BS ISO 7503-3:2016 pdf free

BS ISO 7503-3:2016 pdf free.Measurement of radioactivity一Measurement and evaluation of surface contamination
The applicability and the reliability of direct measurement or indirect evaluation of surface contamination are strongly dependent on the particular circumstances [e.g. the physical and chemical form of the contamination, the adherence of contamination on the surface (fixed or removable), the accessibility of the surface for measurement or the presence of interfering radiation fields].
Direct measurement is used when the surface is readily accessible, reasonably clean, and when no interfering radiation, such as a high background, is present. Direct measurement is used to establish the presence of both fixed and removable contamination.
Direct surface contamination evaluation is addressed in ISO 7503-1.
Indirect evaluation of surface contamination is more generally applicable when the surfaces are not readily accessible because of difficult location or configuration, where interfering radiation fields adversely affect contamination monitors or when methods of direct measurement with standard instrumentation are not available (e.g. tritium). Also, the indirect method cannot assess fixed contamination, and, due to the uncertainty associated to the wiping efficiency, application of this method results in conservative estimations.
The majority of radionuclides do not exhibit simple decay schemes and may have multiple branches from the parent to the ground state, including the emission of photon(s), conversion electrons and secondary emissions such as X-rays and Auger electrons. For any single decay event, it is possible also that more than one emission may be produced, for example, a beta particle followed by a gamma ray, The instrument may detect any or all of the emissions arising from a single decay but only one event is registered as the emissions occur at the same time. This is the key reason why interpreting readings from surface contamination instruments is complex, as it means that it is incorrect to sum the detection probabilities for all the emissions without correction for the summation.
In estimating the appropriate calibration factor (in Bq.cm-2/s-1) for a particular radionuclide, it is necessary to take into account the probabilities of the various emissions, the effect of the surface on each separate emission, and the probability of detecting in coincidence any or all of the emissions from a single decay. The estimation of an appropriate instrument response factor for most radionuclides therefore is a complex issue because it is not possible to apply the same P-factor for each emission involved in the decay and indeed the simplistic definition of the P-factor is not appropriate here.
In practice, high uncertainties (tens of percent) in measurement can normally be tolerated as the measurements may be for screening or re-assurance purposes only. However, it is still necessary to understand the underlying physical processes and the estimation algorithms to check that gross errors are not being made. The following discussion is intended to provide a generic approach which puts these estimations on a sound footing.BS ISO 7503-3 pdf download.