How a nuclear fission reactor works
>>> The Proton-Proton Chain
>>> The Triple-Alpha Process
>>> Advanced Nuclear Burning Stages
>>> The Solar Neutrino "Problem"
The Proton-Proton Chain :
1H + 1H --> 2H + e+ + neutrino
2H + 1H --> 3He + gamma-ray
3He + 3He --> 4He + 2 1H
The individual nuclear reactions proceed rather slowly, and it is a very small fraction of nuclei in the core of the sun with enough energy to overcome the electrical repulsion.
The Triple-Alpha Process :
4He + 1H --> 5X
4He + 4He --> 8X
4He + 4He + 4He --> 12C
Advanced Nuclear Burning Stages :
nuclear burning stages are given below
>>>>Successive nuclear burning stages, involving more massive nuclei with higher charges, will require increasingly high temperatures to overcome the increased electrical repulsion.
>>>>The amount of energy released by each successive reaction stage decreases so that later nuclear burning stages become shorter and shorter.
>>>>Once fusion reactions have produced an iron core, further fusion reactions no longer produce energy, but absorb energy from the stellar core. As we shall see this may have a catastrophic effect on the star as it nears the end of its life.
12C + 4He --> 160 + gamma-ray
160 + 4He --> 20Ne + gamma-ray
12C + 12C --> 24Mg + gamma-ray
160 + 160 --> 32S + gamma-ray
Ray Produced
Radioactivity :
We all are affected by natural radiation from cosmic rays, radioactive substances.alpha ray,gamma ray ,beta ray.So we all should know about all of the rays and their effect and both advantages and disadvantages.
Radioactive substances :
b) uranium isotopes 235 or 233 or 238
c) substances which can be used in a suitable plant to maintain a chain reaction which initiates its own repetition and which are determined in an ordinance having the force of law.
d) spontaneously emit ionizing rays,
Properties of radiation :
>>ALPHA radiation has very low penetrating power. Materials that emit alpha radiation outside the body are harmless, since they are already stopped by the skin. But when these materials enter the body through inhalation or swallowing, they may be harmful.
>>BETA radiation is able to penetrate further through up to 1 or 2cm of tissue. Outside the body materials that emit beta radiation may be harmful to the surface tissue of the body; when such materials enter the body, they may harm the organs in which they are present.
>>GAMMA radiation penetrates even further and is able to go straight through the body. This may harm the organs in the body. X-rays are the same nature as gamma rays and can also affect the organs in the body.
Sources of radiation :
Natural sources of radiation :
This natural radioactivity may be found in rocks, in soil, in materials used for buildings construction, in foods and liquids that we eat and drink, and in the human body itself.
Cosmic radiation, arising from the sun or other galactic bodies, also contributes to natural radiation exposure.
Human -made sources :
The most important of these is the use of radioactive materials for medical applications such as the diagnosis and treatment of cancer patients.
Some manufactured goods also contain small radioactive sources, e.g. smoke detectors. Energy generation - for example nuclear energy production, extraction of oil and natural gas, and burning coal - also involves the release of small amounts of radioactivity to the environment.
There is also a low level of residual radioactivity in the environment from the nuclear bomb tests of the 1950s and 1960s.
A severe nuclear accident, like Chernobyl, can add to this man-made radioactivity in the environment.
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