Views
3 years ago

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/sures should be added together as far as possible and the resultsexpressed in units valid for all types of irradiation. These unitsare the unit of absorbed dose, the rad and — when account is takenof the Quality Factor — the rem. It will therefore be necessaryto convert to rems results obtained in rontgens or curies or in termsof particle flux.4. 1. 3. 2. Spatial distribution of the doseBesides the problems involved in merely adding together thedifferent types of irradiation, there are those of obtaining satisfactorydata on the spatial distribution of the dose. These lattercan be obtained only by precise identification of the radiation andthe radionuclides. This is unavoidable as the maximum permissibledoses recommended by the International Commission on RadiologicalProtection have been established differently for whole-body exposureand for partial exposure affecting the skin or different organs.In practice, therefore, all types of radiation likely to result in arelatively homogeneous distribution of the dose within the body willbe added together. . Thus, the doses due to gamma and neutron radiationand to radionuclides considered as diffusing uniformly inthe organism (sodium, potassium,tritium, etc. )will together formone total. Separate totals will have to be made for the irradiationof particular organs. To take as an example one of the most im ­portant cases, that of the bone, it will be necessary to addtogether all the doses received by incorporation of bone -seeking radionuclides, such as radium, plutonium, strontium,etc. , and by irradiation of the skeleton from generally diffused radionuclides(sodium, potassium, tritium, etc. ). It is thus possibleto determine the doses actually received by the most important o r­gans - skeleton, thyroid, skin, digestive tract, lungs, etc. Separatetotals should also be obtained for exposure of the extremities,especially the hands, comprising the overall exposure of the bodyplus the particular additional exposure of the members in question.This concept of spatial distribution of the dose therefore leads usto consider different kinds of exposure, either of the organism asa whole or of some part of it. Although it might appear advantageousto evaluate the total absorbed dose, this is in reality oflimited importance, as no maximum permissible level has yet beenestablished for the integral dose delivered to the whole body.98

This publication is no longer validPlease see http://www.ns-iaea.org/standards/4. 1. 3. 3. Time distribution of the doseIt is fully acceptable for dose readings to be taken at intervalsof some weeks or months since the period quoted by the ICRP is13 weeks. Measurements covering shorter periods are of valueonly for administrative purposes. As mentioned above, it is relativelyeasy to obtain adequate information on the circumstances ofan external exposure. The wearing of direct-reading dosimetersand the use of personal or portable dose-rate meters often makeit possible to evaluate how exposure has fluctuated in the courseof time. The procedure is more complex in the case of radioactivecontamination and it is often difficult to deduce the dose receivedover a period from a given degree of radioactive contamination. Thehypothesis normally adopted is that there is an exponential decreaseof the dose in time; this is expressed in term s of effective halflife.It will thus be seen that the precise determination of the timedistribution of the absorbed dose is not simple.4. 1. 3.4. Influence of the type of radiation and radionuclideIn addition to the spatial and time distribution of the absorbeddose, the type of radiation also has its part to play in the origin ofradiobiological effects. It is therefore necessary to use the QualityFactors (QF) for alpha, beta, gamma and neutron radiations; onlythus it is possible to determine the sum of the doses in rem s. Itmust not be forgotten, however, that the QF depends on a very largenumber of variables besides the type of radiation, including thecircumstances of exposure, the nature of the effects produced, etc.4. 1. 3. 5. Practical conclusionIn fact, all the above procedures can provide is a tentative evaluationbecause, although relatively accurate data are obtainableon total or partial external exposure, it is a very difficult matterto obtain precise figures on internal contamination of the organismas a whole or of a particular organ. Therefore, when the level ofinternal contamination is not too high, it is usually thought sufficientto try and obtain exact data regarding external irradiation exposureand no more than summary indications concerning internal radioactivecontamination. However, in cases where considerable radioactivecontamination has occurred, or where the hazards associated99

Safety_Series_013_1965 - gnssn - International Atomic Energy ...
Safety_Series_006_1961 - gnssn - International Atomic Energy ...
Radiation Protection Procedures - gnssn - International Atomic ...
Safety_Series_041_1975 - gnssn - International Atomic Energy ...
Safety_Series_008_1962 - gnssn - International Atomic Energy ...
Safe Handling of Radioisotopes - gnssn - International Atomic ...
Safety_Series_016_1966 - gnssn - International Atomic Energy ...
Safety_Series_015_1965 - gnssn - International Atomic Energy ...
Safety_Series_024_1967 - gnssn - International Atomic Energy ...
Safety_Series_019_1966 - gnssn - International Atomic Energy ...
Safety_Series_004_1961 - gnssn - International Atomic Energy ...
Safety_Series_005_1961 - gnssn - International Atomic Energy ...
safety series - gnssn - International Atomic Energy Agency
SAFETY ST; NDARDS - gnssn - International Atomic Energy Agency
No.6-Suppl 1988 - gnssn - International Atomic Energy Agency
Safety_Series_035-S-1_1992 - gnssn - International Atomic Energy ...
SAFETY PR A CTICES - gnssn - International Atomic Energy Agency
LEVEL 3 - gnssn - International Atomic Energy Agency
1 - gnssn - International Atomic Energy Agency
Level 2 - gnssn - International Atomic Energy Agency
SAFETY P R A C TIC ES - gnssn - International Atomic Energy Agency
SAFETY P R A C TIC E S - gnssn - International Atomic Energy Agency
Safety_Series_028_1968 - gnssn - International Atomic Energy ...
Safety_Series_050-SG-S2_1979 - gnssn - International Atomic ...
Safety_Series_010_1963 - gnssn - International Atomic Energy ...
Notes on Certain Aspects of the Regulations - gnssn - International ...
Borchardt - gnssn - International Atomic Energy Agency
Research Reactor - gnssn - International Atomic Energy Agency
Principles for Establishing Limits for the Release of ... - gnssn
O < - gnssn - International Atomic Energy Agency