Half-Life

Recently, in class, we learned about half-lives: their meaning and how to calculate them in real-life examples. Half-life is the time it takes for half of a sample to decay into a stable form. Here is a link to a helpful website that goes more into depth on what a half-life is and relates it to radioactive decay:

Half-Lives Explanation

Here are a couple examples of problems dealing with half-lives that I might see something similar to on a test:

Q: How much of a sample of Uranium with a mass of 150 grams is left after 7 half lives? 

A: 150/(2^7)= 1.17 grams

Q: Radium-225 has a mass of 2.59 grams and decays for 135 days. What was the mass of the original sample?

A: 135 days x 1HL/1.5 days = 9 HL passed

(2.59g)(2^9)= 1326.08 grams

Q: The half-life of radium-255 is 15 days. What percentage of radium is left after 3 months?

A: 3 months x 30 days/1 month x 1 HL/15 days = 6 HL

1=50%

2=25%

3=12.5%

4=6.25%

5=3.125%

**6=1.5625%

Overall, this post will serve as a great resource to look back at when I have to solve half-life problems, because the three examples above accurately represent and explain all of the different types of half-life questions that I will probably see on tests or class work.