All minerals and raw materials contain radionuclides of natural origin, of which the most important for the purposes of radiation protection are the radionuclides in the 238U and 232Th decay series and 40K. For most human activities involving minerals and raw materials, the levels of exposure to these radionuclides are not significantly greater than normal background levels. However, certain activities can give rise to significantly enhanced exposures that may need to be controlled by regulation. Material giving rise to these enhanced exposures has become known as naturally occurring radioactive material (NORM).
A list of industry sectors have been identified as the most likely to produce NORM: oil and gas production, the niobium and iron-niobium industry, manufacture of titanium dioxide pigments, the phosphate industry, the zircon and zirconia industry, and many other conventional mining and milling industries. The enhanced levels of radioactive isotopes of the uranium and thorium decay series in their products, sub products, residues and wastes may originate from physical and/or chemical processing where the material arising from a process may contain more radionuclides than the original raw and raw minerals.
The radiation exposition of the workers and public arising from NORM has to be assessed and at some cases radiation protection controls have to be implanted. The need to perform these assessments is a challenge for NORM industries, which must comply with standards from nuclear industries in addition to the usual environmental and worker safety requirements.