Lecture 2_ Decay Kinetics and Radioactivity Example : to be solved in class @ 40K has an abundance of 0.012 % (other isotope are 41K and 39K ). The molar mass of the natural potassium is 39.13 g. Consider a sample of mass m =3.5g of natural potassium . It emits 68p- per second and its decay scheme through beta and gamma is shown in Figure 1. The ratio emitted per second is N./N. =0.12. 1. What is the period of 40K? 2. We can use this decay to find the age of mineral by measuring the concentration ratio of 4OK and 40 Ar. We assume that all the 40Ar in the mineral came purely from 40K and there is no 40 Ar leakage from the mineral . B What the age of a mineral in the following cases : 40 Ca N 2.1 . when Ar Z = 0.25 2.2 . when N AT = 0.25 40K N 40 Ar Figure 1. decay schema of 40K