Safety_Series_025_1968 - gnssn - International Atomic Energy ...

This publication is no longer validPlease see http://www.ns-iaea.org/standards/1.2.2. Factors governing the biological effects of radiationF rom the p rim ary p rocess occu rrin g after the absorption ofradiation a com plicated reaction develops which may finally em ergeas a v isib le reaction to radiation. As might be expected, this chaino f reactions can be influenced in variou s ways, p articularly in m orecom p lex org a n ism s. Am ong the agents which thus govern the finalrea ction to radiation a re p h y s ic o -c h e m ic a l con d ition s, in cludingtem p eratu re and d e g re e o f h ydration , oxygen and the v a rio u s s o -ca lled p ro te ctiv e su b sta n ces.1 .2 .2 . 1. P h y s ic o -c h e m ic a l con d ition s (tem p era tu re, d egree o fhydration)In general it may be said that a low ering of tem perature reducesthe e ffe ct o f radia tion . H ow ever, in som e c a s e s (b a cte ria ) th ereexists a certain optim um tem perature fo r the reduction of the ra d i­ation effect. A lso in the case of som e anim als it has been ascertainedthat storage at a low tem perature after irradiation retards the effectwhich appears only when the tem perature again r is e s to the norm allev el. The ultim ate radiation in ju ry rem ains the sam e.S im ila rly, it m ay be said that the level o f hydration o f theorganism , sp ores, seeds etc. influences the effect of radiation. Theeffect o f radiation is in creased under conditions of in creased hydration.This is evidently connected with the production o f radicals.1. 2. 2. 2. Role of oxygenIt has a lrea d y been m entioned that in w ater solu tion H2O2 o rra d ica l O2H are form ed in the p re se n ce o f oxygen after irradiationwith X - o r gamma rays. In densely ionizing alpha p articles the localconcentration of H2O2 may attain high valu es. It is th erefore understandablethat the p resen ce o f oxygen during irra d ia tion m ay be ofim portance although the inactivation of d esox yrib on u cleic acid o r ofbacteriophage (both in dried state) seem s to be governed by a m echanismindependent of oxygen tension.Quantitative relation sh ip s betw een ra d iosen sitiv ity and oxygeneffect have been studied by s e v e r a l authors. It w as found that therelation between radiosen sitivity and oxygen tension in a suspensiono f bacteria p roceed s a ccord in g to a sim ple relation, higher con cen ­trations o f oxygen in the m edium sen sitize b a cteria to the action of29