Higher tier: Safe handling of radioactive material
Knowing about half-lives is important because it enables you to work out when a radioactive sample is safe to handle.
With each half-life the activity of the source halves and so it gets weaker, and the activity approaches the level of background radiation, which is considered to be safe.
As a rule, that occurs at 10 half-lives.
So, if radioactive source has a half-life of 4 days, it is considered to be safe in 10 half-lives, or 40 days.
Question
Radioactive Technetium-99m is used in medicine to image the skeleton and heart and has a six-hour half-life.
If it is injected into a patient and considered to be safe in 10 half-lives, how long will this take?
The half life of Technetium-99m = 6 hours.
10 half-lives = 10 x 6 = 60 hours.
It will take 60 hours, or two and a half days, for the Technetium-99m to be considered safe and âgoneâ from the patient.