Half Life
What is it?
The half-life of a radioactive element or compound is the amount of time (measured in years) that it will take for exactly half of that substance to decay. Half-lives apply to nuclear energy mainly in the disposal of nuclear waste. By calculating the half life of radioactive elements, scientists can tell how long radioactive waste will be dangerous for, and therefore how long it must be kept in a secure environment away from humans (Friedland and Relyea, 2015).
Calculating Decay Example Problem
Say the half life of a radioactive element is 35 years. How long will it take this element to decay to 1/32 of its original mass?
To find this answer, you must realize that it will take this element 35 years to decay to 1/2 its starting mass. This means it will take another 35 years for half of that amount to decay, and the mass to be 1/4 the original. Following this pattern, it will take another 35 years to get to 1/8, another 35 years to get to 1/16, and another 35 years to get to 1/32. This amounts to 5 half-lives. So, multiply 35 times 5 to find your answer.
35 X 5 = 175 years
In 175 years, the radioactive element will have decayed to 1/32 its original mass (Friedland and Relyea, 2015).