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Safety_Series_025_1968 - gnssn - International Atomic Energy ...

Safety_Series_025_1968 - gnssn - International Atomic Energy ...

This publication is no

This publication is no longer validPlease see http://www.ns-iaea.org/standards/case of neutron irradiation on the other hand, distribution in thebody is heterogeneous, depending on the orientation and energy ofthe neutron flux. With beta particles, the irradiation is limited tothe surface layers of the organism. However, in all cases of wholebodyexposure the monitoring apparatus is able to supply data fromwhich to estimate the resultant irradiation of the organism. In casesof partial exposure a distinction can be made between segmentarydeep irradiation by gamma rays or neutrons and segmentary superficialirradiation by beta particles. The demarcation of the partof the body irradiated is of great importance, but often it can be inferredonly from the circumstances of the exposure. It is also helpfulto have detectors judiciously placed in body regions particularlyliable to exposure, as for example the wrists, fingers and thorax.In most cases such a procedure makes it possible to determine segmentaryexposure, though certain instances of partial irradiationmay nevertheless pass undetected.(2) Time distribution. Besides its spatial distribution, the timedistribution of the dose is important. Therefore monitors have tobe used which yield data on both the intensity of the incident radiationand the amount of radiation received during a given period. The instrumentsfor measuring intensity are called dose-rate meters andthe most usual type is the portable ionization chamber, used forarea monitoring and warning purposes.(3) Types of radiation. The multiplicity of incident radiations alsopresents a problem for personnel monitoring and influences thechoice of method for measuring external irradiation. Externalirradiation is often due to mixed gamma and beta radiation, to whichneutron radiation must sometimes be added. Workers must thereforebe provided with dosimeters capable of recording these varioustypes of radiation. Personnel dosimeters at present available permitthis, and sometimes also furnish data on the energy of the incidentradiation.(4) Size of the dose. For monitoring under normal working conditions,the evaluation of small radiation doses of some tens or hundredsof millirems is called for, and dosimeters with a range extendingfrom 0 to 3 rem are fully adequate for this work. However,if there is an appreciable risk of accidental exposure, it is essentialfor workers to be equipped also with dosimeters capable of recording92

This publication is no longer validPlease see http://www.ns-iaea.org/standards/doses up to 1 0 0 0 rem at least, otherwise after an accident greatdifficulty may arise in evaluating the doses actually received. Suchdosimeters are com m ercially available and it is, in fact, alreadypossible to obtain dosimeters capable of meeting the requirementsof both routine and emergency monitoring.4. 1. 2. 1. 2. Organization of monitoring in practice. (1) Whole-bodyexposure. Personnel dosimeters yield adequate data. They shouldbe worn continuously and the exposure checked at appropriate intervals.Measurement of total beta/gamma and neutron activity shouldbe systematically performed and the results should also distinguishbetween the gamma, beta and neutron fractions. Doses expressedin rontgen units or in terms of particle flux should be converted intorem Units to indicate accumulation. Film dosimeters can be developedat intervals of from onie to thirteen weeks, depending on thenature of the hazard and on administrative conditions. The currentpractice is to carry out weekly readings, but there is no objectionto making them on a monthly or quarterly basis only, since thesereadings in fact indicate only the dose accumulated during a relativelyshort period, a week or a month for example. All doses are enteredin the external exposure record of each worker and added togetherso as to give the accumulated dose-time curve. From thiscurve it can be decided whether the exposures received are com ­patible with the maximum permissible dose formula recommendedby the International Commission on Radiological Protection.(2) Partial exposure. The above data on whole-body exposure shouldbe supplemented by information on partial exposures. For this purposemonitors should be worn in the region of the hands or thefingers whenever a predominant exposure of the extremities may,occur.In the same way, for ionizing radiation leading chiefly to skinexposure (beta), detectors may usefully be worn which give a separaterecord of doses due to penetrating radiation (X, gamma) andto soft radiation (beta). The results are recorded separately.(3) Accidental exposure. When the work carried on entails a ccidentalexposure hazards (nuclear reactors, particle accelerators),detectors should be worn which can measure high doses of the orderof several tens or hundreds of rems. ,93

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