A radioactive isotope of sodium has a half-life of 15 h .
The table gives data from an experiment to show how the rate of decay of the isotope varies with time.
The background count rate has not been subtracted from these data.
What is the background radiation count rate?
12 counts/s
15 counts/s
20 counts/s
30 counts/s
The graph shows how the count rate registered by a counter near to a sample of a radioactive isotope changes over a period of a few days. The background count rate is 5 counts per minute.
What is the half-life of the isotope?
2.0 days
2.5 days
3.0 days
4.0 days
The background count rate measured by a radiation counter is 40 counts per minute (cpm).
With the counter close to a radioactive source, the counter reading is 960 cpm .
The half-life of the source is 20 minutes.
What is the counter reading one hour later?
115 cpm
120 cpm
155 cpm
160 cpm