Radiation, chemical changes measurement

Other chemical changes can be much faster than the RNA conformational changes illustrated here. Photodissociation of sodium iodide (Nal) in the gas phase occurs on the time scale of a few picoseconds (10-12 seconds). To measure this phenomenon, Nal molecules are irradiated by a sub-picosecond ultraviolet pulse of radiation, and the subsequent events are clocked by another short light pulse that detects the newborn... 

Changes in the properties of polymer materials caused by absorption of high-energy radiation result from a variety of chemical reactions subsequent to the initial ionization and excitation. A number of experimental procedures may be used to measure, directly or indirectly, the radiation chemical yields for these reactions. The chemical structure of the polymer molecule is the main determinant of the nature and extent of the radiation degradation, but there are many other parameters which influence the behaviour of any polymer material when subjected to high-energy radiation. 

In this chapter we will consider the techniques developed to detect and quantitatively measure how much ionization and/or excitation is caused by different nuclear radiations. As all radiation creates ionization and/or excitation, we will separate the discussion of detection methods according to the general techniques used to collect and amplify the results of the interaction of the primary radiation with matter rather than by the type of radiation. These detection methods can be classified as (a) collection of the ionization produced in a gas or solid, (b) detection of secondary electronic excitation in a solid or liquid scintillator, or (c) detection of specific chemical changes induced in sensitive emulsions. 

The concern of cosmochemistry is the investigation of extraterrestrial matter (sun, moon, planets, stars and interstellar matter) and their chemical changes. Meteorites are an object of special interest in cosmochemistry, because of the nuclear reactions induced by high-energy protons in cosmic radiation ( (p) up to about 10 GeV) and by other particles, such as a particles and various heavy ions. Measurement of the radionuclides produced in meteorites by cosmic radiation gives information about the intensity of this radiation in interstellar space and about the age and the history of meteorites. 

Accurate measurement of free-radical and molecular-product yields is important in radiation-chemistry studies on aqueous solutions, for these measurements enable quantitative predictions to be made regarding the extent of chemical changes during irradiations, and lead to an understanding of reaction mechanisms. Therefore, recent research has been directed toward the measurement of these yields, which are generally expressed as G values. An excellent account of the chemical methods used for determining G values... 

Even for uniform-field discharges carrying an unvarying current, problems arise in applying the revised theory to the interpretation of experiment on chemical change. These problems are largely connected with a lack of auxiliary information such as would be available from simultaneous measurement of rates of reaction and emission of radiation, and of electron concentration and distribution in energy. 

A. Chemical Dosimeters. Chemical dosimeters are systems in which measurable chemical changes are produced by ionizing radiation. Radiation produces acids in the system, the amount of which can be determined from visible color changes, or, more accurately, by titration or pH readings. Most chemical systems of practical size are useful only for gamma doses of hundreds to millions of cGy. However, small volume detectors can be found which measure doses in the range of a few cGy to several thousand cGy. 

Chemical Dosimeter - A type of dosimeter that uses a chemical change to measure the radiation. Chemoprophylaxis - Administration of a chemical to prevent the development of an infection or the progression of an infection to active manifest disease. 

Conductivity measurements on solids after irradiation do not seem to yield sufficient information for evaluating the radiation chemical electron yield since the number of the radiation-produced charge carriers cannot be determined by this method alone. The conductivity data are, however, useful for identifying these charge carriers, and they permit determination of the temperature range at which the charge carriers react and the rate constants of their reactions. The temperature behavior of the conductivity can be related to the structural changes expected to occur. 

Dosimetry is the measurement of absorbed dose. The unit of absorbed dose is the gray (Gy). Because dose is a measure of absorbed energy, calorime-try is the fundamental method of measurement. However, calorimetry suffers from being insensitive, complex, slow and highly demanding in technical skills and experience. Primary dose measurement is usually done with substances that are chemically changed quantitatively in response to the amount of radiation absorbed. For most purposes the standard primary system is the Fricke or ferrous sulfate dosimeter. In this system, which consists of a solution of ferrous sulfate in dilute sulfuric acid, ferrous ions Fe are oxidized by absorbtion of radiation to ferric ions Fricke dosimeters are usually presented in glass... 

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