1.

A 280 days old radioactive substance showe an activity of 6000 dps. 140 days later its acitivity becomes 3000 dps. What was its initial acitivity?

Answer»

2000 dps
24000 dps
12000 dps
6000 dps

Solution :TOTAL TIME is 3 half lives
`N/N_(0)=(1/2)^(3) rArr (3000)/(N_(0))=1/8, N_(0)=24000`


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