1. Time it takes for 1/2 of the radioactive atoms in a sample to decay.
1/2 life
Time it takes for 1/2 of the radioactive atoms in a sample to decay.

2. Table of Selected Radioisotopes
1/2 lives are constant for a certain radioisotope
1/2 lives are different for different radioisotopes (nuclides)

3. An atom with a short half-life decays faster than an atom
with a long half life

4. Always a whole number usually between 1 & 5
Calculations
Number of ½ life periods =
Time elapsed
½ life
Always a whole number usually between 1 & 5 1 2
Number of
1/2 life periods
Fraction of
sample remaining =

5. To figure out the mass remaining
Find out how many half lives have elapsed
Cut your number in half that many times.
Ready?

6. Practice
120g of C-14 decays over a period of 17,145 years. What fraction remains after this time has elapsed?
What mass of the original sample remains?
Write the nuclear decay equation that occurs.

7. Practice
120g of C-14 decays over a period of 17,145 years. What fraction remains after this time has elapsed?
1/8
What mass of the original sample remains?
15 g
Write the nuclear decay equation that occurs.

8. The End