Question

how much of 1.0g of I-131 remains after 20 days? (note: t1/2=8.1 days)

Answer 1

for first order decay, you find the decay constant, k:

\[t _{1/2}=\frac{ \ln2 }{ k }\]

then you use the exponential decay/growth equation:

\[A _{t}=A _{0}*e ^{-kt}\]

Ao = initial amount (so 1 g for this question)
At= amount after time has elapsed
t=time elapsed
k= decay constant