NUCLEAR CHEMISTRY © Copyright 1994-2004 R.J. Rusay Dr. Ron Rusay Chem 106 Spring 2004

NUCLEAR CHEMISTRYNUCLEAR CHEMISTRY1

© Copyright 1994-2004 R.J. Rusay© Copyright 1994-2004 R.J. Rusay

Dr. Ron Rusay Dr. Ron Rusay Chem 106Chem 106Spring 2004Spring 2004

NUCLEAR CHEMISTRYNUCLEAR CHEMISTRYNuclear Particles:Nuclear Particles:

MassMass ChargeCharge SymbolSymbol

PROTON PROTON 1 amu 1 amu +1 +1 H+, H, p H+, H, p

NEUTRON NEUTRON 1 amu 1 amu 0 0 n n

1

1

1

1

11

11

01


Nuclear Decay / RadioactivityNuclear Decay / Radioactivity Unstable nuclei “decay” i.e. they lose Unstable nuclei “decay” i.e. they lose

particles which lead to other elements and particles which lead to other elements and isotopes.isotopes.

The elements and isotopes produced may The elements and isotopes produced may also be unstable and go through further also be unstable and go through further decay.decay.


QuickTime™ and aSorenson Video decompressorare needed to see this picture.

Nuclear decay: reactions conserve mass.

Nuclear ParticlesNuclear Particlesemitted from unstable nucleiiemitted from unstable nucleii

Emitted Particles:Emitted Particles: Mass Charge SymbolMass Charge Symbol

alpha particle alpha particle 4 amu +2 4 amu +2

beta particlebeta particle very small very small -1-1

gamma gamma very very small very very small 00

positron positron very smallvery small +1+1

24He2+;(2

4He);24α

−10e

−10β

+10β

γ


Nuclear Penetrating PowerNuclear Penetrating Power


alpha particle: lowalpha particle: low beta particle: moderatebeta particle: moderate gamma: highgamma: high

X-rays? X-rays?

WaterWater

•Dosimeters measure radiation absorbed Dosimeters measure radiation absorbed •Radiation effects are cumulative (Madame Curie)Radiation effects are cumulative (Madame Curie)•rad = radiation absorbed dose ( 0.01 J/kg)rad = radiation absorbed dose ( 0.01 J/kg)•rem= radiation equivalent for man rem= radiation equivalent for man (= rad x Q; Q=1 for X-rays,3 (= rad x Q; Q=1 for X-rays,3 for neutrons, 10 for p+, 20 for for neutrons, 10 for p+, 20 for αα-particles)-particles)•Background radiation = 0.13 remBackground radiation = 0.13 rem•Annual limit is set at 0.17 rem above backgroundAnnual limit is set at 0.17 rem above background

Alpha Decay–Heavy ElementsAlpha Decay–Heavy Elements

238238UU 234234Th + Th + αα + e + e

tt1/2 1/2 = 4.48 x 10= 4.48 x 10 9 9 yearsyears

210210Po Po 206206Pb + Pb + αα + e + e

tt1/2 1/2 = 138 days= 138 days

256256Rf Rf 252252No + No + αα + e + e

tt1/2 1/2 = 7 ms= 7 ms

24He−−−−> + ?

For Cobalt 60 predict the alpha decay product:

2556Mn

2760Co

2760Co

Nuclear Decay SeriesNuclear Decay Series

If the nuclei produced from radioactive If the nuclei produced from radioactive decay are unstable, they continue to decay are unstable, they continue to decay until a stable isotope results.decay until a stable isotope results.

An example is Radium which produces An example is Radium which produces LeadLead

88226Ra−−> −−> −−> −−>

82206Pb


The The 238238U DecayU DecaySeriesSeries

Radiodating MethodsRadiodating Methods


Three isotopes are currently used:Three isotopes are currently used:Carbon-14Carbon-14 half life 5,730 yrshalf life 5,730 yrsPotassium-40 half life 1.3 x 10 Potassium-40 half life 1.3 x 10 9 9 yrs yrs Uranium-238 half life 4.47 x 10 Uranium-238 half life 4.47 x 10 9 9 yrsyrs

The age of samples can be determined by The age of samples can be determined by measuring their disintegrations over time.measuring their disintegrations over time.

Decrease in Number of 14C Nuclei Over Time

Radiocarbon Dating for Determiningthe Age of Artifacts

An ancient wood sample has 6.25% of the 14C of a reference sample. What is the age of the sample?

Nuclear ReactionsNuclear Reactions

The mass of the visible universe is 73% HThe mass of the visible universe is 73% H2 2

and 25% He. The remaining 2%, “heavy” and 25% He. The remaining 2%, “heavy” elements, have atomic masses >4.elements, have atomic masses >4.

The “heavy” elements are formed at very high The “heavy” elements are formed at very high temperatures (T>10 temperatures (T>10 6 o6 oC) by C) by FUSIONFUSION, i.e. , i.e. nuclei combining to form new elements.nuclei combining to form new elements.

There is an upper limit to the production of There is an upper limit to the production of heavy nuclei at A=92, Uranium.heavy nuclei at A=92, Uranium.

Heavy nuclei split to lighter ones by Heavy nuclei split to lighter ones by FISSIONFISSION© Copyright 1994-2003 R.J. Rusay© Copyright 1994-2003 R.J. Rusay

NUCLEAR STABILITYNUCLEAR STABILITYPatterns of Radioactive DecayPatterns of Radioactive Decay

Alpha decay Alpha decay ((αα––heavy isotopesheavy isotopes Beta decay Beta decay (( – –neutron rich isotopesneutron rich isotopes Positron emission Positron emission (())––proton rich isotopesproton rich isotopes Electron capture–Electron capture–proton rich isotopesproton rich isotopes

x-raysx-rays Gamma-ray emission (Gamma-ray emission (γγ Spontaneous fission–Spontaneous fission–very heavy isotopesvery heavy isotopes


NUCLEAR ENERGYNUCLEAR ENERGY EINSTEIN’S EQUATION EINSTEIN’S EQUATION

FOR THE CONVERSION FOR THE CONVERSION OF MASS INTO ENERGY OF MASS INTO ENERGY

E = mcE = mc22

mm = mass (kg) = mass (kg) cc = Speed of light = Speed of light

cc = 2.998 x 10 = 2.998 x 1088 m/s m/s

Mass Mass Energy Energy

Electron volt (ev) The energy an electron acquires when it moves through a potential difference of one volt: 1 ev = 1.602 x 10-19J

Binding energies are commonly expressed in units of megaelectron volts (Mev) 1 Mev = 106 ev = 1.602 x 10 -13J

A particularly useful factor converts a given mass defect in atomic mass units to its energy equivalent in electron volts:

1 amu = 931.5 x 106 ev = 931.5 Mev

Nuclear ReactionsNuclear Reactions

Fission and Fusion reactions are highly exothermic Fission and Fusion reactions are highly exothermic (1 Mev / nucleon).(1 Mev / nucleon).

This is 10 This is 10 66 times larger than “chemical” reactions times larger than “chemical” reactions which are about 1 ev / atom.which are about 1 ev / atom.

Nuclear fission was first used in a chain reaction:Nuclear fission was first used in a chain reaction:

92235U+0

1n→ 92236U→

56141Ba+36

92Kr+301n


Nuclear Reactions:Nuclear Reactions:

Fission and Fusion reactions are highly exothermic Fission and Fusion reactions are highly exothermic (1 Mev / nucleon).(1 Mev / nucleon).

This is 10 This is 10 66 times larger than “chemical” reactions times larger than “chemical” reactions which are about 1 ev / atom.which are about 1 ev / atom.

Fission:Fission: Fusion: Fusion:

Nuclear ReactionsNuclear Reactions Nuclear fission was first used in a chain reaction:Nuclear fission was first used in a chain reaction:

92235U+0

1n→ 92236U→

56141Ba+36

92Kr+301n

Nuclear Reactions / FissionNuclear Reactions / Fission

The Fission Chain Reaction proceeds The Fission Chain Reaction proceeds geometrically: 1 neutron -> 3 -> 9 -> 27 -> 81 geometrically: 1 neutron -> 3 -> 9 -> 27 -> 81 etc.etc.

1 Mole of U-235 (about 1/2 lb) produces 1 Mole of U-235 (about 1/2 lb) produces 2 x 102 x 101010 kJ which is equivalent to the kJ which is equivalent to the

combustion of combustion of 800 tons 800 tons of Coal!of Coal! Commercial nuclear reactors use fission to Commercial nuclear reactors use fission to

produce electricity....Fission bombs were used in produce electricity....Fission bombs were used in the destruction of Hiroshima and Nagasaki, the destruction of Hiroshima and Nagasaki, Japan, in August 1945.Japan, in August 1945.


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are needed to see this picture.

The Nuclear DawnThe Nuclear DawnAugust 6, 1945August 6, 1945

Nuclear Power PlantNuclear Power Plant

Worldwide Nuclear Power PlantsWorldwide Nuclear Power Plants

Chernobyl, UkraineChernobyl, UkraineApril,1986 and April,2001April,1986 and April,2001

Nuclear Reactions / FusionNuclear Reactions / Fusionhttp://crystals.llnl.govhttp://crystals.llnl.gov

Fusion has been described as the chemistry of the Fusion has been described as the chemistry of the sun and stars.sun and stars.

It too has been used in weapons. It has not yet found It too has been used in weapons. It has not yet found a peaceful commercial applicationa peaceful commercial application

2H+3H→ 4He+01n+18.38MeV


The application has great promise in producing The application has great promise in producing relatively “clean” abundant energy through the relatively “clean” abundant energy through the combination of Hydrogen isotopes particularly from combination of Hydrogen isotopes particularly from 22H, deuterium and H, deuterium and 33H, tritium: (NIF/National Ignition H, tritium: (NIF/National Ignition Facility, LLNL)Facility, LLNL)

National Ignition FacilityNational Ignition FacilityLawrence Livermore National LaboratoryLawrence Livermore National Laboratory

National Ignition FacilityNational Ignition FacilityLawrence Livermore National LaboratoryLawrence Livermore National Laboratory


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NUCLEAR CHEMISTRY © Copyright 1994-2004 R.J. Rusay Dr. Ron Rusay Chem 106 Spring 2004