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A 280 day old radioactive substances sho...

A 280 day old radioactive substances shows an activity of 6000 dps, 140 days later its activity becomes 3000 dps. What was its initial activity ?

A

`20000 dps`

B

`24000 dps`

C

`120000 dps`

D

6000 dps`

Text Solution

Verified by Experts

The correct Answer is:
b
We know that `lambda=(2.303)/(t) log .A_(0)/(A)` where `A_(0)` is the initial activity. A is the activity at time t.
`:. lambda=(2.303)/(280)log.(A_(0))/(600) =(2.303)/(420) log.(A_(0))/(3000)`
On solving, we get
`A_(0) =24000 dps`
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