Varian Linatron High-Energy X-ray Applications 2007

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FIGURE 1-3. Linatron M System Diagram 1-3), a Control Console (Fig. 1-4), a modulator cabinet (Fig. 1-5). Among the more important characteristics of the Linatrons are: • Small focal spot size • Appropriate energy selection for the material to be radiographed • Ease of handling and beam positioning • High radiation output • High reliability • Low maintenance cost FIGURE 1-4. The standard operator interface to the Linatron is a Touchscreen Control Console. page 4 FIGURE 1-5. Linatron modulator cabinet contains main power supplies, pulse modulator, and power distribution electronics. Varian Linatron applications
Characteristics of High-Energy Radiation Advantages of High-Energy X-Rays The high energy x-rays produced by Linatrons provide a number of advantages over traditional x-ray radiography. These include: • Making the radiography of very thick sections economically feasible. • Making it possible to achieve large source-toobject/object-to-film distance (D/T) ratios to minimize object distortion. • Allowing short exposure times for high throughput rates. • Combining high film latitude with reduced scatter allowing high detail resolution in radiographs of large complex assemblies. • Making it possible to use slower fine-grained Xray film and real time radiography systems. Generation of High Energy X-Rays Electrons are injected at moderately high energies into a tuned resonant waveguide structure and accelerated toward a target by high electric fields. When these electrons strike the target, they rapidly decelerate. This deceleration creates high-energy bremsstrahlung X-ray spectrum. The spectrum is characteristic of the target material, the target design, and the energy spectrum of the incident electron beam. The same process takes place in conventional X-ray equipment, but the higher energy Linatron electron beam produces a higher efficiency conversion of electrons into X-rays. Measurement of High Energy X-Rays The “Roentgen” is the standard unit of measure for x-rays, which quantifies exposure to a source of ionizing radiation. “Exposure”* is fundamentally a property of the beam rather than a measure of the effect of the beam on the object to be irradiated. The basic quantity that characterizes the energy imparted to matter by ionizing particles is the absorbed dose. The unit of absorbed dose is page 5 the Gray, often abbreviated “Gy”**. Gy is defined as the amount of energy imparted to matter per unit mass of irradiated material and is equal to 1 joule per kilogram. In practice, the radiation output of a Linatron is measured by first measuring exposure, the charge produced by the xray beam in a given volume of air using an ionization chamber dosimeter. Correction factors are then used to calculate the absorbed dose in a material. Ion chamber measurements are normally made at a given depth in a water phantom or with the ion chamber surrounded by a plastic cylinder or equilibrium cap in order to achieve electronic equilibrium. For low-atomic-number materials, a Roentgen measured in air is approximately equivalent to one rad of absorbed dose. Linatron outputs are described in units of Gy per minute at one meter. *The term “exposure” is used primarily to describe the fact that film has received X-ray radiation during radiography of an object under test in subsequent sections of this manual. Exposure refers to the effect of the X-ray beam on the film in this context. **This manual uses Gy values for absorbed energy dose values. 1 Gy (Gray) = 100 rad. Target Characteristics The target is a component in the Linatron, which absorbs high energy electrons and produces x-rays. The intensity of the X-rays produced at the target is a function of the electron beam intensity and the X-ray production efficiency of the target. Target efficiency is defined as the ratio of the total X-ray radiation power produced to the total power of the impinging electron beam. This efficiency depends on both target composition and geometry. The most efficient targets are made of materials with a high atomic number (high Z elements). Tungsten (Z=74) offers the best combined efficiency and physical properties. This is the primary material used in the Linatron target. It has a thickness slightly greater than the range of the electrons in the target material. Varian Linatron applications
Page 1: Varian Linatron High-Energy X-ray A
Page 5: Preface This manual presents theory
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 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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