Nuclear Energy

Nuclear Energy

Presentation Concepts:• Radioactivity • Radioactive decay • Transmutation• Alpha decay• Beta decay • Gamma radiation • Half life • Carbon dating

Atoms with unstable nuclei are constantly changing as a result of the imbalance of energy within the nucleus. When the nucleus loses a neutron, it gives off energy and is said to be radioactive. Radioactivity is the release of energy and matter that results from changes in the nucleus of an atom.

Radioactivity

Transmutation

All elements with atomic numbers greater than 83 are radioisotopes meaning that these elements have unstable nuclei and are radioactive. Elements with atomic numbers of 83 and less, have isotopes (stable nucleus) and most have at least one radioisotope (unstable nucleus). As a radioisotope tries to stabilize, it may transform into a new element in a process called transmutation.

Henri Becquerel (1852-1908) - Henri Becquerel was born into a family of scholars and scientists in Paris. He worked mostly on phosphorescence. He is most famous for his experiment to see if there is any connection between x-rays and naturally occuring phosphorescence. He concluded that rays emitted by uranium differed from x-rays because the uranium rays could be deflected by magnetic or electric fields. This was the discovery of spontaneous radioactivity

Madam Curie (1867-1934)- Marie Curie was born in Warsaw on November 7, 1867. Her early experiments were conducted under poor conditions. She didn't have proper equipment or a proper lab. A lot of her work was inspired by the discovery of radioactivity by Henri Becquerel. During the course of her life, she achieved many things. She discovered 2 elements, polonium and radium. Together with her husband, she was awarded half of the Nobel Prize for Physics in 1903, for their study into the spontaneous radiation discovered by Becquerel. In 1911 she received a second Nobel prize, this time in chemistry, in recognition of her work in radioactivity.

Alpha ( ) decay occurs when the neutron to proton ratio is too low . Alpha decay emits an alpha particle, which consists of two protons and two neutrons. This is the same as a helium nucleus and often uses the same chemical symbol 4 He 2 . Shielding of alpha particles is easily accomplished with minimal amounts of shielding. Examples of alpha particle emitting radio-nuclides include 238 U, 239 Pu, and 241 Am.

Alpha decay

Beta minus decayThere are two types of ß decay; ß + and ß - decay. An excess of neutrons in an atom's nucleus will make it unstable, and a neutron is converted into a proton to change this ratio. During this process, a ß particle is released, and it has the same mass and charge as an electron. The resulting atom and the ß particle have a total mass which is less than the mass of the original atom, But ß particles aren't mono-energetic, and have a broad energy spectrum from zero to the maximum energy predicted.

Beta Plus decayWhen there is an excess of protons in the nucleus, and it is not energetically possible to emit an    particle, ß + decay occurs. This is where the nucleus becomes stable by converting a proton into a neutron. During ß + decay, a positron (a particle with the same mass as an electron but with positive charge), and a neutrino are released. Positrons interact with electrons, causing both to be completely destroyed. Two gamma ray photons with the same energy as the mass of the positron and electron are released .

Gamma radiation emission

Gamma rays have no charge or mass, so their emission doesn't change the chemical composition of the atom. Instead, it results in a loss of radiant energy.

Alpha particles penetrabilityAlpha particles are highly ionizing (e.g. deposits energy over a short distance). Since alpha particles lose energy over a short distance, they cannot travel far in most media. For example, the range of a 5 MeV alpha particle in air is only 3.5 cm. Consequently, alpha particles will not normally penetrate the outermost layer of the skin. Therefore, alpha particles pose little external radiation field hazard. Shielding of alpha particles is easily accomplished with minimal amounts of shielding.

Beta particles penetrability

Beta particles are less ionizing than alpha particles. The range of beta particles depends on the energy, and some have enough to be of concern regarding external exposure. A 1 MeV beta particle can travel approximately 12 feet in air. Energetic beta particles can penetrate into the body and deposit dose to internal structures near the surface. Since beta particles are less ionizing than alpha particles, greater shielding is required. Low Z materials are selected as beta particle shields to take care of X-ray emissions associated with slowing down of beta particles while they travel in a medium.

Gamma radiation penetrability

Gamma rays are the least ionizing of the three forms discussed. A 1 MeV gamma ray can travel an average of 130 meters in air. Since gamma radiation can travel far in air, it poses a significant external radiation hazard. Further, if ingested, it may pose an internal radiation hazard. Shielding of gamma rays is normally accomplished with high atomic number materials such as lead.

Half-life

The radioactive half-life for a given radioisotope is the time for half the radioactive nuclei in any sample to undergo radioactive decay. After two half-lives, there will be one fourth the original sample, after three half-lives one eight the original sample, and so forth.

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Carbon dating

Nuclear Power Plant As of July 2008, there were more than 430 operating nuclear power plants and, together, they provided about 15 percent of the world's electricity in 2007. Of these 31 countries, some depend more on nuclear power than others. For instance, in France about 77 percent of the country's electricity comes from nuclear power. Lithuania comes in second, with an impressive 65 percent. In the United States, 104 nuclear power plants supply 20 percent of the electricity overall, with some states benefiting more than others. Despite all the cosmic energy that the word "nuclear" invokes, power plants that depend on atomic energy don't operate that differently from a typical coal-burning power plant. Both heat water into pressurized steam, which drives a turbine generator. The key difference between the two plants is the method of heating the water. While older plants burn fossil fuels, nuclear plants depend on the heat that occurs during nuclear fission ,To make a nuclear fission it is necessary to bombard the split material with thermal neutrons. After the fission there there are two new atoms and and two or three free neutrons. This free neutrons make a fission of other atoms and so it is a nuclear chain reaction.

Nuclear fission

Nuclear Power Station

Nuclear medicine procedures use pharmaceuticals that have been labeled with radionuclides (radiopharmaceuticals). In diagnosis, radioactive substances are administered to patients and the radiation emitted is detected. The diagnostic tests involve the formation of an image using a gamma camera or positron emission tomography ,