Question

A Geigger Muller counter is used to study the radioactive process. In the absence of eadioactive substance A, it counts 3 disintegration per second (dps). At the start in the presence of A, it records 23 dps; and after 10 min 13 dps.
i. What does it count after 20 min ?
ii. What is the half life of A ?

• A. 8 dps, 10 min
• B. 5 dps, 10 min
• C. 5 dps, 20 min
• D. 5 dps, 5 min

Answer 1

Answer: (A)

8 dps, 10 min

In the absence of A, 3 dps is zero error, hence
Initial count = 23 - 3 = 20 dps
After 10 min = 13 - 3 = 10 dps
After 20 min = 5 dps (recorded = 5 + 3 = 8 dps)
(50% fall in 10 min, $T_{50}$ = 10 min)