Answer
$$ 1.4 \times 10^{14} / \mathrm{y}
$$
Work Step by Step
Eq. $42-20$ leads to
$$
R=\frac{N \ln 2}{T_{1 / 2}}=\frac{5 \times 10^{18} \ln 2}{2.41 \times 10^{4} \mathrm{y}}=1.4 \times 10^{14} / \mathrm{y}
$$
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