Radioactivity and Nuclear Reactions

A.  Radioactivity

1.  Radioactive elements

a.  All elements beyond #83 are radioactive, but isotopes of many others are, also.

b.  The nuclei of radioactive elements are unstable.

c.  Radioactivity is the emission of high energy radiation or particles from the nucleus of an unstable atom.

2.  A nuclide is the nucleus of an isotope with a certain atomic number and mass.

a.  Represented by atomic notation.

b.  Stability of nuclides:

1)  Less massive elements are stable if their neutron-proton ration is about 1 to 1.

2)  More massive elements are stable if their neutron-proton ratio is about 3 to 2.

B.  Nuclear Decay

1.  Types of nuclear radiation:

a.  Alpha particles

1)  The same as a helium nucleus.

2)  Has the least penetrating power (can be stopped by paper).

3)  Has a charge of +2 and a mass of 4 amu.

b.  Beta particles

1)  A very high speed electron.

2)  Has moderate penetrating power (can be stopped by aluminum foil).

3)  Has a charge of -1 and virtually no mass (0 amu).

c.  Gamma rays

1)  Electromagnetic waves of the highest energy.

2)  Has the highest penetrating power (can be stopped by lead or thick concrete).

3)  Has no charge and no mass.

2.  Transmutation

a.  Transmutation is the process of one element changing into another by nuclear decay of alpha or beta particles.

b.  Alpha decay causes a decrease in the atomic number by 2 and the mass number by 4.

c.  Beta decay causes no change in the mass number, but the atomic number increases by 1.

3.  Half-life is the amount of time it takes for half the nuclides in a radioactive sample to decay.

a.  Vary widely by element.

b.  Carbon-14 is 5730 years.

c.  Uranium-238 is 4.5 billion years.

d.  Polonium-214 is 0.001 second.

4.  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.

C.  Nuclear Reactions

1.  Nuclear fission

a.  Fission is the process of splitting a large, unstable nucleus into two smaller nuclei.

b.  Either 2 or 3 neutrons are also produced with the products.

c.  These neutrons act as "bullets" to ram into other unstable nuclei and split them, resulting in a chain reaction.

d.  All nuclear reactors in the world are fission reactors.

1)  They cannot "blow up" like an atom bomb.

2)  They produce radioactive waste which must be stored safely.

2.  Nuclear fusion

a.  Fusion is the process of combining two smaller nuclei into one larger one.

b.  This process requires tremendous amounts of heat.

c.  It has been impossible to control fusion (so far).

d.  Fusion would be much better than fission.

1)  It produces many times more energy.

2)  It has virtually no harmful radioactive waste.

D.  Nuclear Medicine

1.  Tracers are radioisotopes that are put into a person's body to allow doctors to easily monitor a bodily process.

2.  Ionizing radiation therapy can be used to kill cancerous cells, but has side effects.