Ionizing radiation concepts

Dose equivalent or rem is a special radiation protection quantity that is used, for administrative and radiation safety purposes only, to express the absorbed dose in a manner which considers the difference in biological effectiveness of various kinds of ionizing radiation. The ICRU has defined the dose equivalent, H, as the product of the absorbed dose, D, and the quality factor, Q, at the point of interest in biological tissue. This relationship is expressed as H = D x Q. The dose equivalent concept is applicable only to doses that are not great enough to produce biomedical effects. 

Numerous behavioral measures have been evaluated for their usefulness in providing a sensitive index of exposure to ionizing radiation. Radiation-related mental retardation is the most likely type of behavioral abnormality in humans sensitivity peaked between 8 and 15 weeks of conception... 

Absorbed dose is a fundamental and basic physical quantity which can be used in all fields where ionizing radiations are used. It is directly related to the physical, chemical, and biological effects produced by the irradiation. The concept of absorbed dose thus has broad applications and is indeed widely used. Metrological institutions provide standards and calibration of instruments in terms of absorbed dose. 

The Effects of Ionizing Radiation on Solid Catalysts Ellison H. Taylor Organic Catalysis over Crystalline Aluminosilicates P. B. Venuto and P. S. Landis On the Transition Metal-Catalyzed Reactions of Norbornadiene and the Concept of tr Complex Multicenter Processes G. N. SCHRAUZER... 

We are fully aware of the extensive review literature concerning the mechanism of primary processes in interaction of the ionizing radiation with matter.5,1, 20 25 However, the most recent of the cited reviews has been written more than a decade ago. The last ten years are marked by intensive development of experimental studies and by the appearance of new theoretical conceptions that change some of the traditional views on primary processes. In this review we discuss the modern ideas concerning the primary radiolysis stage that take into account the latest developments in this direction. 

There is a long-standing interest in the question of charge and excitation transfer through DNA. This largely resulted from an attempt to protect or to sensitize DNA against the effects of ionizing radiation in radiotherapy. The concept of... 

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 ... 

There is direct evidence that children are more susceptible than adults to at least some kinds of carcinogens, including certain chemicals and various forms of radiation. Data from controlled experimental studies in animals also support the concept that susceptibility to some chemical carcinogens and to various forms of ionizing radiation is greatest during the early stages of life, both before and after birth (Tomatis Mohr, 1973 Napalkov et al., 1989 Bimbaum Fenton, 2003). There is also evidence of increased or even unique... 

Radiation is feared because its delivery cannot be seen, and is often not measured, because it is only in retrospect that one realizes that radiation exposure has occurred. We accept the concept of linear, nonthreshold cancer induction from ionizing radiation (Harley, 2001, 2008) this allows calculation of cancer risk regardless of how small (or large) the dose may be. Calculating very low risks leads to calculating a risk that one would consider acceptably low, that is a risk below the ability to detect a response (Harley, 2001). 

One of the most intensively studied areas of hormesis research is the effects of exposure to low-level ionizing radiation (LLIR). The concept that LLIR can... 

For radiation protection purposes, several theoretical dosimetric quantities have been created that attempt to normalize the responses of different tissues and organs of the body from irradiation by different types of ionizing radiation so that uniform radiation protection guidelines can be promulgated that are insensitive to the particulars of any given irradiation scenario. The traditionally used quantity has been the dose equivalent (DE), which is defined as the absorbed dose (D) multiplied by the quality factor Q. The unit of dose equivalent has been the rem, which is dimensionally the same as the rad the SI unit is the Sievert (Sv). Recently, the DE has been replaced by a similar concept called the equivalent dose. The equivalent dose depends on the relative biological effectiveness rather than on Q. 

Halton DM. 1988. A comparison of the concepts used to develop and apply occupational exposure limits for ionizing radiation and hazardous chemical substances. Regul Toxicol Pharmacol 8 343-355. 

Numerous behavioral measures have been evaluated for their usefulness in providing a sensitive index of exposure to ionizing radiation. Radiation-related mental retardation is the most likely type of behavioral abnormality in humans sensitivity peaked between 8 and 15 weeks of conception and doses >0.4 Gy. No specific mechanism for the production of mental retardation has been established, although proposed mechanisms include the loss of cells, migration of neurons, and failure of synapto-genesis. In studies with rats, operant responses decreased (maintained by positive reinforcement such as food or water) at sublethal radiation doses (3.0-6.75 Gy) under various schedules of reinforcement. Dismpted operant responses under shock avoidance at >LD100 levels are reported in pigs and rhesus monkeys. 

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