The formula for a half-life is T1/2 = ln(2) / λ. In this equation, T1/2 is the half-life. The ln(2) stands for the natural logarithm of two and can be estimated as 0.693, and the λ is the decay constant.
The decay constant for a given element is determined experimentally by measuring the decay rate of the element. Every element will have a different decay constant that can also be defined as the relationship between the amount of the element present and the decay rate. The half-life of an element is independent from temperature, pressure, physical state and other physical factors. Elemental half-lives can be changed only through interacting with particles.