Chemistry Atomic Structure and Radioactivity
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Nuclear Forces

Definition : – Nuclear force is one of the four fundamental forces of nature, the others being gravitational and electromagnetic forces. In fact, being 10 million times stronger than the chemical binding forces, they are also known as the strong forces. In this section, we will discuss this force in detail.

Nuclear Force

Nuclear force is the force that binds the neutrons and protons in a nucleus together. This force can exist between neutrons and neutrons, neutrons and protons or protons and protons. This force is what holds the nucleus together. The charge of protons, which is `+1e`, tends to push them away from each other with a strong electric field repulsive force, following Coulomb’s law. But nuclear force is strong enough to overcome that resistance at short range and keep them together.

Properties
`=>` It is attractive in nature but with a repulsive core. That is the reason that the nucleus is held together without collapsing in itself.

`=>` The range of nuclear force is very short. At 1 Fermi, the distance between particles in a nucleus is extremely small. At this range, the nuclear force is much stronger than the repulsive Coulomb’s force that pushes the particles away. However, if the distance is anything more than 2.5 Fermi, nuclear force is practically non-existent.

`=>` Nuclear force is identical for all nucleons. It does not matter if it is a neutron or proton, once the Coulomb resistance is taken into consideration, nuclear force affects everything in the same way.

`=>` At a distance less than 0.7 Fermi, this force becomes repulsive. It is one of the most interesting properties of nuclear force, as this repulsive component of the force is what decides the size of the nucleus. The nucleons come closer to each other till the point that the force allows, after which they cannot come any closer because of the repulsive property of the force.

Radioactivity

In 1896, a French physicist named Henri Baequeral discovered that uranium-containing crystals emitted rays that could expose and fog photographic plates. He called these rays-uranic rays. Marie curie, later discovered two other elements-polonium and radium
emitting uranic rays. She renamed uranic rays as radioactivity (or radioactive decay). Radioactivity may be defined as disintegration or decay of unstable atoms accompanied by emission of radiation.

Radioactivity can be of two types-Natural and artificial or induced radioactivity.

Natural Radioactivity : A number of elements such as uranium, thorium, radium, polonium, etc. have unstable nuclei. These unstable nuclei disintegrate on their own resulting in the formation of a smaller atomic nuclei of another element. All elements whose atomic nucleus emit highly penetrating radiations are called radioactive elements.

Radioactivity is not affected by temperature, pressure etc. The activity of a radioactive material is measured in terms of the disintegrations per unit time. Its SI unit is becquerel which is the same as 1 disintegration per second. 1 curie = `3. 7 x 10^(30)` disintegrations `s ^(-1)`.

Nature of Radiations

Nuclear Fission

Nuclear fission is a nuclear reaction in which a heavy atomic nucleus (such as that of uranium) disintegrates into two nearly equal fragments with release of large amount of energy. The fission of one atom of uranium does not release much energy. However, if a large number of uranium atoms (`text()_92^235 U`) were to split in a very short period of time a very large amount of energy would be released. If we can control this process of fission then it provides us with a new source of energy that we can use to make steam and to produce electricity.

Nuclear fission reactions are of two types
(i) Uncontrolled chain reaction
(ii) Controlled chain reaction

`=>` The principle of atom bomb is based on uncontrolled nuclear fission reaction.

`=>` The principle of nuclear reactor is based on controlled nuclear fission reaction.

Nuclear Reactor

Controlled fission is carried out in a specially designed plant called a nuclear power reactor or simply nuclear reactor.

`=>` lt is a device that is used to produce electricity and permits a controlled chain nuclear fission.

`=>` It contains fuels e.g' `text()_(92)U^(235)`, moderator (e.g., graphite and heavy water `D_2 O`) to slow down neutrons and control rods (made up of boron steel or cadmium) to absorb neutrons.

`=>` lt also contain heavy water, liquid sodium or potassium as coolant

Nuclear Fusion

The reaction in which two or more lighter nuclei combines to form a heavier nuclei is called nuclear fusion. This reaction takes place at extremely high temperature, therefore, these reactions are called thermonuclear reactions.

`=>` Nuclear fusion is the source of sun's energy and stars.

`=>` Hydrogen bomb is based on nuclear fusion.

Uses of Radioactive Isotopes

Radioactive isotopes are used in food irradiation; in nuclear medicine in two different ways; diagnosis and therapy; as tracers in chemical and biological processes and in carbon dating.

`Tc^(99) -` In the treatment of thyroid, brain, kidney

`I^(123) -` In the treatment of thyroid

`Co^(60) -` Cancer treatment

`C^(14) -` Age determination, photosynthesis research

`Na^(24) -` To measure blood flow in the body

 
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