Where t 12 is the half-life of the particle t is the elapsed time N 0 is the quantity in the beginning and. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable atoms survive. Life Half Life Math Here λ is called the disintegration or decay constant. . N t N_0 times 05 tT N t N 0. The formula for the half-life is obtained by dividing 0693 by the constant λ. If an initial population of size P has a half-life of d years or any other unit of time then. For a first zero order. The half-life formula for a reaction depends upon the order of a reaction. The general equation with half life. T12 2 years. Consider a radioactive substance with a mass of 4kg and a. You can find the half-life of a radioactive element using the formula. By using the following decay formula the number of unstable nuclei in a radioactive element l