You can use the following relationship to go between an element's decay constant, λ, and it's half-life:
T½ = ln2 / λ
The decay constant, λ, is the average number of decays per unit time. If λ is per second then T½ will also be in seconds.
λ doesn't have to be an integer - for example, λ=0.5 would mean that there is an even chance of a decay occuring within the next second.