Question

One $\mu g$ of a radioactive iodine contained in thyroxine is injected into the blood of a patient. How long will it take for radioactivity to fall to $50$%, $25$% and $10$% of the initial value? ($t_{1/2}$ for ${}_{53}^{131}I=8.05$ days)

Answer 1

$Ao=1$ Mg

$t=?$

i) $A=0.50$ Mg

ii) $A=0.25$ Mg

iii) $A=0.10$ Mg

$t1/2=8.05$ days

i) $t=\frac{2.303\times 8.05}{0.693}\times log\left(\frac{1}{0.50}\right)=8.05$ days

ii) $t=\frac{2.303\times 8.05}{0.693}\times log\left(\frac{1}{0.25}\right)=16.10$ days

iii) $t=\frac{2.303\times 8.05}{0.693}\times log\left(\frac{1}{0.10}\right)=26.75$ days