Question

The half-life of $T{e}^{99}$ is $6h$. The activity of $T{e}^{99}$ in a patient, $60h$ after receiving an injection containing this radioisotope is at least $0.125\mu Ci$. What was the minimum activity (in $\mu Ci$) of the sample injected?

• A. $1.25$
• B. $12.5$
• C. $128$
• D. $125$

Answer 1

The correct option is C $128$

Half life of sample, $T=6h$
Age of sample $t=60h=10T$
Number of half lives $n=10$
Activity $A=\frac{A_0}{2^n}\Rightarrow A_0=A{.2}^n=0.125\times 2^{10}=128\mu Ci$