Radioactivity

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Radioactivity
Henri Becquerel discovered X-rays in 1896. As a
result of his experiments, he also discovered
other forms of rays that could be emitted that
had not previously been detected. If you are
interested in his research, read pages 266 267
in your textbook.
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The Nature of Nuclear Radiation

• Nuclear Radiation cannot be seen, but they have
  certain characteristics
• Radiation alters photographic film
• Radiation produces fluorescence
• Electric charge can be detected
• Radiation damages cells in most organisms

3

• Radioactivity is the release of nuclear radiation
  in the form of particles and rays from a
  radioactive element.
• Types of Radiation
• Alpha particles
• Beta particles
• Gamma rays

4
Brain Break
Turn to your partner and list the 3 types of
radiation.
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Alpha Particles

• Nucleus of a helium atom with 2 protons and 2
  neutrons
• Has a positive charge because it has no
  electrons
• Weakest form of nuclear radiation
• Alpha particles can burn skin
• Alpha particles can be stopped by a piece of
  paper
• Uses the symbol a

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Beta Particles

• Beta particles are an electron that is formed
  inside the nucleus when a neutron breaks apart
• Can penetrate 100 times greater than alpha
  particles
• Can pass through 3 mm of aluminum
• Uses the symbol ß

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Gamma Rays
Gamma Rays

• Gamma rays are electromagnetic waves of
  extremely high frequency and short wavelength
• Gamma rays carry much more energy than visible
  light
• Most penetrating radiation given off by
  radioactive elements
• Can pass through several centimeters of lead
• Uses the symbol ?

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Gamma Rays
Brain Break
Tell your partner one thing about alpha
particles, beta particles, and gamma rays.
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Gamma Rays
Nuclear Stability

• Nuclear strong force holds protons and neutrons
  together in the nucleus.
• The energy associated with this is called
  binding energy.
• This energy is essential to the stability of an
  atom.
• Some elements do not have stable nuclei. The
  unstable nucleus will come apart. These elements
  are referred to as radioactive.

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Gamma Rays
Nuclear Stability

• An unstable nucleus can become stable by
  undergoing a nuclear reaction or change.
• There are 3 types of radioactive decay.
• Alpha decay
• Beda decay
• Gamma decay

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Gamma Rays
Alpha Decay

• Occurs when a nucleus releases an alpha
  particle (2 protons and 2 neutrons)
• This decreases the mass by 4 but the number of
  protons is only reduced by 2. Because of this,
  the original element is no longer the same.
• Example Uranium 238 undergoes alpha decay.
  The 238 represents the mass. The atomic number
  of uranium is 92. When it undergoes alpha decay,
  it becomes thorium (Th) which is the element with
  the atomic number 90 since uranium lost 2
  protons.

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Gamma Rays
Beta Decay

• A beta particle is an electron formed inside
  the nucleus when a neutron breaks apart. A
  proton also is produced when a neutron breaks
  apart.
• Beta decay occurs when a beta particle is
  released from a nucleus.
• When beta decay occurs an element with a mass
  number one higher is formed because during beta
  decay, the element gains a proton.
• The process in which one element is changed
  into another as a result of changes in the
  nucleus is called transmutation.

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Gamma Rays
Gamma Decay

• When a gamma ray is emitted by a nucleus, the
  nucleus does not change into a different nucleus.
• A gamma ray is an extremely high-energy wave.
• In gamma decay, the nucleus makes a transition
  to a lower energy state.

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Gamma Rays
Brain Break

• When radium-226 undergoes alpha decay, what
  does it become?
• When radium-226 undergoes beta decay, what does
  it become?

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Gamma Rays
Radioactive Half-Life

• Half-life is the fixed rate of decay of a
  radioactive element.
• Carbon-14 has a half-life of 5,730 years. If I
  had a 22 g sample of carbon-14, I would only have
  11 g left after 5,730 years. I would then after
  11,460 years, I would only have 5.5 g left.
• Barium-139 has a half-life of 86 minutes. If I
  had 20 g of barium-139, after 86 minutes, I would
  only have 10 g left. After 172 minutes, I would
  only have 5 g left. After 258 minutes, I would
  only have 2.5 g left.

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Gamma Rays
Nuclear Fission

• Nuclear fission is the splitting of an atomic
  nucleus into two smaller nuclei of almost equal
  mass.
• Fission does not occur spontaneously like
  radioactive decay.
• When an atom undergoes fission, the amount of
  energy released from one atom is not that great.
  The neutrons released, however, are capable of
  splitting other atoms. This creates a nuclear
  chain reaction in which billions of fission
  reactions can occur each second. This produces
  huge amounts of energy.
• Nuclear power plants use controlled fission
  reactions to produce energy.

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Gamma Rays
Nuclear Fusion

• Nuclear fusion is the joining of two atomic
  nuclei of smaller masses to form a single nucleus
  of larger mass.
• For fusion to occur, the temperature must be
  well over a million degrees Celsius. At
  temperatures this hot, plasma is formed. Plasma
  consists of positively charged ions, which are
  the nuclei of original atoms, and free electrons.
• The energy released in fusion reactions is far
  greater than that released in fission reactions.
  Fusion reactions produce less radioactive waste,
  and possible fuels for fusion are more plentiful.
• Fusion reactions are more difficult to begin,
  to control, and to maintain than fission
  reactions.

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Gamma Rays
Brain Break

• Define fission
• Define fusion
• Calculating half life The half-life of Pa-234
  is 6.75 hours. How much of a 12.5 g sample
  remains after 20.25 hours?

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Gamma Rays
Instruments to Detect Radioactivity

• Electroscope
• Geiger counter
• Cloud chamber
• Bubble chamber

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Gamma Rays
Radioactivity in our Lives

• Carbon dating of organic materials
• Finding leaks or weak spots in metal pipes
• Medical testing
• MRI scans
• Used to destroy unhealthy cells that cause
  cancer
• Killing bacteria that cause food to spoil

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Gamma Rays
Dangers of Radiation

• The same radiation used to treat diseases can
  also cause diseases.
• Damage to biological tissueespecially DNA
• Reddening of the skin and a drop in white blood
  cell count, nausea, fatigue, and loss of hair.
• Exposure can be fatalthis was the cause of
  Marie Curies death in 1934.
• Metal structures can be weakened.