Half-Life

General

A half-life is the amount of time it takes for one-half (or 50%) of the original amount of material to be changed to a different element. Here's what this looks like graphically:

After 10 half-lives, only 0.1% (or 1/1,000th) of the original amount of material is left. The software cannot draw the line thin enough to truly represent the fraction remaining.

Iodine-131 Example

Iodine-131 (¹³¹I) has an eight-day half-life. After eight days, half of the ¹³¹I is gone. After 16 days, half of that is gone. Let's look at this graphically, assuming we have 8,000 Bq at the start. After one half-life, we have 50% of the original amount left, or 4,000 Bq.

After 10 half-lives, only about 1/1,000th of the ¹³¹I remains.