A is for Atom A is for Atom

25.2 Half-Life of Radioisotopes Half-Life t1/2 is the time it takes for half ½ of the amount of a radioisotope to decay and become a new element

Example fossil dating The t1/2 for C-14 is 5700 years At t=0 years a fossil has is 3 g of C-14 At t=5700 years there is now ____ g At t = 11,400 years there is now ____ g At t = ______ years there is now _____ g

Half-Life Curve

Concentration of old and new elements

Half-lives of famous isotopes… Sodium-24 15 hours Iodine-131 8.07 days Hydrogen-3 12.3 years Carbon-14 5700 years Uranium-238 4.5 billion years

Practice Write the beta decay for Sodium-24. What new isotope is formed? How much new isotope is formed after 45 hours? How much old isotope is left after 45 hours?

Journal How much old isotope is present after 5 half lives in % and in fraction How much new isotope is present? Which isotopes from your list would you choose for fossils that are 500 years 5000 years 1 billion years