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Nuclear Physics
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Nuclear Symbols Mass number, A (p+ + no) Element symbol
Atomic number, Z (number of p+)
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Balancing Nuclear Equations
Areactants = Aproducts = (1) = (0) Zreactants = Zproducts
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Balancing Nuclear Equations #2
222 226 = 4 + ____ 222 Rn 86 88 = 2 + ___ 86 Atomic number 86 is radon, Rn
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Balancing Nuclear Equations #3
95 = (1) + ____ 95 Y 39 39 = (0) + ____ Atomic number 39 is yttrium, Y
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Alpha Decay Alpha production (a): an alpha particle is a
helium nucleus Alpha decay is limited to heavy, radioactive nuclei
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Alpha Radiation Limited to VERY large nucleii.
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Beta Decay Beta production (b): A beta particle is an
electron ejected from the nucleus Beta emission converts a neutron to a proton
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Beta Radiation Converts a neutron into a proton.
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Gamma Ray Production Gamma ray production (g):
Gamma rays are high energy photons produced in association with other forms of decay. Gamma rays are massless and do not, by themselves, change the nucleus
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Deflection of Decay Particles
Opposite charges_________ each other. attract Like charges_________ each other. repel
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Positron Production Positron emission:
Positrons are the anti-particle of the electron Positron emission converts a proton to a neutron
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Electron Capture Electron capture: (inner-orbital electron is captured by the nucleus) Electron capture converts a proton to a neutron
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Types of Radiation
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Nuclear Stability Decay will occur in such a way as to return a nucleus to the band (line) of stability. The most stable nuclide is Iron-56 If Z > 83, the nuclide is radioactive
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A radioactive nucleus reaches a stable state by a series of steps
A Decay Series
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Half-life Concept
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Sample Half-Lives
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STOP
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NUCLEAR DECAY KINETICS
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Decay Kinetics Decay occurs by first order kinetics (the rate of decay is proportional to the number of nuclides present) N0 = number of nuclides present initially N = number of nuclides remaining at time t k = rate constant t = elapsed time
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Calculating Half-life
t1/2 = Half-life (units dependent on rate constant, k)
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Example Determine the amount of Rn-222 that remains after 5.0 days if the the half-life is 3.8 days and you started with 80,000 particles. No = 80,000 particles k = day-1 N = ? First find decay constant. k = ln2 / t1/2
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Example 2 Determine the activity of Rn-222 that remains after 7.0 days if the the half-life is 3.8 days and you started with 285 counts/min. Ao = 285 counts/min k = day-1 N = ? First find decay constant. k = ln2 / t1/2
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Example 3 Determine the percentage of Rn-222 that remains after 9.0 days if the the half-life is 3.8 days. No = ??? particles k = day-1 N = ? First find decay constant. k = ln2 / t1/2
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Nuclear Fission and Fusion
Fusion: Combining two light nuclei to form a heavier, more stable nucleus. Fission: Splitting a heavy nucleus into two nuclei with smaller mass numbers.
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Energy and Mass Nuclear changes occur with small but measurable losses of mass. The lost mass is called the mass defect, and is converted to energy according to Einstein’s equation: DE = Dmc2 Dm = mass defect DE = change in energy c = speed of light Because c2 is so large, even small amounts of mass are converted to enormous amount of energy.
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Example Calculate the mass defect and energy released during this typical fission reaction. + + g g g 4 x g g g DE = Dmc2 = kg x 3.0 x 108 m/s DE = x 107 J
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Fission
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Fission Processes A self-sustaining fission process is called a chain reaction.
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A Fission Reactor
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Fusion
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