X Physics - Chapter 19 - Nuclear Physics

Nuclear Physics
It is the branch of Physics that deals with the structure, properties and reaction of particles found in the nuclei of atoms.




Radioactivity
The phenomenon of emission of radiation from Uranium and other substances is known as radioactivity. The substances that emit radiation are known as radioactive elements.


Experiment

A small quantity of a radioactive element such as radium is placed in a cavity of a lead block in such a way that the radiation from radium can only come out through this cavity. A photographic plate is placed at some distance above the lead block so that the radiation from radium falls upon it. The apparatus is placed in a vacuum light chamber which is evacuated by a powerful pump. This chamber is then placed between the poles of a powerful magnetic field. Under the action of magnetic field, two or three types of radiation are deflected forming three separate images on the photographic plate.




Properties of Alpha Particles
Alpha particles are Helium nuclei.
The charge on alpha particles is positive.
The velocity of alpha particles is 1/100th of the velocity of light.
Ionization power is greates.
Penetration power is the least.
It effects the photographic plate.
It produces florescence with zinc sulphide solution.



Properties of Beta Particles
Beta particles are fast moving electrons.
The charge on beta particles is negative.
Its velocity is slightly less than the velocity of light.
Ionization power is less than alpha particles.
Its penetration power is greater than alpha particles.
It effects the photographic plate.
It produces florescence with barium platino cyanide solution.



Properties of Gamma Rays
Gamma rays are electromagnetic in nature.
They are neutral rays.
Its velocity is equal to the velocity of light.
Ionization power is least.
Its penetration power is the greatest.
It effects the photographic plate.
It produces florescence with Barium Platino Cyanide.

Nuclear Fission
The splitting of a nucleus into fragments with the emission of energy when bombarded by a neutron is called a fission process.




Chain Reaction
In a fission reaction, each nucleus emits three neutrons. These neutrons collide with other uranium nuclei and cause fission in them emitting three more neutrons. These neutrons produce further fission in other nuclei and this process continues. This is called a Chain Reaction.




Nuclear Reactor
A system used to obtain a controlled amount of heat from nuclear fission is called a nuclear reactor.


Working of a Nuclear Reactor

The fission material in a nuclear reactor is Uranium. This is called fuel element. The neutrons released from fission move with high velocities. The fast moving neutrons have to be slowed down before they cause further fission. The process of slowing down neutrons is called moderation. heavy water is used as a moderator. When a chain reaction starts, it may produce large number of neutrons, which may cause too much fission. The rate of chain reaction is controlled by inserting control rods which are commonly made of Boron.

The heat produced is a nuclear reactor is carried away by the circulation of pressurized water or carbon dioxide gas inside the core of the reactor. This heat is used to produce steam. This steam can be used to run a power station for the generation of electricity.




Nuclear Fusion
The process in which two lighter nuclei are brought together to form another heavy nucleus is called the Fusion Reaction.

When Deuterium and Tritium nuclei are brought together they form a Helium nucleus and release a large amount of energy and a neutron.