radioactivity - srm institute of science and .• the nucleus –this is the centre of the atom

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R

J.KAVITHA, M.Pharm.,

Lecturer,

Department of Pharmaceutical Analysis,

SRM College of Pharmacy

SRM University.

UNIT-I

What is Radiation?

Thebreakingdownofunstableatomicnuclei Asthenucleusofanunstableatombreaksdown,itgivesoutraysandparticlescalledemissions.

Thebreakingdownofunstablenucleihappensspontaneously itisunaffectedbyheat,pressure,orwhethertheelementissolid,liquidorgas.

What is Radiation?

Isotopes(atomsofthesameelementwithdifferingnumbersofneutrons)whosenucleibreakdownatrandomarereferredtoasradioactive.

Theyarealsoknownasradioisotopes. Therearethreedifferenttypesofatomicradiation alpha(),beta(),orgamma().

Atomic Structure

TheNucleus Thisisthecentreoftheatom.Itcontainsprotonsandneutrons.Themassoftheatomisconcentratedinthenucleus.

Protons Thesehaveapositivechargeandamassof1.

Neutrons Thesedonthaveachargeandhaveamassof1.

Electrons Thesemovearoundthenucleus.Theyhavevirtuallynomassandhaveanegativecharge.

Alpha Radiation

2protonsand2neutrons(=heliumnucleus)ejectedfromthenucleus

Positivechargeof+2 Veryhighionising power thismeansitcollideswithlots

ofatomsandknockselectronsoffthem,makingthemions

Shortrangeinair afewcentimetres Stoppedbyapieceofpaper.

238U 234Th + 4He92 90 2

Beta Radiation

Anneutronthatbreaksdownintoaprotonandanelectron

Theelectronisejectedfromthenucleus;theatomicnumberoftheatomchangesbecausethereisanextraprotoninthenucleus

Negativechargeof1 Lowionisingpower Stoppedbyapieceofaluminiumfoil Travelsseveralmetresinair

14C 14N + 0e6 7 -1

Gamma Radiation

Notmadeofprotonsorelectrons Ahighenergyelectromagneticwave Emittedfromnucleichangingfromahighenergyleveltoalowerone

Frequentlyaccompaniesandemissions Nocharge,soverylowionisationpower Themostpenetratingatomicradiation cantravelhugedistancethroughair

Stoppedbyseveralfeetoflead

Important Experiments

WilhelmConradRoentgen(18451923) OnNovember8th1895RoentgendiscoveredXrays,amomentouseventthatinstantlyrevolutionizedthefieldofphysicsandmedicine.

HedeterminedthataglowingfluorescentscreenonanearbytablewascausedbyinvisibleraysoriginatingfromthepartiallyevacuatedglassHittorfCrookestubehewasusingtostudycathoderays.

Theserayspenetratedtheopaqueblackpaperwrappedaroundthetube.

Forthisdiscovery,RoentgenreceivedtheNobelprizeforphysicsin1901.

Important Experiments

PierreCurie(18591906)MarieCurie(18671934) In1895,MarieandPierreCurieweremarriedandworkedtogetherontheirresearch.

ThetermradioactivitywasfirstcoinedbyMarie. TheCuriesexperimentedwiththechemicalextractionof

uraniumfromtheore.Theconclusionwasthattheorecontained,inadditiontouranium,newelementsthatwerealsoradioactive.

Thisledtotheirdiscoveriesoftheelementsofpoloniumandradium.

FortheirworktheCurieswereawardedtheNobelprizeinphysicsandyearslater,MariewasawardedtheNobelprizeinchemistry.

Important Experiments

AntoineHenriBecquerel(18521908) InitiallyBecquerelbelievedthatthesunsenergywasbeingabsorbedbytheuraniumwhichthenemittedXrays.

Hefoundthaturaniumemittedradiationwithoutanexternalsourceofenergysuchasthesun.

Becquerelhaddiscoveredradioactivity,thespontaneousemissionofradiationbyamaterial.

Forthisdiscoveryhewasawardedthe1903Nobelprizeforphysics.

Half-Life

Thetimetakenforthenumberofatomsinasampleofanelementtodecaybyhalf

Halflifeisfixed nomatterhowbigthesample,whatthetemperatureorpressureis,itisalwaysthesamelengthoftime.

Asampleofaradioisotopewillnevercompletelydisappear

itsradioactivityalwaysdisappearsbyhalf,eveninthetiniestamounts.

Some Half-Life Examples

ThisisanexampleofahalflifegraphforAmericium242

Itcanbeusedtofindthehalflifeofaradioisotope

TheheaviestnaturallyoccurringradioisotopeisUranium,whichhasahalflifeof4.5x109 years

Themoreunstablearadioactiveisotopeis,theshorteritshalflife

Isotopes and Isobars and Radioisotopes

Isotopes are variants of a particular chemical element. While all isotopes of a given element share the same number of protons, each isotope differs from the others in its number of neutrons.

For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13 and 14 respectively. The atomic number of carbon is 6 which means that every carbon atom has 6 protons, so that the neutron numbers of these isotopes are 6, 7 and 8 respectively.

Isobars one of multiple nuclides with the same mass number but of different chemical elements

The isotopes of an element are all the atoms that have in their nucleus thenumber of protons (atomic number) corresponding to the chemical behavior ofthat element. However, the isotopes of a single element vary in the number ofneutrons in their nuclei. Since they still have the same number of protons, allthese isotopes of an element have identical chemical behavior. But since theyhave different numbers of neutrons, these isotopes of the same element mayhave different radioactivity. An isotope that is radioactive is calleda radioisotope or radionuclide.

RADIOISOTOPES

Isobars

Biological Effects of Radiation

Themaindangerfromradioactivityisthedamageitdoestothecellsinyourbody.

Mostofthisdamageisduetoionisationwhentheradiationpasses.

Iflevelsofradiationarehightherecanbedamageduetoheatingeffectsasyourbodyabsorbstheenergyfromtheradiation,ratherlikeheatingfoodinamicrowaveoven.

Thisisparticularlytrueofgammarays.

AlphaParticles Theseareslowandhaveashortrangeinair.Thesearethemostdangeroustypeofparticleandcanturncellscancerous.

BetaParticles Thesehavealongerrangethanalphaparticles,butionisemuchlessstrongly.Theyhavemorepenetratingpowerwhichmeanstheycangetthroughyourskinandaffectthecellsinsideyou.

GammaRays Gammarayshardlyioniseatall,sodonotcausedamagedirectlyinthisway.Theyareverydifficulttostopandwhentheyareabsorbedbyanatomtheycangainquiteabitofenergy,andmaythenemitotherparticles.

Biological Effects of Radiation

Uses of Radioactivity - Alpha

Smokedetectors: ThecontainasmallamountofAmericium241,whichemitsradiation.Thisionisestheairsoacurrentflows.

Whensmokeentersthedetectoritabsorbstheradiationandthecircuitisbroken.Analarmsounds.

Uses of Radioactivity - Beta

Thicknesstesting: Aradioactivesourceemittingemissions,andaGeigercounter,areplacedeithersideofthepaper.

Theamountofradiationreachingthecounterthroughthepaperismeasured

Iftoolittleortoomuchradiationgetsthrough,themachineisautomaticallyadjustedtomakethepaperthinnerorthicker

Uses of Radioactivity - Gamma

Tracers: Medicalpurposesusedtofollowtherouteofsubstancesthroughthebodye.g.Todetectablockedkidney

Civilpurposesusedtodetectleaksinpipesbyputtingsourceintopipe&measuringemissionsusingaGeigercounter

Uses of Radioactivity -Gamma

Radiotherapy: Cancercellsareexposedtogammarayswhichkillsthemoff Makesthepatientfeelunwell Correctdosevital toomuchcankillhealthycells,toolittle

wontpreventspreadofcancer

Sterilisation: Civiluse radiationusedtokillbacteriaonsomefoods.

Prolongsshelflifebutmaychangethetaste. Medicaluse sterilisesmedicalequipmentthatwouldbe

damagedbyheate.g.Syringes

Welding Gammaemissionspassedthroughmetalontophotographic

film,tocheckforbubbles

Uses of Radioactivity Half-life

Carbon14Dating: AlllivingthingscontainafixedproportionofradioisotopeCarbon14(14C)

Whenanimalsandplantsdie,theproportionof14Cstartstofall,becausedecaying14Cisnolongerbeingreplacedby14Cbeingtakenine.g.food

14Calsohasaknownhalflife,of5700years Scientistscanworkouttheageofancientorganicsubstancese.g..bones,bycomparingtheamountof14Clefttotheproportioninlivingorganisms,andusinghalflife

Beneficial uses of radioactivityControlled radioactivity can be used to (click on the picture for more

information):

Kill cancer cells

Sterilize food and medical equipment

Find leaks in pipesControl

thickness in industry

Check organs work properly

Tracers in medicine

The patient drinks some iodine 131. A -probe measures the amount of radioactive iodine the thyroid gland takes in to check it works properly.

N.B.

All isotopes taken into the body should be GAMMA or BETA sources and neverALPHA.

Explain whyThese tracers must have short half-life

Tracers in medicine

The patient drinks some iodine 131. A -probe measures the amount of radioactive iodine the thyroid gland takes in to check it works properly.

N.B.

All isotopes taken into the body should be GAMMA or BETA sources and neverALPHA.

Explain whyThese tracers must have short half-life

Tracers in industry

Why dont they use or ?

These tracers must have short half-life

Gamma source

Curing cancer

High doses of gamma rays will kill all living cells

Gamma rays can be directed only at the cancer cells to cure the cancer

Sterilizing foodFor the same reason gamma rays can be used to kill the microbes in food and medical instruments.

UNSTERILIZED

STERILIZED

RadioactivityUnits

InternationalUnitbecquerel(Bq)

U.S.Unit curie(Ci)

1Ci=37GBq1mCi=37MBq1Ci=37kBq

ii) RadioactivityWhat is Radiation?What is Radiation?Atomic StructureAlpha RadiationBeta RadiationGamma RadiationImportant ExperimentsImportant ExperimentsImportant ExperimentsHalf-LifeSome Half-Life ExamplesSlide Number 13Slide Number 14Biological Eff

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