Discovery of Radiation

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NUCLEAR CHEMISTRY
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Discovery of Radiation
Roentgen (1895)

• Studied fluorescent materials that glowed when
  hit with a beam of electrons.

• Discovered a mysterious form of radiation was
  given off even without electron beam. This
  radiation could pass through paper and other
  objects but not dense materials (lead, bone).

• Called them X-rays

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Becquerel (1896)

• Studied fluorescent minerals containing uranium.

• Discovered radioactivity by accident on a cloudy
  day

• Thought that an external source was needed to
  produce the mysterious radiation.

• Found that uranium emits radiation without
  external source.

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Pierre and Marie Curie
Thought radioactivity was a property of heavy
elements.
During study, discovered new radioactive
elements Polonium and Radium.
Wondered how small mass can give off large amount
of energy
Explained by Einstein with Emc2.
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Rutherford

• Studied radioactivity and named types of nuclear
  radiation.

• Discovered that elements decay into other
  elements after emitting nuclear radiation. Called
  it Nuclear Decay.

• Gold foil experiment revealed that the mass of an
  atom is concentrated in the nucleus (atom is
  mostly space)

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Nuclear Forces

• Electric repulsion ________ charge particles
  repel each other

same

• Strong Nuclear Force causes protons and
  neutrons to ________ each other

attract

• Stable Nuclei strong nuclear force is ________
  than repulsion force

greater

• Unstable Nuclei strong nuclear force is
  ________ than repulsion force

less

• Have too many or too few neutrons in nucleus
• Have more than 83 protons in nucleus
• Will undergo radioactive decay to form a more
  stable nucleus

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Nuclear Decay

• Why nuclides decay
• need stable ratio of neutrons to protons

• Transmutation-One element becomes another.

More than 83 protons means that the nuclei is
unstable (radioactive)
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Nuclear Symbol

• Where mass number protons neutrons
• X element symbol
• Atomic protons

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Types of Radiation
Charge
Shielding

• Alpha particle (?)
• helium nucleus

2
paper

• Beta particle (?-)
• electron

1-
lead

• Positron (?)
• positron

1
concrete

• Gamma (?)
• high-energy photon

0
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Alpha Emission
occurs when the nucleus has too many protons
which cause excessive repulsion.
Numbers must balance!!
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Alpha Emission
Ex. Plutonium-239 undergoes alpha decay



239
235
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Atomic Mass


92
94
2
Atomic
Masses must be equal Conservation of mass
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Alpha Emission
Ex. Polonium-210 undergoes alpha decay to produce
this daughter nuclide

Atomic Mass
Atomic

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Beta Emission
Occurs when the neutron to proton ratio is too
great (too many neutrons). A neutron breaks down
to form a proton and an electron, beta particle,
which is ejected.
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Beta Emission
Ex. Polonium-210 undergoes beta decay to produce
this daughter nuclide

Atomic Mass
Atomic

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Positron Emission
Occurs when the neutron to proton ratio is too
small (too many protons). A proton changes into
a neutron and a positron (a.k. antimatter) which
is ejected.
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Positron Emission
Ex. Polonium-210 undergoes positron emission to
produce this daughter nuclide

Atomic Mass
Atomic

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Electron Capture
Occurs when the neutron to proton ratio in the
nucleus is too small (too many protons). An inner
orbital electron is captured by a proton which
turns into a neutron.
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Electron Capture
Ex. Polonium-210 captures an electron to produce
this daughter nuclide

Atomic Mass
Atomic

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Gamma Emission
occurs when the nucleus is at too high an energy.

• Emission of high energy electromagnetic wave.

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Gamma Emission
High energy electromagnetic radiation no mass
no atomic number.

Atomic Mass
Atomic

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Write Nuclear Equations!

• Write the nuclear equation for the beta emitter
  Co-60.