Radiations induced ionization

Radiation induced ionization in an argon -filled detector. 

The most energetic radiation (far UV, X-rays, and y-radiation) induces ionization ... 

DNA suffers radiation damage by both a direct mechanism and an indirect mechanism. The direct damage results from radiation-induced ionization of DNA itself. The indirect damage results from attack on DNA by other free radicals. Since water is the predominant molecule in cells, the major source of indirect radiation DNA damage is from water radiolysis. 

With the objective of oxidizing the fullerene core, radiolysis of any chlorinated hydrocarbon solvent provides the means of forming strongly oxidizing radical species [71]. For example, the radiation-induced ionization of dichloroethane (DCE) yields the short-lived and highly reactive solvent radical cation. In general, the electron affinity of [DCE] + is sufficient to initiate one-electron oxidation of the fullerene moiety (Eq. 6) [72-76]. 

Zessoules, N., Brinkerhoff, J., and Thomas, A., Recombination and mobility of nuclear radiation induced ionization in liquid hydrogen, /. Appl Phys., 34, 2010,1963. 

The Onsager theory of ionic escape is widely used for the analysis of photo- and radiation-induced ionization in nonpolar liquids. Here an electron is trying to escape from its positive parent ion. Application of the model of Brownian motion requires the mean free path of the Brownian particle to be small compared to the characteristic... 

The theory of radiation-induced grafting has received extensive treatment. The direct effect of ionizing radiation in material is to produce active radical sites. A material s sensitivity to radiation ionization is reflected in its G value, which represents the number of radicals in a specific type (e.g., peroxy or allyl) produced in the material per 100 eV of energy absorbed. For example, the G value of poly(vinyl chloride) is 10-15, of PE is 6-8, and of polystyrene is 1.5-3. Regarding monomers, the G value of methyl methacrylate is 11.5, of acrylonitrile is 5.6, and of styrene is >0.69. 

Ionizing radiation is unselective and has its effect on the monomer, the polymer, the solvent, and any other substances present in the system. The radiation sensitivity of a substrate is measured in terms of its G value or free radical yield G(R). Since radiation-induced grafting proceeds by generation of free radicals on the polymer as well as on the monomer, the highest graft yield is obtained when the free radical yield for the polymer is much greater than that for the monomer. Hence, the free radical yield plays an important role in grafting process [85]. 

Among the various radiation-induced modifications, the EB-processing of polymers has gained special importance as it requires less energy, is simple, fast, and versatile in application. The overall properties of EB-irradiated polymeric materials are also improved compared to those induced by other ionizing radiation. 

Brcimer, L.H. (1988). Ionizing radiation-induced mutation. Br. J. Cancer 57, 6-18. 

Cancer is the major latent harmful effect produced by ionizing radiation and the one that most people exposed to radiation are concerned about. The ability of alpha, beta, and gamma radiation to produce cancer in virtually every tissue and organ in laboratory animals has been well-demonstrated. The development of cancer is not an immediate effect. In humans, radiation-induced leukemia has the shortest latent period at 2 years, while other radiation induced cancers have latent periods >20 years. The mechanism by which cancer is induced in living cells is complex and is a topic of intense study. Exposure to ionizing radiation can produce cancer at any site within the body however, some sites appear to be more common than others, such as the breast, lung, stomach, and thyroid. 

The areas where the use of the track model has been found particularly expedient are (1) LET variation of product yields in the radiation chemistry of liquids (2) the yield of escaped ions and its variation with particle LET (3) energy loss in primary excitations and ionizations (4) radiation-induced luminescence and (5) particle identification. 

In the preceding ten chapters of this book, we have described various important chemical and physical changes brought about by the absorption of ionizing radiation in gaseous and condensed media. Wherever possible, we have tried to elucidate the underlying mechanism with a discussion of the properties and reactivities of the intermediate species. However, the book would remain incomplete without discussion of some of the various uses that have been found for radiation-induced reactions in science and industry. 

Radiation is carcinogenic. The frequency of death from cancer of the thyroid, breast, lung, esophagus, stomach, and bladder was higher in Japanese survivors of the atomic bomb than in nonexposed individuals, and carcinogenesis seems to be the primary latent effect of ionizing radiation. The minimal latent period of most cancers was <15 years and depended on an individual s age at exposure and site of cancer. The relation of radiation-induced cancers to low doses and the shape of the dose-response curve (linear or nonlinear), the existence of a threshold, and the influence of dose rate and exposure period have to be determined (Hobbs and McClellan 1986). 

Figure 32.10 Relation between body weight and radiation-induced LD50 (30 days postexposure) for selected mammals. (Modified from United Nations Scientific Committee on the Effects of Atomic Radiation [UNSCEAR]. 1988. Sources, Effects and Risks of Ionizing Radiation. United Nations, New York. 647 pp.)...

Sankaranarayanan, K. 1991a. Ionizing radiation and genetic risks II. Nature of radiation-induced mutations in experimental mammalian in vivo systems. Mutat. Res. 258 51-73. 

Thacker, J. 1990. Molecular nature of ionizing radiation-induced mutations of native and introduced genes in mammalian cells. Pages 221-230 in Ionizing Radiation Damage to DNA Molecular Aspects. Proceedings of a Radiation Research Society — UCLA Symposia Colloquium. Lake Tahoe, CA, January 16-21, 1990. Wiley-Liss, New York. 

Lastly, we mention one more excitation mechanism that has been observed in molecules. It is well-established that following strong field ionization in atoms and molecules, under certain conditions, the ionized electron can be driven back to the ion core where it can recombine to produce high-harmonic radiation, induce further ionization, or experience inelastic scattering. However, there is also the possibility of collisional excitation. Such excitation was observed in [43] in N2 and O2. In both molecules, one electron is tunnel ionized by the strong laser field. When the electron rescatters with the ion core, it can collisionally ionize and excite the molecular ion, creating either N + or Ol+ in an excited state. When the double ion dissociates, its initial state can... 

The sensitivity to ionizing radiation is maximal in those cells able to activate a co-ordinate program of cell death (apoptosis) primed by the radiation-induced oxidative stress. Albeit apoptosis is a nuclear event and radiation-induced DNA damage is probably the most relevant mechanism of initiation of apoptosis, the control of the execution phase (and sometime also the initiation) takes place at the mitochondrial level. Radioresistance occurs... 

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