Liquid chemical dosimeters

Scientists are often faced with problems directly related to the problem of equivalence of the radiation effects produced by different types of radiation. The most typical are the two following problems. The first has to do with prediction of the radiation effect produced by a given type of radiation based on the data of radiative transformations produced by another type of radiation. This problem is very closely related to the problem of determining the limits of applicability of dosimetric systems (especially, of liquid chemical dosimeters). The second problem concerns the choice of equivalent radiation that can be substituted for a difficult-to-study type of radiation we might be interested in. 

The problem of equivalence of the radiation effects produced by different types of radiation is very important in dosimetry of ionizing radiation (especially, for liquid chemical dosimeters). As we have shown in Section IX.A, in the general case, the radiation effect in a condensed... 

The most well-known liquid chemical dosimeter, the Fricke solution is based on the radiation-induced oxidation of ferrous ions, Fe(II), to ferric ions, Fe(III), in acidic media (E1026 Fricke Reference Standard Dosimeter, ASTM standard). The standard Fricke solution consists of 0.001 mol dm ferrous ammonium sulfate (Fe(NH4)2(S04)2(6H20)), or ferrous sulfate (FeS04(7H20)), and 0.4 mol dm H2SO4 in aerated aqueous solution. It is applicable for measuring doses in the 40 to 400 Gy range. 

Most of the chemical dosimeters consist of a bulk component, often a liquid in which practically the total energy imparted by the ionizing radiation is deposited, and a solute that reacts with the radiation-induced species formed by the reaction of the bulk component to produce the observed chemical change. 

All of the preceding dosimeters for sonochemistry (both chemical and physical) are applicable in, and have been studied under, homogeneous conditions. On the other hand, most of the potential industrial applications of ultrasound concern solid-liquid mixtures. The use of such dosimeters under heterogeneous conditions could lead to some discrepancies, however, since the presence of a suspended solid may result in scattering and dampening of the wave. For this reason the search for accurate dosimeters working under heterogeneous conditions is of considerable interest. 

Calorimetry can be used for routine monitoring of these electron pulses for liquid irradiations. However, even for the simple cells described in this paper, it requires too many pulses and is too time consuming to be used routinely for gases. In the larger more complex cells used for pulse radiolysis studies, calorimetry is impractical. Thus, a chemical gaseous dosimeter is required. 

The amount of radiation energy absorbed in a substance is measured with dose meters (or dosimeters). These may react via a variety of processes involving (a) the heat evolved in a calorimeter, (b) the number of ions formed in a gas, (c) the chemical changes in a liquid or in a photographic emulsion, and (d) the excitation of atoms in a glass or crystal. The first two ones are primary meters in the sense that they can be used to accurately calculate the exposure or dose absorbed from a radiation source. They can be used to calibrate the secondary meters. 

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