Surveys for Removable Contamination cont'd

DOE-STD-1128-98

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 swipe 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

A minimum = MDA x 100 cm2

(4.1)

where L is the removable surface radioactivity value in dpm/100 cm2 of the

potential contaminant, given in Table 4.1. and MDA is in dpm.

The purpose of a technical smear survey is to locate and quantify removable

contamination that is known or suspected to exist. For small items, a

technical smear may be used at any time to verify the item's contamination

status. A technical 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

wipe should be taken with a dry medium using moderate pressure. A

common field practice is to use two fingers to press the wipe medium against

the surface to be wiped. The wipe 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 to assure 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.

4-15