Question

The count rate of activity of a radioactive sample of a very large population decreased from 1024 to 128 in 3 minutes. Then the rate of disintegration at the end of 5 minutes is ______.

Options

• 96

• 64

• 48

• 32

Answer 1

The count rate of activity of a radioactive sample of a very large population decreased from 1024 to 128 in 3 minutes. Then the rate of disintegration at the end of 5 minutes is 32.

Explanation:

`"A"/"A"_0 = 128/1024 = 1/8 = (1/2)^3 = (1/2)^((3"min")/"T")`

⇒ T = 1 min

A' = A₀ = `(1/2)^(5/1)`

= `"A"_0/32`

= `1024/32`

= 32