Radioactive Decay and Half-Life Quiz

What percentage of the sample remains after 3 years if it initially contained 100% of the radioactive isotope?

• 25%

• 50%

• 12.5%

• 3.1%

Why is it more accurate to express half-life in days rather than months?

• Days are a smaller unit of time.

• Months are not used in scientific calculations.

• Months have varying numbers of days.

• Days are easier to calculate.

How many half-lives does it take for a sample to decay from 100% to 3.1%?

• 5

• 3

• 6

• 4

If a radioactive sample's mass becomes 2 grams after five half-lives, what was its initial mass?

• 16 grams

• 32 grams

• 8 grams

• 4 grams

What is the half-life of a substance if it takes 6 days to reduce from 1200 to 600 units?

• 24 days

• 12 days

• 6 days

• 3 days

If a sample's activity reduces by 3/4 over two half-lives, what fraction remains?

• 1/8

• 1/16

• 1/4

• 1/2

How does background radiation affect the measurement of radioactive decay?

• It fluctuates with time.

• It remains constant and does not affect decay.

• It increases the decay rate.

• It decreases the decay rate.

What is the recorded count on the GM tube after one half-life if the initial count was 200 and the background radiation is 20?

• 100

• 90

• 110

• 180

How many half-lives are needed to reduce a sample's activity from 200 to 42 counts per second?

• 1

• 2

• 3

• 4

What is the half-life of a substance if three half-lives equal 24 minutes?

• 6 minutes

• 4 minutes

• 8 minutes

• 12 minutes