NUCLEAR CHEMISTRY

NUCLEAR CHEMISTRY

Nuclear chemistry is a subfield of chemistry dealing radiactivity, nuclear processes and nuclear properties. It is the chemistry of radioactive elements such as the actinides, radium and radon together with the chemistry associated with equipment (such as nuclear reactors) which are designed to perform nuclear processes. Nuclear chemistry is a branch which deals with the study of the composition of nuclei atoms and the reactions. The energy released during a nuclear reaction is called nuclear energy.

Nuclear reactions

These reactions involve changes in the no. of nucleons present in the nucleus. This results in the formation of a new species. The energy changes associated with nuclear reactions are about million times more than those associated with chemical reactions. These are determined by using Einstein’s mass–energy equation.
E= mc2

E = Energy
m = mass
c = velocity of light

Mass defect and Binding energy
Mass defect
Mass defect is the loss of mass during the formation of the nucleus of the isotope. The actual mass of an isotope of an element is less than the sum of masses of the protons, neutrons and electrons present in it. This defect is called mass defect (Δm).

Binding energy
During the formation of a nucleus from nucleons, some mass is lost. The mass loss is converted into energy. The release of energy imparts stability of the nucleus. The energy released when constituent nucleons combine to form a nucleus is called binding energy of the nucleus.
E = Δmc2
Δm = mass defect
c = 3 × 108 m/s.
Higher the binding energy of an isotope, greater is its stability.

Nuclear reactions are divided into two categories.
1. Natural radioactivity
2. Artificial radioactivity
1. Natural radioactivity
In this, nucleus undergoes a spontaneous change and only a single nucleus
is involved.
2. Artificial radioactivity
In this, the interaction of two nuclei brought about artificially. This is generally
carried out by bombarding a relatively heavier nucleus with a lighter one.
Nuclear Fission
Definition
Nuclear fission is defined as “the process of splitting of heavier nucleus into two (or) more smaller nuclei with simultaneous liberation of large amount of energy”.

4.1.2 Mechanism of nuclear fission
Nuclear fission reactions can be brought about by high, moderate or low speed neutrons without being repulsed.
When U235 is bombarded by thermal neutron (slow moving) unstable U236 is formed. The unstable U236 then divides into two approximately equal nuclei with release of neutrons and large amount of energy.