1. nucleus                7. beta particles
                                                    2. fission                 8. gamma rays
                                                    3. fusion                  9. half-life
                                                    4. radioactive         10. decay
                                                    5. nuclide               11. isotope
                                                    6. alpha particles    12. unstable
                                                                                 13. plasma
 
 

All elements are made of atoms. The nucleus of atoms contain protons and neutrons. A strong nuclear force holds the particles together. The nuclei of some elements, however, are not held together strongly enough, these are said to be unstable.        

UNSTABLE - a nucleus emits a particle or radiation. This process is called radioactive decay. A new nucleus results from this decay, it may be either stable or unstable.

RADIOACTIVE DECAY - process in which unstable nuclei emit a particle or radiation with a large amount of kinetic energy.

RADIOACTIVITY - the emitting of high energy radiation or particles from nuclei of radioactive atoms.

ISOTOPE - atoms of the same element that have different numbers of neutrons in their nucleus.

NUCLIDE - the nucleus of an isotope that has a specific atomic number and atomic mass.
NOTE: Radioactive nuclides have many practical uses. Examples: medical uses, agricultural uses.
 
 

ALPHA PARTICLE - a helium nucleus with two protons and two neutrons (it carries a positive charge). An alpha particle does not have much power to penetrate matter. It can be stopped by a sheet of paper or after traveling through a few centimeters of air. 

BETA PARTICLES - these are negatively charged electrons. The penetrating power of beta particles is about 100 times greater than that of alpha particles. They can be stopped by a sheet of aluminum one centimeter thick. 

GAMMA RAYS - these are charged particles. They are electro-magnetic waves of short wavelength and high frequency traveling at the speed of light. They are very penetrating. It takes dense materials such as lead or concrete to stop them.

HALFLIFE - the time it takes for half of a sample of radioactive material to decay to form another nuclide. Example: If you have 10g of barium-139, it would take 86 minutes for half of the atoms to decay into lanthanum-139, there would be 5g of barium-139 remaining.
 
 

NUCLEAR FISSION - the splitting of the nucleus resulting in the release of neutrons along with a tremendous amount of energy. (Two new nuclei are formed.)

NOTE: This reaction is much more violent than emitting an alpha or beta particle or a gamma ray.

NOTE: Fission takes place under controlled conditions in a nuclear reactor.

NUCLEAR REACTOR - a device for obtaining and using the energy from a controlled (fission) nuclear chain reaction.

NUCLEAR FUSION - occurs when nuclei join together to form a larger nucleus. It occurs only under extremely high temperatures. Example: Two hydrogen nuclei may fuse together under high temperatures to form helium.

Nuclear fusion is called a thermonuclear reaction (thermo refers to heat). At the tremendous temperature of the thermonuclear reactions (over one million degrees celsius) neutral atoms no longer exist. The atoms lose their electrons, ionize and become plasma.
 

PLASMA - the state of matter consisting of nuclei or positive ions free electrons.
NOTE: Plasma occurs on the sun and stars.