Topic 5 Atomic physics

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1、IGCSEPhysics0625notes:unit5–AtomicPhysics:Revisedon01December20111TOPIC5–ATOMICPHYSICSRadioactivityorradioactivedecay:1.Itistheprocessinwhichcertainunstableatomicnuclei(pluralofnucleus)emitradiationstobecomestable.2.Theelementsthatemitradiationsarecalle

2、dradioactivematerials.Thecommonexamplesofradioactivematerialsareuranium(U),radium(Ra),polonium(Po),thorium(Th),Radon(Rn)etc.3.TherearethreetypesofradiationsinIGCSEcourse:alphaparticles,betaparticlesandgammaradiations4.Radioactivityisarandomprocess;itmea

3、nsthatinaradioactivesampleonecannotpredictwhichatomicnucleusisgoingtoemitradiationatanyparticulartime,buttheprobabilityofemissionisconstant.5.Radioactivityisspontaneous;itmeansthatitdoesnotdependontheenvironmentalconditions.Radioactiveemissionissameatal

4、ltemperatureandpressure.Radioactivitycannotbespeeduporslowdownbyanyscientificmethod.6.Backgroundradiationisthelowintensityradiationpresentintheearth’satmosphere.Thesearelowlevelradiationsthatourbodycantolerate.Thesourcesoftheseradiationsare:a.radiationf

5、romearth’scrusts(rocks)whichcontainradioactiveelements,b.radiationfromouterspacefromstarsandplanetsandc.emissionfromnuclearexperimentsandnuclearpowerstations.Whendetectingandmeasuringtheradiationfromaradioactivesourceitisimportanttosubtractthebackground

6、radiationsforthecounterreadings.Propertiesofradiations:Thethreetypesofradiationshavefollowingdistinctproperties.AlphaParticles(α)BetaParticles(β)GammaRays(γ)Natureheliumionorheliumhighenergyelectronshighenergynucleusmadeupoftwoemittedfromthenucleuselect

7、romagneticradiationprotonsandtwoneutronsCharge+2-1nochargeMass4units1/1836unitsnomassIonizationeffecthighestionizationeffectmuchlessionizationleastionizationeffectingasesduetofrequentcollisioneffectthanalpharayswithgasmoleculesPenetrationstoppedbytheshe

8、etofrangeoffewmillimetersveryhighpenetrationeffectpaperandhaverangeofinaluminumandseveraleffect,canonlybestoppedfewmillimeterinairmetersinairbythicksheetoflead.Deflectiondeflectedbyelectricanddeflectedbyelectricandnotdeflectedbye