Chapter 28 Notes, part II

1. Chapter 28 Notes, part II Half-life Transmutation Transuranium elements

2. Half-life • Every radioisotope has a specific rate of decay. • It is measured by its half life (t1/2); the amount of time it takes for ½ of a sample to decay into new elements.

3. Half-life • Half-lives of isotopes can range from billions of years to fractions of a second. • Uranium-238 vs. Polonium-214

4. Half-Life Formula End amt.=start amt. x ( ) OR End amt.=start amt. x ( ) 12 # half lives Time elapsed length of h.l. 12

5. Problem #1 • Nitrogen-15 decays to carbon-13 with a ½ life of 10 minutes. How long is 3 half lives? • If there is originally 2.00g of nitrogen-15, how much remains at the end of 3 half lives?

6. Problem #2 • Manganese-56 is a b emitter with a half life of 2.6 hours. What is the mass of manganese-56 in an original 1.00mg sample after 10.4 hours?

7. Problem #3 • A sample of thorium-234 undergoes decay with a half life of 25 days. If the original sample is 0.5g how much is left at the end of 50 days?

8. Transmutation • Transmutation is the changing of an atom of one element into an atom of another element. • Radioactive decay (which we have already seen) is a natural transmutation. Many times there is a complex series of reactions that occur as an unstable isotope stabilizes, which is called a reaction series.

9. Transmutation • Other transmutations occur in the laboratory—usually done by bombarding the nucleus of an element with high speed particles in a particle accelerator.

10. Transuranium Elements • All elements above the atomic number 92 are not found in nature; they are formed in particle accelerators and nuclear reactors.