Nuclear Chemistry

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Nuclear Chemistry

• Nuclear chemistry is the study of the changes of
  the nucleus of atoms.
• Nuclear Reactions involve changes within the
  nucleus where as chemical reactions involve the
  loss, gain or sharing of electrons.

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The Nucleus

• Remember that the nucleus is made up of protons
  and neutrons. The are collectively called
  nucleons.

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Radioactivity

• A stable nucleus holds together well. An
  unstable nucleus will decay or break down,
  releasing particles and/or energy in order to
  become stable.
• An atom with an unstable nuclei is considered
  radioactive.

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Nuclear Transformations

• Nuclear transformations can be induced by
  accelerating a particle and colliding it with the
  nuclide.

These particle accelerators are enormous, having
circular tracks with radii that are miles long.
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There are several ways radioactive atoms can
decay into different atoms!

• Transmutation
• Type of nuclear reaction that will change the
  number of protons and thus will create a
  different element.
• Atoms with an atomic number larger than 92 are
  created through this process

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Alpha Decay

• Loss of an ?-particle (a helium nucleus)
• Atomic number decreases by 2 and mass number
  decreases by 4
• Penetrating Power LOW Can be blocked by
  clothing or thin paper
• Example

OR
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Alpha Decay
http//education.jlab.org/glossary/alphadecay.gif
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Alpha Decay
Uranium Thorium
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Beta Decay

• Loss of a ?-particle (a high energy electron)
• Atomic number increases by 1 and mass number
  stays the same. A neutron becomes a proton and a
  high speed electron that is discharged from the
  nucleus.
• Penetrating Power Medium Can be blocked by
  thin metal or wood
• Example

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Beta Decay
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Beta Decay
Thorium
Protactinium
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Gamma Emission

• Loss of a ?-ray (high-energy radiation that
  almost always accompanies the loss of a nuclear
  particle)
• Atomic number and mass number stays the same
• Penetrating Power High Can only be blocked by
  thick metal or thick concrete
• Example

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Radioactivity

• Radioactive isotopes decay at a characteristic
  rate measured in half life.
• A half life is the time required for half of the
  amount of radioactive atoms to decay. The time
  ranges from seconds to millions of years
•  

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Examples

• Beta decay of zircomium-97
•  
• Alpha decay of americium-241
• Alpha decay of uranium-238
• Complete this

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Common Radioactive Isotopes
Isotope Half-Life Radiation
Emitted Carbon-14 5,730 years b,
g Radon-222 3.8 days a Uranium-235 7.0 x
108 years a, g Uranium-238 4.46 x 109 years
a
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Radioactive Half-Life

• After one half life there is 1/2 of original
  sample left.
• After two half-lives, there will be
• 1/2 of the 1/2 1/4 the original sample.

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Graph of Amount of Remaining Nuclei vs Time
AAoe-lt
A
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Half Life Calculations

• HOW TOs
• 1. To calculate the number of half lives, divide
  the half life (T1/2) into the total time (T). 
• T/T1/2 of half lives 
• 2. Use the equation to calculate remaining
  amount left over after a certain number of half
  lives have passed.
• Amt remaining (initial amt) (.5)n ( of half
  lives)

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Example

• You have 100 g of radioactive C-14. The half-life
  of C-14 is 5730 years.
• How many grams are left after one half-life?
• How many grams are left after two half-lives?

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Examples

• Suppose you have 20 grams of sodium-24. Its
  half-life is 15 hours. How much is left over
  after 60 hours.

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Examples

• Uranium-238 has a half life of 4.46 x 109 years.
  How long will it take for 7/8th of the sample to
  decay?

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Examples

• The half life of radium-222 is 38 s. How many
  grams of a 12.0 g sample are left after 114 s?

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Examples

• A sample of 3x107 Radon atoms are trapped
• in a basement that is sealed. The half-life of
• Radon is 3.83 days. How many radon atoms
• are left after 31 days?
• answer1.2x105 atoms

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Nuclear Fission How does one tap all that
energy?

• Large atoms split into smaller atoms that
  generate huge amounts of energy.
• Carried out in nuclear reactors.
• Could result in a chain reaction of fission like
  the atomic bomb

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Nuclear Fission

• Bombardment of the radioactive nuclide with a
  neutron starts the process.
• Neutrons released in the transmutation strike
  other nuclei, causing their decay and the
  production of more neutrons.
• This process continues in what we call a nuclear
  chain reaction.

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Nuclear Fission

• If there are not enough radioactive nuclides in
  the path of the ejected neutrons, the chain
  reaction will die out.
• Therefore, there must be a certain minimum amount
  of fissionable material present for the chain
  reaction to be sustained Critical Mass.

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Nuclear Reactors

• In nuclear reactors the heat generated by the
  reaction is used to produce steam that turns a
  turbine connected to a generator.

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Nuclear Reactors

• The reaction is kept in check by the use of
  control rods.
• These block the paths of some neutrons, keeping
  the system from reaching a dangerous
  supercritical mass.

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Nuclear Fusion

• Fusion would be a superior
• method of generating power.
• The good news is that the
• products of the reaction are
• not radioactive.
• The bad news is that in order to achieve fusion,
  the material must be in the plasma state at
  several million kelvins.
• Tokamak apparati like the one shown at the right
  show promise for carrying out these reactions.
• They use magnetic fields to heat the material.

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Nuclear Fusion

• Smaller atoms are combine to form a large atom.
• Occurs in the sun and stars
• Generates huge amounts of energy