Surveys for Removable Contamination cont'd

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

For transuranic radionuclides, the guideline values for removable contamination are lower than the

MDA of portable instruments. During a wipe survey, the surface area of the material must be large

enough that the quantity of radioactivity collected on the wipe will be greater than the MDA of the

instrument. Wipe surveys of areas smaller than this minimum surface area require more sophisticated

measuring instruments, such as a scaler measurement, and the entire surface of the material should be

wiped. The minimum area for using a large-area wipe survey is given by where GV is the guideline value

of the potential contaminant, given in Table 4-1.

The purpose of a smear survey is to locate and quantify removable contamination that is known or

suspected to exist. For small items, a smear may be used at any time to verify the item's contamination

status. A smear or swipe survey is performed by wiping a cloth, paper, plastic foam, or fiberglass disk

over a 100-cm2 area of the surface. The swipe should be taken with a dry medium using moderate

pressure. A common field practice is to use two fingers to press the swipe medium against the surface to

be swiped. The swipe is then moved along an "S" shaped path that has a nominal length of 8 in. (20 cm)

to 10 in. (25 cm).

When the potential contaminant emits alpha radiation, paper or fiberglass filter papers should be used

so that alpha activity is not attenuated by becoming imbedded in the wipe. To improve the detection limit,

smears may be taken over areas larger than 100 cm2. However, the size of the area smeared should be

limited to prevent buildup of material (radioactive or otherwise) that would attenuate alpha radiation. The

current practice at DOE facilities is to use the 100 cm2 area as the minimum size of objects being smeared.

Appropriate corrections should be made for objects smaller than 100 cm2

If contamination is detected during a scan survey for fixed contamination, a swipe survey for

removable contamination should be performed to determine if the contamination is fixed and to quantify

any removable contamination. If no contamination above the guideline values for removable

contamination in Table 4-1 is detected during the smear survey, the contamination is fixed, and the area

should be posted appropriately.

A smear survey may be used routinely to detect removable contamination, especially for

contamination surveys of radiological areas.

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