MANAGEMENT OF NORM IN THE PETROLEUM INDUSTRY Akpojevwa Tega Naomi, october 2016 | Page 36

contamination can occur mainly due to inhalation or ingestion of material
containing radionuclides such as dust particles.
Irradiation from external sources occur in the proximity of the source and
decreases with distance, dropping to effectively ‘zero’ at a sufficient distance.
In the case of NORM, this is usually a few metres from contaminated
equipment and will follow the ‘inverse square law’ whereby intensity is
inversely proportional to the square of the distance from the source. Absolute
exposure at one metre will be four times greater than exposure at two metres.
However, such models assume a single point-source for the radiation whereas,
in real-life, NORM may be encountered over a large area. This has direct
bearing upon the size of the controlled area around a NORM contaminated site.
Internal sources lead to irradiation of tissues and organs and persist after the
introduction of radionuclides in the body. Reduction of irradiation depends
mainly from the intrinsic propriety of the radionuclide (half life time) and
excretion rate (depending of chemical composition of the contaminant). Control
of dust and protection from inhalation during the handling of NORM is
therefore one of the principal mechanisms by which exposure can be limited.
For a point source, absolute exposure at one metre will be four times greater
than exposure at two metres. However, point sources are rarely encountered
under operational conditions where NORM generally accumulates across an
area.
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