Nuclear Chemistry

1
Nuclear Chemistry

• Chapter 25

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Radiation

• In 1896, Antoine Henri Becquerel discovered
  radiation by accident.
• His associates at the time were Marie and Pierre
  Curie.
• Marie Curie gets credit for naming radioactivity.

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Radioisotopes

• Nuclei of unstable isotopes are called
  radioisotopes.
• An unstable nucleus releases energy and/or mass
  by emitting radiation during the process of
  radioactive decay

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Radiation

• Three Types
• Alpha ? Helium Nucleus
• Beta ? Electron
• Gamma ? Light wave

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Symbols
Alpha
Beta
Gamma
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Radiation
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Radiation
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Nuclear Symbols

• Table O

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Nuclear Stability

• For smaller atoms, a ratio of 11 neutrons to
  protons helps to maintain stability
• C-12, N-14, O-16
• For larger atoms, more neutrons than protons are
  required to maintain stability
• Pb-207, Au-198, Ta-181

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Nuclear Stability
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Radioactive Decay

• Radioisotopes will undergo decay reactions to
  become more stable
• Alpha Decay
• Beta Decay
• Positron Emission

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Nuclear Reactions

• Unstable isotopes of one element are transformed
  into stable isotopes of a different element.
• They are not affected by outside factors, like
  temp and pressure. They can not be sped up or
  slowed down.

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General Reaction Format
Reactants
Products
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Reaction Format

• In Math class you might say
• A B C
• In Science, we dont use subtraction
• A ? B C
• A breaks into B and C

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Decay Reactions

• Decay reactions involve one unstable nuclei
  decaying (breaking down) into 2 (or more) smaller
  nuclei.
• Alpha Decay - one of the products is an alpha
  particle
• Beta Decay - one of the products is a beta
  particle

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Nuclear Reactions

• Reactions must always Balance
• Mass Numbers have to balance (top row)
• Atomic Numbers have to balance (bottom row)

238 4 234
92 2 90
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Alpha Decay
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Alpha Decay
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Alpha Decay
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Beta Decay
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Beta Decay
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Beta Decay
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Positron Emission
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Transmutations

• Any reaction where one element is transformed
  into a different element
• Two main types
• Natural
• Artificial

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Transmutations

• Natural
• Usually has one reactant
• Alpha and Beta Decay
• Artificial
• Usually has more than one reactant
• Particle Accelerators

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Example
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Example
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Example
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Fission

• Splitting of a larger atom into two or more
  smaller pieces
• Nuclear Power Plants
• One Example

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Fission
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Energy Production

• Energy is produced by a small amount of mass
  being converted to energy
• Emc2

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Chain Reaction

• Reaction that produces material that can initiate
  more than one reaction

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Chain Reaction
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Fusion

• Joining of two or more smaller pieces to make a
  larger piece
• Sun, Stars
• One Example

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Fusion

• More Examples

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Fusion
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Energy Production

• Energy is produced by a small amount of mass
  being converted to energy
• More energy is produced by fusion than any other
  source
• Emc2

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Fission vs. Fusion

• Advantages of Fission
• Produces a lot of energy
• Can be a controlled reaction
• Material is somewhat abundant

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Fission vs. Fusion

• Disadvantages of Fission
• Uses hazardous material
• Produces hazardous material
• Long Half Life
• Reaction can run out of control.
• Limited amount of fissionable material

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Fission vs. Fusion

• Advantages of Fusion
• Lighter weight material
• Easily available material
• Produces waste that is lighter and has shorter
  half-life
• Produces more energy than fission

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Fission vs. Fusion

• Disadvantages of Fusion
• Must be done at very high temperatures
• Only been able to attain 3,000,000K
• Have not been able to sustain stable reaction for
  energy production

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Half Life

• Amount of time for half of a sample to decay into
  a new element
• Parent Atoms
• Undecayed atoms
• Daughter Atoms
• Decayed atoms

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Half Life
Number of Half-lives Fraction left
0 1
1 1/2
2 1/4
3 1/8
4 1/16
5 1/32
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Half Life

• Number of half-lives

t amount of time elapsed
T half-life
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Example

• How many half lives does it take for a sample of
  C-14 to be 11430 yrs old?

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Half Life

• Fraction Remaining

t amount of time elapsed
T half-life
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Example

• What fraction of P-32 is left after 42.84days?

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Example

• How long will a sample of Rn-222 take to decay
  down to 1/4 of the original sample?

7.646d
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Fraction Remaining
Mass Left

Original Mass
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Practice

• How much Carbon-14 was originally in a sample
  that contains 4g of C-14 and is 17145 years old?

32g
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More Practice

• How much 226Ra will be left in a sample that is
  4797 years old, if it initially contained 408g?

51g
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And One More.

• What is the half life of a sample that started
  with 144g and has only 9g left after 28days?

7d
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Uses of Radioisotopes

• Smoke Detectors
• Food Irradiation
• Radioactive Dating
• Medical Tracers
• Nuclear Power Plants
• Nuclear Weapons
• Origin of Elements

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Smoke Detectors

• Americium produces radiation that is monitored by
  an electrical circuit
• Smoke interferes with the current, triggering the
  alarm

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Food Irradiation

• Food is exposed to radiation, killing bacteria
  and mold
• Food is cleaner and lasts longer

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Radioactive Dating

• Ratio of Parent atoms to Daughter atoms provides
  an age
• Examples
• C-14 used to date organic material
• U-238 used to date geological formations

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Medical Tracers

• Radioisotopes replace stable isotopes
• Radiation produced can be detected by machines
• Example
• I-131 is used for thyroid disorders
• Barium milk shakes
• Co-60 for Cancer

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Radioisotopes

• You must know these radioisotopes and uses
• I-131
• Diagnosing and treating thyroid disorders
• Co-60
• Treating cancer

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Radioisotopes

• You must know these radioisotopes and uses
• C-14
• Dating once-living organisms
• Compare to C-12
• U-238
• Dating geologic formations
• Compare to Pb-206

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Nuclear Power Plants
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Nuclear Power Plants
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Nuclear Power Plants
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Nuclear Weapons
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Video

• Origin of Elements
• YouTube

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Stability

• Elements 1-26 are made in the core of stars
• Elements 27-92, excluding 43 and 61, are made
  during a Supernova explosion
• No element larger than 83 has a stable isotope
• No element larger than 92 is made in nature