The intensity of a radiation source was measured by a Geiger-Müller counter to be 236 counts per minute when the counter was place 124 ft from the source. What will be the intensity when the counter is 248 ft from the source?
A)59.0 counts per minute
B)236 counts per minute
C)118 counts per minute
D)472 counts per minute

Question

The intensity of a radiation source was measured by a Geiger-Müller counter to be 236 counts per minute when the counter was place 124 ft from the source.   What will be the intensity when the counter is 248 ft from the source?
A)59.0 counts per minute
B)236 counts per minute
C)118 counts per minute
D)472 counts per minute

Quizplus · Accepted Answer

The intensity of radiation decreases with the square of the distance from the source, according to the inverse square law. When the distance is doubled (from 124 ft to 248 ft), the intensity is reduced by a factor of 4 (2^2). Therefore, the new intensity is 236 counts per minute / 4 = 59 counts per minute.

The Intensity of a Radiation Source Was Measured by a Geiger-Müller