Half Lives: Quantifying Radioactive Decay Over Time

The video tutorial explains the concept of radioactive decay, emphasizing its random nature and the inability to predict when individual nuclei will decay. It introduces the concept of half-life, which is the time required for half of the radioactive nuclei in a sample to decay. The tutorial provides examples and calculations to illustrate how the number of unstable nuclei decreases over time, using both half-life and percentage decay rates. Graphical representation of decay is also discussed, showing the exponential nature of the process.

What is the main characteristic of radioactive decay?

• It can be controlled.

• It is a random process.

• It is a predictable process.

• It occurs at a constant rate.

How is the concept of half-life best described?

• The time it takes for the number of nuclei to double.

• The time it takes for half of the nuclei to decay.

• The time it takes for the nuclei to stop decaying.

• The time it takes for all nuclei to decay.

If a substance has a half-life of 40 seconds, how many nuclei remain after 80 seconds if you start with 10,000?

• 1,250

• 5,000

• 10,000

• 2,500

What shape does the decay curve of radioactive nuclei typically take?

• Circular

• Quadratic

• Exponential

• Linear

After three half-lives, what fraction of the original radioactive nuclei remains?

• 1/8

• 1/16

• 1/4

• 1/2

If 20% of a substance decays each year, what percentage remains after one year?

• 20%

• 40%

• 80%

• 60%

How many nuclei remain after three years if you start with 2000 and 20% decay each year?

• 800

• 1600

• 1280

• 1024