Natural radiation sources

Average equivalent dose rates received from natural radiation sources are listed in Table 22.8. The values vary appreciably with the environmental conditions. The influence of cosmic radiation increases markedly with the height above sea level, and terrestrial radiation depends strongly on the local and the living conditions. 

Table 22.8. Average radiation exposure by natural radiation sources.

UNSCEAR 2000a. United Nations Scientific Committee on the Effects of Atomic Radiation, Annex B. Exposures from Natural Radiation Sources. Vienna UN. 

Natural Radiation There are two main sources of ionizing radiation natural and artificial. Natural radiation sources include cosmic and gamma radiation found in certain sods. Building products made from these radioactive soils also give off natural radiation. Natural radiation is also present in some ingested food and water and some inhaled air. Natural exposures vary considerably by geographic location. 

Natural radiation sources create both external and internal exposures. External exposures are those arriving at the outside of a human body. Internal exposures are those received on internal tissue through ingested and inhaled... 

Finally, averaged worldwide exposure to natural radiation sources are listed in Table 55.16. There is a wide distribution of exposures from many sources therefore, typical annual effective doses are also distributed over a wide range, from 1 mSv to 13 mSv and the (population-weighted) average is 2.4 mSv of which 0.39 mSv is due to cosmic rays, 0.48 mSv to external terrestrial radiation, and 1.26 mSv to radon and thoron inhalation, and 0.29 mSv to the ingestion of and uranium and thorium. As shown in the table, radon and its daughters constitute the largest contribution to the total exposure. 

Average worldwide exposure to natural radiation sources (UNSCEAR 2000c)... 

According to Directive 96/29/EURATOM when carrying out work involving exposure to natural radiation sources which can result in an annual effective dose higher than 1 mSv, these workers should be considered exposed and the requirements of surveillance, monitoring and radiation protection must be applied. 

Radiation, like air, has a ubiquitous presence in the human environment. Humans are exposed to approximately 100 to 200 millirem/ year depending on their location in the world (120 millirem/year at Harrisburg vs. 190 at Denver). The principal natural radiation sources are cosmic rays from outer space, radon from geologic sources, and potassium-40 within the human body (see Fig. 31.4). 

There are two basic types of watertube boilers assisted and natural circulation. Assisted circulation might apply where heat is from convection rather than a radiation source such as a waste heat application. Natural circulation is more suited where radiant heat and high gas temperatures are present. 

Exposure to natural sources of radiation is unavoidable. Externally, individuals receive cosmic rays, terrestrial X-rays, and gamma radiation. Internally, naturally occurring radionuclides of Pb, Po, Bi, Ra, Rn, K, C, H, U, and Th contribute to the natural radiation dose from inhalation and ingestion. Potassium-40 is the most abundant radionuclide in foods and in all tissues. The mean effective human dose equivalent from natural radiations is 2.4 milliSieverts (mSv). This value includes the lung dose from radon daughter products and is about 20% higher than a 1982 estimate that did not take lung dose into account (Table 32.4). 

The basic instrumentation used for spectrometric measurements has already been described in Chapter 7 (p. 277). The natures of sources, monochromators, detectors, and sample cells required for molecular absorption techniques are summarized in Table 9.1. The principal difference between instrumentation for atomic emission and molecular absorption spectrometry is in the need for a separate source of radiation for the latter. In the infrared, visible and ultraviolet regions, white sources are used, i.e. the energy or frequency range of the source covers most or all of the relevant portion of the spectrum. In contrast, nuclear magnetic resonance spectrometers employ a narrow waveband radio-frequency transmitter, a tuned detector and no monochromator. 

The unique appearance of an infrared spectrum has resulted in the extensive use of infrared spectrometry to characterize such materials as natural products, polymers, detergents, lubricants, fats and resins. It is of particular value to the petroleum and polymer industries, to drug manufacturers and to producers of organic chemicals. Quantitative applications include the quality control of additives in fuel and lubricant blends and to assess the extent of chemical changes in various products due to ageing and use. Non-dispersive infrared analysers are used to monitor gas streams in industrial processes and atmospheric pollution. The instruments are generally portable and robust, consisting only of a radiation source, reference and sample cells and a detector filled with the gas which is to be monitored. 

The human body is equipped to deal with nominal levels of radiation doses. Background (natural) radiation from radon gas, cosmic sources, soil, and water produces an average dose of about 0.3 rem (0.003 Sv) per year.4 However, large doses of radiation generated after a terrorist attack can overwhelm the body s ability to repair damage, leading to stochastic or acute health effects. 

The exposure to ionizing radiation from natural sources is continuous and unavoidable. For most individuals, this exposure exceeds that from all human-made sources combined (UNSCEAR 2000a). The two main contributors to natural radiation exposures are high-energy cosmic ray particles incident on the earth s atmosphere and radioactive nuclides that originate in the earth s crust and are present everywhere in the environment, including the human body itself. 

We are constantly exposed to ionizing and nonionizing radiation from naturally occurring sources as well as radiation generated and managed by our society. The challenge is to understand and manage the risk and benefits of our individual exposure. 

Background Radiation amount of natural radiation detected in the absence of nonnatural radioactive sources Base a substance that yields hydroxide ions in solution or accepts protons Becquerel SI unit for activity equal to one disintegration per second, abbreviated Bq... 

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