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What happens to an unstable nucleus?
• They will undergo decay
• The type of decay depends on the reason for the instability
Radioactive Half-Life (t1/2 ):
• The time for half of the radioactive nuclei in a given sample to undergo decay.
Common Radioactive Isotopes
Isotope Half-Life Radiation Emitted
Carbon-14 5,730 years , b g
Radon-222 3.8 days a
Uranium-235 7.0 x 108 years , a g
Uranium-238 4.46 x 109 years a
Radioactive Half-Life
• After one half life there is 1/2 of original sample left.
• After two half-lives, there will be 1/2 of the 1/2 = 1/4 the original sample.
Example
You have 100 g of radioactive C-14. The half-life of C-14 is 5730 years.
• How many grams are left after one half-life? Answer:50 g
• How many grams are left after two half-lives?
Formula
Amount Remaining = (Initial Amount) x (1/2)n
Where: n = to the number of half lives
You can calculate n by taking the elapsed time and dividing it by the duration of a half life of the substance.