1. Half-life

2.  Half-Life - the time required for one half of a sample of a radioisotope to decay, while the other half remains unchanged  Half-lives vary greatly depending on the element  Fractions of a second (lithium-5 324 X 10 -24 )  Billions of years (Uranium-238 4.5 billion years

3. Half-life  Unlike chemical reaction rates which change depending upon conditions  Rate of nuclear decay is constant

5. Calculating half-lives elapsed  Half-lives elapsed= Total time of decay/half- life  1 gram sample of iridium-182  Iridium half-life= 15 min.  45 min. have elapsed  45 min. / 15 min = 3 half lives After 45 min. iridium would have been reduced by half 3 times.

6. Calculating…  ½ X ½ X ½ = 1/8  1/8 x 1 gram=.0125 grams of iridium-182

7. Radiocarbon Dating  In radioactive dating, the age of an object is determined by comparing an objects carbon-14 levels with carbon-14 levels in the atmosphere  Half-life carbon-14 is 5,730 years  If the fossil has half the ratio of the atmosphere then the organism lived 5,730 years ago