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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/0.39 R for c a e s iu m -137. The gam m a-ray en ergies are 0.2-2.2 meVfor radium -226; 1.17-1.33 m eV for cob a lt-6 0 ; and 0.662 m eV forcaesiu m -137.(2) B eta-ray sou rces are used for su p erficial external irra d ia ­tion. The sou rces m ainly used are 32P or 90Sr/9°Y sou rces. Theya re ch a ra cte riz e d m ainly by the am ount o f m a teria l p re sen t, thequality of the beta radiation em itted and the maximum energy of thebeta radiation. This is 1.710 meV for p h osphoru s-32 and 0.544 meVfor stron tium -90/yttriu m -90. The beta p articles thus emitted filterless well into the organism , and the range isO. 7cm for phosphorus-32and 0.9 cm for stron tium -90/yttriu m -90.2. 2. 1.2. Internal sou rcesA ll internal radiation sou rces are radionuclide sou rces, eithersealed or unsealed.Sealed sou rces are designed to prevent the radioactive m aterialfrom being diffused into the body and m etabolized. The so u rce s inquestion a re a p p lica to rs, n eed les o r th read containing the r a d io ­a ctive m a teria l within a tight e n clo su re . The ra d io isoto p e s u sedare gamma or beta plus gamma em itters but the protective enclosurew hich preven ts ra d ioa ctiv e lo s s a lso acts as a filte r and only letsout the gamma radiation. The sm allest sou rces (in term s of length)are m ade of radiu m -226, radon -222, cob a lt-6 0 , gold -1 9 8 and tantalum -182. T h eir ch a ra cte ris tics a re dependent on the amount ofradionuclide they contain, the en ergy of the gam m a radiation em itted,the h a lf-life of the radion u clide and the g e o m e trica l shape o fthe so u rce . T here are s o u rce s containing v e ry s h o rt-liv e d ra d io ­n u clid es (222Ra, 198Au) which can be left within the body, w h ereasthe oth ers must be withdrawn.Unsealed sou rces are so made that once introduced into the bodythey diffuse and can particip ate in the m etabolic p r o c e s s . T h e r e ­fo r e only ra d ion u clid es with su itable p h y sica l, p h y s ic o -c h e m ic a land ch em ical ch a ra cteristics should be used. F or exam ple, use ism ade o f 198Au or ch rom iu m phosphate ra d io co llo id s, as w ell as ofm a teria ls in ionic fo rm with known m etabolism (32P, 1311). T hesesou rces are ch aracterized by the amount of radionuclide introduced,the nature and en ergy o f the beta o r gam m a radiation em itted andthe h a lf-life o f the radion u clide con cern ed.56

This publication is no longer validPlease see http://www.ns-iaea.org/standards/2. 2. 2. F orm s o f m edical exp osu reA ccord in g to th eir ch a ra cte ristics, the foregoing sou rces maybeused in m e d ica l ra d iolog y fo r eith e r d ia gn ostic o r th erapeu ticp u rp oses.2. 2. 2. 1. D iagn ostic u sesF or diagnostic pu rp oses X -r a y or radionuclide s o u rce s can beused.X -r a y s a re by fa r the m ost w idely u sed. The apparatus e m ­p loyed fo r the p u rp ose is the con ven tion al type o f g e n e ra to r withvoltage betw een 50 and 100 kV.The use of radionuclides for diagnostic purposes is in the mainlim ited to unsealed s o u rce s , w hose d istribu tion in the body can beu sed fo r a n a to m ica l (sca n n in g) o r fu n ction a l (tu rn o v e r) stu d ie s.2. 2. 2. 2. T h e ra p e u tic u sesThe foregoin g sou rces have a great variety o f therapeutic u seswhich can be divided into teletherapy (or rem ote radiotherapy), su p erficial therapy and in terstitial therapy.The m ain s o u rce s u sed in teleth erapy a re h ig h -en erg y X -r a yapparatus (in the 200-kV range — Van de G raaff m a ch in es, lin ea ra c c e le r a to r s and betatron s), ele ctro n radiation g en era tors (lin eara c c e le r a t o r s and b eta tron s) and g a m m a -ra y g e n e ra to rs (radium ,cob a lt o r ca e siu m units).F or s u p e rficia l radioth erapy the follow in g types o f apparatuscan be u sed : v e r y -lo w -e n e r g y X -r a y apparatu s; seale d gam m as o u r c e s (radiu m -226 and c o b a lt-6 0 a p p lica to rs); and sea led betaso u rce s (phosphorus-3 2 and stro n tiu m -9 0 /y ttriu m -9 0 a p p lica tors).In terstitia l radioth era p y can u s e : seale d gam m a s o u r c e s(radiu m -226, co b a lt-6 0 o r g o ld - 198); and u n s e a le d 's o u rce s (gold-198, p h osp h oru s-32 o r iod in e-131).2. 2. 3. Results o f medical exposureIn con sid erin g the resu lts o f m e d ica l e x p osu re, a d istin ctionshould be m ade betw een the irra d ia tion o f sta ff engaged in r a d io ­lo g ica l exam inations and treatm ent, and the irradiation of patients.A s the irradiation o f staff is dealt with in the next section , only i r ­57

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