Nuclear Decay Processes

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Nuclear Decay Processes
http//www.curtin.edu.au/curtin/centre/waisrc/OKLO
/
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Nuclear Processes

• Chemical processes have been involved with the
  electron (outside the nucleus)
• Sharing, losing, or gaining
• Speed of reaction
• Energy involved in change
• Nuclear processes are involved in processes
  involving the nucleus (inside)
• What is being lost, gained?
• Speed of reaction
• Energy involved in change

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Nucleus
Nucleons Protons and neutrons in the nucleus
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Representing the Nucleus

• 23892U (or U-238)
• 238 Mass number (A)
• 92 Atomic number (Z)
• 92 represents the number of protons
• 238 represents the number protons neutrons
• 146 neutrons
• Isotopes occur due to variations in the numbers
  of neutrons found in the nucleus

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Nuclear Equations

• Representations which show the changes in the
  nuclear structure, that is, changes in protons
  and neutrons.
• 23892U
• 23892U ? 23490Th ?
• Radioactive decay spontaneous decomposition of
  the nucleus
• Radioisotopes atoms containing nuclei that are
  spontaneously decomposing.

Alpha particle (a)
42He
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Nuclear Stability

• n to p ratio
• High
• Above belt
• Low
• Below belt
• Z gt 84
• Magic numbers
• Even-Even

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Types of Radioactive Decay

• Alpha radiation
• Beta radiation
• Gamma radiation
• Positron emission
• Electron capture

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Alpha Radiation

• 23892U ? 23490Th 42He
• Properties of an alpha particle
• Charge Mass Alias Penetrating Power 2 4
  amu He low
• nuclei

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Beta Radiation

• 6328Ni ? 6329Cu 0-1b
• Properties of an beta particle
• Charge Mass Alias Penetrating Power -1 0
  amu electron moderate

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Gamma Radiation

• 23892U ? 23490Th 42He 2 00g
• Properties of an beta particle
• Charge Mass Alias Penetrating Power
  0 0 amu photon high

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Positron Emission

• 116C ? 115B 01b
• Properties of an beta particle
• Charge Mass Alias Penetrating Power
  1 0 amu Anti- moderate
• electron

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Electron Capture

• 5526Fe 0-1b ? 5525Mn hn (x-ray)
• Electron captured from
• low-energy electron orbital

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Decaying TowardStability
Z gt 84 Alpha
Beta
23892U ? 23490Th 42He
6328Ni ? 6329Cu 0-1b
Positron or electron capture
116C ? 115B 01b
5526Fe 0-1b ? 5525Mn
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Rate of Radioactive Decay

• Uses 1st order kinetics
• ln Nt -kt ln No
• Where N can be various measurements.
• g, Ci, counts/minute, disintegrations/min
• t1/2 0.693
• k
• Radioactive dating

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Problem

• A sample of waste has a radioactivity, measured
  at 0.245 Ci/g, caused solely strontium-90.
• What reason might be used to explain why
  strontium-90 is radioactive?
• Write an equation representing the most likely
  decay process for strontium-90.
• How much time will it take for this sample of
  waste to decrease in radiation to a level of 1.00
  x 10-6 Ci/g? (t1/2 28.1 yr)

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Rate of Radioactive Decay
Rate k No

• Uses 1st order kinetics
• ln Nt -kt ln No t1/2 0.693/k
• Where N can be various measurements.
• g, Ci, counts/minute, disintegrations/min

Radioactive dating
Carbon-14
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Problem

• A sample of waste has a radioactivity, measured
  at 0.245 Ci/g, caused solely strontium-90.
• How much time will it take for this sample of
  waste to decrease in radiation to a level of 1.00
  x 10-6 Ci/g? (t1/2 28.1 yr)

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Rate of Decay

• According to current regulations, the maximum
  permissible dose of strontium-90 in the body of
  an adult is 1mCi. Calculate the number of atoms
  of strontium-90 to which this dose corresponds.
  What mass of strontium-90 is this? (t1/2 28.8
  years)

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Radioactive Dating (kinetics)

• A sample of carbon of mass 1.00 g from scrolls
  found near the Dead Sea underwent 1.4 x 104
  carbon-14 disintegrations in 20 hours. Estimate
  the approximate time since the sheepskins were
  removed from the sheep, assuming that 1.00 g from
  a modern source underwent 1.84 x 104
  disintegrations in 20 hours. The t1/2 of C-14 is
  5730 years.

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Sea of Instability
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Fermi National Laboratory
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Transmutation Processes

• 3216S 10n ? 11p 3215P
• 3216S (n,p) 3215P
• 20983Bi 6428Ni ? 272111X 10n
• 20983Bi (Ni-64, p) 272111X

Possible particles, symbols Proton, p Electron,
b or 0-1e
Neutron, n Positron, b or 01e Alpha, a or 42He
A variety of nuclides
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Transmutation Processes

• Used to generate synthetic isotopes designed for
  specific uses.
• Co-60 radiation therapy isotope for cancer
• 5826Fe 10n ? 5926Fe ? 5927Co 0-1b
• 5927Co 10n ? 6027Co

This process is done inside nuclear fission
reactors because fission reactors are excellent
sources of neutrons
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Uses for Radioisotopes

• I-131 hyperthyroidism
• P-32 leukemia and polycythemia vera
• Cs-137, Ir-192, I-125, Pd-103 brachytherapy
• B-10 neutron-capture therapy
• Tl-201 Cardiac imaging
• Sr-85 Bone scanning
• Tracers use of radioisotopes as beacons
• Chemistry used to trace chemical pathways
• Material flow
• NAA neutron activation analysis
• Food irradiation

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Biological Damage from Radiation

• Two ways to
• interact with matter
• Excitation
• Ionization
• Ionizing radiation
• a - ionizes the most
• b - middle
• g - ionizes the least

Inside body a gt b gt g
Outside body g gt b gt a
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Biological Damage from Radiation

• H2O g ? H2Os e-
• H2Os H2O ? H3O OHs
• e- H2O ? Hs OH-
• Membrane structure changed
• Hs RCHCHR ? RCH2-CsHR

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Radiation Dose Measurements

• rad - radiation absorbed dose
• 1 x 10-2 J per kg
• RBE relative biological
• effectiveness
• 1 for g and b radiation
• 20 for a radiation
• rem effective dosage of
• exposure
• rem (number of rads) (RBE)

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Problem

• A 5.0 gram sample of muscle tissue absorbs 2.0 J
  of energy as a result of exposure to a radiation.
  Calculate the dose in rads and gray (Gy) and the
  dose equivalent in rems and in sieverts (Sv).

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Energy Changes

• 23592U 10n ? 14156Ba 9236Kr 3
  10n
• STEPS
• 235U 234.9935 amu 1) Calculate the
• 141Ba 140.8833 amu change in mass
• 92Kr 91.9021 amu 2) E mc2
• 10n 1.00866 amu mass in kg

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Binding Energy

• 11 11p 12 10n ? 2311Na
• STEPS
• 23Na 22.98733 amu 1) Calculate the mass
• 11p 1.00728 amu defect (change
  in
• 10n 1.00866 amu mass)
• 2) E mc2
• 3) Divide by nucleons

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The Most Stable Nuclei?

• Which of the following nuclei is likely to have
  the largest mass defect per nucleon?
• 118Sn 243Cm 59Co 11B

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Group Problem

• What is the nuclear binding energy of 1 x 10-7
  mol of P-31?
• Given that P-31 has an amu of 30.965533 amu
• H-1 has an atomic weight of 1.00728 amu
• 10n has an atomic weight of 1.00866 amu

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Nuclear Power

• Nature
• www.curtin.edu.au/curtin/centre/waisrc/OKLO/
• Fission
• www.world-nuclear.org
• www.ans.org/
• www.nuclearfiles.org
• Fusion
• http//europa.eu.int/comm/dg12/fusion1.html
• www.jet.efda.org

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Natures Fission Experiment

• 1st Fission Process?
• 3500 million
• years ago
• U mobilization
• Ore/reactor formation
• Reactor operation 2000 million years ago
• operated for 1 million years
• Waste movement (For the last 2000 million
  years)

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Nuclear Fission
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Fission Chain Reaction
Critical mass quantity of fissionable material
necessary to sustain reaction - 1 effective
neutron
Supercritical mass quantity of fissionable
material necessary to lead to explosion
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23592U 10n ? 3 10n
Control rods absorb neutrons to regulate the
amount of neutrons present
Moderator slows down neutrons to enhance the
fuels ability to capture neutrons
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Fusion

• Proposed
• Fusion on
• Sun
• 11H 11H ? 21H 01b
• 11H 21H ? 32He
• 32He 32He ? 42He 2 11H
• 32He 11H ? 42He 01b

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tokamak torus shaped magnetic chamber