The Geiger-Nuttal Relationship
It gives the relationship between decay constant of an a- radioactive substance and the range of the a-particle emitted.
Where R is the range or the distance which an a-particle travels from source before it ceases to have ionizing power. A is a constant which varies from one series to another and B is a constant for all series. It is obvious that the greater the value of l the greater the range of the a-particle.