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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/the pertinent lim iting dose - 5, 15 or 30 rem s a year - to the criticalorg a n . It is assu m ed that th ere is a state o f eq u ilibriu m and thatthe contamination is regular and continuous. Assum ing that w orkersare exposed throughout th eir working day, the daily doses in ex cesscounterbalance the daily doses beneath the maximum values.The maximum p erm issible body burdens (MPB) are given in theIC R P tables fo r approxim ately 250 d ifferen t ra d ion u clid es. T ocalculate these values one must know the radioactive ch a racteristicso f these radionuclides and th eir m etabolism . The ICRP has th e re ­fo re established the ch a ra cte ristics of a standard man on the basiso f b iolog ica l data. Thus his m u scle counts fo r 30 kg, skin 6. 1 kg,fat 10 kg, sk eleton 7 kg, red m a rrow 1 .5 kg, y ellow m a rro w1. 5 kg, e t c .The standard m an is estim ated to inhale 2X 107 cm 3 o f a ird a ily . During his 8 -h ou r w orking day he inhales as m uch a ir asduring the 16 h ours he is not at w ork . He is a lso a ssu m ed to a b ­s o r b 1. 2 litr e s o f w ater a day in liquid fo rm plus 1000 g o f w atercontained in his food, and water from oxidation p rocess is estimatedat 300 g; the total is th erefore 2 .5 litre s a day. The d ose is thendeterm ined as a function o f the body burden, as follow s:D. kqf E (QF)nmw here k is a unit con v ersion fa ctor; q is the radionuclide burden;f is the fraction o f radionuclide retained in the critica l organ (equalto 1 fo r the whole body); E is the energy d elivered by the p a rticles;QF is the quality fa ctor; n is a fa cto r o f n on -u n iform distribu tion(in som e ca se s radion u clid es a re not d istribu ted even ly with theresu lt that th ere is m ore exp osu re at one point than another); andm is the total m ass of the organ where the radionuclide is deposited.With this form ula the maximum p erm issib le body burden can becalculated, D being the maximum p erm issib le dose (5, 15 o r 30 rem sannually).. T his form u la can be applied to alm ost all radion u clidesexcep t th ose w hich behave in the bod y lik e .radium . Many humanob serv a tion s on radium are available fo r occu p ation ally exposedw ork ers, so it has been p ossib le to establish sep a ra tely the m a x i­mum p e rm issib le body burden fo r radium only.M axim um p e rm is s ib le body burdens fo r m a teria ls s im ila r toradium are calcu lated by m eans o f form u la (1), but substituting q'fo r q:p . kq’ fE' (Q F)n'm76

This publication is no longer validPlease see http://www.ns-iaea.org/standards/where f is the sam e since these are bon e-seekin g radionuclides; QFis the sam e sin ce they are alpha-em itters; and m is also unchangedsin ce it is the m ass of the bone system . Knowing that q' for radiumis equal to 0. 1 m ic r o c u r ie s , the differen t values o f the m axim ump e rm is s ib le body burden fo r su bstan ces s im ila r to radium can bed eriv ed .. It is thus p o ssib le to know the m axim um p e rm is s ib le bodyburdens fo r about 250 radion u clid es.E ach table o f m axim u m p e r m is s ib le body bu rdens re la te s tocontinuous exposu re under p articu lar con ditions, either 40 hours aweek; o r continuous exposu re fo r a week of 168 h ou rs.Though maximum p erm issible body burdens are of interest, theycannot solv e e v e ry p roblem as the burden o f radion u clides in ahuman body cannot be m easured d irectly, except for gam m a-em itters,w here sp e ctro m e te rs can be used fo r this pu rp ose, though withd ifficu lty.F or pure beta-em itters o r alpha-em itters recou rse must be hadto indirect m easurem ent o f intakes o r excreta.E xcretion m easu rem en ts are useful from the point o f view ofm onitoring person nel. T hey represen t a convenient m ethod, thoughit is difficu lt to deduce from a value fo r excreta activity m e a su re ­ment a value for the body contamination itself. The manner in whichradioactive substances are elim inated by the body is fa irly w ellknown. It also depends on the tim e that has elapsed sin ce the c o n ­tamination o ccu rred . Thus, from any given tim e when the body con ­tains a certa in quantity o f ra d ioa ctiv e su b sta n ces, e x cre tio n p r o ­ceeds according to a known law which is usually either an exponentialfunction, a pow er function o r a com bination of functions. In the caseo f acciden tal contam ination, from m easu rem en ts m ade at v ariou stim es it w ill be p ossib le to estim ate the amount present in the bodyat the tim e o f the acciden t.If, as is u su ally the ca s e , no in form ation is available on howthe contam ination o ccu rred o r the contam ination is irreg u la r, it b e­com e s exceed in g ly d ifficu lt to deduce in tern al con tam ination fro mm easurem ents made la ter. T h erefore, instead of trying to establishthe values fo r the m axim um p e rm is s ib le con cen tration in ex creta ,p referen ce has been given to establishing such values in inhaled o ringested substances. This has been done fo r air and drinking water,but not for food.In the fie ld o f in d u stria l h ygien e, con tam ination h aza rd s a rem ainly due to inhalation only. It is th erefore possible to solve som eproblem s of industrial hygiene by air m onitoring.77

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