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Nuclear ChemistryNuclear Chemistry

2Units for Measuring Units for Measuring RadiationRadiation

Curie: 1 Ci = 3.7 x 10Curie: 1 Ci = 3.7 x 101010 distintegrations/s distintegrations/s

SI unit is the becquerel: 1 Bq = 1 dpsSI unit is the becquerel: 1 Bq = 1 dps

Rad: measures amount of energy absorbedRad: measures amount of energy absorbed

1 rad = 0.01 J absorbed/kg tissue1 rad = 0.01 J absorbed/kg tissue

Rem: based on rad and type of radiation. Rem: based on rad and type of radiation.

Quantifies biological tissue damageQuantifies biological tissue damage

Usually use “millirem”Usually use “millirem”

3Chronic Radiation ExposureChronic Radiation Exposure

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Effects of Acute RadiationEffects of Acute Radiation

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Half-LifeHalf-LifeSection 15.4 & Screen 15.8Section 15.4 & Screen 15.8

• HALF-LIFEHALF-LIFE is the time it takes for 1/2 a is the time it takes for 1/2 a sample is disappear.sample is disappear.

• The rate of a nuclear transformation depends The rate of a nuclear transformation depends only on the “reactant” concentration.only on the “reactant” concentration.

• Concept of HALF-LIFE is especially useful for Concept of HALF-LIFE is especially useful for 1st order reactions.1st order reactions.

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Half-LifeHalf-Life

Decay of 20.0 mg of Decay of 20.0 mg of 1515O. What remains after 3 half-lives? O. What remains after 3 half-lives? After 5 half-lives?After 5 half-lives?

8Kinetics of Radioactive Kinetics of Radioactive DecayDecay

Activity (A) = Disintegrations/time = (k)(N)

where N is the number of atoms

Decay is first order, and so

ln (A/Ao) = -kt

The half-life of

radioactive decay is

t1/2 = 0.693/k

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Carbon-14 Dating

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Radiocarbon DatingRadiocarbon DatingRadioactive C-14 is formed in the upper atmosphere Radioactive C-14 is formed in the upper atmosphere

by nuclear reactions initiated by neutrons in cosmic by nuclear reactions initiated by neutrons in cosmic radiationradiation

1414N + N + 11oon ---> n ---> 1414C + C + 11HH

The C-14 is oxidized to COThe C-14 is oxidized to CO22, which circulates through , which circulates through

the biosphere.the biosphere.

When a plant dies, the C-14 is not replenished.When a plant dies, the C-14 is not replenished.

But the C-14 continues to decay with tBut the C-14 continues to decay with t1/21/2 = 5730 years. = 5730 years.

Activity of a sample can be used to date the sample.Activity of a sample can be used to date the sample.

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TransuraniTransuranium um

Elements & Elements & Glenn Glenn

SeaborgSeaborg

106106SgSg

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Transuranium ElementsTransuranium Elements

Elements beyond 92 Elements beyond 92 (transuranium)(transuranium) made made

starting with an starting with an n,n, reaction reaction

2382389292U + U + 11

00n ---> n ---> 2392399292U + U +

2392399292U U ---> ---> 239239

9393Np + Np + 00-1-1

2392399393Np Np ---> ---> 239239

9494Pu + Pu + 00-1-1

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FUSION and FISSION: Nuclear Weapons

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Nuclear ReactionsNuclear Reactions

• Natural decay– Alpha– Beta

•Fusion (together)•Fission (break apart)

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Nuclear FusionNuclear Fusion

The process in which The process in which small nuclei combine at small nuclei combine at

extremely high extremely high temperatures, forming temperatures, forming

larger nuclei and larger nuclei and releasing energy.releasing energy.

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Fusion: Adv / Disad.• Great weapon because releases

large amounts of energy

• Can make new elements with atomic numbers greater than 92

• NOT used for Nuclear energy because not able to control reaction

(Energy in greater than energy out)

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Nuclear FissionNuclear Fission

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Nuclear Nuclear Fission & Fission &

Lise Lise MeitnerMeitner

109109MtMt

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Nuclear Bomb: FissionNuclear Bomb: Fission

• Nuclear Chain Reaction

• Critical Mass

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1.1. Initiation.Initiation. Reaction of a Reaction of a single atom starts the single atom starts the chainchain

(e.g., (e.g., 235U + neutron)U + neutron)

2. 2. PropagationPropagation. . 236U fission U fission releases neutrons that releases neutrons that initiate other fissionsinitiate other fissions

3. 3. TerminationTermination..

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Fission: Adv / Disad.• Great weapon because releases

large amounts of energy

• Used for Nuclear energy because CAN control reaction

• Dis: Nuclear waste and radiation generated

26Nuclear Fission & Nuclear Fission & POWERPOWER

• Currently about 103 Currently about 103

nuclear power plants in nuclear power plants in

the U.S. and about 435 the U.S. and about 435

worldwide.worldwide.

• 17% of the world’s 17% of the world’s

energy comes from energy comes from

nuclear.nuclear.

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Nuclear Power: Nuclear Power: AdvantagesAdvantages

•More power for less amount of fuel

•Non-air polluting

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Nuclear Power: Nuclear Power: disadvantagesdisadvantages

• Radioactive waste.

• Waste disposal

• Possibility of melt-down

• 30 year operational life.

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Nuclear Medicine: Nuclear Medicine: Imaging Imaging Radioactive isotopes are

used to diagnosis and treat diseases

Thyroid imaging using Tc-99mThyroid imaging using Tc-99mIF RADIATION IS BAD FOR YOU WHY INTENTIONALLY EXPOSE YOURSELF?

31Nuclear Medicine: Nuclear Medicine: ImagingImaging

Technetium-99m is used in more than 85% Technetium-99m is used in more than 85%

of the diagnostic scans done in hospitals of the diagnostic scans done in hospitals

each year. Synthesized on-site from Mo-99.each year. Synthesized on-site from Mo-99.

99994242Mo ---> Mo ---> 99m99m

4343Tc + Tc + 00-1-1

99m99m4343Tc decays to Tc decays to 9999

4343Tc giving off Tc giving off ray. ray.

Tc-99m contributes in sites of high activity.Tc-99m contributes in sites of high activity.

32Nuclear Medicine: Nuclear Medicine: ImagingImaging

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Nuclear Radiation: Nuclear Radiation: BeneficialBeneficial

• Can be used to treat cancer

• Can be used as tracers in agriculture, medicine, and scientific research.

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Food Irradiation

• Gamma radiation from Cobalt-60

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Smoke Detectors

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Medical Imaging

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PET SCANNER

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PET SCAN IMAGES