Question

A radioactive isotope having a half-life of $3$ days was received after $12$ days. It was found that there were $3$g of the isotope in the container. Find the initial weight of the isotope, when it was packed.

(antilog $1.203=16$).

• A. $12$g
• B. $24$g
• C. $36$g
• D. $48$g

Answer 1

Answer: (D)

$48$g

No. of half-lives, $n=\frac{12}{3}=4$
Amount left after n half-lives $A=\frac{A_0}{2^n}$

$3g=\frac{A_0}{2^4}$

or $3g=\frac{A^0}{16}$

$\therefore A^0=48g$.