Nuclear Chemistry

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Nuclear Chemistry

• Chapter 28

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Comparison of Chemical and Nuclear Reactions
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Radioactivity

• Radioisotopes are isotopes that have an unstable
  nucleus. They emit radiation to attain more
  stable atomic configurations in a process called
  radioactive decay.
• Radioactivity is the property by which an atomic
  nucleus gives off alpha, beta, or gamma
  radiation.
• Marie Curie named the process.
• In 1898, Marie Pierre Curie identified 2 new
  elements, polonium radium.
• The penetrating rays and particles emitted by a
  radioactive source are called radiation.

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Radioactivity (cont)

• The presence of too many or too few neutrons,
  relative to the number of protons, leads to an
  unstable nucleus.
• The types of radiation are alpha (a), beta (ß),
  or gamma (?).
• An unstable nucleus loses energy by emitting
  radiation during the process of radioactive
  decay.
• Spontaneous and does not require any input of
  energy.

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The effect of an electric field on a,ß, and ?,
radiation. The radioactive source in the shielded
box emits radiation, which passes between two
electrodes. Alpha radiation is deflected toward
the negative electrode, ß radiation is strongly
deflected toward the positive electrode, and ?
radiation is undeflected.
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Nuclear Equations

• For a nuclear reaction to be balanced, the sum of
  all the atomic numbers and mass numbers on the
  right must equal the sum of those numbers on the
  left.
• To figure out the unknown isotope, you need to
  balance the equation.

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Example
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Natural Radioactive Decay

• Why
• The nucleus has many positively charged protons
  that are repelling each other.
• The forces that hold the nucleus together cant
  do its job and the nucleus breaks apart.
• All elements with 84 or more protons are unstable
  and will eventually undergo nuclear decay.
• How
• Alpha particle emission
• Beta particle emission
• Gamma radiation emission
• Positron emission (less common)
• Electron capture (less common)

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Alpha radiation

• A type of radiation called alpha radiation
  consists of helium nuclei that have been emitted
  from a radioactive source.
• These emitted particles, called alpha particles,
  contain 2 protons and 2 neutrons and have a
  double positive charge.

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Alpha Radiation (cont)

• Because of their large mass and charge, alpha
  particles do not tend to travel very far and are
  not very penetrating.
• They are easily stopped by a piece of paper or
  the surface of skin.
• Radioisotopes that emit alpha particles are
  dangerous when ingested.

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Alpha radiation occurs when an unstable nucleus
emits a particle composed of 2 protons and 2
neutrons. The atom giving up the alpha particle
has its atomic number reduced by two. Of course,
this results in the atom becoming a different
element. For example, Rn undergoes alpha decay to
Po.
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Beta Particles

• A beta particle is essentially an electron thats
  emitted from the nucleus.
• A neutron is converted (decayed) into a proton
  electronso the atomic number increases by 1 and
  the electron leaves the nucleus.
• Isotopes with a high neutron/proton ratio often
  undergo beta emission, because this decay allows
  the of neutrons to be decreased by one the
  of protons to be increased by one, thus lowering
  the neutron/proton ratio.

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Beta radiation occurs when an unstable nucleus
emits an electron. As the emission occurs, a
neutron turns into a proton.
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Positron Emission

• A positron is essentially an electron that has a
  positive charge instead of a negative charge.
• A positron is formed when a proton in the nucleus
  decays into a neutron a positively charged
  electron.
• It is then emitted from the nucleus.
• The positron is a bit of antimatter (seen in Star
  Trek). When it comes in contact with an
  electron, both particles are destroyed with the
  release of energy.

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Positron emission occurs when an unstable nucleus
emits a positron. As the emission occurs, a
proton turns into a neutron.
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Positron emission tomography, also called PET
imaging or a PET scan, is a diagnostic
examination that involves the acquisition of
physiologic images based on the detection of
radiation from the emission of positrons.
Positrons are tiny particles emitted from a
radioactive substance administered to the
patient.
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Antimatter

• National Geographic Article
• When a particle and its antiparticle meet, they
  annihilate each other and their entire mass is
  converted into pure energy.
• Compared to conventional chemical propulsion
  systems, antimatter energy would slash the travel
  time to Mars and back from roughly two years to a
  few weeks.
• The world's largest maker of antimatter, the
  Fermi National Accelerator Laboratory in Batavia,
  Illinois, makes only one billionth of a gram a
  year at a cost of 80 million.

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An artist's concept of a robotic
antimatter-powered probe sailing past planets in
an imaginary nearby solar system. Credit
Laboratory for Energetic Particle Science at
Pennsylvania State University.
This artist's concept of an antimatter-powered
rocket ship looks like a big space-borne linear
accelerator. Credit Laboratory for Energetic
Particle Science at Pennsylvania State
University.
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Gamma Radiation

• Gamma radiation is similar to x-rays high
  energy, short wavelength emissions (photons).
• The symbol is ?, the Greek letter gamma.
• It commonly accompanies alpha and beta emission,
  but its usually not shown in a balanced nuclear
  reaction.
• Some isotopes, such as Cobalt-60, give off large
  amounts of gamma radiation.
• Co-60 is used in the radiation treatment of
  cancerthe gamma rays focus on the tumor, thus
  destroying it.

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Gamma radiation occurs when an unstable nucleus
emits electromagnetic radiation. The radiation
has no mass, and so its emission does not change
the element. However, gamma radiation often
accompanies alpha and beta emission, which do
change the element's identity.
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Electron Capture

• Electron capture is a rare type of nuclear decay
  in which an electron from the innermost energy
  level (1s) is captured by the nucleus.
• This electron combines with a proton to form a
  neutron.
• The atomic number decreases by one but the mass
  stays the same.
• Electrons drop down to fill the empty space in
  the 1s orbital, releasing energy.

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Man-Made Radioactive Decay on Earth

• Fission
• Fusion
• Occurs naturally in space
• Powers the sun
• Supernovas allow atoms to fuse into heavier
  elements, this is how the other elements came
  into existence

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Fission

• Nuclear fission occurs when scientists bombard a
  large isotope with a neutron.
• This collision causes the larger isotope to break
  apart into two or more elements.
• These reactions release a lot of energy.
• You can calculate the amount of energy produced
  during a nuclear reaction using an equation
  developed by Einstein Emc2

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Einstein

• "The intuitive mind is a sacred gift and the
  rational mind is a faithful servant. We have
  created a society that honors the servant and has
  forgotten the gift." 

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Chain Reactions

• A chain reaction is a continuing cascade of
  nuclear fissions.
• This chain reaction depends on the release of
  more neutrons then were used during the nuclear
  reaction.
• Isotopes that produce an excess of neutrons in
  their fission support a chain reaction -
  fissionable.
• There are only two main fissionable isotopes used
  during nuclear reactions uranium-235
  plutonium-239.

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Chain Reactions (cont)

• The minimum amount of fissionable material needed
  to ensure that a chain reaction occurs is called
  the critical mass.
• Anything less than this amount is subcritical.

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Chain Reaction Figure
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Atomic Bombs

• Because of the tremendous amount of energy
  released in a fission chain reaction, the
  military implications of nuclear reactions were
  immediately realized.
• The first atomic bomb was dropped on Hiroshima,
  Japan, on August 6, 1945.
• In an atomic bomb, two pieces of a fissionable
  isotope are kept apart. Each piece by itself is
  subcritical.
• When its time for the bomb to explode,
  conventional explosives force the two pieces
  together to cause a critical mass.
• The chain reaction is uncontrolled, releasing a
  tremendous amount of energy almost
  instantaneously.

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Mushroom Cloud
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Nuclear Power Plants

• If the neutrons can be controlled, then the
  energy can be released in a controlled way.
  Nuclear power plants produce heat through
  controlled nuclear fission chain reactions.
• The fissionable isotope is contained in fuel rods
  in the reactor core. All the fuel rods together
  comprise the critical mass.
• Control rods, commonly made of boron and cadmium,
  are in the core, and they act like neutron
  sponges to control the rate of radioactive decay.

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Nuclear Power Plants (cont)

• In the U.S., there are approximately 100 nuclear
  reactors, producing a little more than 20 of the
  countrys electricity.
• Advantages
• No fossil fuels are burned.
• No combustion products (CO2, SO2, etc) to pollute
  the air and water.
• Disadvantages
• Cost - expensive to build and operate.
• Limited supply of fissionable Uranium-235.
• Accidents (Three Mile Island Chernobyl)
• Disposal of nuclear wastes

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A nuclear power plant. Heat produced in the
reactor core is transferred by coolant
circulating in a closed loop to a steam
generator, and the steam then drives a turbine to
generate electricity.
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Three Mile Island
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Chernobyl
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Nuclear Fusion

• Fusion is when lighter nuclei are fused into a
  heavier nucleus.
• Fusion powers the sun. Four isotopes of
  hydrogen-1 are fused into a helium-4 with the
  release of a tremendous amount of energy.
• On Earth, H-2 (deuterium) H-3 (tritium) are
  used.

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Plasma

• Plasmas are conductive assemblies of charged
  particles, neutrals and fields that exhibit
  collective effects.
• Further, plasmas carry electrical currents and
  generate magnetic fields.
• Plasmas are the most common form of matter,
  comprising more than 99 of the visible universe,
  and permeate the solar system, interstellar and
  intergalactic environments.

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Nuclear Fusion (cont)

• The first demonstration of nuclear fusion the
  hydrogen bomb was conducted by the military.
• A hydrogen bomb is approximately 1,000 times as
  powerful as an ordinary atomic bomb.
• The goal of scientists has been the controlled
  release of energy from a fusion reaction.
• If the energy can be released slowly, it can be
  used to produce electricity.
• It will provide an unlimited supply of energy
  that has no wastes to deal with or contaminants
  to harm the atmosphere.
• The 3 problems are temperature, time, containment

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Nuclear Fusion (cont)

• Temperature
• Hydrogen isotopes must be heated to 40,000,000 K
  (hotter than the sun).
• Electrons are goneall thats left is positively
  charged plasma.
• Time
• The plasma needs to be held together for about
  one second at 40,000,000 K.
• Containment
• Everything is a gasceramics vaporize. A
  magnetic field could be used but the plasma leaks
  from those as well.

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Half Life

• A half-life (t1/2) is the time required for
  one-half of the nuclei of a radioisotope sample
  to decay to products.
• Half-lives may be as short as a fraction of a
  second or as long as billions of years.
• This is an example of exponential decay.
• If you want to find times or amounts that are not
  associated with a simple multiple of a half-life,
  you can use this equation
• ln(N0/N) (.6963/t1/2)t
• lnnatural log, N0amnt iso start, Namnt iso
  left
• ttime, t1/2half-life

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Radioactive Dating

• Radioactive dating is a useful application of
  half-lives.
• Carbon-14 is produced in the upper atmosphere by
  cosmic radiation.
• Plants absorb C-14 during photosynthesis.
  Animals eat plants. C-14 is part of the cellular
  structure of all living things.
• As long as an organism is alive, the amount of
  C-14 remains constant.
• When the organism dies, the C-14 begins to
  decrease.
• The half-life of C-14 is 5,730 years.
• For nonliving substances, another isotope is
  used. Usually potassium-40.

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Is this the face of Christ? A new study reignites
the argument that the Shroud of Turin, from which
this impression was taken, is the burial cloth of
Jesus of Nazareth. A 1988 carbon-dating study
determined that a piece of the shroud was created
between A.D. 1260 and 1390. Ever since, the
conventional wisdom has been that the shroud,
which resides in Turin, Italy, was a medieval
fake. But new tests show that the piece that was
tested is of a different material from the rest
of the shroud, says chemist Raymond Rogersit was
a patch added in medieval times. Published in the
journal Thermochimica Acta, the findings greatly
increase the possibility that the shroud may be
as old as Christianity itself.
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Human Exposure to Radiation
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