Q. The half life of 92U238undergoing α-decay is 4.5 × 109 Its activity of 1g sample is
(a) 1.23 × 104 Bq
(b) 2.4 × 105 Bq
(c) 1.82 × 106 Bq
(d) 4.02 ×108 Bq
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Ans: (a)
Sol: Half life , T1/2 = 4.5 × 109 ×365×24×60×60 sec
Number of atoms, N = 6.023×1023/238
Activity , A = λN
$\displaystyle A = \frac{0.693}{T_{1/2}} \times N $
$\displaystyle A = \frac{0.693}{4.5 \times 10^9 \times 365 \times 24 \times 60 \times 60} \times 6.023 \times 10^{23}/238$
= 1.23 ×104 dps