ASNT

(2 to 6 ft) from the shot location. Flash dose is minimized or eliminated when the device is in camera mode. Some devices can be dual mode, meaning that they can operate either in projector mode, with a guide tube and drive cable, or in SCAR mode, with an internal directional collima- tor. Figure 37 shows a 2997 GBq (81 Ci) selenium 75 dual-mode exposure device. Figure 38a shows examples of SCAR exposure devices; Figure 38b shows a device’s internal construction when in SCAR mode (Category I mode). The SCAR technique can also be implemented using any category I exposure device.

COBALT 60 EQUIPMENT Due to the high emitted energy of cobalt 60,

exposure devices require large and heavy gamma shielding, which is generally made using depleted uranium. Such devices are also Type-B transport containers. Due to their size and weight, they are not regarded as portable; however, the devices are generally mounted onto movable trolleys to enable mobility, as shown in Figure 39. Applications include radiography of bridge/rebar structures or other large, thick, or dense fixtures where linear accelerators may be impractical to use. Some projectors contain an S-tube channel; others contain a helicoidal channel.

Figure 37 Dual-mode 2997 GBq (81 Ci) small controlled-area radiography device in projector mode.

Stainless steel shield housing

Automatic locking mechanism (rear plate)

Protective plastic jacket with carry handle

Plunger lock

Protective cover

Outlet port — collimator (shown) or front plate

Source assembly

Tungsten shield

Internal tungsten shutter

Figure 38 Small controlled-area radiography exposure devices: (a) examples of three devices; (b) schematic. (a) (b)

CHAPTER 3

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Part 3