Isotope a Has a Decay Constant Of $0.861 \mathrm {~s} ^ { - 1 }$

Multiple Choice

Isotope A has a decay constant of $0.861 \mathrm {~s} ^ { - 1 }$ and isotope B has a decay constant of $0.627 \mathrm {~s} ^ { - 1 }$ . Which isotope has a longer mean life (time constant) ?

A) isotope $A$
B) isotope B