An 8-centimeter-diameter by 8-centimeter-long
NaI(Tl) detector detects gamma rays of a specific
energy from a point source of radioactivity. When
the source is placed just next to the detector at
the center of the circular face, 50 percent of all
emitted gamma rays at that energy are detected.
If the detector is moved to 1 meter away, the
fraction of detected gamma rays drops to

Question

An 8-centimeter-diameter by 8-centimeter-long
NaI(Tl) detector detects gamma rays of a specific
energy from a point source of radioactivity. When
the source is placed just next to the detector at
the center of the circular face, 50 percent of all
emitted gamma rays at that energy are detected.
If the detector is moved to 1 meter away, the
fraction of detected gamma rays drops to