BS ISO 7503-1:2016 pdf download – Measurement of radioactivity — Measurement and evaluation of surface contamination Part 1 : General principles Due to the inherent shortcomings of both the direct measurement and the indirect evaluation of surface contamination, in many cases, the use of both methods in tandem can help ensure results which best meet the aims of the evaluation. 5.2 Direct method The direct method is the best approach whenever possible. In the direct method, the monitor probe is moved over a surface, with the face of the probe at a minimal distance of approximately 3 mm from the surface. The probe shall be kept stationary for a minimum to obtain sufficient accuracy. This measurement can then be used to determine the radiation emitted from the surface. There are many circumstances where the above measurement might not be possible. A surface may be so convoluted that it is not possible to monitor it directly, or the background radiation may be so high that it is impossible to obtain meaningful results from the measurements; however, these results should be recorded because a calibration could be provided later. In these instances, an indirect measurement has to be made using a wipe test. 5.3 Indirect method (wipe tests) A test procedure is often carried out using a filter paper or other wipe, typically 20 mm to 60 mm in diameter, which can be placed in commercial holder for measurement. The filter paper should be wiped over the area, usually at least 100 cm 2 , or whatever area is locally defined for the surface that may be contaminated with radionuclides. The filter paper can either be placed in a lab counter drawer to assess the level and type of activity, or sent to a radiochemistry laboratory for a full assessment of nuclide type and activity. In both instances, all measurements should be traceable to national standards or governed by local requirements. Wipe tests can be either “dry wipe” or “wet wipe”. In general, it is a senior health physics professional who makes the decision on which to use. The indirect surface evaluation contamination method is described in detail in ISO 7503-2. 5.4 Wipe test uncertainties A brief discussion on uncertainties is given in 10.3. 6 Radionuclide identification and spectral analysis Normally, the radionuclides are known. If not, they need to be identified. Radionuclide identification of contaminants using hand-held instruments is only practicable...
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