Nuclear Physics Question 6
Question 6 - 29 January - Shift 2
Substance A has atomic mass number 16 and half life of 1 day. Another substance B has atomic mass number 32 and half life of $\frac{1}{2}$ day. If both $A$ and $B$ simultaneously start undergo radio activity at the same time with initial mass $320 g$ each, how many total atoms of A and B combined would be left after 2 days.
(1) $3.38 \times 10^{24}$
(2) $6.76 \times 10^{24}$
(3) $6.76 \times 10^{23}$
(4) $1.69 \times 10^{24}$
Show Answer
Answer: (1)
Solution:
Formula: Radioactive Decay
$(N_0) A=\frac{320}{16}=20$ moles
$(N_0) B=\frac{320}{32}=10$ moles
$N_A=\frac{(N_0) _A}{(2)^{2 / 1}}=\frac{20}{4}=5$
$N_B=\frac{(N_0) _B}{(2)^{2 / .5}}=\frac{10}{2^{4}}=0.625$
Total $N=5.625$
No. of atoms $=5.625 \times 6.023 \times 10^{23}$
$=3.38 \times 10^{24}$
Ans. (1)
