Nuclear Chemistry a.k.a. Radiation Duck and cover!

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Nuclear Chemistrya.k.a. RadiationDuck and
cover!
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What do you know?

• All nuclear materials remain highly toxic for
  thousands of years.
• false -Some radioisotopes have-lives of seconds
  or days, while others like plutonium-239 has a
  half-life of 2.4 x 104 years.

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What do you know?

• Man-made radiation is more toxic to humans than
  naturally occurring radiation even if the dose is
  the same.
• false - The body makes no distinction it sees
  radiation as deposited energy regardless of its
  source.

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What do you know?

• The human body has the capability to repair
  damaged caused by exposure to radiation.
• true - Many of the DNA lesions induced by
  ionizing radiation are similar to identical to
  those induced as a consequence of normal
  metabolic activity. DNA repair mechanisms can act
  to reduce the consequences of this damage. 

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What do you know?

• In the US, most cases of cancer in humans are
  known to be caused by man-made radiation.
• false - Most cancers have an unknown cause or
  etiology.

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What do you know?

• I would rather live within a 50 mile radius of a
  coal-burning plant than a nuclear power plant.
• false - Actually a coal burning plant gives off
  slightly more radioactivity due to the thorium
  and uranium content in coal. But in both cases
  the levels are extremely low. 

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What do you know?

• One of the chief dangers from nuclear power
  plants is that they can explode like a nuclear
  bomb.

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• false - There's a big difference between a
  nuclear core and a nuclear bomb. After
  detonation, the density of uranium (or plutonium)
  atoms in a bomb is incredibly high, enough for
  fissions to take place and energy to be released
  in a hundred millionth of a second! So it flies
  apart. The density of atoms in a nuclear core is
  much less, and, even in a meltdown situation
  would generate heat at a much slower rate than is
  necessary to fly apart. The act of meltdown
  actually terminates the explosive process,
  because when a core "melts down" it spreads out
  and goes sub-critical.

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What do you know?

• It is safer to drive behind a tanker truck
  carrying gasoline than a truck load of spent
  nuclear fuel.
• false - People occasionally die in gasoline truck
  accidents, but the DOE and the nuclear industry
  claim that no one has died or been hurt by a
  radiation release due to a nuclear waste
  transportation accident.

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What do you know?

• On average, people are exposed to more radiation
  from nuclear power plants than from radon gas in
  homes.
• false - An individual gets about 200 millirems of
  radiation per year from naturally occurring
  radon. A normally functioning nuclear power plant
  exposes a person to about.01 millirem, if the
  person lives within 50 miles of the plant.

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What do you know?

• Since the construction of the first nuclear power
  plant, man-made radiation in known to have
  resulted in new species of plants and animals.
• false - New species don't occur any more
  frequently today than before nuclear plants were
  built.

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What do you know?

• The fact that nuclear power plants have elaborate
  evacuation plans for the surrounding area
  indicates they are inherently more dangerous than
  other types of plants.

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What do you know?

• false - Evacuation plans have only been around
  since 1980 and are an example of "regulatory
  ratcheting" by the Nuclear Regulatory Commission.
  Other countries do not have these plans. Chemical
  plants do not have evacuation plans even though
  evacuations in their vicinity are more likely to
  be necessary than around a nuclear power plant.
  Most evacuations are due to rail or truck
  accidents involving toxic chemicals.

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The Nucleus

• Remember that the nucleus is comprised of the two
  nucleons, protons and neutrons.
• The number of protons is the atomic number.
• The number of protons and neutrons together is
  effectively the mass of the atom.

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Isotopes

• Not all atoms of the same element have the same
  mass due to different numbers of neutrons in
  those atoms.
• There are three naturally occurring isotopes of
  uranium
• Uranium-234
• Uranium-235
• Uranium-238

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Radioactivity

• It is not uncommon for some nuclides of an
  element to be unstable, or radioactive.
• We refer to these as radionuclides.
• There are several ways radionuclides can decay
  into a different nuclide.

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Types of Radioactive Decay Alpha Decay

• Loss of an ?-particle (a helium nucleus)

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Types of Radioactive Decay Beta Decay

• Loss of a ?-particle (a high energy electron)

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Types of Radioactive Decay Positron Emission

• Loss of a positron (a particle that has the same
  mass as but opposite charge than an electron)

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Types of Radioactive Decay Gamma Emission

• Loss of a ?-ray (high-energy radiation that
  almost always accompanies the loss of a nuclear
  particle)

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Alpha, Beta and Gamma can be separated using an
electric or magnetic field.
Gamma rays and neutrons do not bend in the
electric field.
Positively charged alpha (?) particles move
toward the negative.
Negatively charged beta (?-) particles move
toward the positive.
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Alpha particles have the lowest penetrating
power, gamma the highest.
Alpha particles wont pass through paper.
Alpha particles have the highest ionizing power.
They knock off electrons and leave a trail of
ions as they pass through the air.
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Page 5

• Homework Read Page 5 and answer page 6 in packet.

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Stable Nuclei

• There are no stable nuclei with an atomic number
  greater than 83.
• These nuclei tend to decay by alpha emission.

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Nuclear Equations

• Just like a math equation.
• Both sides must equal.
• Remember there are six decay modes.

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Example 1
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Example 2
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Example 3
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Page 8 Questions

• Homework finish page 8

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Radioactive Series

• Large radioactive nuclei cannot stabilize by
  undergoing only one nuclear transformation.
• They undergo a series of decays until they form a
  stable nuclide (often a nuclide of lead).

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Nuclear Fission

• How does one tap all that energy?
• Nuclear fission is the type of reaction carried
  out in nuclear reactors.

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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 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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Page 10

• Which type of reaction occurs in a nuclear power
  plant and in an atomic bomb?
• Which type of reaction occurs in stars such as
  the sun?
• How is fission different than alpha or beta
  decay?
• What characteristic of fission makes a chain
  reaction possible?
• If fusion releases more energy than fission, why
  isnt fission used as a source of energy on
  earth?
• What is the fuel that runs fusion in stars?
• Why is fusion only possible with small nuclei?

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Page 11
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Half Life(no,not middle age)

• The half-life of a radioactive nuclide is the
  amount of time it takes for half of that nuclide
  to decay into a stable nuclide.

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The half-life of Carbon-14 is 5730 years

• After 5730 years, ½ the mass of an original
  sample of Carbon-14 remains unchanged.
• After another 5730 years, ¼ (half of the half) of
  an original sample of Carbon-14 remains
  unchanged.
• The half-life of a radioactive nuclide cannot be
  changed.

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Regents Question
As a sample of the radioactive isotope 131I
decays, its half-life (1) decreases (2)
increases (3) remains the same
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How to determine how much of a radioactive
isotopes remains unchanged after a period of
time.

• Determine how many half-lives have gone by
  (Time/half-life)
• Halve the mass of the starting material for each
  half-life period that goes by.
• How much of a 20.g sample of 131I remains
  unchanged after 24 days?
• The half-life period is 8 days so 24 days is 3
  half-lives. Half the mass three times.
• 20.g 10.g 5.0g
  2.5g

8 days
8 days
8 days
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Regents Question

• Exactly how much time must elapse before 16 grams
  of potassium-42 decays, leaving 2 grams of the
  original isotope?
• 8 x 12.4 hours
• (2) 2 x 12.4 hours
• (3) 3 x 12.4 hours
• (4) 4 x 12.4 hours

16 ? 8 ? 4 ? 2
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Page12

1. What is the half-life of a 100.0 g sample of
   nitrogen-16 that decays to 12.5 grams in 21.6
   seconds?

21.6/37.2
Mass(g) Time Elapsed Half-Life Fraction Percent
100 0 0 1 100
50 7.2 1 1/2 50
25 14.4 2 1/4 25
12.5 21.6 3 1/8 12.5
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Benefits of Radioactive isotopes

• Tracers are used to follow the course of
  chemical (organic) or biological reactions
• (C-14)
• Medical isotopes (radioactive), with short
  half-lives are quickly eliminated from body
• Technetium-99 pinpoints brain tumors
• Iodine-131 diagnosis and treatment of thyroid
  disorders
• Radium and Cobalt-60 treatment of cancer

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Benefits of Radioactive isotopes

• Food can be stored longer because radiation kills
  bacteria, yeast and molds
• Radioactive dating
• Geologic dating is based on half-life.
  Uranium-238 occurs naturally in rock.
• Dating living materials (organisms that were
  previously alive). The ratio of C-14 to C-12 can
  determine the age of a sample.
• Nuclear Power produces electricity

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Benefits of Radioactive isotopes

• Nuclear Power produce electricity
• Industrial Measurement a beam of subatomic
  particles (alpha, beta or gamma) is blocked by a
  metal of a certain thickness. Measuring the
  fraction of the beam that is blocked determines
  the thickness of the metal.

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Risks of Radioactive isotopes

• Biological Damage exposure to radiation can
  damage cells, or an organism. When sex cells
  are damaged, offspring may be affected.
• Long term storage it is not known if storing
  radioactive isotopes is safe.
• Accidents cause fuel to escape nuclear reactors
  (earthquake in Japan).