Nuclear Reactions

1
Nuclear Reactions Decay

• CPS Chemistry
• Ch.22

2
Nuclear Binding Energy

• A nucleus is stable if it has a certain ratio of
  neutrons to protons. It becomes unstable if the
  ratio is below 1 proton to 1 neutron, or is
  higher than 1.5 neutrons to 1 proton
• Remember, the protons are positive charges, that
  left alone would repel each other. The neutrons
  are the rubber bands that hold the nucleus
  together

3
Band of stability
4
Nuclear Reactions

• Unstable nuclei undergo spontaneous changes that
  will alter the number of protons and/or neutrons
  in doing so, this process gives off energy
• Mass must be conserved and accounted for

5
Nuclear Reactions cont.
Atomic Mass
PTE Abbreviation
Atomic Number
6
Nuclear Reaction cont.
The total atomic mass on the right must equal the
atomic mass on the left
4
Pb
He

2
The total atomic number on the right must equal
the atomic number on the left
7
Nuclear Reaction cont.
The total atomic mass on the right must equal the
atomic mass on the left
208
4
Pb
He

82
2
The total atomic number on the right must equal
the atomic number on the left
8
Nuclear Reaction cont.
The total atomic mass on the right must equal the
atomic mass on the left
4
He

2
The total atomic number on the right must equal
the atomic number on the left
9
Nuclear Reaction cont.
The total atomic mass on the right must equal the
atomic mass on the left
230
4
Th
He

90
2
The total atomic number on the right must equal
the atomic number on the left
10
Radioactive Decay

• Alpha Particle (a) is two protons and two
  neutrons bound together and is emitted from the
  nucleus during some kinds of radioactive decay
• Alpha emission is limited to very heavy nuclei

208
4
Pb
He

82
2
11
Radioactive Decay

• Beta emission occurs when there are too many
  neutrons in a nucleus. The neutron can be split
  into a proton and an electron, or beta particle,
  (ß)

12
Radioactive Decay

• Positron emission when there are too many
  protons, protons can be converted into a neutron
  by emitting a positron
• Positrons are particles with the same mass as an
  electron, but have a positive charge

13
Radioactive Decay

• Electron Capture If a nucleus captures a
  electron from one of its inner orbitals, it
  combines with a proton to form a neutron

14
Radioactive Decay

• Gamma Emission different from the other types
  of radioactive decay because it is NOT an
  emission of particles, but an emission of high
  energy electromagnetic waves

15
Half-Life

• Since radioactive decay happens over time, we use
  half-life as a measure for the time it takes ½ of
  the original sample to decay into new particles

16
Half-Life

• Example March Madness (Basketball)
• If you count only the days games are played, than
  every 2 days the number of teams is cut in half
• 64 teams?32?16?8?4?2?1
• 6 half lives

17
Half Life
Sample Size Half life Total time Number of Half Lives
64 2 days 0 days 0
32 2 days 2 days 1
16 2 days 4 days 2
8 2 days 6 days 3
4 2 days 8 days 4
2 2 days 10 days 5
1 2 days 12 days 6
18
Half-Life

• How long will it take for there to be 7.8 grams
  of a sample of radioactive iodine, needed for
  medical testing, if the half-life is 14 days and
  the original sample is 1 kilogram?
• Hint first start by converting to grams

19
Half-life
Sample Size Half life Total time Number of Half Lives
1000 g 14 days 0 days 0
500 g 14 days 14 days 1
250 g 14 days 28 days 2
125 g 14 days 42 days 3
62.5 g 14 days 56 days 4
31.3 g 14 days 70 days 5
15.6 g 14 days 84 days 6
7.8 g 14 days 98 days 7
20
Nuclear Fission

• Heavy nuclei split into more stable, lighter
  nuclei and neutrons while releasing energy.

21
Nuclear Fusion

• The process where lighter nuclei combine to form
  heavier nuclei

22
Nuclear power plants

• Run on uranium fuel.
• In the reactor, uranium atoms are split through
  a process known as fission.
• When atoms are spilt, they produce a large amount
  of energy that is then converted to heat.
• The heat boils water, creating steam that is used
  to turn turbines, which spins the shaft of a
  generator.

23

• Schematic of a Nuclear Power Plant

24
Inside the generator

• coils of wire spin in a magnetic field and
  electricity is produced.
• Nuclear power plants in the United States use two
  types of reactors to achieve this process
  boiling water reactors and pressurized water
  reactors.

25
How a Nuclear Power Plant Works

• http//www.youtube.com/watch?vcnjGYHOePu0