Nuclear Engineering
Nuclear Engineering

It is the study, design and application of devices that involve nuclear phenomena (fission, fusion, radiation...). Nuclear Engineering is based on the principles of nuclear physics. It includes, but is not limited to, the interaction and maintenance of nuclear fission systems and components— specifically, nuclear reactors, nuclear power plants, and/or nuclear weapons. The field may also include the study of nuclear fusion, medical and other applications of (generally ionizing) radiation, nuclear safety, heat/thermodynamics transport, nuclear fuel and/or other related (e.g., waste disposal) technology, nuclear proliferation, and the effect of radioactive waste or radioactivity in the environment.

Even though nuclear science and technology is still fairly young, the industry accounts for a large number of people and their inventions that have been beneficial to humanity.

Basic Nuclear Science

Atoms are the smallest units of matter that have all the characteristics of an element. All matter (solid, fluid or gaseous) consists of elements.

For example, an iron atom is the smallest unit of iron that has all the characteristics of the element iron. A helium atom is the smallest unit of helium that has all the characteristics of the element helium. Atoms are the building blocks of everything in the universe.

Most atoms consist of three basic particles: protons (with a positive electrical charge), electrons (with a negative electrical charge) And neutrons (with no electrical charge). Protons and neutrons are bundled together in the center of the atom, called the nucleus. The electrons move around the nucleus, each in its own orbit like the moon around the earth. Each atom of the same element is characterized by a certain number of protons in the nucleus. That number is called the atomic number. Normally, the atom has the same number of electrons in orbit around the nucleus. This atomic number identifies the elements.

Even though the number of protons in the nucleus is the same for all atoms of a particular element, the number of neutrons in the nucleus can differ for different atoms of the same element. Atoms of an element that contain the same number of protons, but different numbers of neutrons, are called isotopes of the element. Adding the number of protons and neutrons together -- a number which is referred to as the mass number, identifies isotopes.

Notice that even though the masses of atoms are sometimes different, each nucleus has only one proton. The one proton identifies all these atoms as hydrogen isotopes. It is the number of neutrons that defines them as different types of hydrogen isotopes. Normally, atoms have the same number of protons and electrons.

The number of positively charged protons is the same as the number of negatively charged electrons so that the atom is electrically neutral. The electrons orbiting at the outside of an atom are the part of the atom that takes part in chemical reactions. They identify the atom chemically. The atom can throw off these electrons, or more can be absorbed. An atom that has lost one or more electrons is positively charged; one that has picked up electrons is negatively charged. These "charged" atoms are called ions.

The nucleus of the atom also contains neutrons. Neutrons are about the same size as protons but have no electric charge. Neutrons are bound very tightly in the atom's nucleus with the protons. When the atom's nucleus contains as many neutrons as protons, the atom is stable. Most atoms are stable. However, when the atom's nucleus contains more neutrons than protons, the nucleus is unstable. The nucleus of such an unstable atom will try to become stable by giving off particles or packets of energy (quanta). These emissions are called radioactivity. The particles and quanta are emitted from the nucleus at high energy. If a particle or quantum hits the electron of another atom, it can knock that electron off of the atom, which makes that atom positively charged and, therefore, an ion. That is why we refer to the particles and quanta emitted by radioactive nuclei as "ionizing radiation."

Very large and heavy atoms that occur in nature are unstable and, therefore, radioactive. These include atoms of the elements uranium (atomic number 92), thorium (atomic number 90), radon (atomic number 86), and radium (atomic number 88), among others. Many smaller atoms are made radioactive artificially for specific uses. Smaller elements like carbon (atomic number 14), often have a stable, non-radioactive form as well as an unstable radioactive form.

Radiation and Radioactivity

Radiation

Radiation refers to the propagation of waves and particles through space and includes both electromagnetic radiation and atomic and subatomic particle radiation. Electromagnetic radiation has a broad, continuous spectrum of energy (see The Radiation Spectrum) that includes visible light, radio waves, microwaves, x-rays, gamma rays, and infrared and ultraviolet radiation. All electromagnetic radiation travels at the speed of light. Particle radiation includes alpha and beta particles, neutrons, protons and heavy ions. The speed and energy of particle radiation depends upon the source of the radiation and any subsequent interaction of the particle with other matter.

While there are many different sources of radiation, it generally arises from or is produced by radioactive decay, energy change of an atomic electron or nucleus, motion of atoms or molecules, or the interaction between particles or electromagnetic radiation and atoms or nuclei. There are many sources and types of naturally occurring radiation such as the sun, radioactive materials, visible light, solar and cosmic radiation, and thermal radiation (what is typically referred to as heat). Radiation can also be generated to diagnose and treat illness, eliminate or reduce harmful microorganisms to enhance the safety of medical equipment and the food supply, cook food, transmit information (radio, television, cellular phones, etc.), and many other applications addressed on this website.

Radioactivity

Radioactivity refers to the property of spontaneous emission of particles or electromagnetic radiation exhibited by certain materials. Unstable atoms emit this radiation as they undergo a transition to a more stable state; the transition is called radioactive decay. Unstable atoms that exist in nature are said to be naturally radioactive. Examples of radioactive atoms found in nature are carbon-14, potassium-42, radon-222, uranium-235, uranium-238 and thorium-232. In addition to naturally occurring radioactive materials, radioactive atoms can be produced when the nucleus of an atom is made to interact with a particle or electromagnetic radiation to form an unstable nucleus; this is typically done in nuclear reactors and particle accelerators.

As radioactive atoms go through the transition to a stable state they emit radiation in several forms as follows:

  • Charged particles (alpha particles, beta particles and positrons)

  • Uncharged particles (neutrons)

  • Electromagnetic radiation (gamma rays and x-rays)

Nuclear science and technology improves our life in many ways and in many different areas. It makes our food safer; it improves the quality of tools, gauges, and machines; it diagnoses abnormalities of the metabolism and treats cancers; it powers space applications; and it offers one of the cleanest and most environmentally friendly ways of generating electricity.

Any human endeavor produces waste, whether you cook a meal, drive a car, or wash your clothes. Any form of energy production creates waste too, whether we use coal, solar, wind, gas or nuclear energy. Waste is simply part of living, and the only way to deal with it, is to find solutions for the challenge.

In the nuclear science and technology industry, waste comes from different activities. It arises from the use of radioisotopes in medicine, in research, and in agriculture; it arises as a byproduct of the generation of electricity through nuclear fuels, from the use of sources in manufacturing processes and more.

Contrary to what some antinuclear activists would like you to believe, the nuclear industry has found a solution for its waste challenges.

Radioactive materials are being transported safely, and have been transported safely, without significant impact on public or occupational health, for more than 30 years. In the United States, radioactive material transportation is regulated by the U. S. Department of Transportation (USDOT) and by the U. S. Nuclear Regulatory Commission (USNRC), and is better regulated, with a considerably better safety record, than any other hazardous material transported.

Only 5% of all the hazardous materials shipped annually in the United States, contain radioactive materials. Of that 5%, approximately five million packages, almost all are transported for medical, research, industrial, or educational use.

Radioactive materials from nuclear power plants account for only 4% of all radioactive materials transported.

Nuclear Physics

Nuclear physics is the branch of physics concerned with the nucleus of the atom. It has three main aspects: probing the fundamental particles (protons and neutrons) and their interactions, classifying and interpreting the properties of nuclei, and providing technological advances.

An atom consists of a positive charged atomic nucleus where you can find protons and neutrons and it consists of a negative charged atomic shell with electrons. In every atom the number of the electrons is equal to the number of the protons so it is neutral. The number of the protons decides which chemical element the atom is. The first element in the "Periodic table of the elements" is hydrogen. The number of the protons sorts the elements in the “Periodic table of the elements”. The atomic nucleus of a hydrogen atom consists of only one proton. But there are a few isotopes of every element. Isotopes are atoms with the same number of protons, but another number of neutrons. The different isotopes of one element do not differ in their chemical properties. There are for example three isotopes of hydrogen. The first isotope is the one I wrote about. The second isotope of hydrogen is deuterium with one proton and one neutron in his atomic nucleus and the third isotope is tritium that has got one proton and two neutrons in his atomic nucleus. In the atomic nucleus of a tritium atom there is no balance between the protons and the neutrons so it is instable and decays. The particle, which is emited from this decay, is radioactive and it is charged. You can make ions of atoms. We can say that an ion is an atom that has got less or more electrons than protons. An ion is not neutral a so it is radioactive.

Radioactivity means that atoms decays. The reason for this decay is that they are instable. A atomic nucleus is instable when it is too heavy or when a balance is missing between the protons and the neutrons. Every atom which has got a higher number of nucleons (protons and neutrons togehter) than 210 is instable. There are three types of decays: alpha decay, beta decay and gamma decay.

Because it is impossible today to say which atomic nucleus will be the next to decays. We can say how many atomic nucleus will decay in a certain time. This is the principle for half-life. After one half-life a half of the atomic nucleus of a certain material has decayed. Plutonium-239 for example has got a half life 24,000 years, radium-228 has got a half life of 6.7 years, thorium-232 has got a half life of 14,000,000,000 years and polonium-212 has got a half life 0.0000003 seconds. There are many physical properties, but I will talk about the activity now. The activity is the number of decays divided by a certain time. The unit of the activity is becquerel. 1 becquerel is one decay per second. So 20 becquerels are 20 decays per second. To prove these decays there is a geiger counter. It consists of a closed tube which is often filled with argon. At the end of the tube there is a wire, which is not allowed to touch the other end of the tube or the walls. The wire is charged positive and the walls are charged negative. A radioactive particle which flows into the tube ionizes one or a few gas atoms. The out-pushed electrons go to the wire. The consequence is a voltage surge. This voltage surge is shown on an output device as a decay.

When we talk about the alpha decay then it means that a twice positive charged heliumion (helium atomic nucleus) is emited from the atomic nucleus. Then we find two protons ans two neutrons less in this atomic nucleus, so it is lighter. The alpha radiation is the most dangerous of the three types of radiation, but a sheet of paper is enough to protect oneself. The skin protects us also from alpha radiation.

There are two types of the beta decay. The one is the beta minus decay and the other is the beta plus decay. When we talk about the beta minus decay a neutron decays into a proton, an electron and an antineutrino. The electron and the antineutrino are emited. The radioactive particle is the electron. The number of nucleons do not change, but we have got one proton more than before the decay. 2 or 3 cm of wood are enough to protect oneself.

When we talk about the beta plus decay a proton decays into a neutron, a positron (the antiparticle of the electron) and a neutrino. The positron and the neutrino are emited. The radioactive particle is the positron.

When we talk about the gamma decay high-energy electromagnetic waves are emited from the atomic nucleus. This waves are photons, which have got a higher frequency and less wave long than light. A gamma decay can happen after an alpha decay or a beta decay, because the atomic nucleus is very energetic. You need a big wall of lead to protect yourself from gamma radiation.

Everyone knows that strong radiation is not good fot the health, but we use radioactive materials for nuclear power plants and nuclear weapons.

But there are good sides for radioactivity, too. Another example is nuclear medicine. An X-ray instrument sends X-Rays throught our body onto a photo plate. Where the photo plate becomes black the X-rays goes throught our body, there where the photo plate stays transparent the X-rays do not pass our body. Another positive aspect is the radiotherapy. It is used to destroy cancer. In old clocks which have illuminated you can find radium and thorium which were used to bring the zinc sulfite to illuminate. The glowing trunk for camping lamps contained thorium. The energy source for the batteries for cardiac pacemaker is plutonium-238. There is not any nuclear fission in those batteries, because the energy source is the natural nuclear decay. Radionuclide batteries are also used for space probes like Voyager I, Voyager II and Cassini who are very long in space and so they need radionuclide batteries who are an energy source for a long time.

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