Thursday, February 5, 2015

Nuclear Fission and Nuclear Fusion

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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