Radiation, ionizing natural background

Sources of Ionizing Radiation We are continuously exposed to ionizing radiation from natural and artificial sources (Table 23.6, next page). Indeed, life evolved in the presence of natural ionizing radiation, called background radiation. The same radiation that can alter bonds in DNA and cause harmful mutations also causes beneficial mutations that, over time, allow organisms to adapt and species to change. 

The effects of short-term exposure to radiation appear in TABLE 21.9. An exposure of 600 rem is fatal to most humans. To put this number in perspective, a typical dental X-ray entails an exposure of about 0.5 mrem. The average exposure for a person in 1 year due to all natural sources of ionizing radiation (called background radiation) is about 360 mrem (V FIGURE 21.25). 

Life on earth has evolved in the presence of naturally occurring ionizing radiation, which is continuous and ubiquitous. In addition to natural background radiation exposure, mankind is now exposed also to radiation from various man-made sources. 

In contrast, risk management for substances that cause deterministic effects must consider unavoidable exposures to the background of naturally occurring substances that cause such effects. Based on the assumption of a threshold dose-response relationship, the risk from man-made sources is not independent of the risk from undisturbed natural sources, and the total dose from all sources must be considered in evaluating deterministic risks. In the case of ionizing radiation, thresholds for deterministic responses are well above average doses from natural background radiation (see Section 3.2.2.1)... 

Current opinion is that there is a small risk to human health from even low levels of exposure to ionizing radiation, but there is also a known quantity of natural background radiation that the human species has always encountered. In 1984, an employee at a nuclear power plant began to set off radiation alarms while walking into the plant. An investigation found that his home contained high levels of radon gas from natural minerals. Radon tests are now routinely performed in many homes. 

Altmann H, Tuschl H (1978) DNA repair investigations in lymphocytes of persons living in elevated natural background radiation areas (Bad Gastein). In Late biological effects of ionizing radiation, vol I. IAEA, Vienna, pp 437-445... 

Radiation, background or natural. The amount of ionizing radiation to which a member of the population is exposed from natural sources, such as terrestrial radiation due to naturally occurring radionuclides in the soil, cosmic radiation originating in outer space, and naturally occurring radionuclides deposited in the human body. 

Natural resources account for most radiation exposure. Attempts to determine if there are subtle effects from background irradiation have only begun to yield information about these widely dispersed effects. Advent of new techniques for such estimation has increased the sensitivity and reliability of detection. The objectives of this chapter are to describe common types of ionizing radiation, discuss radiation toxicity in humans, and provide information on the possible benefits and risks associated with ionizing radiation. 

Natural background consists of the highly variable sum of aU ubiquitous sources of ionizing radiation encountered on the planet (Ref. 2). Background in general can be divided into the following four major contributions ... 

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