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Half lives of two radioactive elements A...

Half lives of two radioactive elements A and B are 20 minutes and 40 minutes respectively. Initially, the samples have equal number of nuclei. Calculate the ratio of decayed numbers of A and B nuclei after 80 minutes.

Text Solution

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80 minutes = 4 half lives of A = 2 half live of B
Let the initial number of nuclie in each sample be N
`N_(A)` after 80 minutes = `N/2^(4)`
Number of A nuclides decayed =`15/16` N
`N_(B)` afte r80 minutes= `N/2^(4)`
Number of B nuclides decayed= `3/4` N
Required ratio= `15/16 xx4/3=5/4`
`N_(A):N_(B)=5:4`
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