chapter 28 notes, part ii

Chapter 28 Notes, Chapter 28 Notes, part IIpart IIHalf-lifeHalf-life

TransmutationTransmutation

Transuranium elementsTransuranium elements

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.

Half-life• Half-lives of isotopes can range

from billions of years to fractions of a second.–Uranium-238 vs. Polonium-214

Half-Life Formula

End amt.=start amt. x ( )OREnd amt.=start amt. x ( )

12

# half lives

12

Time elapsed length of h.l.

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?

Problem #2• Manganese-56 is a 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?

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?

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.

Transmutation• Other transmutations occur in

the laboratory—usually done by bombarding the nucleus of an element with high speed particles in a particle accelerator.

Transuranium Elements• All elements above the atomic

number 92 are not found in nature; they are formed in particle accelerators and nuclear reactors.