Decay Constant
The decay constant is the rate of decay of radioactive atoms per active atom. It is also called the disintegration constant. The radioactive constant may be defined as the reciprocal of the time interval during which the number of active nuclei in a given radioactive sample reduces to 36.8% (or 1/e times) of its initial value. It gives the probability per unit time for a nucleus of a radioactive substance to decay. The value of λ depends on the nature of the radioactive substance.
λ =
It is known that, t = 1/ λ , then we get,
N = N0 e-1
= N/2.718
= 0.368N0
So, N = 36.8% of N0
First Order Radioactive Decay
The phenomenon of spontaneous emission of radiation by radioactive substances came to be known as radioactivity. A naturally occurring heavy nucleus is unstable. It spontaneously emits a particle, without the stimulus of any outside agency, transforming into a different nucleus. Such a nucleus is said to be radioactive, and the process of transformation is called radioactive decay.