The phenomenon of spontaneous emission of radiations from radioactive substance is known as radioactivity. The radioactive substances are uranium, radium, polonium. radon, thorium etc.

As you must be knowing these elements are heavy and in order to attain st ability they disintegrate themselves into elements of comparatively lighter mass.

Two types of radioactivity we come across.

(a) Natural

(b) Artificial

The phenomenon of spontaneous emission of radiations exhibited by the heavier elements found in nature is called natural radio-activity.

Artificial radioactivity involves emission of radiations from elements much lighter than those occurring in nature by modern techniques of artificial transmutations

`text(LAWS OF RADIOACTIVITY )`

Following facts are known as laws of radioactivity:

(i) Radioactivity is due to the spontaneous disintegration of a nucleus.

(ii) Rate of disintegration is not affected by the external conditions like temperature and pressure etc.

(iii) Law of conservation of charge holds good in radioactivity. It means the total charge before and after disintegration must be same.

(iv) Radioactivity is a random process. This means we can't talk about decay of a particular nucleus and its disintegration is matter of chance only.

(v) Each of the product of disintegration is a new element having physical and chemical properties different from those of the parent atom.

(vi) The process of radioactivity is statistical in nature. We know that laws of statistics are used when population is very large. Any amount of radioactive sample (even very small quantity) will always contain large number of nuclei. Hence, laws of statistics can be used.

(vii) Rate of disintegration of the radioactive substance, at any instant, is directly proportional to the number of atoms present at the instant. This is known as `text(statistical law of radioactivity.)`