ASNT

Gamma radiation interferes with critical safety and process control systems. Examples include ultraviolet f lame detectors, radiation monitoring systems, and nuclear level and density gauges. These systems may not distinguish between gamma rays from a radiography source and ultravi- olet photons from a fire or gamma rays from a cesium 137 nuclear gauge. The ever-increasing emphasis on reducing occupational exposure and exposure to members of the public often requires radiographic testing (RT) to be performed in

shooting windows or during off-shifts, reducing overall inspection efficiency. SCAR is the concept of controlling the radiation utilized for RT. This allows for radiographic inspection without restric- tive shooting windows (24/7 radiography concept), in close proximity to other trades, and without impacting critical sensor systems. SCAR applications enable operation near nuclear gauges and ultraviolet detectors. Very low dose rates are achieved near members of the public with an exclusion zone as little as 0.6 to 1.8 m

Figure 33 Category II iridium 100 or iridium 192 exposure device with S-tube design.

Figure 34 Category II iridium 192 exposure device with straight-through channel.

Figure 36 Lightweight selenium 75 exposure device uses tungsten internal gamma-ray shielding.

Figure 35 Category II dual-isotope exposure device can accept iridium 192 or selenium 75 sources.

CHAPTER 3

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Part 3