Medical Imaging Systems · Nuclear Imaging · 2 marks · Multiple choice
Radionuclide P has half-life four times that of Q. At t=0 both have N₀ atoms. At what time do their activities become equal? Express the answer in terms of P’s half-life T.
Decay constants obey λQ=4λP. Equal activities require λP N₀e⁻λᴾᵗ=4λP N₀e⁻⁴λᴾᵗ, so e³λᴾᵗ=4. Hence t=ln4/(3λP)=(2/3)T≈.66T, B. Equal initial atom counts do not mean equal initial activities.
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