Question

$A.G.M$ counter is used to study the radioactive process of first - order in absence of radioactive substance $A$, it counts 3 disintegrations per second (dps). When A Is placed in the G.M. Counter, it record 23 dps at the start and 13 dps after 10 minutes . It records x dps after next 10 minutes and A has a half-life period of y minutes. x and y are:

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

Answer 1

The correct option is A $8dps,10min$

In Absence of radioactive substance A, G.M counter counts 3 dps. This means 3 dps is an error.

Therefore, Initial = 23-3 = 20 dps

After 10 min = 13 -3 = 10 dps

As the fall is 50% in 10 mins, Half Life is 10 min.

After another 10 min, i.e 20 min = 5 dps

But reading will be 5 + 3 = 8 dps

x = 8 dps and y = 10 min