An example of nuclear reactions are given below.
14N7 + 1n0 = 14C 6 + 1p1
This can be simplified as below.
14N7 (n, p) 14C6.
This was discovered by the French scientist Henri Becquerel in 1896. All elements with atomic numbers higher than 83 is radioactive.
The spontaneous emission of radiations by atomic nuclei resulting in their disintegration is called natural radioactivity. There are three kinds of radiations:- alpha, beta and gamma.
- Alpha radiations are nuclei of helium atom. Its velocity is nearly 1/10th of light velocity. Of the three radiations it has the least penetrating power. It has the highest ionising power.
- Beta radiations consist of highly energetic electrons. Their speed is almost 90% that of light. Their penetrating power is almost 100 times that of alpha radiations. Their ionising power is nearly 1/100th of that of alpha radiation. They produce fluorescence on ZnS screen.
- Gamma radiations are electromagnetic radiations. Their penetrating power is immensely high. They have no ionising power. They produce weak fluorescence on ZnS screen.
Cause Of Radioactivity
An atom is radioactivity because of its unstable nucleus. In the nucleus there is a ratio between the neutrons and the protons, called the n/p ratio which determines the stability of the nucleus.
If there are too many neutrons, a neutron will be converted to a proton and an electron. The electron will be ejected as beta particle. If there are too many protons, either a helium nucleus is ejected or a positron is ejected.
The conversion of one element into another is known as transmutation.
Artificial transmutation is carried out by bombarding an element with projectiles such as protons, neutrons, alpha particles etc. Neutrons are the best projectiles because of its neutral charge. It does not experience any repulsion from the nucleus. Accelerators such as cyclotrons are used to energise the projectiles.
The process of making a stable element radioactive by bombarding it with projectiles is called artificial radioactivity.
The new atoms formed may be stable or unstable.
27Al13 + 4He2 = 30P15 + 1n0
30P15 = 30Si14 + 0e1
Mass Defect and Binding Energy.
The difference between the sum of the masses of the nucleons and the actual mass of the nucleus is called the mass defect. The energy equivalent to mass defect is called binding energy. Higher the value of binding energy per nucleon, the more stable will be the nucleus.