Answer
The decay constant is $4.27\times 10^{-4}$.
Work Step by Step
The half-life is given by
$$\frac{\ln 2}{k}\Longrightarrow 1622= \frac{\ln 2}{k}\Longrightarrow k= \frac{\ln 2}{1622}=4.27\times 10^{-4}. $$
So the decay constant is $4.27\times 10^{-4}$.
