READ: Nuclear Energy
READ: Nuclear Energy
Nuclear fission is the splitting of the nucleus of an atom into two smaller nuclei. This type of reaction releases a great deal of energy from a very small amount of matter. For example, nuclear fission of a tiny pellet of uranium-235, like the one pictured in the figure below, can release as much energy as burning 1,000 kilograms of coal!
This pellet of uranium-235 can release a huge amount of energy if it undergoes nuclear fission.
Nuclear Energy by Fusion and Fission
As shown in Figure below, the reaction begins when a nucleus of uranium-235 absorbs a neutron. This can happen naturally or when a neutron is deliberately crashed into a uranium nucleus in a nuclear power plant. In either case, the nucleus of uranium becomes very unstable and splits in two. In this example, it forms krypton-92 and barium-141. The reaction also releases three neutrons and a great deal of energy.
The fissioning of a nucleus of uranium-235 begins when it captures a neutron.
Using Energy from Nuclear Fission
If a nuclear chain reaction is uncontrolled, it produces a lot of energy all at once. This is what happens in an atomic bomb. If a nuclear chain reaction is controlled, it produces energy more slowly. This is what occurs in a nuclear power plant. The reaction may be controlled by inserting rods of material that do not undergo fission into the core of fissioning material (see Figure below). The radiation from the controlled fission is used to heat water and turn it to steam. The steam is under pressure and causes a turbine to spin. The spinning turbine runs a generator, which produces electricity.
This diagram shows the main parts of a nuclear power plant.
Energy from Nuclear Fusion
Nuclear fusion is the opposite of nuclear fission. In fusion, two or more small nuclei combine to form a single, larger nucleus. An example is shown in Figure below. In this example, two hydrogen nuclei fuse to form a helium nucleus. A neutron and a great deal of energy are also released. In fact, fusion releases even more energy than fission does.
In this nuclear fusion reaction, nuclei of two hydrogen isotopes (tritium and deuterium) fuse together. They form a helium nucleus, a neutron, and energy.
Nuclear fusion of hydrogen to form helium occurs naturally in the sun and other stars. It takes place only at extremely high temperatures. That’s because a great deal of energy is needed to overcome the force of repulsion between positively charged nuclei. The sun’s energy comes from fusion in its core, where temperatures reach millions of Kelvin (see figure below).
The extremely hot core of the sun radiates energy from nuclear fusion.
Energy of Nuclear Changes
A nucleus (with one exception, hydrogen-1) consists of some number of protons and neutrons pulled together in an extremely tiny volume. Since protons are positively charged and like charges repel, it is clear that protons cannot remain together in the nucleus unless there is a powerful force holding them there. The force which holds the nucleus together is generated by nuclear binding energy.
This nuclear binding energy shows how the mass number of an atom relates to the energy needed to hold the nucleus together. Iron atoms tend to have the most stable nuclei.
A nucleus with a large amount of binding energy per nucleon (proton or neutron) will be held together tightly and is referred to as stable. These nuclei do not break apart. When there is too little binding energy per nucleon, the nucleus will be less stable and may disintegrate (come apart).
When nuclei come apart, they come apart violently accompanied by a tremendous release of energy in the form of heat, light, and radiation. This energy comes from some of the nuclear binding energy. In nuclear changes, the energy involved comes from the nuclear binding energy. However, in chemical reactions, the energy comes from electrons moving energy levels. A typical nuclear change (such as fission) may involve millions of times more energy per atom changing compared to a chemical changes (such as burning)!
Nuclear reactions produce a great deal more energy than chemical reactions. Chemical reactions release the difference between the chemical bond energy of the reactants and products, and the energies released have an order of magnitude of
The effects of radiation on humans and other living things
You may have seen this sign before—maybe in a hospital. The sign means there is danger of radiation in the area. Radiation consists of particles and energy that are given off by radioactive isotopes, which have unstable nuclei. But you don’t have to go to a hospital to be exposed to radiation. There is radiation in the world all around you.
Radiation in the Environment
A low level of radiation occurs naturally in the environment. This is called background radiation. One source of background radiation is rocks, which may contain small amounts of radioactive elements such as uranium. Another source is cosmic rays. These are charged particles that arrive on Earth from outer space. Background radiation is generally considered to be safe for living things.
Dangers of Radiation
Long-term or high-dose exposure to radiation can harm both living and nonliving things. Radiation knocks electrons out of atoms and changes them to ions. It also breaks bonds in DNA and other compounds in living things. One source of radiation that is especially dangerous to people is radon. Radon is a radioactive gas that forms in rocks underground. It can seep into basements and get trapped inside buildings. Then it may build up and become harmful to people who breathe it. Long-term exposure to radon can cause lung cancer.
Exposure to higher levels of radiation can be very dangerous, even if the exposure is short-term. A single large dose of radiation can burn the skin and cause radiation sickness. Symptoms of this illness include extreme fatigue, destruction of blood cells, and loss of hair.
Nonliving things can also be damaged by radiation. For example, high levels of radiation can weaken metals by removing electrons. This is a problem in nuclear power plants and space vehicles because they are exposed to very high levels of radiation.
Q: Can you tell when you are being exposed to radiation? For example, can you sense radon in the air?
A: Radiation can’t be detected with the senses. This adds to its danger. However, there are other ways to detect it.
Using Radiation
Despite its dangers, radioactivity has several uses. For example, it can be used to determine the ages of ancient rocks and fossils. It can also be used as a source of power to generate electricity. Radioactivity can even be used to diagnose and treat diseases, including cancer. Cancer cells grow rapidly and take up a lot of glucose for energy. Glucose containing radioactive elements can be given to patients. Cancer cells take up more of the glucose than normal cells do and give off radiation. The radiation can be detected with special machines like the one in the figure below. The radiation may also kill cancer cells.
This machine scans a patient’s body and detects radiation.
Summary
- A low level of radiation occurs naturally in the environment. This background radiation is generally assumed to be safe for living things.
- Long-term or high-dose exposure to radiation can harm living things and damage nonliving materials such as metals.
- One reason radiation is dangerous is that it generally can’t be detected with the senses. It can be detected only with devices such as Geiger counters.
- Radiation has several important uses, including diagnosing and treating cancer.
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