therefore, image data
must be regularly erased to make room for more data.
Operator Control - Early real-time radiography system
operator controls were a collection of the individual
component controls mounted on an operators console.
The trend for present systems is to integrate all of the
controls from the separate components that make up a
real-time system into one centralized control system. This
is most often accomplished by controlling all system
components with a centralized computer system.
Today it is possible to use a real-time radiography system as
the control core of an automated radiographic inspection
system. This requires communication and control
protocols between the imaging system and the parts
handling device (manipulator) - and possibly other
peripherals - and the ability for the imaging system to
perform programmable inspection sequences. Then, after
the part is loaded and the x-ray source and camera are
aligned to an initial position, the control computer can
control the rest of the inspection process.
Applications
Real-time radiography applications can be generally
divided into two subsections, actual real-time imaging
where processes are examined for dynamic function and
automated test sequences where high test throughput and
low-cost is the primary function.
Test procedures such as observing the pattern of metal
filling molds and observing the function of motor
components while the motor is actually running are typical
dynamic function applications. It is also often necessary to
use real-time systems to properly position test objects
where the inner mechanism is unknown or obscure.
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Automated testing has become more important in recent
times because of an emphasis upon 100% testing of critical
components. Real time systems, in conjunction with parts
handling systems (manipulators) and integrated system
control, allow automated test sequencing with higher
throughputs and more coverage than previous film systems.
Figure 6-3 illustrated a real-time automated inspection
system.
The following characteristics should be considered when
planning a real-time radiography application:
X-ray energy - Selection of an x-ray energy for real-time
imaging should be based upon several considerations.
Selection of an energy that is too great for the part being
inspected can lead to difficulties. When the energy is so
high that the material does not present at least 1.5 half
value layers, small changes in attenuation may be lost.
Additionally, radiation buildup can cause tremendous
scatter problems when x-raying thin sections. This is
stabilized after approximately 1.5 HVLs. This thickness is
called the “equilibrium” thickness.
Selecting too low an energy also presents problems,
especially when actual real-time images are important. In
general, dynamic real-time radiography is like taking
pictures at a thirtieth of a second per image. If the
radiation energy or output is too low, little detail will be
seen in the image. This imaging time can be lengthened by
averaging two or more frames together. However, enough
radiation must be reaching the imaging screen to provide
the amount of light on the conversion screen needed for
proper image evaluation.
Ideally, x-ray energy and output is chosen so that 4 to 7
half value layers are being examined and the radiation to
the imaging screen exceeds 15 to 25 rads/min. However,
real-time systems can be useful at extremes outside of this
ideal envelope.
Varian Linatron applications