Nuclear Fission
It is experimentally observed that binding energy per nucleon
will be decreasing with atomic number after iron. Uranium is a element which
has less stability, it always tries to get the stability. When a slow moving
neutron strikes a uranium atom, it splits into barium, krypton and there is some
emission of the energy also. Simultaneously in this process there is emission
of three more neutrons. These available neutrons can further participate in
reactions and break three more uranium nucleus and it can happen continuously.
This process is actually called chain reaction.
Nuclear fusion is simply a process of heavy nucleus splitting
up into lighter nuclei and the emission of energy. When a uranium atom splits
into multiple atoms there is emission of energy that is approximately equal to
200,000,000 electron volt. But for the uranium atom to split it need only a
slow moving neutron. The slow moving neutron will give enough time for the
nucleus is to absorb the energy therefore it can split up further into
different elements. The energy released in the process is in the form of
kinetic energy at a major level. The pressure and temperature in this process
are going to be very high.
The average number of the neutrons emitted in each step is
approximately 2.5. The emitted neutrons can initiate further fission and that
leads to chain reaction. In each reaction three neutrons are emitted and hence
in each step the number of the neutrons increases in multiples of three. Over
the time, because of this release of the energy which is in very high in
magnitude that was generated in a small amount of time, there could be
explosion. This way of creating the explosion with a high-energy is called
nuclear fission bomb or atomic bomb.
For the nuclear chain reaction to happen there shall be
minimum mass of the uranium elements and the minimum required mass is called
critical mass. There is another condition that has to be satisfied for the
chain reaction to continue. That is the numerical value of neutron
multiplication factor shall be greater than one. This is also called
reproduction factor. Reproduction factor is defined as the ratio of number of
the neutrons available in the present generation when compared with the number
of the neutrons available in the previous generation of the chain reaction.
When the reproduction factor is less than one, the chain
reaction is not going to be sustained. This is called sub critical state. When
the reproduction factor is equal to one, it is called just critical state and
the chain reaction is going to happen but not with the enormous amount of
release of energy. If the reproduction factor is greater than one the chain
reaction becomes uncontrolled reaction and it leads to atomic bomb.
Uncontrolled chain reaction leads to emission of high-energy
at a very high temperature which leads to disaster situations. If we are able
to control the energy that is emitted in a systematic way, we can convert that
energy into other formats of energy like electricity and can be used for the
real-life requirements. This can be done with the controlled chain reaction. We
can achieve controlled chain reaction using some devices like the nuclear
reactor. The very purpose of the nuclear reactor is to produce a nuclear
reaction in a controlled manner therefore we can use that energy into our
requirements.
A nuclear reactor consists of some major parts like a fuel to
initiate the process. The fuel could be uranium or thorium.
We need slow-moving neutrons for the nuclear chain reaction
to happen. We can use elements called moderators to slow down the fast moving
neutrons. Graphite, carbon, water can be used as moderators as per the
requirement.
To control the number of the neutrons available so that the
chain reaction can be in control, we have a device called control rods. The
very purpose of the control rods is to absorb the neutrons so that the number
of the neutrons will be in the control. Cadmium or boron can be used for the
purpose of the control rods. Whenever it is required this control rods are get
into the system therefore they can start absorbing neutrons.
The coolant like water is circulated around the system to
control the temperature of the nuclear reactor. A strong shield is also
provided around the system to protect the environment from possible radioactive
emissions.
By using this kind of nuclear reactor we can get electricity
and that kind of energy is called nuclear energy. So by using the nuclear
energy in a productive way, we can use the sciences for the development in the
comfort of people.
We know that, with each nuclear fission there is energy
emission of approximately 200,000,000 electron volts. What is the total power
that is available with a nuclear reactor can be calculated as the multiple of
number of the Frisians per second the energy per fission. We can solve small
problem on this concept as shown below.
Nuclear fusion
The process of the formation of a single stable nucleus by
fusing the two or more lighter nuclei is called nuclear fusion.
One of the simple example is the formation of the helium
nucleus by fusing four hydrogen nuclei. In this process there is a release of
energy. This energy at the outlook appears like a smaller energy than that of
fission. But the energy emitted per nucleon is much higher in the case of the
fission than that of the fusion. Therefore the energy of the fusion is higher
in magnitude. There is a small difference in between the mass of for hydrogen
nuclei together when compared with the mass of the helium. This missing mass
converts into energy and is released in the process. For the fusion to happen, different
nuclei have two combined together. This is possible only when we are able to dominate
the force of the repulsion. Hence there is a very high amount of energy is
required for the nuclear fusion to happen and it approximately demands 1000000
Kelvin of temperature.
We cannot get this temperature easily and in fact we need to
run nuclear fission to get this much of high-temperature. Therefore nuclear
fission initiates the process of nuclear fusion. Nuclear fusion can happen in different
processes like hydrogen and hydrogen cycle and the carbon and nitrogen cycle.
Nuclear fusion is the energy source of the sun and the stars which are emitting
huge energy for us. Depending on the temperature of the star it could be any of
the cycles therefore energy could be emitted by the stars.
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