The Half Life of Radioactive Materials

Many substances have an unstable nucleus that might emit alpha or beta particles. Radium-226 is an example of an unstable nuclear material that will change over time to a stable nucleus. Radium was at one time used in paint for watches. The radium would decay and emit particles which would strike other materials in the paint which would then emit a small amount of light. The light was very dim, but visible in a darken area. It would appear like small twinkles of light which would appear and disappear quickly. Larger watches like pocket watches had more radium and were later banned. It was thought that the increased radiation produced and the proximity of the pocket watch to male reproductive organs would pose a significant threat of gene mutation. It was also found that workers painting the dials were becoming ill from radiation poisoning from contact with the radioactive materials. (Some were touching the tip of the brush to their tongue to make a pointier tip.)

The radioactive material will have a point at which one half of the radiation will have been emitted and this is the half life for that substance. The half life can be a little as fractions (nanoseconds) of a second or into the millions or even billions of years. Because the half life of materials used in nuclear reactors is so long the disposal of used but still highly radioactive spent materials is a critical concern to all nations. These materials must be placed in some location and then sealed in such a way that the materials will stay out of the environment for centuries. The need for more energy and the proposal to build more nuclear reactors is bound to create a lot of controversy in the future.

Carbon 14 is a radioactive material that is used to help determine the age of materials. Any living thing incorporates carbon into its body and the carbon could be normal carbon or radioactive carbon 14. When the organism dies it no longer takes in carbon 12 or carbon 14, but the carbon 14 that was present at death will continue to decay. With a half life of 5715 years calculations can be made that will date materials that were once living back in time, but as we go back past 50,000 years the accuracy of such dating gets much less accurate because that is over 10 times the half life of Carbon 14.

Students can be given a jar with a large number of pennies (1000) and then told that the jar of pennies has a half life of one week. They can take 500 pennies out of the jar and this would represent the amount of pennies left after one week. For the second week they would take out 250 pennies and this would represent the half life of the 500 pennies for a second week. It would not take long for students to realize that a half life of one week would result in no pennies in a relatively short time.