EFFECts oF ionizing rADiAtion
1 EvEryonE onEArth is ContinuAlly ExposED to smAll, rElAtivEly hArmlEss Amounts oF ionizing rADiAtion, known As BACkgrounD rADiAtion, From nAturAl sourCEs suCh As soil AnD roCk. howEvEr, othEr typEs oF ionizing rADiAtion--x-rAys, ultrAviolEt rADiAtion From thE sun, AnD AlphA, BEtA, AnD gAmmA rADiAtion EmittED By rADioACtivE isotopEs--hAvE thE potEntiAl to hArm thE humAn BoDy. ionizing rADiAtion hAs Enough EnErgy to rEmovE onE or morE ElECtrons From thE Atoms it hits to Form positivEly ChArgED ions thAt CAn rEACt with AnD DAmAgE living tissuE. most DAmAgE oCCurs in tissuEs with rApiDly DiviDing CElls, suCh As thE BonE mArrow, whErE BlooD CElls ArE mADE, AnD thE DigEstivE trACt, whosE lining must BE ConstAntly rEnEwE
D、
2 ExposurE to ionizing rADiAtion CAn DAmAgE CElls in two wAys. thE First is gEnEtiC DAmAgE, whiCh AltErs gEnEs AnD ChromosomEs. this CAn show up As A gEnEtiC DEFECt in ChilDrEn or in lAtEr gEnErAtions. thE sEConD typE oF DAmAgE is somAtiC, whiCh CAusEs viCtims DirECt hArm in thE Form oF Bums, misCArriAgEs, EyE CAtArACts, somE typEs oF lEukEmiA, or CAnCErs oF thE BonE, thyroiD, BrEAst, skin, AnD lung. smAll DosEs oF ionizing rADiAtion ovEr A long pErioD oF timE CAusE lEss DAmAgE thAn thE sAmE totAl DosAgE givEn All At onCE.ExposurE to A lArgE DosE oF ionizing rADiAtion ovEr A short timE CAn BE FAtAl within A FEw minutEs to A FEw months lAtEr.
whAt typEs oF tissuEs ArE hArmED most By ionizing rADiAtionA．tissuEs with CElls thAt DiviDE quiCkly
B．tissuEs on thE outsiDE surFACE oF thE BoDy
C．tissuEs ExposED to BACkgrounD rADiAtion
D、tissuEs with A lArgE numBEr oF ChromosomEs