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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/1 .2 . 2. 5. AdaptationT here is at presen t no convincing evidence that organ ism s canadapt them selves to high levels o f radiation. Experim ents perform edwith D rosophila and yeasts in a high radiation background have notyielded m ore resistant strains. In som e instances, a higher ra d ioresistan ce was ob serv ed in tum ours treated with a su b-leth al d ose.T h is fa ct m ay be attribu ted to a d e c r e a s e d le v e l o f oxygen in thetu m ou r tissu e , due to p a th o lo g ica l ch anges in the b lo o d v e s s e ls .It is , h ow ever, not im p o ssib le that som e ra d ia tion -a d a p tedorgan ism s w ill be found in geographic region s where a high level ofnatural radioactivity exists. Certain densely populated areas o f theg lobe (parts o f India and B ra zil) have an unusually high content ofradioactive substances in the environm ent. H ow ever, even if suchadaptation occu rs in the population, it is always n ecessa ry to bear inmind the influence of selection , in which the m ore resistant organismsu rvives.1. 2. 2. 6. Relative radiosen sitivityIt has been observed that the radioresistance of certain bacterialc e lls is substantially in creased by mutation. C linical experien ce inradiotherapy also indicates that som e individuals are probably m oreresista n t to radiation than oth ers. Since this ex p erien ce is basedla rg ely on the e ffe cts of p artial irra d ia tion , the sign ifica n ce o f theobservation cannot be extended to the whole body. F o r the present,we can only say that th ere is a wide variation in the d egree o fsen sitivity o f variou s organ ism s, sin ce a few rads are su fficien t tok ill lym ph ocytes, w h ereas som e hundreds o f thousands o f rads arerequ ired to kill an adult in se ct and o v e r a m illion rads to d estroyv iru s e s and b a cteria com p letely .The various organs d iffer con siderably in their radioresistan ce.Although it is not p ossib le to con stru ct an exact sca le o f ra d io ­resistan ce fo r the organs, it may be roughly concluded that the blood -form in g organ s, gonads and len ses o f the eyes are am ong the m osts e n sitiv e . M u scle, con n ectiv e tissu e and adult bone have a r e la ­tively high resista n ce to radiation. The skin, in testin es and en d o­crin e glands fall into an interm ediate category. This cla ssifica tio ncannot, h ow ev er, be exact, b eca u se sen sitiv ity depends on m anyfa ctors (physiological state, oxygen content, tem perature, etc. ) andon the method of observation, i.e. whether m orp h ological o r p h ysiolo g ica l changes are registered .32

This publication is no longer validPlease see http://www.ns-iaea.org/standards/1.2.3. C onclusionsIt should be em phasized that today's knowledge of the effects ofradiation on living organ ism s is in com plete, p rim a rily beca u se thep resen t knowledge o f biology is not su fficien t to esta blish soundc r ite ria for distinguishing injury from the norm al state o f the o r g a ­n ism . N everth eless, ou r knowledge o f radiation in ju ry fro m bothhuman e x p e rie n ce and anim al experim en t is su fficien t to m ake itp ossib le to esta blish m axim um p e rm issib le d oses o f radiation witha con sid era b le d egree o f con fid en ce that adequate p rotection isp rovid ed .1.3. RADIOPATHOLOGY1. 3. 1. Acute radiation effects1.3. 1.1. Acute syndrom eA fter irra d ia tion o f the g re a te r part o f the body, a s e r ie s ofp ath ological sym ptom s ensue, which orig in a lly w ere d e s crib e d as1rOntgen s ic k n e s s '. Only after the exp erien ce gained at H iroshim aand Nagasaki has our knowledge of the aspects and the sym ptom s ofa typical radiation d isea se been em phasized and in crea sed .B a sica lly , this d isea se can o c c u r as the acute radiationsyndrom e, resu ltin g fro m w h ole-b od y irra d ia tion by a d ose aboveabout 100 rads delivered at relatively high dose rates (several rad/h)and showing signs and sym ptom s within minutes to 30 to 60 days subsequentto exposure.Radiation d isease is caused principally by irradiation with gammarays, X -r a y s and neutrons. Alpha and beta rays e x e rcis e an effectwhen rad ioisotop es in la rge quantities have been taken into e x p erimental anim als and deposited lo ca lly .Acute radiation d isea se is ch aracterized by a latent p eriod , whichsu pervenes after in itial sym ptom s of m ala ise, lo s s of appetite andfatigue, during which the su fferer feels no other untoward symptom sand the length of which is roughly in versely proportional to the radiationdose receiv ed . At the end of the latent period, the onset of theilln ess o ccu rs: early lethality, destruction of bone m arrow , damageto the gastro-in testinal tract associated with diarrhoea and h aem orrhage,dam age to the cen tral nervous system , epilation, ra d io d e r­m atitis, drop in sp erm count and ste rility .33

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