Ionizing radiation, energy deposition

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). 

Quality—A term describing the distribution of the energy deposited by a particle along its track radiations that produce different densities of ionization per unit intensity are said to have different "qualities."... 

DEPTH PROFILE. The secondary electrons produced by ionization processes from an incident beam of high-energy electrons are randomly directed in space. Spatial "equilibrium" is achieved only after a minimum distance from the surface of a polymer in contact with a vacuum or gaseous environment (of much lower density). Consequently, the absorbed radiation dose increases to a maximum at a distance from the surface (2 mm for 1 MeV electrons) which depends on the energy of the electrons. The energy deposition then decreases towards zero at a limiting penetration depth. 

With hadrons (i.e., neutrons, protons, and heavy ions), new radiation qualities are introduced in therapy. The distributions of the ionizations (and energy deposition events) along the particle tracks are different, and, as a result, different and increased biological effects (at equal absorbed dose) may be expected compared with the conventional photon beams. Fig. 1 illustrates the differences in dose necessary to produce a given biological effect as a function of radiation quality [15]. 

At low and medium doses, it is well established that the nutritional value of proteins, carbohydrates, and fats as macronutrients are not significantly impaired by irradiation, and neither the mineral bioavailability is impacted. Like all other energy depositing process, the application of ionizing radiation treatment can reduce the levels of certain sensitive vitamins. Nutrient loss can be minimized by irradiating food in a cold or frozen state and under reduced levels of oxygen. Thiamin and ascorbic acid are the most radiation sensitive, water-soluble vitamins, whereas the most sensitive, fat-soluble vitamin is vitamin E. In chilled pork cuts at the 3 kGy maximum at 0-10°C, one may expect about 35 0% loss of thiamin in frozen, uncooked pork meat irradiated at a 7 kGy maximum at —20°C approx., 35 % loss of it can be expected [122]. 

The adiabatic character of EB energy deposition is used in calorimetry, which is the primary absolute method of measuring the absorbed dose (energy per unit mass).1 It measures the amount of heat produced by the absorption of the ionizing radiation. An example is the water calorimeter developed by Risp National Laboratory in Denmark.2-3 This instrument is reported to be suitable for electrons from a linear accelerator with energies higher than 5 MeV and shows accuracy of 2%.4... 

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