Mr. ShieldsMr. Shields Regents Chemistry Regents Chemistry U02 L05 U02 L05

Nuclear FissionNuclear Fission

FissionFissionsplitting large nuclei up into splitting large nuclei up into smaller more smaller more stable nucleistable nuclei accompanied by the release of accompanied by the release of ENERGYENERGY

235235U + U + 11n n 142142Ba +Ba + 91 91Kr + 3 Kr + 3 11nn

92 0 56 36 092 0 56 36 0

EnergySmaller nuclei are more stable because theSmaller nuclei are more stable because theBinding energy per nucleonBinding energy per nucleon increases. increases.

FissionFissionWhy do nuclei Fission?Why do nuclei Fission?

Fission reactions release energyFission reactions release energyFusionFusionRxnsRxnsReleaseReleaseenergyenergy

Ni-62Ni-62

Fe-56Fe-56

Reducing mass Reducing mass increases binding increases binding EnergyEnergy above Mass # 50 above Mass # 50

235235U + U + 11n n 142142Ba +Ba + 91 91Kr + 3 Kr + 3 11n n

92 0 56 36 092 0 56 36 0

Once the uranium atom fissions by slamming it with one Once the uranium atom fissions by slamming it with one

neutron, neutron, 3 more neutrons are released3 more neutrons are released

These three neutrons can now interact with 3 other uranium These three neutrons can now interact with 3 other uranium

atoms etc. etc. etc.atoms etc. etc. etc.

uraniumuranium

neutronneutron

FISSIONFISSION

                                                                      

235U  + 1n 142Ba + 91Kr + 31n +

1n -> 3n -> 9n -> 27n -> 81n -> 243n1n -> 3n -> 9n -> 27n -> 81n -> 243n

Chain ReactionChain Reaction

Etc. untilEtc. until

LOTS OF ENERGY!

Uncontrolled releaseUncontrolled releaseOf neutronsOf neutrons

Critical MassCritical Mass

If the sample is sufficient in size the released neutronsIf the sample is sufficient in size the released neutronswill cause other U-235 to fission exponentially.will cause other U-235 to fission exponentially.

The amount necessary to sustain a chain reaction is calledThe amount necessary to sustain a chain reaction is called

the the CRITICAL MASSCRITICAL MASS

If a critical mass is present then …If a critical mass is present then …

Released EnergyReleased Energy

So where does this energy come from??So where does this energy come from??

CRITICAL MASSCRITICAL MASS is necessary to is necessary to sustainsustain a chain reaction. a chain reaction.

                                                                                   

                                                                                                                               

Detonating a nuclear deviceDetonating a nuclear device

When these 2 When these 2 subcriticalsubcritical pieces are joined together pieces are joined togetherthe mass becomes the mass becomes criticalcritical …. Detonation occurs …. Detonation occurs

Indian Point

Buchanan, NY

Nuclear Power PlantsNuclear Power Plants

Production of power in a nuclear reactorProduction of power in a nuclear reactor

Nuclear WasteNuclear WasteOne of the problems society faces is what to do withOne of the problems society faces is what to do withNuclear waste materials.Nuclear waste materials.

Several industries are the main generators of this materialSeveral industries are the main generators of this material- nuclear power industry- nuclear power industry- medical industry- medical industry- Weapons industry- Weapons industry- Research- Research

SO… WHAT DO WE DO WITH THIS MATERIAL???SO… WHAT DO WE DO WITH THIS MATERIAL???

Nuclear WasteNuclear Waste

Rememeber … the problem is Rememeber … the problem is

- - This material can be extremely radioactiveThis material can be extremely radioactive thus dangerous to lifethus dangerous to life

- And the half-life of some of these materials- And the half-life of some of these materials can be thousands of yearscan be thousands of years

So what do we do with it?So what do we do with it?

We are dealing with a time scale of the several thousand yearsthat the nuclear waste would take to fully decompose.  Theunpredictability of climate changes over periods of thousands of yrscould threaten the geological and environmental stability that YuccaMountain is currently prized for.

Nuclear WasteNuclear Waste

Medical Use of RadioactivityMedical Use of Radioactivity

In the U.S…In the U.S…

- 30 million people are hospitalized yearly - 30 million people are hospitalized yearly

- one in three are diagnosed or treated with nuclear medicine- one in three are diagnosed or treated with nuclear medicine

- Radionuclides are used in more than 11 million nuclear- Radionuclides are used in more than 11 million nuclear medicine procedures medicine procedures

- Radionuclides are used in 100 million laboratory tests- Radionuclides are used in 100 million laboratory tests on body fluid and tissue specimens.on body fluid and tissue specimens.

Radionuclides used in MedicineRadionuclides used in Medicine

To be useful as a radionuclide it must have a To be useful as a radionuclide it must have a short half short half lifelifeand be and be readily expelledreadily expelled from the body. from the body.

Technetium-99mTechnetium-99m Imaging can help diagnose bone infections inImaging can help diagnose bone infections in young children at the earliest possible stage and treatment ofyoung children at the earliest possible stage and treatment of Brain tumorsBrain tumors

Cobalt-60Cobalt-60 is used to treatis used to treat cancercancer

Iodine-123Iodine-123 widely used to diagnose widely used to diagnose thyroid disordersthyroid disorders..

Iron-59Iron-59 used to image used to image circulatory systemcirculatory system

And there are many other radioisotopes used in medicine.And there are many other radioisotopes used in medicine.

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* Know these radionuclides!* Know these radionuclides!

Radionuclides used for Dating Radionuclides used for Dating MaterialsMaterials

Carbon-14:Carbon-14: Used for dating archeological finds (must have Used for dating archeological finds (must have once been living) once been living)

Half-life = 5260 yrsHalf-life = 5260 yrs

Uranium-238:Uranium-238: Used to date the age of rocks or geological Used to date the age of rocks or geological areasareas

Half-life = 4.5 billion yearsHalf-life = 4.5 billion years

Compares U-238 present to the amount of Pb-206 Compares U-238 present to the amount of Pb-206 present. present.

Remember the U-238 decay curve? Pb-206 isRemember the U-238 decay curve? Pb-206 isstable.stable.

Nuclear FusionNuclear Fusion

Energy

Fusion Fusion small nuclei combine to form larger nucleismall nuclei combine to form larger nuclei

22H + H + 33H H 44He + He + 11n +n + 1 1 2 01 1 2 0

Deuterium TritiumDeuterium Tritium

This is one example of a fusion rxn but other This is one example of a fusion rxn but other small nuclei also can also undergo fusionsmall nuclei also can also undergo fusion

Requires High temperature and pressure to Requires High temperature and pressure to Overcome positive nuclear repulsionOvercome positive nuclear repulsion

Nuclear fusion in the Nuclear fusion in the sun. Last step of a sun. Last step of a multi-step process that multi-step process that can be represented bycan be represented byThe overall equation: The overall equation:

4 4 11H H 44He + 2 He + 2 00e + Ee + E

1 1 2 -1 2 -1

Overall equation forOverall equation forThe fusion of H into HeThe fusion of H into He

                                                  

The sun ‘s energy, as well as all other stars, create theirThe sun ‘s energy, as well as all other stars, create theirenergy using fusionenergy using fusion

Hydrogen is converted to Helium and then all the otherHydrogen is converted to Helium and then all the otherElements follow in kind. If the star then super nova’s all theseElements follow in kind. If the star then super nova’s all theseElements are dispersed into the universe. Elements are dispersed into the universe.

The SunThe Sun

You might sayYou might sayWe are all We are all Children of theChildren of theStars!Stars!

FusionFusionWhy do nuclei undergo Fusion? Why do nuclei undergo Fusion?

Fission reactions release energyFission reactions release energyFussionFussionRxnsRxnsReleaseReleaseenergyenergy

Ni-62Ni-62

Fe-56Fe-56

Binding energy increasesBinding energy increasesAs we inc. mass to up toAs we inc. mass to up toabout 50about 50

The H-BombThe H-Bomb

A thermonuclear reaction. Min. temperature required forA thermonuclear reaction. Min. temperature required forDetonation is Detonation is 40 million40 million degrees K. degrees K.

A nuclear bomb is need to detonate a hydrogen bomb toA nuclear bomb is need to detonate a hydrogen bomb tocreate both the necessary Temp and Pressure. create both the necessary Temp and Pressure.