Half-life

Front

What is half-life?

Back

Half-life is the time required for half of the radioactive atoms in a sample to decay.

Front

How do you calculate the remaining amount after n half-lives?

Back

Remaining amount = Initial amount × (1/2)^n, where n is the number of half-lives.

Front

If a substance has a half-life of 10 years, how much of a 100g sample remains after 20 years?

Back

25g remains after 20 years (2 half-lives).

Front

What fraction of a radioactive sample remains after 1 half-life?

Back

1/2 of the original sample remains.

Front

What fraction of a radioactive sample remains after 2 half-lives?

Back

1/4 of the original sample remains.

Front

What fraction of a radioactive sample remains after 3 half-lives?

Back

1/8 of the original sample remains.

Front

If 80g of a substance has a half-life of 4 days, how much will remain after 12 days?

Back

10g will remain after 12 days (3 half-lives).

Front

What is the relationship between half-life and decay constant?

Back

The decay constant (λ) is related to half-life (t1/2) by the formula: λ = ln(2) / t1/2.

Front

How many half-lives are needed for a sample to decay to less than 1% of its original amount?

Back

Approximately 7 half-lives are needed to decay to less than 1%.

Front

If a radioactive isotope has a half-life of 5 years, how much of a 40g sample remains after 15 years?

Back

5g remains after 15 years (3 half-lives).