Radiation effect, equivalence

In treated water for high-pressure boilers or where radiation effects are important, as in some nuclear projects, impurities are measured in very small units (e.g. g/litre or p.p. 10 ), but for most purposes it is convenient to express results in mg/litre. In water analysis, determinations (except occasionally for dissolved gases) are made on a weight/volume basis but some analysts still express results in terms of parts per million (p.p.m.). The difference between mg/litre and p.p.m. is small and for practical purposes the two units are interchtmgeable. For some calculations, the use of milli-equivalents per litre or equivalents per million (e.p.m.) has advantages but has not found much application. Hardness, whatever the constituent salts, is usually expressed as p.p.m. CaCOs (see Table 2.10). 

Effective dose equivalent The weighted sum, in sieverts (Sv), of the radiation dose equivalents in the most radiosensitive organs and tissues, including gonads, active bone marrow, bone surface cells, and the lung. 

Optically active icco-nucleosides of type 1.1 of 2-nitromidazole were prepared from tartaric acid ester by conversion to the dioxolan followed by reduction and acylation to give 1154, which was converted to 1155. Its coupling and deacylation gave 1156 (94MIP1). All the optically active isomers showed a radiation-sensitization effect equivalent to that of the racemate. 

As long as radiation dose equivalent exposures are low, radiation damage is non-detectable. General effects of short-term radiation exposure are summarized in Table 17.5. The dose equivalents in Table 17.5 are listed in rems. These values are several orders of magnitude greater than what humans received in a year. Annual human exposure... 

To compare doses resulting from different types of radiation it is necessary to formulate a measure of radiation effects on the crystal structure doses can be recalculated to the number of displacements per atom (dpa). A dose of 0.1 dpa, for example, means that one of ten atoms was displaced from its initial position. Equivalent values in dpa units may be calculated for different types of radiation from the effects of its interaction with the crystal lattice. To recalculate a-dose to dpa the following formula is used ... 

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... 

In order to take into account the radiation sensitivity of different tissues, tissue weighting factors wt are introduced, and the effective equivalent dose received by the tissue E is defined by... 

In this equation, the risk of cancer is assumed to be 100% for an effective equivalent dose of 20 Sv. The equation is based on the probabilities listed in Table 22.10. In order to take into account that a dose dehvered with a relatively low dose rate over a longer period of time has an appreciably smaller effect than a single dose, a dose reduction factor of 2 is recommended for smaller dose rates. However, in the report of the United Nations Scientific Committee on the Effects of Atomic Radiation... 

Because of the varying radiation sensitivities of the different cell types, a tissue weighing factor, Wj, is introduced. It represents the relative contribution of that tissue to the total detriment from uniform irradiation of the body Table 18.6 gives tissue weighing factors. This leads to another dose concept (cf. eqn. 18.1), the effective equivalent dose, 0g, which is the sum of the weighted equivalent doses in all tissues, as given by... 

The effective equivalent dose limit refers to the sum of the equivaloit doses to all tissues from external sources and from radioactivity taken into the body. The limits do not include contributions from any medical procedure or from normal natural radiation. 

---