Chemical Effects of Ionizing Radiation

The major chemical processes in radiation chemistry are reduction and oxidation reactions, according to the following examples. In the gas phase, ionization predominates 

In water and aqueous solutions, dissociation and ionization take place 

Both VUV light and ionizing radiation can lead to the formation of dissociative excited states, e.g. 

Organic molecules such as hydrocarbons can be excited to high energy states which lead to ionization or dissociation 

Another important process is ion recombination, when a solvated electron meets a positive ion. One of the neutral products can be formed in an electronically excited state and its chemical reactions are then similar to photochemistry 

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Hems G (1960) Chemical effects of ionizing radiation on deoxyribonucleic acid in dilute aqueous solution. Nature (London) 186 710-712... 

The values of the rodielytle yields compiled in these Tables cover fM actically the entire period of quantitative research on the chemical effects of ionizing radiation, more precisely from 1905 until Januiry... 

Chapiro, A. Physical and chemical effects of ionizing radiations on polymeric systems , in Sterilization by Ionizing Radiation Gaughran, E.R.L., Goudie, A.J., eds Multiscience Publ. Ltd., Montreal, Canada, 1974. 

In order to quantify the radiation chemical effects of ionizing radiation one has to know the amount of molecules transformed or produced and the quantity of absorbed radiation energy that caused this effect. The ratio of the two is the radiation chemical yield, also called the G-value. 

Radiochemistry is a branch of chemistry, but in this context it exhibits various characteristics that make it a somewhat autonomous discipline. To be sure, the radionuclides obey the same chemical laws as their inactive isotopes do there are, however, additional aspects that have to be considered. The mechanisms in the formation of the radionuclides have to be taken into account, as well as the chemical effects of ionizing radiation and of possible chemical reactions of highly excited atoms ( hot atom chemistry ). The properties of ionizing radiation and the techniques to be applied for their measurement are additional aspects specific to radiochemistry. Generally speaking, one can define radiochemistry as an independent branch situated between inorganic chemistry, physical and analytical chemistry and nuclear physics. 

Indirect effect phys chem A chemical effect of ionizing radiation on a dilute solution caused by the interaction of solute molecules with highly reactive transient molecules or ions formed by reaction of the radiation with the solvent., in-da rekt i fekt Indirubin See indigo red., in-da rii-ban )... 

Lind (1961) defines radiation chemistry as the science of the chemical effects brought about by the absorption of ionizing radiation in matter. It can be said that in 1895, along with X-rays, Roentgen also discovered the chemical action of ionizing radiation. He drew attention to the similarity of the chemical effects induced by visible light and X-rays on the silver salt of the photographic plate. This was quickly followed by the discovery of radioactivity of uranium by Becquerel in 1896. In 1898, the Curies discovered two more radioactive elements—polonium and radium. 

About 1910, M. Curie suggested that ions were responsible for the chemical effects of radioactive radiations. Soon thereafter, mainly due to the pioneering work of Lind on gases, the notation M/N was introduced for a quantitative measure of the radiation effect, where N is the number of ion pairs formed and M is the number of molecules transformed—either created or destroyed. This notation, referred to as the ion pair yield, was most conveniently employed in gases where N is a measurable quantity. However, for some time the same usage was extended to condensed systems assuming that ionization did not depend on the phase. This, however, is not necessarily correct. The notation G was introduced by Burton (1947) and others to denote the number of species produced or destroyed per 100 eV absorption of ionizing radiation. In this sense, it is defined... 

It is clear that, along with the discovery of x-rays in 1895, Roentgen also found the chemical action of ionizing radiation. He drew attention to the similarity of the photographic effect induced by light and x-rays. Application to medicine appeared very quickly, followed by industrial applications. However, this field of investigation remained nameless until Milton Burton, in 1942, christened it radiation chemistry to separate it from radiochemistry which is the study of radioactive nuclei. Historical and classical work in radiation chemistry has been reviewed by Mozumder elsewhere [1]. Here we will only make a few brief remarks. 

Lind [2] has defined radiation chemistry as the science of the chemical effects brought about by the absorption of ionizing radiation in matter. It should be distinguished from radiation damage which refers to structural transformation induced by irradiation, particularly in the solid state. The distinction is not always maintained, perhaps unconsciously, and sometimes both effects may be present simultaneously. Following a suggestion of M. Curie around 1910, that ions were responsible for the chemical effects of radioactive radiations, the symbol MjN was introduced to quantify the radiation chemical effect, where M is the number of molecules transformed (created or destroyed) and N is the number of ion pairs formed. Later, Burton [3] and others advocated the notation G for the number of species produced or destroyed per 100 eV (= 1.602 x 10 J) absorption of ionizing radiation. It was purposely defined as a purely experimental quantity independent of implied mechanism or assumed theory. 

Chemical and biological effects of ionizing radiation are thought to occur through two main mechanisms direct interaction of the radiation with food components and living cells in materials exposed to it, and indirect action from radiolytic products, such as the radicals formed from water molecules (see Chap. 12). 

The Phototherapy of Cancer a Mode of Treatment Still at the Research Stage. Cancer is the uncontrolled proliferation of cells which build up into tumours. Treatments rely on the elimination of diseased cells, through surgery, through the effects of ionizing radiation or through chemicals. 

Daniels M, Scholes G, Weiss J. Chemical action of ionizing radiations in solution. Part XV. Effect of molecular oxygen in the irradiation of aqueous benzene solutions with x-rays. J Chem Soc 1956 832-834. 

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