Nuclear ChemistryNuclear Chemistry

The weird world of the nucleusThe weird world of the nucleus

Isotope RefresherIsotope Refresher

Atoms of the same Atoms of the same element all have the element all have the same number of same number of protonsprotons

Atoms of the same Atoms of the same element may have element may have different neutrons and different neutrons and therefore mass therefore mass numbers (pnumbers (p++ + n + n00))

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Nuclear InstabilityNuclear Instability

Not all combinations of protons and Not all combinations of protons and neutrons are created equalneutrons are created equal

Some are more unstable than others.Some are more unstable than others. If they are unstable they will do one of the If they are unstable they will do one of the

following:following:Radioactive decayRadioactive decayNuclear fissionNuclear fissionNuclear fusionNuclear fusion

Nuclear “Reactions”Nuclear “Reactions”

Nuclear “reactions” must still be balanced.Nuclear “reactions” must still be balanced.

Notice 238 = 4 + 234 “Mass balanced”Notice 238 = 4 + 234 “Mass balanced”Notice 92 = 2 + 90 “Charge balanced”Notice 92 = 2 + 90 “Charge balanced”

ThHeU 23490

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Radioactive DecayRadioactive Decay

Radioactive DecayRadioactive Decay Radioactive decayRadioactive decay – the nucleus of an – the nucleus of an

atom undergoes a change so that it is no atom undergoes a change so that it is no longer the same elementlonger the same element

Decay is a totally random event. Nothing Decay is a totally random event. Nothing has an effect when an atom decayshas an effect when an atom decays

Two Main Types of Radioactive DecayTwo Main Types of Radioactive Decay1.1. Alpha decayAlpha decay2.2. Beta decayBeta decay

Alpha DecayAlpha Decay

Alpha decayAlpha decay – emission of an alpha – emission of an alpha particle from the nucleusparticle from the nucleus

Alpha (Alpha (αα) particle ) particle - a helium-4 nucleus - a helium-4 nucleus

Uranium-235, “enriched uranium,” decays Uranium-235, “enriched uranium,” decays by alpha decayby alpha decay

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ThHeU 23190

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Beta DecayBeta Decay

Beta decay Beta decay – emission of a beta particle – emission of a beta particle from the nucleusfrom the nucleus

Beta (Beta (ββ) particle) particle – electron – electron

Thorium-231 decays by beta decayThorium-231 decays by beta decay

e01

PaeTh 23191

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Practice Decay ReactionsPractice Decay Reactions

Beta decay by cesium-137Beta decay by cesium-137

Alpha decay by polonium-210Alpha decay by polonium-210

BaeCs 13756

01

13755

PbHePo 20682

42

21084

Decay SeriesDecay Series

Some atoms require Some atoms require multiple decays to multiple decays to become stablebecome stable

Most decay series of Most decay series of naturally occurring naturally occurring isotopes end in lead.isotopes end in lead.

Half LifeHalf Life

Half LifeHalf Life

Half lifeHalf life – the amount of time it takes for ½ – the amount of time it takes for ½ of a radioactive isotope to decay into of a radioactive isotope to decay into something else.something else.

Notice the atoms don’t disappear, they just Notice the atoms don’t disappear, they just change their identity.change their identity.

Half Life ProblemHalf Life Problem

A 100.0g radioactive A 100.0g radioactive sample decays for 5 sample decays for 5 hours. Only 12.5g of hours. Only 12.5g of the original isotope the original isotope remains after 5 hours. remains after 5 hours. How long is the half How long is the half life?life?

3 half lives = 5 hours3 half lives = 5 hours 5hours/3half lives = 5hours/3half lives =

1.67hours/halflife1.67hours/halflife

Number Number of half of half liveslives

Mass of Mass of samplesample

TimeTime

00 100.0g100.0g 00

11 50.0g50.0g

22 25.0g25.0g

33 12.5g12.5g 5 hours5 hours

25.2 days

Half Life Half Life ProblemProblem

Selenium-72 has a half Selenium-72 has a half life of 8.40 days. life of 8.40 days. How much of a How much of a 450.0g sample of 450.0g sample of selenium-72 will selenium-72 will remain after 42.0 remain after 42.0 days?days?

Number Number of half of half liveslives

Mass of Mass of samplesample

TimeTime

00 450.0g450.0g 00

11 225.0g225.0g 8.40 days8.40 days

22 112.5g112.5g 16.8 days16.8 days

33 56.25g56.25g 33.6 days33.6 days

44 28.13g28.13g 33.6 days33.6 days

55 14.06g14.06g 42.0 days42.0 days

Radiocarbon Dating TechniqueRadiocarbon Dating Technique

Uses the known half life of C-14 to Uses the known half life of C-14 to estimate death of organic matterestimate death of organic matter

Based on the known ratio of C-14 to C-12Based on the known ratio of C-14 to C-12

Nuclear Fission and FusionNuclear Fission and Fusion

Nuclear FissionNuclear Fission

Nuclear fissionNuclear fission – one atom’s nucleus splits – one atom’s nucleus splits apart.apart.

A neutron strikes a nucleus causing it to A neutron strikes a nucleus causing it to split into small piecessplit into small pieces

Releases lots of energy.Releases lots of energy.Extra neutrons are also produced.Extra neutrons are also produced.

nKrBanU 10

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Nuclear FissionNuclear Fission The extra neutrons can cause a chain reactionThe extra neutrons can cause a chain reaction

Uses of Nuclear FissionUses of Nuclear Fission

Nuclear powerNuclear power

Energy produced by Energy produced by fission is transferred fission is transferred as heat to a coolantas heat to a coolant

Nuclear PowerNuclear Power

Uses of Nuclear FissionUses of Nuclear Fission

Mushroom cloud from Nagasaki

Uses of Nuclear FissionUses of Nuclear Fission

Nuclear weaponryNuclear weaponry ““Atomic bomb”Atomic bomb” ““A-bomb”A-bomb”

Runaway fission Runaway fission reaction resulting in reaction resulting in an explosion.an explosion.

Nuclear FusionNuclear Fusion

FusionFusion – combining of nuclei – combining of nuclei

Above reactions describe fusion in the Sun.Above reactions describe fusion in the Sun.Releases more energy than fission.Releases more energy than fission.Also requires very high temperatures.Also requires very high temperatures.

HHHeHeHe

HeHH

eHHH

11

11

42

32

32

32

11

21

01

21

11

11

Uses of Nuclear FusionUses of Nuclear Fusion

Uses of Nuclear FusionUses of Nuclear Fusion

Fusion weaponsFusion weapons Hydrogen bombHydrogen bomb ““H-bomb”H-bomb” Thermonuclear bombThermonuclear bomb

Uses a fission reaction to Uses a fission reaction to start the fusion reactionstart the fusion reaction

““A-bomb” is the detonator for A-bomb” is the detonator for an “H-bomb”an “H-bomb”

RadiationRadiation

3 Primary Types of Radiation3 Primary Types of Radiation1.1. Alpha radiationAlpha radiation – – αα – alpha particles – alpha particles

Low energyLow energy Result of alpha decayResult of alpha decay Low penetrationLow penetration Stop with a sheet of paperStop with a sheet of paper

2.2. Beta radiationBeta radiation – – ββ –beta particles (electrons) –beta particles (electrons) Higher energyHigher energy Result of beta decayResult of beta decay Some penetration abilitySome penetration ability Stop with several sheets of aluminum foilStop with several sheets of aluminum foil

3.3. Gamma radiationGamma radiation – – γγ –high energy gamma rays –high energy gamma rays Very high energyVery high energy Can result from any type of decayCan result from any type of decay Very highly penetrating and damagingVery highly penetrating and damaging Stop with several centimeters of lead or very thick concreteStop with several centimeters of lead or very thick concrete

3 Primary Types of Radiation3 Primary Types of Radiation

Sources of Human ExposureSources of Human Exposure