The half-life of a nuclear reaction is defined as the amount of time required for half of the original sample to react. This is calculated using the equation, t1/2 = 0.693/k,
Where:
This equation is for a first order process and the resulting units of t1/2 will be dependent on the units of k, but will be a measurement of time (minutes, seconds, years...etc.)
Whitten, et al. "Chemistry" 10th Edition. Pp. 863