Half-life

Half-life 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

Half-life Unlike chemical reaction rates which

change depending upon conditions Rate of nuclear decay is constant

http://ch302.cm.utexas.edu/images302/half-life-graph.jpg

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.

Calculating…

½ X ½ X ½ = 1/8

1/8 x 1 gram= .0125 grams of iridium-182

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