Intro to Nuclear Chemistry

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Intro to Nuclear Chemistry

• Honors Chemistry
• Mrs. Coyle

http//www.chem.orst.edu/graduate/pics/Reactor.jpg

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How does a nuclear reactor work?
http//www.lanl.gov/science/1663/images/reactor.jp
g
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How does a small mass contained in this bomb
cause

• Nuclear Bomb of 1945 known as fat man

http//www.travisairmuseum.org/assets/images/fatma
n.jpg
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this huge nuclear explosion?
http//library.thinkquest.org/06aug/01200/Graphics
/705px-Nuclear_fireball.jpg
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Is there radon in your basement?
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Notation

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• Nucleons are bound together by the strong force.
  

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Isotopes

• Atoms of a given element with
• same protons
• but
• different neutrons

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• H H H

http//education.jlab.org/glossary/isotope.html
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Isotopes of Carbon
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Radioactive Isotopes

• Isotopes of certain unstable elements that
  spontaneously emit particles and energy from the
  nucleus.
• Henri Beckerel 1896 accidentally observed
  radioactivity of uranium salts that were fogging
  photographic film.
• His associates were Marie and Pierre Curie.

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Marie Curie born 1867, in Poland as Maria
Sklodowska

• Lived in France
• 1898 discovered the elements polonium and radium.

http//www.radiochemistry.org/nuclearmedicine/pion
eers/images/mariecurie.jpg
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Marie Curie a Pioneer of Radioactivity

• Winner of 1903 Nobel Prize for Physics with Henri
  Becquerel and her husband, Pierre Curie.
• Winner of the sole 1911 Nobel Prize for
  Chemistry.

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3 Main Types of Radioactive Decay

• Alpha a
• Beta b
• Gamma g

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Alpha Decay

• Emission of alpha particles a
• helium nuclei
• two protons and two neutrons
• charge 2e 
• can travel a few inches through air
• can be stopped by a sheet of paper, clothing.

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

• Beta particles b electrons ejected from the
  nucleus when neutrons decay
• ( n -gt p b- )
• Beta particles have the same charge and mass as
  "normal" electrons.

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Beta Decay

• Beta particles b electrons ejected from the
  nucleus when neutrons decay
• n -gt p b-
• Beta particles have the same charge and mass as
  "normal" electrons.
• Can be stopped by aluminum foil or a block of
  wood.

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Beta Decay
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Beta Decay
Thorium
Protactinium
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Gamma Decay

• Gamma radiation g electromagnetic energy that
  is released. 
• Gamma rays are electromagnetic waves.
• They have no mass.
• Gamma radiation has no charge.
• Most Penetrating, can be stopped by 1m thick
  concrete or a several cm thick sheet of lead.

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Examples of Radioactive Decay

• Alpha Decay
• Po ? Pb He
• Beta Decay p? n e
• n ? p e
• C ? N e
• Gamma Decay
• Ni ? Ni g
• (excited nucleus)

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Which is more penetrating? Why?
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Part II

• Nuclear Stability
• Half-Life

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Nuclear Stability

• Depends on the neutron to proton ratio.

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Band of Stability
Number of Neutrons, (N)
Number of Protons (Z)
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What happens to an unstable nucleus?

• They will undergo decay
• The type of decay depends on the reason for the
  instability

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What type of decay will happen if the nucleus
contains too many neutrons?

• Beta Decay

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Example
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0
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• C ? N e
• In N-14 the ratio of neutrons to protons is 11

-1
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• Nuclei with atomic number gt 83 are radioactive

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Radioactive Half-Life (t1/2 )

• The time for half of the radioactive nuclei in a
  given sample to undergo decay.

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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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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?
  Answer50 g
• How many grams are left after two half-lives?

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Problem

• 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