Nuclear Chemistry

1
Nuclear Chemistry

• A subfield of chemistry dealing with
  radioactivity, nuclear processes and nuclear
  properties

2
History of Nuclear Chemistry

• Traditional chemical reactions occur as a result
  of the interaction between valence electrons
  around an atom's nucleus.
• In 1896, Henri Becquerel expanded the field of
  chemistry to include nuclear changes when he
  discovered that uranium emitted radiation.
• Soon after Becquerel's discovery, Marie
  Sklodowska Curie began studying radioactivity and
  completed much of the pioneering work on nuclear
  changes. Curie found that radiation was
  proportional to the amount of radioactive element
  present, and she proposed that radiation was a
  property of atoms (as opposed to a chemical
  property of a compound).
• Marie Curie was the first woman to win a Nobel
  Prize and the first person to win two (the first,
  shared with her husband Pierre and Becquerel for
  discovering radioactivity the second for
  discovering the radioactive elements radium and
  polonium).

3
Radiation and Nuclear Reactions

• In 1902, Frederick Soddy proposed the theory that
  "radioactivity is the result of a natural change
  of an isotope of one element into an isotope of a
  different element."
• Nuclear reactions involve changes in particles in
  an atom's nucleus and thus cause a change in the
  atom itself. All elements heavier than bismuth
  (Bi) (and some lighter) exhibit natural
  radioactivity and thus can "decay" into lighter
  elements.
• Unlike normal chemical reactions that form
  molecules, nuclear reactions result in the
  transmutation of one element into a different
  isotope or a different element altogether
  (remember that the number of protons in an atom
  defines the element, so a change in protons
  results in a change in the atom).
• There are three common types of radiation and
  nuclear changes

4
Alpha Radiation (a)

• The emission of an alpha particle from an atom's
  nucleus. An a particle contains two protons and
  two neutrons (and is similar to a He nucleus
  ). When an atom emits an a particle, the atom's
  atomic mass will decrease by four units (because
  two protons and two neutrons are lost) and the
  atomic number (z) will decrease by two units. The
  element is said to "transmute" into another
  element that is two z units smaller. An example
  of an a transmutation takes place when uranium
  decays into the element thorium (Th) by emitting
  an alpha particle, as depicted in the following
  equation
• 238 ? 4 234
• 92 2 90
• (Note in nuclear chemistry, element symbols are
  traditionally preceded by their atomic weight
  (upper left) and atomic number (lower left).

He
Th
U
5
Beta Radiation (ß)

• The transmutation of a neutron into a proton and
  a electron (followed by the emission of the
  electron from the atom's nucleus -1 ).
  When an atom emits a ß particle, the atom's mass
  will not change (since there is no change in the
  total number of nuclear particles), however the
  atomic number will increase by one (because the
  neutron transmutated into an additional proton).
  An example of this is the decay of the isotope of
  carbon named carbon-14 into the element
  nitrogen
• 14 ? 0 14
• 6 -1 7

0 e
e
N
C
6
Gamma Radiation (?)

• Involves the emission of electromagnetic energy
  (similar to light energy) from an atom's nucleus.
  No particles are emitted during gamma radiation,
  and thus gamma radiation does not itself cause
  the transmutation of atoms, however ? radiation
  is often emitted during, and simultaneous to, a
  or ß radioactive decay. X-rays, emitted during
  the beta decay of cobalt-60, are a common example
  of gamma radiation.

7
Half-Life

• Radioactive decay proceeds according to a
  principal called the half-life. The half-life
  (T½) is the amount of time necessary for one-half
  of the radioactive material to decay. For
  example, the radioactive element bismuth (210Bi)
  can undergo alpha decay to form the element
  thallium (206Tl) with a reaction half-life equal
  to five days.
• If we begin an experiment starting with 100 g of
  bismuth in a sealed lead container, after five
  days we will have 50 g of bismuth and 50 g of
  thallium in the jar. After another five days (ten
  from the starting point), one-half of the
  remaining bismuth will decay and we will be left
  with 25 g of bismuth and 75 g of thallium in the
  jar. As illustrated, the reaction proceeds in
  halfs, with half of whatever is left of the
  radioactive element decaying every half-life
  period.

                                                                                                      
8

• The fraction of parent material that remains
  after radioactive decay can be calculated using
  the equation
• Fraction remaining   1  2n ( n
  half-lives elapsed)
• The amount of a radioactive material that remains
  after a given number of half-lives is therefore
• Amount remaining Original amount Fraction
  remaining
• The decay reaction and T½ of a substance are
  specific to the isotope of the element undergoing
  radioactive decay. For example, Bi210 can undergo
  a decay to Tl206 with a T½ of five days. Bi215,
  by comparison, undergoes b decay to Po215 with a
  T½ of 7.6 minutes, and Bi208 undergoes yet
  another mode of radioactive decay (called
  electron capture) with a T½ of 368,000 years!

9
Stimulated Nuclear Reactions

• While many elements undergo radioactive decay
  naturally, nuclear reactions can also be
  stimulated artificially. Although these reactions
  also occur naturally, we are most familiar with
  them as stimulated reactions. There are two such
  types of nuclear reactions

10
Nuclear Fission

• Reactions in which an atom's nucleus splits into
  smaller parts, releasing a large amount of energy
  in the process. Most commonly this is done by
  "firing" a neutron at the nucleus of an atom. The
  energy of the neutron "bullet" causes the target
  element to split into two (or more) elements that
  are lighter than the parent atom.
• During the fission of U235, three neutrons are
  released in addition to the two daughter atoms.
  If these released neutrons collide with nearby
  U235 nuclei, they can stimulate the fission of
  these atoms and start a self-sustaining nuclear
  chain reaction. This chain reaction is the basis
  of nuclear power. As uranium atoms continue to
  split, a significant amount of energy is released
  from the reaction. The heat released during this
  reaction is harvested and used to generate
  electrical energy.
• Two Types of Chain Reactions

11
Nuclear Fusion

• Reactions in which two or more elements "fuse"
  together to form one larger element, releasing
  energy in the process. A good example is the
  fusion of two "heavy" isotopes of hydrogen
  (deuterium H2 and tritium H3) into the element
  helium.
• Fusion reactions release tremendous amounts of
  energy and are commonly referred to as
  thermonuclear reactions.  Although many people
  think of the sun as a large fireball, the sun
  (and all stars) are actually enormous fusion
  reactors.  Stars are primarily gigantic balls of
  hydrogen gas under tremendous pressure due to
  gravitational forces.  Hydrogen molecules are
  fused into helium and heavier elements inside of
  stars, releasing energy that we receive as light
  and heat.
• Nuclear Fusion Simulation