Can you please help me with the following question.?

Question

A sample of cobalt-60 has an activity of 24 Bq. The back ground count is 6 Bq.
The half life of cobalt-60 is 5 years. How long will it take for the sample to reach a safe level of activity?

Answer 1

For any one atom, we can't predict when it will emit radiation but we can predict statistically when half of a large enough sample of similar radioactive atoms will have emitted their radiation (each turning into an isotope or into an atom of another element altogether as they do so).

After five years, the activity (the rate at which atoms are emitting radiation) will be 12 Bq (half of the original activity).

After ten years, the activity will be 6 Bq (one quarter of the original activity).

Since the activity now equals what the background count is anyway (6 Bq), you could say the level of activity after ten years was therefore safe.

Answer 2

After 5 years it will have halved from 24Bq to 12Bq
After a further 5 years it will halve again from 12Bq to 6Bq, which equals tha background count

So the answer is 10 years

Answer 3

a 108 years two months, four days and twelve mins,but not a second later!!!!