Assessment of Exposure to Ionizing Radiation

In comparison with the average effective dose equivalent to the general population from cosmic radiation, which approximates 0.27 mSv (27 mrem) annually, the average dose to the thorax of an individual from a standard x-ray examination of the chest is of the order of 0.10 mSv (10 mrem). Other diagnostic procedures may deliver substantially larger doses, e.g., the average effective dose equivalent of an individual from a barium enema examination of the colon is approximately 4 mSv (400 mrem). 

Units used for radiation exposure, radiation dose and radiation dose equivalent are in transition (ICRU, 1980 NCRP, 1985). The relationship between the SI units and the conventional units are given in Thble 4.2. 

The unit used for expressing the collective dose to a population is the person-sievert (person-rem), which is the product of the number of people exposed times the average dose per person, e.g., 10 mSv to each of 1,000 people = 10,000 person-mSv = 10 person-Sv (1 rem to each of 1,000 people = 1,000 person-rem). 

The conventional unit of radioactivity, the curie (Ci), is equivalait to 3.7 X 10 radioactive events per second. The SI unit used for denoting the amount of radioactive material contained in a given sample of matter is the becquerel (Bq) one becquerel is that quantity of a radioactive nuclide in which there is one radioactive event per second (1 Bq = 2.7 x 10 Ci). Since radionuclides decay exponentially with time, each element at its own rate, the time required for a given quantity of a radionuclide to lose one-half of its radioactivity is call its physical half-Ufe. 

The dose of radiation delivered by an internally deposited radionuclide depends on the quantity of radioactive material residing in situ. This quantity decreases as a function of the physical half-life of the radionuclide and the rate at which the element is redistributed or excreted (i.e., its biological half-life). Because the physical half-life is known precisely and the biological half-life can be characterized within limits for most radionuclides, the dose to a tissue that will ultimately be delivered by a given concentration of a radionuclide deposited therein can be predicted to a first approximation. The collective dose to a population that will be delivered by the radionuclide—the so-called collective dose commitment—serves as the basis for assessing the relevant long-term health effects of the nuclide. 

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A variety of units have been used for the assessment of exposures to ionizing radiation. The current international standard terminology is shown in Table 32.3. This chapter uses the new terminology exclusively this frequently necessitated data transformation of units from early published accounts into the currently accepted international terminology. 

Conduct a risk assessment to any employee and other persons to identify measures needed to restrict exposure to ionizing radiation and to assess magnitude of risk including identifiable accidents. 

A brief examination of Thbles 5.1 and 5.2 shows many chemicals that are common in the environment. In contrast to the relatively extensive assessment of human exposure to ionizing radiation, assessment of the extent of human exposures to these and other chemicals is fragmentary. Because there are some 6,000,000 known chemicals (NAS/NRC,... 

Measurements of ionizing radiation and radionuclides in foods and environmental samples are required for the assessment of exposure to both natural and artificial radiation sources, determination of compliance with government regulations, and studies of the movement and retention of artificial radionuclides in food and environmental media and of the composition of the natural radiation enviromnent. 

Any system of protection should include an overall assessment of its effectiveness in practice. The international standards (IBSS 1996) established on the bases of the ICRP recommendations specify the basic requirements for protection of people against exposure to ionizing radiation and for the safety of radiation sources. In addition to the viewpoints of protection and safety in radiation, the technical developments, economics, and social situations are to be included in the general requirements of the system. Therefore ... 

Oil-field NORM are an environmental concern because of the potential for human exposure to ionizing radiation. The radium and radium decay products in oil-field NORM present a hazard only if taken into the body by ingestion or inhalation. The external radiation from equipment or waste containing NORM is almost never a significant concern. The discharge of radium in produced water is of concern because it may accumulate in seafood consumed by humans. Since no estabhshed safe level exists for the intake of radium, any consumption of radium in food is of potential concern. However, for the case of radium discharged in produced water, risk assessment studies show that consumption of fish caught near produced water outfalls will not pose an unacceptable human health risk, even in the worst cases. 

Today, radon and its decay products in indoor air are by far the most important contributors to the exposure of the public to ionizing radiation and may be responsible for as much as 10-20% of the lung cancer cases (Steindorf etal. 1995, Lubin 1994). Synergism with smoking was found in several studies, but recent assessments of the data indicate that the two agents may act in part additively. Smoking may also reduce the latent period. 

Assess worker exposure to external gamma radiation, the inhaled and ingested radioactive dust, and alpha radiation from radon and estimate the total dose of ionizing radiation to which workers may be exposed. 

Estimation of the probability of a response from exposure to radionuclides (or any other source of ionizing radiation) is greatly facilitated by the knowledge that radiation dose is the common measure of insult to any organ or tissue for any exposure situation (e.g., see NCRP, 1993a 1993b). All radiation dose or risk assessments are... 

Sir Edward Pochin (1978) Why be Quantitative about Radiation Risk Estimates Hymer L. Friedell (1979) Radiation Protection-Concepts and Trade Offs Harold O. Wyckoff (1980) From Quantity of Radiation and Dose to Exposure and Absorbed Dose -An Historical Review James F. Crow (1981) How Well Can We Assess Genetic Risk Not Very Eugene L. Saenger (1982) Ethics, Trade-offs and Medical Radiation Merril Eisenbud (1983) The Human Environment-Past, Present and Future Harald H. Rossi (1984) Limitation and Assessment in Radiation Protection John H. Harley (1985) Truth (and Beauty) in Radiation Measurement Herman P. Schwan (1986) Biological Effects of Non-ionizing Radiations ... 

Numerous sources of ionizing radiation can lead to human exposure natural sources, nuclear explosions, nuclear power generation, use of radiation in medical, industrial and research purposes and radiation-emitting consumer products. Before assessing the radiation dose to the population, one requires a precise knowledge of the activity of a number of radionuclides. The basis for the assessment of the dose to the population from a release of radioactivity to the environment, the estimation of the potential clinical health effects due to the dose received and, ultimately, the implementation of countermeasures to protect the population is the measurement of radioactive contamination in the environment after the release. The types of radiation one should consider include ... 

In conclusion, the various causes of infertility in women need to be carefully evaluated by use of the appropriate imaging techniques. The conventional HSG is still a widely available, rather safe, and rapid as well as easy performable technique to assess tubal patency. HSG is minimally invasive and also entails exposure to low ionizing radiation. Sonohysterogra-... 

When dealing with hazards of environments, there are additional important factors. Environments include such things as heat, light, noise, vibration, pressure, chemicals, and radiation (non-ionizing and ionizing). Designers must know what level of exposure exists or could exist. One must consider the exposure s effects on people. There is a need to know how exposures occur. There is a need to detect and measure the exposures. People cannot observe many environmental hazards or assess them accurately on their own. 

In general, to assess the delayed effects of current exposure, dose quantities of the ionizing radiations are introduced. The term dose is used in a general sense as a measure of the quantity of radiation or the energy deposited by radiation in a target. For the strictest use in dosimetry, the term must be specified as absorbed dose, equivalent dose, organ dose, etc. These quantities may refer to exposed individuals (individual dose) or to a group of people (collective dose). 

The main objective of the current system of radiation protection is to provide humans with adequate protection from the unacceptable effects of ionizing radiation therefore, it requires the assessment of pathways leading to their exposure. A certain level of contamination in the environment will imply a certain dose in humans. Envirorunental radiation protection therefore deals with those pathways that originate from envirorunental media and edible biota in areas liable to contamination by artificial radionucKdes (or enhanced levels of natural radioactive materials). 

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