It’s better to have a half-life It’s better to have a half-life than no life!than no life!

Radioactive DecayRadioactive Decay

What does it mean to be What does it mean to be radioactive?radioactive?

Atoms that are radioactive have nuclei that Atoms that are radioactive have nuclei that spontaneously decompose to form a different spontaneously decompose to form a different nuclei and produce one or more particlesnuclei and produce one or more particlesThese particles can be any of the followingThese particles can be any of the following– Alpha particle (Alpha particle (44

22He)He)

– Beta particle (Beta particle (00-1-1e)e)

– Gamma particle (Gamma particle (0000γγ))

– Positron (Positron (0011e)e)

– Cosmic raysCosmic rays

Radioactive (cont’d)Radioactive (cont’d)

Atoms that are radioactive have a Atoms that are radioactive have a neutron/proton ratio much greater than 1neutron/proton ratio much greater than 1Radioactivity can be detected by a Geiger Radioactivity can be detected by a Geiger countercounter

How do we measure decay?How do we measure decay?

The term “half-life” is used to time The term “half-life” is used to time radioactive decayradioactive decayHalf-life means the time it takes for half of Half-life means the time it takes for half of a sample to decay.a sample to decay.After one half-life ½ of the nuclei have After one half-life ½ of the nuclei have decayed to different nucleidecayed to different nucleiAfter two half-lives ¾ of the nuclei have After two half-lives ¾ of the nuclei have decayed to different nucleidecayed to different nuclei1414C = 5.73x10C = 5.73x1033yr yr 238238U = 4.46x10U = 4.46x1099yryr

Nuclear Reactions?Nuclear Reactions?

A nuclear reaction details how nuclei are A nuclear reaction details how nuclei are changed through the emission (radioactive changed through the emission (radioactive decay) or absorption (nuclear decay) or absorption (nuclear transformation) of alpha, beta, and gamma transformation) of alpha, beta, and gamma particlesparticlesEquations are balanced by making sure Equations are balanced by making sure the sums of the atomic numbers and mass the sums of the atomic numbers and mass numbers on both sides of the equation are numbers on both sides of the equation are equal equal

Radioactive DecayRadioactive Decay

Alpha, beta, and gamma particles are Alpha, beta, and gamma particles are emitted from radioactive nucleiemitted from radioactive nucleiAlpha particle productionAlpha particle production– EX: EX: 222222

8888Ra Ra 4422He + He + 218218

8686RnRnBeta particle productionBeta particle production– EX: EX: 234234

9090Th Th 2342349191Pa + Pa + 00

-1-1eeGamma ray emission (usually accompanies Gamma ray emission (usually accompanies alpha and betaparticles)alpha and betaparticles)– EX: EX: 238238

9292U U 4422He + He + 234234

9090Th + Th + 0000γγ

Nuclear TransformationNuclear Transformation

Heavier elements are made from lighter Heavier elements are made from lighter ones by absorption of alpha particles, beta ones by absorption of alpha particles, beta particles, or smaller nucleiparticles, or smaller nucleiEX: EX: 1414

77N + N + 4422He He 1717

88O + O + 1111HH

EX: EX: 27271313Al + Al + 44

22He He 30301515P + P + 11

00nn

Try These!Try These!

Find the missing particle:Find the missing particle:– ? + ? + 11

00n n 2492499797Bk + Bk + 00

-1-1e e

– 20201010Ne + ? Ne + ? 2424

1212Mg + Mg + 0000γγ

Write the balanced nuclear equation for Write the balanced nuclear equation for the following radioactive decays: (a) beta the following radioactive decays: (a) beta decay of nickel-63; (b) alpha decay of decay of nickel-63; (b) alpha decay of gold-185. gold-185.

What use is radioactivity?What use is radioactivity?

Medicine – radioactive materials are used Medicine – radioactive materials are used as tracers in the bodyas tracers in the bodyEnergy sources – energy can be obtained Energy sources – energy can be obtained through two nuclear processesthrough two nuclear processes– Fission: a nucleus divides into smaller Fission: a nucleus divides into smaller

fragmentsfragments– Fusion: nuclei combine to form a larger Fusion: nuclei combine to form a larger

nucleusnucleus

FissionFission

Splitting nuclei releases large quantities of Splitting nuclei releases large quantities of energyenergyHarnessed in nuclear power plantsHarnessed in nuclear power plantsReaction is controlled by 2 methodsReaction is controlled by 2 methods– Neutron moderation: reduces speed of Neutron moderation: reduces speed of

neutronsneutrons– Neutron absorption: decreases number of Neutron absorption: decreases number of

neutronsneutrons

What happens in a reactor?What happens in a reactor?

So what is Fusion?So what is Fusion?

Fusion is much better than fissionFusion is much better than fission– Fuels are cheaperFuels are cheaper– Products are not radioactiveProducts are not radioactive

Unfortunately it takes a high temperature Unfortunately it takes a high temperature for fusion to occurfor fusion to occurFusion is what produces the energy for the Fusion is what produces the energy for the sun.sun.