Varian Linatron High-Energy X-ray Applications 2007

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Normally, the light generated in the imaging screen is coupled to the lens-camera system by a front surface mirror mounted at 45 degrees to the screen. This positions the camera and lenses outside the cone of direct radiation, minimizing damage to these components. In general, two types of low-light video cameras are used in real-time radiography, Silicon Intensified Target (SIT) and Image lsocon video tube cameras. SIT cameras have excellent low-light sensitivity and are compact, rugged and require no special cooling. Image lsocons have more dynamic range and spatial resolution but are very position sensitive and require special cooling. Because Image lsocons are physically larger tubes, these cameras are generally larger and vibration sensitive. SIT tubes are small, low cost and more adaptable to special applications. Signal Processing - Signals from real-time cameras are digitized and stored in digital memory for further processing or archival storage. The digital memory is part of an image processor, which is a specialized computer system designed to process image data, most often in real time. FIGURE 6-2. Schematic of ER real-time system functional elements. page 54 Image processors can vary considerably from systems that only have the ability to acquire individual video frames to systems that can perform complicated image filtering and/or transforms. Images stored and processed by the image processor are displayed on a high resolution video monitor for interpretation. This is illustrated in Figure 6-2. Archival Storage - Archival storage is necessary to keep an image record of inspection procedures performed. Two basic methods are used to store real-time radiography images, analog and digital. The most popular, and presently least expensive, method to store real-time images is high bandwidth analog video tape. Any image presented on the video monitor will be recorded on video tape. Additionally, images can be annotated verbally on the video tape’s audio track. Images may also be stored digitally on hard disk, floppy diskette, magnetic tape and optical laser disk. Magnetic tape and optical laser disk have the most capacity, but magnetic tape is classified as a volatile medium with a definite possibility for the data to be corrupted by magnetic fields, erased or being overwritten. Varian Linatron applications
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. page 55 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
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Varian Linatron High-Energy X-ray A
Page 5:
Preface This manual presents theory
Page 8 and 9: FIGURE 1-3. Linatron M System Diagr
Page 10 and 11: Linatron targets are specially desi
Page 12 and 13: FIGURE 2-3. Half-value layer for pr
Page 14 and 15: Beaming and Field Flatness. Electro
Page 16 and 17: FIGURE 3-2. Linatron x-ray intensit
Page 18 and 19: It is most convenient to have expos
Page 20 and 21: Vacuum cassettes are recommended wh
Page 22 and 23: Table 4-3 lists some relative speed
Page 24 and 25: Manufacturers publish density versu
Page 26 and 27: FIGURE 4-5. Plot of density versus
Page 28 and 29: The total unsharpness is reduced to
Page 30 and 31: This wedge block is then radiograph
Page 32 and 33: Increasing Latitude With Multiple F
Page 34 and 35: FIGURE 4-12. Linatron 2 MeV typical
Page 38 and 39: FIGURE 4-16. Linatron typical expos
Page 44 and 45: Radiographic Procedures General Con
Page 46 and 47: When radiographing curved sections,
Page 48 and 49: Radiography of Welds Radiography is
Page 50 and 51: The width of separation required fo
Page 52 and 53: The propellant in large motors is o
Page 54 and 55: Grain Radiography Coverage Requirem
Page 56 and 57: Bibliography Books Practical Radiog
Page 60 and 61: FIGURE 6-3. Real-time automated ins
Page 62 and 63: Real-time image acquisition display
Page 64 and 65: D/T RATIO Ratio of the distance bet
Page 66 and 67: LINEAR ATTENUATION COEFFICIENT Cons
Page 68: Security & Inspection Products 6883
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Varian Linatron High-Energy X-ray Applications 2007

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