Describe how half life of a source can be measured

Before the source is used, the background count rate is measured using a GM tue connected to a counter, the count rate from the source is measured at fixed intervals over a period of time the background count is then subtracted from each measurement of the count rate and the actual count rate from the source is calculated (this is known as corrected count rate) a table and a graph can then be plotted of corrected count rate against time and this can be used to calculate the half life of the source