Safety_Series_025_1968 - gnssn - International Atomic Energy ...
Safety_Series_025_1968 - gnssn - International Atomic Energy ...
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/1. 3. 2. 3. Late effects after whole-body irradiationUnder continuous w h ole-bod y irradiation at d ose rates as highas 0. 5 ra d /d , no d ifferen ce in life-sp a n between irradiated and control animals was observed (F ig. 10).D elayed in ju ries have been ob served in b lo o d -fo rm in g organ s.They m anifest th em selves in the form of aplastic anaemia orpancytopenia. E xact rela tion sh ip s betw een d ose and e ffe ct a relack ing. Am ong the su rv iv o rs at N agasaki and H iroshim a delayedin ju ries (with the exception of leukaem ia) are generally ra re . Someirradiated p erson s died from cach exy connected with d istu rban cesin the haem atopoietic apparatus.1.3. 2. 4. Genetic effectsIrradiation of the germ tissu es m ay cause mutations which appearin later generations. The follow ing features are ch aracteristicof mutations:(a) Mutations having once occu rred are permanent. The mutantgenes may be restored only by a re v e rse mutation and this has onlya slight probability o f o ccu rrin g . In the p rocess of selection som eof the mutant genes m ay be elim inated.•(b) The great m a jority of ob serv ed mutations are d e le te rio u s.(c) It has not thus fa r been p roved w hether a th resh old d o seex ists fo r m utations. T his m eans that every ion izin g radiationlocated in a germ cell should be assum ed to have a sm all statisticalprobability of causing a mutation.(d) Sm all d oses m ay be cum ulative and the end resu lt m ay notappear until many generations la ter.(e) The gen etic d o se req u ired to double the m utation ra te inman is of the ord er of 10 to 100 rads. It cannot be less than 3 radssin ce this level is attained in a human generation of 30 yea rs as theresu lt of natural radiation. However, recent work may indicate thatat low d ose rates the d ose requ ired to double the m u tation -rate inman m ay be la rg e r than indicated h ere.A whole range of ch a ra cte ristics m ay be influenced by gen eticdam age, including variou s m orp h olog ica l and b io m e trica l ch a ra cte r is tic s (life-sp a n , weight at birth, in tellig en ce, fe rtility , lethaleffects, etc.). Owing to the uncertainty of som e of the genetic m echanism s in volved, it is safest to assum e that approxim ately 4% ofchildren born are at present burdened with hereditary disturbances.42