First slide
Radioactivity - Nuclei
Question

After 280 days, the activity of a radioactive sample is 6000dps.  The activity reduces to 3000 dps after another 140 days.  The initial activity of the sample in dps is

Moderate
Solution

t1=280daysN1=6000dps 

t2=280+140=420days,N2=3000dps

N0=?N0=6000×2n=3000×2n

6000×2280T=3000×2420T

2×2280T=2420T21=2140T

1=140TT=T12=140days

N0=6000×2280140=6000×4=24000dps                                 

 

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