Higher tier: Dealing with background radiation
Scientists must always take into consideration the amount of background radiation when working or experimenting with radioactive sources and subtract it from their results when making measurements.
The corrected count rate for a source is found using:
Corrected count rate = measured count rate â background count rate.
Example
In an experiment with a radioactive source, the average count rate measured using a GM-tube is found to be 250 counts per minute.
If the background count rate is 18 counts per minute, what is the corrected count rate due to the source alone?
Answer
Measured count rate = 250 counts per minute.
Background count rate = 18 counts per minute.
Corrected count rate = measured count rate â background count rate.
Corrected count rate = 250 â 18 = 232 counts per minute.
The corrected count rate due to the source alone is 232 counts per minute.