25.1 Nuclear Radiation

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25.1 Nuclear Radiation
California Chemistry Standards
Know that some naturally occurring isotopes of
elements are radioactive. Explain how the
nucleus changes in alpha beta and gamma
decay. Describe the different penetration and
damage associated with each type of radiation
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A. Radioactivity
1895 Roentgen was studying fluorescence some
materials emit light when struck by UV
Some materials fluoresce when struck by cathode
rays (cathode rays are emitted by a charged
cathode in vacuum tube)
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X-rays
Roentgen observed that florescent paper glowed
even when the path of visible light was
blocked He called the mysterious rays X-rays
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X-rays and radiation
Roentgen observed that florescent paper glowed
even when the path of visible light was
blocked He called the mysterious rays X-rays
Becquerel (1896) looking for flourescent minerals
uranium would blacken photographic paper.
Discovered radioactivity (spontaneous emission of
nuclear radiation) Radioactivity originates in
the nucleus of the atom distinct from x-rays and
fluorescence.
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Radiation
Marie and Pierre Curie discovered Polonium and
Radium All uranium-containing compounds are
radioactive.
Radioisotopes- radioactive isotopes Nuclear
reactions not affected by temperature,
pressure, or catalysts. Cannot be speeded up or
slowed down
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B. Types of Radiation1. Alpha Decay

Alpha particle 2 protons and 2 neutrons Same as a
helium-4 nucleus
Alpha radiation is often given off by
radioactive isotopes of elements with atomic
numbers gt83
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B. Types of Radiation1. Alpha Decay

Easily stopped outside the body (by only a few cm
of air) BUT once inside cause great damage
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Alpha Decay

The Orange, N.J. radium dial factory in the
mid-1920s. (Courtesy Argonne National Labs)
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Alpha Decay

On Nov. 1, Alexander Livinenko had two meetings ,
including former KGB officer Andrei Lugovoi and
Russian businessman Dmitry Kovtun The evening of
Nov. 1, Litvinenko grew ill. He was later
hospitalized and immediately thought he had been
poisoned, according to his wife, Marina. On Nov.
23, he died.
A day later, British health authorities announced
that a rare radioactive element, polonium-210,
was found in Litvinenko's urine.
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Alpha Decay


Radium-226
Radon-222
Alpha Particle
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Beta Decay
In beta decay, a fast moving electron (a beta
particle) is released One neutron changes to a
proton and the emitted electron (the beta
particle)
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Beta Decay
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Gamma Radiation
Gamma rayshigh energy electromagnetic
radiation photon no atomic mass or atomic
number Gamma rays can penetrate and travel great
distances, but they do less damage than alpha or
beta rays
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Relative Penatating Power
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25.2 Nuclear Transformations
California Chemistry Standards
Understand protons and neutrons are held
together by nuclear forces overcoming
electromagnetic repulsion. Be able to calculate
the amount of a radioactive substance remaining
after an integral number of half lives have
passed. Identify the lathanide, actinide, and
transactinide elements Know that the
transuranium elements were synthesized and
identified through the use of nuclear accelerators
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25.2 Nuclear Transformations

• Stability and Decay
• Positive protons repel each other
• But held together by nuclear force
• Only significant at VERY short distances

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25.2 Nuclear Transformations
B. Half Life

• The Radioactive Clock
• One half life time for one half of total atoms
  to decay
• At the end of one half life, half of the original
  atoms are present

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Carbon-14 Dating

Carbon-14 is incorporated into living organisms
until they die. Once they die, half of the C-14
decays every 5,730 years. If an organism has
one-fourth the original concentration of C-14,
how long ago did it die? 11,460 years ago
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Carbon-14 Dating

• If an organism has one-fourth the original
  concentration of C-14, how long ago did it die?
• 11,460 years ago

• Half-lives 0 years - 100 of C-14 remains
• 1 Half life 5730 years - 50 of C-14 remains
• 2 Half lives 11460 years 25 of C-14 remains

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The Ice Man

1991 in the Alps
The Ice Man had about half of the C-14 of living
humans. How long ago did he die? 5300 ya
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Sample Problem 25.1 p806
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Sample Problem 25.1 p806
7. 10.4h / 2.6 h/half-life 4 half-lives 1.0
mg/ 24 0.063 mg Mn-56 8. 48.2
da/24.1d/half-life 2 half-lives No, (1/2)2 or
1/4 of the sample will remain
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25.2 C. Transmutation Reactions
Decay or Bombardment 1919 Ernest Rutherford
Nitrogen-14
Fluourine-18
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25.2 C. Transmutation Reactions
Transuranium Elements Atomic number gt 92 All
produced artificially In nuclear reactors or
particle accelerators