Safety_Series_025_1968 - gnssn - International Atomic Energy ...

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This publication is no longer validPlease see http://www.ns-iaea.org/standards/In the event of intake of several radionuclides which are takenup by different organs, whole-body exposure must be consideredto have occurred, even though these organs are not the bloodformingorgans or gonads. In the first case the standard pertinentto the critical organ involved must be applied, and in the second case5 rems a year - the standard corresponding to the whole body -is used.If the nature of the radionuclide mixture is unknown, as is oftenthe case, the mixture is considered to be composed of the most toxicradionuclides. As this works out in an exceptionally severe manner,it is always desirable in practice to check on the presence or theabsence of a particular nuclide in an unknown mixture. The newtables give information on this point. Thus for a mixture in whichthere are no alpha-emitters, these being the most toxic, a lessstrict value is taken.The ICRP tables give typical examples where the most dangeroussubstances are eliminated one after another to arrive at the valuecorresponding to the most toxic nuclide the mixture can possiblycontain. In this way it is possible to get factors of 100, 1000 or even1 0 0 0 0; depending on the case.This procedure must be followed in every instance where airor water is contaminated by mixtures whose nature is not entirelyknown. It is always desirable to make a few qualitative analysesto prove certain highly toxic substances are not present or, if theyare. to determine them separately. Otherwise one must assumethat these substances make up the whole of the mixture, which maywell cause difficulty in applying the standards.Finally, when the nature of the mixture is known, the variouscontributions made by the different radionuclides must be taken intoaccount. The ICRP recommendations contain model formulas forsuch calculations.On a practical level this implies that the composition of themixture and the proportion of each radionuclide should be perfectlywell known. When an atmospheric analysis is being made, withfluctuations according to place and time, it will be essential to undertakeall necessary weighting calculations so as to determine themaximum permissible concentration, due account being taken of eachsubstance and the absence of any external irradiation being assumed.82
This publication is no longer validPlease see http://www.ns-iaea.org/standards/4. HEALTH SUPERVISION4. 1. RADIOLOGICAL MONITORINGAs stated earlier, the protection of workers against ionizingradiation requires both individual monitoring and medical examinations.The two types of supervision being complementary, in somecountries responsibility for both types of supervision is assumedby the medical service, in others it is divided between physicistsand physicians. When physicians are responsible for both individualmonitoring and medical examinations, their qualifications should,of course, extend to all the methods involved. When the physiciansare in charge of the medical examinations only, they should neverthelesstake account of the data obtained from physical monitoringin the interpretation of their findings.Therefore, as an aid to the physician, the methods of measuringexternal exposure or radioactive contamination to which personnelmay be subjected are described in this section of part 4.4. 1. 1. Methods of measurement of irradiation4. 1. 1.1. Measurement of external irradiation4. 1. 1. 1. 1. Measurement of electromagnetic (X, 7 ) radiation. Personnelmonitoring for electromagnetic ionizing radiation may bedone with films, pocket dosimeters, pocket ionization chambers orphotoluminescent or thermoluminescent dosimeters.Films (film badges) have a range varying according to the emulsionused, but no single emulsion can cover all requirements. Itis necessary sometimes to measure extremely low-level exposuresof the order of 10 to 1000 mR, and at other times doses of the orderof 1 to 1000 R. Detectors containing several emulsions may thereforebe used to record doses of interest for radiological protectionpurposes. The error of film badges is of the order of 20%, alwaysin the direction of a high reading, which constitutes a safety factor.The individual dose received may also be measured by meansof small ionization chambers. Some types are equipped withelectrometers and are known as pocket dosimeters (or pocketelectrom eters), while others are without electrom eters and aretermed pocket ionization chambers. The pocket dosimeters (pocketelectrometers) allow direct self-reading since the detector and the83
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26Table 6-2. Fracture-specific EC i
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