ASNT

accelerators: one using the principle of the traveling wave, like SLAC and certain commercial systems, and the other using a standing-wave technique of acceleration. Most of the commercially produced electron linear accelerator systems used in the field are of the standing-wave type, because this type of accelerator can generally be approximately 2 × shorter than a traveling-wave accelerator (which saves cost, size, and weight). Radiographic linear accelerator system products are available that have X-ray energies of 1 to 15 MeV and with outputs over 10 000 rad/min (100 Gy/min) at 1 m (40 in.) at the highest energy levels, which is a very high dose rate relative to other sources. These highest energy and dose

solid-propellant rocket booster that may be 3.05 m (120 in.) in diameter. Although more complex than lower-voltage HVDC machines, some have been in service for over 30 years. Lower energies, such as the 6 MeV system in Figure 8, are capable of penetrating over 400 mm (15.75 in.) of steel and are much more economical than 15 MeV systems. Linear accelerator systems of 9 MeV are also available, such as that in Figure 10, at a price point in between that for 6 MeV and 15 MeV. Even more economical and more compact are systems designed closer to 2.5 MeV for the purpose of replacing live sources, such as cobalt 60; these systems can provide far more dose than a typical gamma source and provide an additional safety benefit by completely eliminating radioactive material handling and disposal.

systems are generally applied to the largest and most dense units under test, such as a

Figure 10 Linear accelerator system with 9 MeV X-ray output, used here to inspect a 25.40 MT (28 T) steel casting of a main steam stop and control valve for an advanced power plant. Cooling lines and high-voltage power and signal cables required to operate the X-ray head are routed off the gantry to linear accelerator drive and control electronics elsewhere in the facility.

CHAPTER 3

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Part 2