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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/It is also of in terest to know the fluctuations in these amounts,which m ay ea sily be as m uch as 200 to 300%.The amount o f natural radioactivity re ce iv e d is low fo r peopleliving in b rick houses, but the figure can be m ultiplied by two, three,four o r even five for people living in granite houses, owing to gammaem ission and the fact that granite d iffu ses radon into a ir and waterwhen uncoated. In som e p arts, such as India, this m u ltip licationfa cto r m ay be as high as 10, 12 o r 15. Thus it can be seen thatpopulations have developed in areas where they have been subjectedto ex p osu res ranging betw een 0. 1 and 1 rem p er y e a r without anyex tra ord in a ry e ffe cts appearin g.If the natural radiation dose is taken as 5 rem s o v e r a p eriodo f 30 years, one should not forget that actual doses received by individuals(ov er a 3 0 -y r period) v a ry betw een 3 and 50 rem s and thatm ost of the population living in sedim entary areas are exposed nearthe m inim um valu e, i.e. about 5 re m s o v e r 30 y e a r s . With suchd oses th ere is no risk of known th resh old e ffe cts and th is p erm itsus to estim ate an upper lim it fo r e ffe cts without a th resh old , e.g.in cid en ce o f m utations.3 .1 . 1. 2. A nim al exp erim en tsA second type of inform ation is provided by the extensive animalexperim en ts that have been m ade p r e c is e ly in o r d e r to e sta b lishca u sa l rela tion sh ip s betw een d ose and e ffe c t. T he lite ra tu reco v e rin g p ra ctica lly a ll th resh old e ffe cts is v e ry substantial, butit is thinner fo r effects without a threshold which, as has been seen,a re m uch m o re d ifficu lt to study. F ro m the gen etic point o f v iewfo r instance, the literatu re cov ers only som e sp ecies, som e m ic r o ­o rg a n ism s, som e in sects and, above a ll, the fru it fly D rosop h ila.R ecent litera tu re b ea rs on m ic e .A very large amount of inform ation is available which m akes itp ossib le on the one hand to com pare variou s sp ecies from the pointo f view of radiobiology and derive threshold values and on the otherto plot d o se-e ffe ct cu rves in the case o f genetic m utations.H ow ever, there are always uncertainties in extrapolating fromanimal to man, so that the above inform ation must be supplem entedby data concerning human observation s.3.1. 1. 3. Human observations. T hese observation s relate fir s tly to people exp osed fo r th era ­peutic pu rposes. In these ca ses it is no lon ger the ben eficial effects64

This publication is no longer validPlease see http://www.ns-iaea.org/standards/o f the radiation that are studied but the possible hazards. Radiationm a y , fo r in stan ce, resu lt in skin m o d ifica tio n s, lung tro u b le s ,s o m e tim e s the in cid en ce o f c a n c e r s , etc.Human ob serv a tio n s a lso co m e fro m p eop le who have u n d ergoneoccupational exposure. As far as radium is concerned they areo f the utm ost valu e, sin ce a w hole s e r ie s o f a u top sies have m adeit p o ssib le to d eterm in e the amount o f radium in side the body andthe varyin g d ose le v e ls and d eg rees o f dam age.T here is finally a third category of data, nam ely those relatingto atom bom b v ictim s, fo r whom causality relation sh ips have beenestablished, esp ecia lly fo r leukaem ia, skin and blood changes, etc.In the fie ld o f g en etics th ere a re p ra c tic a lly no data o f v alu e.As a human gen eration is o f the o r d e r o f 30 y e a rs and b eca u se o fthe relative novelty o f the su bject, it is cle a r that little inform ationis yet available.A whole a rra y of m ateria l is th erefore to hand. P h y sica l dataa re m ainly useful to d eterm in e what steps it is rea son a b le to takein the case of effects without a threshold. B iological data, fo r theirpart, throw a great deal of light on th resh old e ffe cts and so m akeit p o ssib le to d eterm in e the approp riate le v e ls .3.1.2. C ategories o f exp osureB efore turning to a p re cis e definition o f p e rm issib le le v e ls , itis desirable to indicate the general concepts underlying the standards,in particular those o f ca tegories of exposure and the m axim um p e r­m issib le d ose.A ll radiation can be cla ssifie d in two ca te g o rie s, natural background radiation and m an-m ade radiation.3.1. 2.1. Natural background radiationWhen standards are drawn up, whether for radiation w orkers orfo r the population at large, no account is taken o f natural radioactivity.T his g en eral tenet is o f the utm ost im p orta n ce. Naturalra d ioactivity can be used as a b a sis o f re fe re n ce in drawing upstandards, but it is not taken into account subsequently as it is subject to fluctuations and the ICRP has pointed out that it y a rie s co n ­sid era b ly fro m lo ca lity to lo ca lity . T h e re fo re the resu ltin g d osesto va riou s organs are not w ell known.65

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