A certain radioactive substance has a half of 30 minutes. If the count rate was observed to be 300 after 90 minutes, determine its count rate at the beginning.
2 answers
The count rate at the beginning would be 900. This is because the half-life of the substance is 30 minutes, so after 90 minutes, the count rate would have decreased by a factor of 3 (half of the original count rate three times). Therefore, the original count rate would be 3 times the current count rate, or 900.
x at start
1/2 x at 30 min
1/4 x at 60 min
1/8 x at 90 min
x = 8 * 300
1/2 x at 30 min
1/4 x at 60 min
1/8 x at 90 min
x = 8 * 300
2 answers