Rutherford-Soddy Law of Radioactive Decay:
In 1902, Rutherford and Soddy studied the disintegration of many radioactive substances and found the following conclusions regarding radioactive decay known as Rutherford and Soddy Rules. According to:
1. Radioactivity is a nuclear phenomenon and the rate of emission of radioactive ray cannot be controlled by physical or chemical process that mean neither can it be extended nor can it be reduced.
2. The nature of the disintegration of radioactive substance is statistical, this is, it is very difficult to say which nucleus will be disintegrated and which particle will emit α, β and γ With the emission of α , β and γ rays in the process of disintegration one element change into another new element, its chemical and radioactive qualities are completely new.
3. At any time the rate of decay of radioactive atom is proportional to the number of atoms present at that time.
Let the number of atoms present at any given time t is N and at the time t + Δt this number decreases N – ΔN to its value then, the rate of decay of atoms is \(-\frac{\Delta N}{\Delta t}\). Therefore, according to the law of Rutherford and Soddy.
If at the time Δt the nucleus ΔN will be disintegrated then the rate of disintegration,
Where N0 is the number of active nuclei at time t = 0. From equation (2), it is apparent that the number of nuclei to be decayed decreases exponentially. It is shown in figure
