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صدای سرزمین مادری - atomic energy
شنبه 28 آبان 1390

atomic energy

   نوشته شده توسط: mohammad torabi    

Einstein
chain reaction

Chain reaction: A neutron hits a nucleus, which splits. The split releases energy and more neutrons, which then strike other nuclei. As more nuclei are split, more energy and neutrons are released.

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How is uranium related to energy?

Uranium is an element found in nature. Used as a nuclear fuel, it is a source of energy. Uranium fuel is emissions-free, making it safe for the environment and in comparison to other fuels, only a tiny quantity is required to generate an equivalent amount of electricity. All the uranium produced by Cameco is used to generate electricity.

Society depends on electricity. It wakes us up, cooks our food, keeps us warm, cools us off, runs the factories, and connects us to the Internet. We may take these conveniences for granted but many of the things we do require electricity.

Electricity is a form of energy. The universe is made up of both matter and energy. Matter is all those things that have weight, or mass - rocks, trees, lakes, people, animals. Energy is harder to describe, but it is observed all the time. Energy is the force that makes things move and change. In other words, if the universe were a watch... energy would make it tick.

uranium pellet
A typical pellet of uranium weighs about 7 grams (0.24 ounces). It can generate as much energy as 3.5 barrels of oil, 17,000 cubic feet of natural gas, or 1,780 pounds of coal.
atom
An atom consists of protons and neutrons that form a nucleus around which electrons orbit.

What are the sources of energy?

There are six basic kinds of energy. As you throw a basketball, your arms give it mechanical energy in the form of movement. A burning log gives off chemical energy, which you can see as light and feel as heat. A hot burner on the stove receives electrical energy from an outlet and supplies thermal energy to a frying pan with eggs. The sun sends radiant energy to Earth every day in the form of light but gets its own nuclear energy from reactions inside the nuclei of its own atoms. Nuclear energy can be produced in two ways. In the sun, energy is created by the joining of the nuclei of hydrogen atoms in a process called fusion. On Earth the nuclei of larger atoms such as uranium split apart to create energy in a process called fission. All types of energy are essentially different forms of one another.

How is nuclear energy produced?

How can something so small generate so much energy? The secret is in the basic building block of all matter - the atom. All matter in the universe is made up of atoms, particles so tiny that they cannot be observed even under a microscope.

Atoms

The atom resembles a miniature solar system. In the centre of the atom is the nucleus around which electrons orbit, like planets moving around the sun. The nucleus, composed of protons and neutrons, contains most of the mass of the atom. Tiny electrons move around in relatively large orbits with nothing in between.

Atoms that contain an equal number of protons and electrons are referred to as elements. There are 90 kinds of naturally occurring elements and at least 14 other artificial elements have been created by scientists in controlled experiments. Elements are listed in a periodic table arranged according to their number of protons (atomic number). For example, an atom of hydrogen, the lightest element, has just one proton in the nucleus. An atom of uranium, the heaviest element found in nature, has 92 protons.

Periodic Table of the Elements
Elements are listed in a periodic table arranged according to their number of protons.

Isotopes

The number of protons in the nucleus of an element is always the same but the number of neutrons may vary. For example, carbon atoms that have six protons usually have six neutrons. However, some have eight. Atoms that have a different number of neutrons than protons are called isotopes. Each isotope is identified by its atomic mass, the sum of its protons and neutrons.

Naturally occurring uranium is made up primarily of two different uranium isotopes. Approximately 99.3% is uranium 238 (U-238) with 92 protons and 146 neutrons, and 0.7% is uranium 235 (U-235). Under certain conditions the nucleus of U-235 can be made to split, or fission. Because of this property, U-235 plays an important role in the creation of nuclear energy.

nucleus of an atom
Splitting the nucleus of an atom - a process called nuclear fission - releases the binding energy. The energy released is nuclear energy.
Einstein
Einstein's equation, E = mc2, explains how matter can become so much energy.

Fission

Fission describes the splitting of an atom's nucleus into two or more smaller nuclei. Most atoms will not fission because a binding energy that holds the protons and neutrons together prevents it. However, some atoms with big, unstable nuclei, like U-235, can be broken apart. Under certain conditions, when U-235 is struck with a neutron it divides and produces two lighter atoms. The mass of these two lighter atoms added together is less than the original U-235 atom. In the process of fission the mass that seems to have disappeared has been converted into energy.

According to Einstein's formula E = mc2, even a small amount of mass (m) inside the atom can be magnified by a huge number (c2, the speed of light squared) to create enormous amounts of energy (E). The fission-ing of one U-235 nucleus releases 50 million times more energy than the combustion of a single carbon atom. Nuclear fission produces far more heat than burning a comparable volume of hydrocarbon fuel such as oil, natural gas or coal.

Chain reaction

In addition to the creation of two new smaller nuclei, fission frees some neutrons to make other atoms divide. They strike other U-235 atoms and release more neutrons. As long as there are uranium atoms present, the fission process continues. This is called a chain reaction. It is this chain reaction that makes a sustained nuclear reaction possible. It creates an ongoing release of energy from one atom to the next and therefore provides a continuous source of energy.

If uncontrolled, the fission reaction multiplies rapidly and can produce an explosion. However, in a nuclear reactor, fission is controlled. Only one neutron is allowed to produce another fission. Control rods prevent the number of neutrons in a nuclear reactor from growing too large by absorbing excess neutrons. To do this, control rods are inserted into the core of the reactor. Pushed in, they soak up neutrons and slow down the reaction; pulled out they allow it to speed up again. In this way the chain reaction is controlled.

chain reaction
nuclear fission
 
Chain reaction: A neutron hits a nucleus, which splits. The split releases energy and more neutrons, which then strike other nuclei. As more nuclei are split, more energy and neutrons are released.
Controlled chain reaction: For each fission only one neutron will create a second fission.
 

 
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