ASNT

The activity of ytterbium 169, iridium 192, and selenium 75 sources reduces to almost zero before disposal; however, a tiny amount of long-lived radioisotope impurity always remains in very old sources. For example, the long-lived isomer iridium 192 m2 (t1/2 241 y) and platinum 193 (t1/2 50 y) are present at levels of several nanocuries in old iridium 192 sources. EXPOSURE DEVICES Exposure devices are sometimes referred to as projectors or cameras. They are categorized as I, II, and X based on how they operate. Category I keeps the source inside the safety shielding of the device and operates as a camera or lantern. Category II operates by cranking out the source into a guide tube and remote collimator. Category X is a specialist device such as a crawler head, which does not conform to international standards applicable to either category I or II devices. A category II device cranks out a source from its protective shield into a guide tube connected to one side of a device, using a drive cable connected to the other side of the device. A cranking system

Figure 25 Two-hole source changer with overpack.

DISPOSAL, RECYCLING, AND STORAGE FOR DECAY When manufacturers take back used sources, they are generally stored for 5 to 10 years until the decayed activity is low enough to allow disposal as low-level radioactive waste (LLW). Used sources are stored in safe and secure radiologically controlled locations at manufacturers’ facilities until disposal as LLW.

Figure 27 Ten-hole source changer.

Figure 26 Two-hole source changer.

CHAPTER 3

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Part 3