HalfLives
Calculations Worksheet 

1.  What is meant by the term halflife? 
2.  Strontium90 has a halflife of 28 years. How long will it take for all of the strontium90 presently on earth to be reduced to 1/32 of its present amount? 
3.  The halflife of cesium137 is 30 years. Of an initial 100 g sample, how much cesium137 will remain after 300 years? 
4.  You are at a dinner party and your host brings out a bottle of brandy for which he paid a great deal of money because he was told that it was bottled in the time of Napoleon (17691821). Since you are a research chemist you are asked if there is any way in which the age of the brandy can be determined. You assert that tritium(H^{3}) dating is the way to do it. Ordinary water contains a very small amount of tritium that is formed in the earth's atmosphere by reactions involving cosmic rays. Tritium disintegrates by betaemission at a rate equal to that at which it is formed. Water exposed to the atmosphere will contain a constant tritium content. Since brandy contains water, it should be possible to estimate its age. Since tritium in the bottle will not be replaced after it decays, the older the brandy, the lower its tritium content should be. You agree to test a sample of your host's brandy. You find that the sample has a tritium content of 30.6% of that of presentday water. How long ago was the brandy bottled? t_{½} for H^{3} = 12.3 years 
5.  A 24.0 g sample of Ra226 is supplied to a lab in the year 2000. In the year 2040, it is noted that only 20.0 g of Ra226 remains. What is the halflife of Ra226? 
6.  If radioactive wastes must be stored for seven halflives before
disposal a) how long must P32 be held? b) what fraction of the P32 originally set side remains after this time? 
7.  Woven rope sandals found in a cave in Oregon were analyzed by radiocarbon dating methods. The specific activity of the carbon was found to be 4.55 g^{1} min^{1}. What is the age of these sandals? 