nuclear chemistry nuclear particles: mass chargesymbol mass chargesymbol proton 1 amu +1 h+, h, p...

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

11

11

01

© Copyright 1994-2002 R.J. Rusay© Copyright 1994-2002 R.J. Rusay

Number of Stable Nuclides Elements 48 through 54

Atomic Number ofElement Number (Z) Nuclides

Cd 48 8In 49 2Sn 50 10Sb 51 2Te 52 8I 53 1Xe 54 9

Magic numbers are 2, 8, 20, 28, 50, or 82 protons or neutrons.Even numbers of protons and neutrons are more stable than odd.

Distribution of Stable NuclidesDistribution of Stable Nuclides

Protons Neutrons Stable Nuclides %Protons Neutrons Stable Nuclides % Even Even 157 58.8Even Even 157 58.8 Even Odd 53 19.9Even Odd 53 19.9 Odd Even 50 18.7Odd Even 50 18.7 Odd Odd 7 2.6Odd Odd 7 2.6

267 100.0%Total =

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.


Nuclear decay reactions conserve mass & energy.

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

Exposure to Radiation

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-rays:X-rays: Gamma-ray emission (Gamma-ray emission (γγmost all unstable isotopesmost all unstable isotopes Spontaneous fission–Spontaneous fission–very heavy isotopesvery heavy isotopes

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

2760Co 2

4He−−−−> + ?For Cobalt 60 predict the alpha decay product:

Beta Decay–Electron EmissionBeta Decay–Electron Emission

n n p p++ + + + Energy + Energy

1414C C 1414N + N + + Energy + Energy tt1/21/2= 5730 years= 5730 years

9090Sr Sr 9090Y + Y + + Energy+ Energy

tt1/21/2= 30 years= 30 years

247247Am Am 247247Cm + Cm + + Energy + Energy tt1/21/2= 22 min= 22 min

131131I I 131131Xe + Xe + + Energy + Energy

tt1/21/2 = 8 days = 8 days

Electron Capture–Positron EmissionElectron Capture–Positron Emission

p+ + e- n + Energy = Electron capture

p+ n + e+ + Energy = Positron emission

51Cr + e- 51V + Energy t1/2 = 28 days

7Be 7Li + + Energy t1/2 = 53 days

? + e- 177Ir + Energy

144Gd ? + + Energy

Nuclear DecayNuclear Decay

Predict the Particle or element:Predict the Particle or element: Thallium 206 decays to Lead 206.Thallium 206 decays to Lead 206. What What

particle is emitted?particle is emitted? Cesium 137 goes through Beta decay. Cesium 137 goes through Beta decay. What What

element is produced and what is its mass?element is produced and what is its mass?

Thorium 230 decays to Radium 226.Thorium 230 decays to Radium 226.What particle is emitted?What particle is emitted?


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

Nuclear Decay MeasurementNuclear Decay Measurement

Decay can be measured with an instrument Decay can be measured with an instrument that detects “disintegrations”. The rate can be that detects “disintegrations”. The rate can be obtained by “counting” them over a period of obtained by “counting” them over a period of time. time. e.g. disintegrations / second (dps)e.g. disintegrations / second (dps)

The rate of decay follows first order kineticsThe rate of decay follows first order kinetics The rate law produces the following equation The rate law produces the following equation

for the for the half life: half life: t1/2

=0.693/k© Copyright 1994-2002 R.J. Rusay© Copyright 1994-2002 R.J. Rusay

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>10temperatures (T>106 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 1994-2002 R.J. Rusay© Copyright 1994-2002 R.J. Rusay

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

Binding Energy per NucleonBinding Energy per Nucleon of Deuterium of Deuterium

Deuterium has a mass of 2.01410178 amu.

Hydrogen atom = 1 x 1.007825 amu = 1.007825 amu Neutrons = 1 x 1.008665 amu = 1.008665 amu 2.016490 amu

Mass difference = theoretical mass - actual mass = 2.016490 amu - 2.01410178 amu = 0.002388 amu

Calculating the binding energy per nucleon:

Binding energy -0.002388 amu x 931.5 Mev/amu Nucleon 2 nucleons

= -1.1123 Mev/nucleon

=

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 geometrically: 1 neutron 3 3 9 9 27 27 81 etc. 81 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 tons800 tons of Coal!of Coal! Commercial nuclear reactors use fission to Commercial nuclear reactors use fission to

produce electricity....Fission [“atomic”] bombs produce electricity....Fission [“atomic”] bombs were used in the destruction of Hiroshima and were used in the destruction of Hiroshima and Nagasaki, Japan, in August 1945.Nagasaki, Japan, in August 1945.

© Copyright R.J.Rusay 1994-2002© Copyright R.J.Rusay 1994-2002

QuickTime™ and aCinepak decompressor

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 / Fusion

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

Hydrogen Burning in Stars and Fusion Reactions

1H + 1H 2H + + 1.4 Mev

1H + 2H 3He + 5.5 Mev

2H + 2H 3He + 1n + 3.3 Mev

2H + 2H 3H + 1H + 4.0 mev

2H + 3H 4He + 1n + 17.6 Mev Easiest! 2H + 3He 4He + 1H + 18.3 Mev

Helium “Burning” Reactions in StarsHelium “Burning” Reactions in Stars

12C + 4He 16O

16O + 4He 20Ne

20Ne + 4He 24Mg

24Mg + 4He 28Si

28Si + 4He 32S

32S + 4He 36Ar

36Ar + 4He 40Ca

nuclear chemistry nuclear particles: mass chargesymbol mass chargesymbol proton 1 amu +1 h+, h, p...

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