Ch. 22: Nuclear Chemistry

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Ch. 22 Nuclear Chemistry

• Nuclear forces, and radioactive decay
• Alpha, beta, and gamma particles
• Transmutation, disintegration series, carbon
  dating
• Fission vs. fusion
• Effects of radiation

San Onofre Nuclear Power Plant San Clemente,
CA (61 miles south of Los Angeles)
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Chemical reaction vs. Nuclear reaction
Nuclear chemistry the chemistry of radioactive
substances study of the atomic nucleus,
including fission and fusion and their products

• Chemical reactions
• Atoms attain stable isotopes by losing or
  sharing electrons
• Reactions affected by changes in temperature,
  pressure, or the presence of catalysts

• Nuclear reactions
• The nuclei of unstable isotopes gain stability
  by undergoing changes
• The changes are accompanied by emission of large
  amounts of energy

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The Nucleus

• Atomic nuclei are made of protons and neutrons,
  which are collectively called nucleons
• In nuclear chemistry an atom is referred to as a
  nuclide and is identified by the number of
  protons and neutrons in its nucleus.
• Two types of notations Radium-228 or 228Ra
• 
  88

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Nuclear Reaction

• a reaction that affects the nucleus of an atom.
• Occurs to increase stability
• Give off large amounts of energy
• Total of atomic s mass s is equal on both
  sides of equation.
• Identity of atom does not change till atomic
  changes, When atomic changes, the identity of
  element changestransmutation

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Natural Radioactivity

• Discovered in 1896 by Antoine Henri Becquerel,
  who saw a uranium salt produce an image on a
  photographic film.
• The term radioactivity was coined in 1898 by
  Marie Curie, a Polish physicist, who was doing
  research with her husband Pierre. (They did much
  of the initial work on radioactivity, and
  eventually died of radiation-related illnesses.)
• Radioactive Decay spontaneous disintegration of
  a nucleus into a slightly lighter more stable
  nucleus, accompanied by emission of particles,
  electromagnetic radiation or both.

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What determines the type of decay a radioisotope
undergoes?
The nuclear force is an attractive force that
acts between all nuclear particles that are
extremely close together, such as protons and
neutrons in a nucleus At these short distances,
the nuclear force dominates over electromagnetic
repulsions and hold the nucleus together. More
than 1,500 different nuclei are known. Of those,
only 264 are stable and do not decay or change
with time. These nuclei are in a region called
the band of stability.
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Types of Radioactive Decay
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• Alpha particle emissions
• Helium nucleus 2 protons and 2 neutrons, 2
  charge.
• For large, unstable nucleus which needs to reduce
  both the number of protons and the number of
  neutrons.
• Example

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• Alpha emission

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• Beta particle emissions
• Electron emission, -1 charge.
• For unstable nucleus which needs to reduce the
  number of neutrons.
• A neutron is converted into a proton and an
  electron, the electron is given off as a beta
  particle.
• Example

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• Beta emission

Some of the tiny particles that exist and
transform in nuclear reactions have various names
such as neutrinos and quarks. This can lead to
the discussion of matter and antimatter.
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• Positron emissions
• Positron emission, 1 charge.
• For unstable nucleus which needs to reduce the
  number of protons.
• A proton is converted into a neutron and a
  positron, the positron is emitted.
• Example

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• Electron capture
• An inner orbit electron combines with a proton
  and forms a neutron.
• For unstable nucleus which needs to reduce the
  number of protons.
• Example

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• Electron capture

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• Gamma emissions
• High energy electromagnetic waves (photons) like
  visible light, except with a shorter wavelength.
• For high energy nucleus when it jumps down from
  an excited state to a ground state.
• Example

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• Gamma emission

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1. Using the examples above, write the reaction
of bismuth-214 emitting an alpha particle
2. Write the reaction of silicon-27 emitting a
beta particle
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Half Life

• The time required for ½ the amount of a
  radioactive material to disintegrate.
• Phosphorus-32 radioactively decays to form
  Sulfur-32
• Half life 32P 14 days

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Arificial Transmutation

• First accomplished by Rutherford in 1919, even
  though alchemists tried for hundreds of years.
• Transmutation of lead into gold was achieved by
  Glenn Seaborg, who succeeded in transmuting a
  small quantity of lead in 1980. He also first
  isolated plutonium for the atomic bomb and
  discovered/created many elements. (NY Times,
  Feb 1999)
• There is an earlier report (1972) in which Soviet
  physicists at a nuclear research facility in
  Siberia accidentally discovered a reaction for
  turning lead into gold when they found the lead
  shielding of an experimental reactor had changed
  to gold.
• Accomplished with particle accelerators like the
  Stanford Linear Accelerator (SLAC)

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Disintegration Series (Decay Series)

• Heavy atoms (greater than Bismuth, 83)
  naturally decay to smaller atoms along a
  consistent path, or series, of decays.

Radioactive U-238 ? Th-234 a Th-234 ? Pa-234
b Pa-234 ? U-234 b U-234 ? Th-230 a Th-230 ?
Ra-226 a Ra-226 ? Rn-222 a Rn-222 ? Po-218
a Po-218 ? Pb-214 a Pb-214 ? Bi-214 b Bi-214
? Po-214 b Po-214 ? Pb-210 a Pb-210 ? Bi-210
b Bi-210 ? Po-210 b Po-210 ? Stable Pb-206 a
Source http//www.frontiernet.net/jlkeefer/urani
um.html
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Nuclear Fission

• Fission process in which the nucleus of a large,
  radioactive atom splits into 2 or more smaller
  nuclei
• Caused by a collision with a energetic neutron.

• A neutron is absorbed by a U-235 nucleus. The
  nucleus is now less stable than before. It then
  splits into 2 parts and energy is released.
  Several neutrons are also produced they which
  may go on to strike the nuclei of other atoms
  causing further fissions.

Fission animation http//www.howstuffworks.com/n
uclear-bomb3.htm
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• In a fission reaction that is working properly,
  more than one neutron ejected from the fission
  reaction causes another fission to occur. This
  condition is known as supercriticality.
• The process of neutron capture and nucleus
  splitting happens very quickly (takes about 1 x
  10-12 seconds).
• An incredible amount of energy is released
• As heat and gamma radiation
• Because the product atoms and neutrons weigh less
  than the original U-235 atom the missing mass
  has been converted to energy by Emc2

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A Fission Chain Reaction
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Harnessing Fission A nuclear power plant

• Nuclear power plants utilize the energy released
  in a controlled fission reaction in the core to
  heat water in one pipe, which is used to vaporize
  water into steam in another pipe, which drives a
  turbine and generates electricity.

• The vaporized H2O is in a closed circuit, and is
  never exposed to the radiation itself.
• The speed of the fission chain reaction is
  regulated using carbon control rods which can
  absorb extra neutrons.

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The Atomic Bomb

• Uses an unregulated fission reaction in a very
  fast chain reaction that releases a tremendous
  amount of energy.
• Critical mass the minimum amount of
  radioactive, fissionable material needed to
  create a sustainable fission chain reaction
• Site of fission reaches temperatures believed
  to be about 10,000,000C.
• Produces shock waves and a, b, g, x-rays, and UV
  radiation.

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The classic mushroom cloud is a result of dust
and debris lifted into the air as a result of the
detonation.

• US Army aerial photograph from 80 km away, taken
  about 1 hour after detonation over Nagasaki,
  Japan, August 9, 1945.

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Nuclear Fusion

• Fusion process in which 2 nuclei of small
  elements are united to form one heavier nucleus
• Requires temperatures on the order of tens of
  millions of degrees for initiation.
• The mass difference between the small atoms and
  the heavier product atom is liberated in the form
  of energy.
• Responsible for the tremendous energy output of
  stars (like our sun) and the devastating power of
  the hydrogen bomb.

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Stars the Hydrogen Bomb

• The first thermonuclear bomb was exploded in 1952
  in the Marshall islands by the United States, the
  second was exploded by the Russia (then the USSR)
  in 1953.
• H bombs utilize a fission bomb to ignite a
  fusion reaction.

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Cold fusion

• Martin Fleischmann and Stanley Pons
• 1989
• Univ. of Utah
• Cold fusion lie

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Mass-Energy Relationship

• The energy that can be released from 2 kg of
  highly enriched U-235 (as used in a nuclear bomb)
  is roughly equal to the combustion of a million
  gallons of gasoline. 2 kg of U-235 is smaller
  than a baseball a million gallons of gasoline
  would fill a rectangular tank that is 50 feet per
  side.

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Measurement of Radioactivity

• ionizing radiation-
• radiation from radioactive sources
• When it strikes an atom or a molecule, one or
  more electrons are knocked off and an ion is
  created
• Measured with a Geiger counter, film badge or a
  Scintillation counter
• Curie-measures radioactivity emitted by a
  radionuclide.
• Roentgen Rad - measures exposure to gamma rays
  or X-rays
• Rem- takes into account the degree of biological
  effect caused by the type of radiation exposure.

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Biological Effects of Radiation Acute
Ionizing radiation energy emitted from
radioactive matter it can directly affect
(ionize) the structure of materials which it
passes through, including human tissue.

• High level radiation (gamma ray xray) causes
  death
• Damage centered in the nuclei of the cells cells
  that are undergoing rapid cell division most
  susceptible
• Gamma rays from a Co-60 source are often used to
  treat cancer (cells that multiply rapidly)

Effects of Radiation Long Term
Long term exposure can weaken an an organism and
lead to onset of malignant tumors, even after
fairly long time delays. Largest source
Xrays Sr-90 isotopes are present in fallout from
atmospheric testing of nuclear weapons. Contaminat
ed foods can increase incidence of leukemia and
bone cancers.