Atomic Energy 3U Physics. Mass-Energy Equivalence All matter is a form of stored energy.
6 Mass-Energy Equivalence
Transcript of 6 Mass-Energy Equivalence
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Mass-Energy
Equivalence
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Work is required to remove a nucleon from
a stable nucleus because of the strongnuclear force
The binding energy of a nucleus is the
energy required to separate all of its
nucleons and move them infinitely far
apart
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The maximum binding energy per nucleon is
between A =50 and A =74 (most stable)
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Comparison of Atomic & Nuclear
binding energy
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Mass Defect
The mass of a nucleus is always less than
the mass of all the separate nucleons(protons and neutrons)
this difference in mass is called the mass
defect
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the binding energy is related to the mass
defect by the equation E = mc2
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Example
Determine the mass defect and binding
energy of an alpha particle.
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Solution alpha particle mass (2 protons, 2 neutrons) =
6.65 x 10-27 kg (data sheet)
mass of 2 protons = 2 x 1.67 x 10-27 kg =3.34 x 10-27 kg
mass of 2 neutrons = 2 x 1.67 x 10-27 kg =3.34 x 10-27 kg
total mass of separate nucleons = 6.68 x 10-27
kg
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mass defect = proton mass + neutron
mass - mass = 0.03 x 10-27 kg E = mc2
E = (0.03 x 10-27
kg)(3.00 x 108
m/s)2
E = 2.70 x 10-12 J
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in nuclear reactions, mass is converted to
energy or energy is converted to mass
Conservation of mass-energyprinciple
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Example
Calculate the energy produced in the reaction
2H mass = 3.34341 x 10-27 kg3H mass = 5.00661 x 10-27 kg
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Solution
Total mass of reactants = 8.35002 x 10-27 kg
The total mass of the products = 8.3212x10-27 kg
Mass defect
=8.35002x10-27 kg 8.3212x10-27 kg
= 2.882 x 10-29 kg
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E = mc2
E = (2.882 x 10-29 kg)(3.00 x 108 m/s)2
E = 2.59 x 10-12 J
in the form of kinetic energy of products
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STS
In a CANDU reactor, 1 kg of fuel (natural
uranium) produces 3.4 x 105 MJ of heatthat is converted to electricity
in oil and coal power plants 1 kg of fuel
produces about 4 MJ of heat
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Pair Production
a very high energy photon may create
matter
The process must produce 2 particleswhose total charge is zero, since charge &
momentum must be conserved.
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A particle and its antiparticle (antimatter) are
often produced (i.e. an electron and antielectron)have the same mass and other properties, but
opposite signs
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Bubble chamber track
Neutral particles do not leave a
track
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Example
A 8.50 x 1020 Hz photon produces an
electron and an anti-electron. Determinethe total kinetic energy of the particles.
Conservation of Mass-Energy!!!
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