Varian Linatron High-Energy X-ray Applications 2007

More documents

Recommendations

Info

Real-time image acquisition displays a new image at the basic frame rate. This is normally an image every thirtieth of a second. This mode of obtaining images is useful for observing the proper positioning of a part, collimator setup and screening applications where plenty of radiation output is available. Quantum fluctuation can have a large effect upon the detail that can be observed in an image. Recursive Averaging is a frame summing procedure that provides for a moving average image. The result of this procedure is to accumulate in memory an exponentially weighted sum of previously input frames. Because the memory is constantly being refreshed with a new image, it is possible to conduct motion imaging with an improved signal to noise ratio. The random noise will be reduced. However, as more frames are averaged, the time lag of the image also increases, making the use of this averaging technique less useful for motion imaging. Therefore, a balance must be found between noise improvement and image lag. Considering random noise only, integration (summation) increases the signal to noise ratio of the image by a factor of the square root of the number of integrated frames- (N) 1/2 . This method of image acquisition compares with film exposure methods and is widely used to improve image quality. Integration is used most often for static imaging rather than dynamic processes. For any given time of image acquisition, summation improves the image signal to noise ratio of the image more than recursive averaging. Image Processing - Real-time radiography provides several different types of image processing to improve the detectability of defects in the test object. page 58 Contrast Enhancement or Stretching is the most common form of image processing. Often the important information in an image is contained in a small part of the contrast range available. Contrast enhancement allows using the total dynamic contrast range over a small statistical range. Contrast enhancement does not modifiy the original image data. It only modifies the way the data is displayed. Subtraction techniques subtract one image from another after moving either the x-ray source, the test object (or part of the test object) or the camera between images. Any data, such as systemic noise, that are common between the two images is subtracted out of the image. Several different subtraction methods can be used (shift subtract, mask subtract, etc.) depending upon the application. Care must be taken during subtract processes not to introduce false information into the resultant image. Additionally, the direction that the x-ray source, the object or the camera is moved is critical. Digital Filtering can remove high or low spatial frequency data from an image or Edge Enhancement can sharpen the representation of internal structure in a test object. Conclusion Real-time radiography is a nondestructive testing technique that is useful for dynamic imaging and automated highthroughput radiographic testing. Present real-time systems include an x-ray source, test-object manipulator, (partshandling system) and an imaging system for image acquisition, processing and archival. High energy applications of real-time radiography are rocket motor, ordnance and heavy casting inspection. Varian Linatron applications
Glossary ABSORPTION Process in which X-ray photons, as they pass through a material, are absorbed in the material. (See PHOTOELECTRIC ABSORPTION and PAIR PRODUCTION). ATTENUATION Combination of absorption and scattering processes in which X-rays, as they pass through material, are either stopped, or diverted from straight and forward travel. Total Attenuation, depending upon the X-ray energy, consists of: PHOTOELECTRIC ABSORPTION, COMPTON SCATTERING and PAIR PRODUCTION. BACKSCATTER Secondary radiation produced by scattering of X-rays from their original (forward) direction through angles greater than 90 degrees. BEAM FLATTENER Cone shaped X-ray absorber placed centrally in the beam of a high-energy X-ray source, to absorb a relatively greater proportion of the high-intensity central rays than of the rays at the edges of the beam, to produce a more uniform X-ray intensity at the plane of the X-ray film. Also referred to as a BEAM COMPENSATOR. BEAMING The condition that higher radiation intensity occurs in the forward, central X-rays from a high-energy X-ray source (target) than is emitted in all other directions. Caused by the large forward momentum of the accelerated electrons which strike the target to produce the X-rays. BLOCKING Use of lead or other shielding material around the edges of the object being radiographed, to absorb scattered radiation that would otherwise expose and excessively darken areas of the X-ray film under the object. page 59 BROAD BEAM Arrangement of the source, object and x-ray film (or other radiation detector) in which scattered radiation from the object contributes to the total exposure (at a given point) on the film; specifically, scattered radiation at solid angles greater than 0.01 steradian. The solid angle is formed by the point on the film and the perimeter of the exposed cross- sectioned area of the object. NARROW BEAM arrangements are those where scatter reaching the x-ray film or detector is only that scatter radiation within angles less than 0.01 steradian. CENTRAL RAY Line within the x-ray beam, coincident with the direction of peak x-ray intensity, the (usually) central axis of the electron accelerator, and with the axis of the collimator. (It also coincides with the laser beam indicator in a Linatron.) COLLIMATOR High-density metal absorber with a conical (sometimes pyramid-shaped) opening for passage of x-rays to produce a well-defined beam of x-rays from the target. COMPENSATOR (See BEAM FLATTENER) COMPTON SCATIERING X-ray attenuation process in which a photon transfers energy and momentum to an orbital electron of the attenuating material, and continues to travel through the material at an angle to the original photon direction. CONTRAST RADIOGRAPHIC CONTRAST is the magnitude of the difference in density from one area to another on a radiograph resulting from variation in x-ray intensity transmitted through the corresponding sections (thicknesses) of the object being radiographed. SUBJECT CONTRAST refers to the ratio of radiation intensities transmitted through selected sections of the object, and is therefore a function of the thicknesses of those sections. (Also see: FILM CONTRAST) Varian Linatron applications
Page 1:
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 58 and 59: Normally, the light generated in th
Page 60 and 61: FIGURE 6-3. Real-time automated ins
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
show all

Varian Linatron High-Energy X-ray Applications 2007

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?