Safety_Series_041_1975 - gnssn - International Atomic Energy ...

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This publication is no longer valid Please see http://www.ns-iaea.org/standards/ 30 SECTION VIII CRITICAL NUCLIDES AND PATHWAYS OF EXPOSURE 804. E xperience has shown that, when radioactive m aterials are introduced in the environm ent, a few nuclides and certain exposure pathways w ill be much m ore im portant than others and w ill be resp on sible fo r m ost of the dose received by m em bers of the public. These nuclides and pathways are designated 'c r it ic a l' . DERIVED WORKING LIMIT 805. Many of the m easurem ents made in a m onitoring program m e cannot be expressed d irectly in term s of d ose-equ ivalent fo r com p arison with the lim its recom m ended by ICRP. In these circu m stances the use o f stylized exposure m odels can provide quantitative links between the quantities m easured and the dose o r intake lim its recom m ended by ICRP. The values of the quantities that corresp on d in the exposure m odel to the recom m ended lim its are called D erived W orking Lim its (DWL). Due to con servatism in selectin g the exposure m od els, the adherence to a DWL p rovid es virtual certainty of c o m pliance with the ICRP recom m ended Dose L im its. DOSE, ABSORBED 806. The absorbed dose due to any d irectly o r in d irectly ionizing radiation is the en ergy im parted by ionizing p a rticles to a unit m ass of irradiated m aterial. The sp ecia l unit is the rad, which is equal to 0.01 joule per kilogram . DOSE COMMITMENT 807. The dose com m itm ent is the infinite tim e integral of the average dose rate caused by a given operation o r unit p ractice exposing a sp ecified population: o
This publication is no longer valid Please see http://www.ns-iaea.org/standards/ SECTION VIII 31 The dim ension o f the dose com m itm ent is absorbed dose o r d ose -equivalent, depending upon whether it is the dose rate D(t) o r the dose equivalent rate H(t) that is integrated o v e r tim e. The population ov e r which the dose rate is averaged may be any population o f in terest; e.g . the whole w orld population o r the critic a l group with regard to the given sou rce of exp osu re. An extrem e case is the integration o f the dose rate fo r a single individual, in which case the dose c o m m itm ent is sim ply his expected total future d ose, e .g . per unit intake of a sp ecified radionuclide. When the dose com m itm ent is calcu lated, the tissue o r organ fo r which the dose rate is integrated must be indicated. If the sou rce is constant in tim e, the equilibrium dose p er any sp ecified unit of tim e is n u m erically equal to the dose com m itm ent p er unit tim e of the p ractice causing the exposu re. F or exam ple, the annual dose in equilibrium is equal to the dose com m itm ent of one year of the operation causing the exposu res. DOSE-EQUIVALENT 808. The d ose-equ ivalen t fo r a given type of radiation and at a given location in the body is n u m erically equal to the p r o duct of the absorbed dose in rads fo r that radiation at that p osition , and appropriate m odifying fa ctors such as the quality fa cto r, which accounts fo r the d ifferen ce in the lin ear en ergy tra n sfer of different d irectly ionizing ra d ia tions at the location of in terest. The sp ecia l unit is the rem . EM ERGENCY SURVEY 809. An em ergen cy su rvey is a su rvey related to an accident involving loss o f con trol o v e r radiation sou rces o r ra d io active m aterial which could give rise to external radiation exposure levels o r intakes o f radioactive m aterials in ex cess o f those perm itted in the applicable regulations fo r n orm al operation.
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