Half – LifeAll radioisotopes have a half life. The

half is of any given radioisotope is the amount of time required for one

half (50%) of the sample to decay

The equation

# of half lives

Total Time elapse (HOW LONG)

Half – Life (can be found in table N)

80g 40g 20g10g

1 2 3

The sample above went through 3 half lives, meaning it was cut in half 3 times.

It is now 1/8 it’s original amount½ ½ ½ = 1/8

Sample Problem

288Ac has a half life of 6.13 hours. How much of a 60 mg sample would remain after 24.52 hours?# of half

lives24.52 HR

6.13 HR

60g 30g 15g7.5g 3.75g

1 2 3 4

3.5 g would remain

4So, 60 is

going to get cut in ½ 4

times