There are 68 radioactive isotopes in the Earth's crust being
important potassium-40 (40K), rubidium-87 (87Rb) and those that make part of the three natural
chains: uranium-235 (235U) that includes 17 radioisotopes, uranium-238 (238U) that includes 19 radioisotopes and thorium-232 (232Th) that includes 12 radioisotopes. All of them are known by the acronym NORM (Naturally
Materials), and, in
conjunction with cosmic radiation, are the largest source of radiation to
which human beings are exposed.
There are 68 radioactive isotopes in the Earth's crust being the most important potassium-40 (40K), rubidium-87 (87Rb) and those that make part of the three natural chains: uranium-235 (235U) that includes 17 radioisotopes, uranium-238 (238U) that includes 19 radioisotopes and thorium-232 (232Th) that includes 12 radioisotopes. All of them are known by the acronym NORM (Naturally Occurring Radioactive Materials), and, in conjunction with cosmic radiation, are the largest source of radiation to which human beings are exposed.
Whenever some material is exposed to a radiation beam such a material absorbs a portion of the radiation energy. The ratio between the absorbed energy and the irradiated mass is called dose. If the irradiated material is a living being the definition of dose is slightly modified including parameters that depend on the type of radiation and the affected tissue, leading to effective dose concept.
The 88% of the effective dose to which an average person is exposed come from natural sources and only the 12% are due to artificial sources. But the 94.5% of the latter have their origin in medical applications (diagnosis and therapy). That is to say that just 5.5% of the artificial radiation dose come from other sources (fall-out, nuclear power stations, non-nuclear industries, consumer goods, occupational).
From these figures the need of studying in deep the effects of natural radiation on human beings appears. That is especially important for people who work in some activities such as oil and gas industries.
Oil and gas industries
Since the 90's, several industrialised countries have been studying the effects of natural radioactive materials in workers from these industries. They have taken into account especially the existence some radium isotopes in formation water as calcium, barium and strontium salts. In addition, radon concentrations in propane or butane have been also considered.
Scales, sludges, depositions, tools, downhall tubing, vessels, process units and industrial waste stores have been analysed in order to evaluate the impact in the environment as well as the dose on workers and public members due to external and internal irradiation.
It is convenient to underline that irradiation can have its origin not also in an external source, that is to say in contaminated materials without physical contact, but also in an internal source, which means that the radioactive material was ingested or inhaled as a consequence of its passage to the atmosphere or to the food chain.
From these studies some recommendations were issued such as periodic monitoring, classification of areas according to their dose level, decontamination of tools, materials, vessels, etc., dosimetric control of involved workers and environmental impact analysis.
Periodic control of radon concentration in air has become a standard practise in the United States and other industrialised countries. This verification is especially important in closed environments where the lack of air circulation makes it difficult the reduction in the radon concentration.
In temperate zones the radon concentration inside buildings is around eight times the concentration outside while in extremely cold areas it uses to be up to five thousands times higher.
Regarding the limit of acceptable
radon concentration in air the Argentinean Nuclear Regulatory Authority
recommends to take special actions when the average annual concentration
is higher than 400 Bq / m3.
There are several techniques for measuring radon-222 using more or less complex instruments and equipment. NOLDOR propose the application of small samplers based on activated charcoal adsorption and liquid scintillation measurement. This technique has shown to be very cheap and reliable. More information ...