Medical Imaging Systems · Nuclear Imaging · 2 marks · Numerical answer
A radioisotope has activity 2 mCi, decay constant 3.22×10⁻⁵ s⁻¹ and atomic molar mass 98 g/mol. Avogadro constant is 6.02×10²³ mol⁻¹. Find isotope mass in picograms, nearest integer.
Activity two millicuries equals .002×3.7×10¹⁰=7.4×10⁷ decays/s. The required nucleus count is N=A/λ≈2.29814×10¹². Mass=98N/(6.02×10²³) grams≈3.7412×10⁻¹⁰ g. Since one gram is 10¹² picograms, the mass is about 374 pg, within the official interval.
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