please help in photons and half life time !! Two different isotopes are used for

Question

please help in photons and half life time !!

Two different isotopes are used for an experiment; one has a half?life time of 90 days, the
other has a half?life time of 70 days. You are required to use the isotopes for 160 days before they are
replaced. In order to obtain similar output from the isotopes over the study period, you decide to make
sure that, half way through the study period, the two isotopes provide equal output. What ratio of
output is necessary at the beginning of the study period?

Explanation / Answer

so at 80 days

we want

x1=x2

A 2^(-80/90)=B*2^(-80/70)

A/B = 2^(-80/70)*2^(80/90)= 0.839

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