A Geiger counter registers counts per minute from a radioactive sample placed near it

PHYSICS · Single correct · A Level · Physics · Nuclear physics · Nuclear physics

Problem

A Geiger counter registers

480

counts per minute from a radioactive sample placed near it. The background count rate is known to be constant at

30

counts per minute. After

4\,\text{h}

, the counter reading (including background) drops to

135

counts per minute. Predict the counter reading, including background, after a further

2\,\text{h}

. (a)

66

counts per minute (b)

108

counts per minute (c)

81

counts per minute (d)

57

counts per minute