1. Half-Life

2. Half-Life
Time required for ½ any given mass of radioactive nuclei to decay
Characteristic for each isotope
Ranges from fractions of second to billions of years
NOT affected by chemical or physical environment of nuclide

3. Half-Life Map 1  ½  ¼  1/81/161/32 0  1  2  3  4  5
Fraction
Remaining
# of
Elapsed Half-lives
0  1  2  3  4  5
multiply by fraction
Minitial
Mfinal
 multiply by denominator or

4. No. of half-lives Number of half-lives = ____time elapsed__
length of 1 half-life
Look up half-lifes in Table N