Nuclear fusion and Radioactivity

PDP Physics

Image: http://en.wikipedia.org/wiki/Exoplanet

GENERATING ELECTRICITY

Electricity generation

• wind• hydroelectric• coal• oil• natural gas• biofuel• solar power• geothermal• (nuclear)

Electricity generation presentation• in a group of 2 or 3• on google drive or prezi• about 3-4 minutes

Your presentation should answer the following:• How does it work?• What energy conversions are involved?• How efficient is it?• How much power does a typical plant produce?• How much power is generated in total in Sweden?• Where do the resources originate?• What are the benefits of this method of

generating electricity?• What are the problems? How significant are they?• What is the future potential?

Electricity bill in kWh

http://www.dolceta.eu/sverige/Mod6/Elrakningen.html

kiloWatthours are units of energy

1kWh = 1kW used for 1 hourEnergy = power × time1kWh ≈ 4MJ

Comparing different energy uses

Fluctuations kWh per daykWh/d is a unit of powerpower = energy/time

Energy density of a fuel

energy density = energy released mass of fuel

energy density in MJ/kgUranium 79 500 000MJ/kgCoal 24MJ/kg

Efficiency

What percentage of the energy comes out as useful energy?

efficiency = energy out × 100 energy in

WHAT IS NUCLEAR FUSION?

WHAT ARE ATOMS BUILT FROM?

Atoms

• atomic number• mass number• relative atomic mass• electron shell• isotope• atomic mass unit, u• elementary charge, e• electronVolt, eV

Atomic structure

7

Li3

Atomic number, Z

Mass number, A

Atomic nucleus

Strong nuclear force (protons and neutrons)

Electrostatic force (protons and electrons)

Subatomic particlesProton Electron Neutron

Charge, e +1 -1 0

Mass, u 1.007 0.00548 1.009

Location in atom nucleus shells nucleus

ELEMENTARY PARTICLES

An elementary particle has no internal structure and is not made

from smaller constituents.A composite particle is made from

elementary particles.

Particles are made of particles

A proton is built from 3 quarks

composite:atom

protonneutron

elementary:electron

quarkneutrino

proton

RADIOACTIVITY

Ionizing radiation

consists of

mass charge penetrating power

α alpha

β- beta

γ gamma

Background radiation

• is the natural radiation from materials in the environment including rocks, the air and living organisms

• varies with location

What is the relationship between Z and N?

• Research the stable isotopes of as many atoms as possible and plot a graph of N against Z

• Plot a trendline and write down the gradient. Explain what the gradient means for this graph.

• Explain why this pattern occurs using ideas about the strong nuclear force and the electrostatic force.

Nuclear Radiation

Stable or unstable?

Geiger-Müller tube (GM tube)

Image: http://en.wikipedia.org/wiki/Geiger_counter

Nuclear symbols

The nucleus of an atom can be represented as:

AZX

• A is the atomic mass (number of protons + neutrons)• Z is the atomic number (number of protons- see

Periodic Table)• X is chemical symbol (see Periodic Table)

Alpha decay

21986Rn 215

84Po + 42α

Z decreases by 2A decreases by 4

Write nuclear decay equations for the alpha decay of:

Polonium-218Gold-196

Beta decay

146C 14

7N + 0-1β + 0

0ν

Z increases by oneA constant

Write nuclear decay equations for the beta decay of:

Phosphorous-32Iodine-131

Radioactivity

α-decay

β-decay

γ decay

Decay series

HOW LONG DOES IT TAKE AN UNSTABLE ATOM TO DECAY?

Half lifeThe time it takes for the number of nuclei of the isotope in a sample to halveorThe time it takes for the count rate from a sample containing the isotope to fall to half its starting level

Images: http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/atoms_radiation/nuclearradiationrev7.shtml

Half life

Activity

• The activity of a sample, A, is the number of decays in one second.

• The decay constant, λ, is the probability that a single nucleus will decay in one second.

• N is the total number of unstable nuclei

Radioactive decay law

ARTIFICIAL TRANSMUTATION

Artificial transmutations

• a nucleus can ‘capture’ another particle• this is the only way to speed up radioactive

decay

NUCLEAR BINDING ENERGY

Bang! Trinity test

• plutonium fission• 84 TeraJoules = 20 kton TNT

Bang! first H bomb test in 1952

• hydrogen fusion• 44 PetaJoules = 10 Mtons of TNT

Nuclear fission

Nuclear fusion

unified atomic mass unit

1u is 1/12 of the mass of a carbon-12 atom

mp = 1.007276u

mn = 1.008665u

me = 0.0005486u

Atoms are lighter than the nucleons which they are built from

the mass defect, δ is the difference between the total mass of the individual nucleons and the mass of the atomic nucleus

mass defect of HeliummHe = 4.0026u

Binding energybinding energy of the nucleus is the energy needed to separate the nucleons

How much energy is released when a helium nucleus is formed?

• mp = 1.00728u• mn = 1.00866• mass of 42He nucleus = 4.00153u• 1u = 1.66054 x 10-27kg = 931.494MeVc-2

Atoms are lighter than the nucleons which they are built from

the mass defect, δ

mass from n and p energy released as nucleus is

made

Tsokos p.387qn1

binding energy per nucleon

Fission and fusion

How does the curve of binding energy per nucleon explain why fission of heavy elements releases energy, while fusion of light elements releases energy?

NUCLEAR FISSION

Nuclear Fission

• a nuclear chain reaction sustained by neutrons1

0n + 23592U 141

56Ba + 9236Kr + 31

0n

a. What is the mass change?b. How much energy is released per nucleus in Joules?c. How much energy in Joules is released by 1g of Uranium enriched to 3% U-235?U-235 = 235.04392u neutron = 1.0086Ba-141 = 140.91441u Kr-92 = 91.92615u

The fission of one atom of U-235 generates 202.5 MeV

= 3.244 × 10−11 Jequivalent to 19.54 TJ/mol

= 83.14 TJ/kg

Designing a nuclear reactor: maintaining

the reaction• enrichment• size of fuel block• speed of neutrons

moderator- slows neutronscontrol rods- absorb neutronsheat exchanger- transfer heat

Reactor core

Nuclear power plantAdvantages:high energy densityhuge reserves of U

Disadvantages:radioactive wasteAccident riskProliferationNon-renewable

Nuclear waste: mix of isotopes with short and long half lives

spent fuel in a storage pondunderground storage

Production of Plutonium-239

23892U + 1

0n 23992U

23992U 239

93Np + 0-1β + 0

0ν239

93Np 23994Pu + 0

-1β + 00ν

plutonium is toxic, but can be reprocessed and used in a fast breeder reactor (or for a fission bomb)

NUCLEAR FUSION

Nuclear Fusion Reaction

21H + 3

1H 42He + 1

0n

How much energy is released in nuclear fusion?

Deuterium 2.01410uHydrogen 1.00783uHelium-4 4.00260uneutron 1.0086u

Nuclear binding energy

Fusion reactors

Benefits• Very high energy density• Large resources of fuel in seawater• Less radioactive wasteProblems• Complex technology• Not currently viable• Waste

Joint European Torus10MW for 0.5s (50% of input power)

3m radius3.45T magnetic fieldcurrent 3MA

ITER

Teaching notes