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Radioactivity and Nuclear Reactions
Radioactivity
• Radioactive elements
All elements beyond #83 are radioactive, but
isotopes of many others are also.
The nuclei of radioactive elements are unstable.
Radioactivity is the emission of high energy
radiation or particles from the nucleus of an
unstable atom.
• A nuclide is the nucleus of an isotope with a certain
atomic number and mass.
Represented by atomic notation
Stability of nuclides
Less massive elements are stable if their
neutron – proton ratio is about 1 to 1.
More massive elements are stable if their
neutron – proton ratio is about 3 to 2.
Nuclear Decay
• Types of nuclear radiation
Alpha particles
The same as a helium nucleus
Has the least penetrating power (can be stopped
by paper)
Has a charge of +2 and a mass of 4 amu.
Beta particles
A very high speed electron
Has moderate penetrating power (can be
stopped by aluminum foil)
Has a charge of -1 and virtually no mass (0 amu)
Gamma rays
Electromagnetic waves of the highest energy
Has the highest penetrating power (can be
stopped by lead or thick concrete)
Has no charge and no mass
• Transmutation
Transmutation is the process of one element
changing into another by nuclear decay of
alpha or beta particles
Alpha decay causes a decrease in the atomic
number by 2 and the mass number by 4.
Beta decay causes no change in the mass
number, but the atomic number increases by 1
(a neutron decays into a proton & an electron)
• Half-life is the amount of time it takes for half of
the nuclides in a radioactive sample to decay
Vary widely by element
Carbon-14 is 5730 years
Uranium-238 is 4.5 billion years
Polonium-214 is 0.001 second
• Radioactive dating is a method to find the
approximate age of something based on
measuring the percentage of a radioactive
nuclide remaining in a sample
Nuclear reactions
• Nuclear fission
Fission is the process of splitting a large,
unstable nucleus into two smaller nuclei.
Either 2 or 3 neutrons are also produced with
the products; these neutrons act as “bullets” to
ram into other unstable nuclei and split them,
resulting in a chain reaction.
All nuclear reactors in the world are fission reactors.
They cannot “blow up” like an atom bomb.
They produce radioactive waste which must be
stored safely.
• Nuclear fusion
Fusion is the process of combining two
smaller nuclei into one larger one.
This process requires tremendous amounts of
heat.
It has been impossible to control fusion (so
far).
Fusion would be much better than fission.
It produces many times more energy.
It has virtually no harmful radioactive
waste.