Chapter 15- Nuclear Energy The Big Idea: The atomic nucleus is the source of a tremendous amount of energy, which poses both risks and benefits.

15.1 Radioactivity Atoms are composed of protons, neutrons, and electrons Radioactive- atoms with unstable nuclei Radioactive decay in Earth’s interior heats the water that spurts from a geyser or wells up from a natural hot spring Atoms are the basic unit of matter. Radioactive decay means nuclei have become unstable because the number of protons and neutrons have become unbalanced. Radioactivity is the cause for geothermal energy. .natural background radiation is everywhere, and caused by the sun. The atmospheric blanket reduces background radiation, but it is more intense at higher altitudes. This is why the flight time of aircrew members is limited.

15.2 Alpha, Beta, and Gamma Rays The atoms of radioactive elements emit 3 distinct types of radiation- alpha, beta, and gamma. Alpha- helium nucleus. Adds a +2 charge to an element’s atomic number. Beta- electron. Subtracts a -1 charge to an element’s atomic number. Gamma- Ultra high energy. No change (0) in charge There used to be the same apprehension about electricity as we have about nuclear technology today. Overtime ppl determined that the benefits outweighed the dangers. Nuclear technology gives us x rays, radiation, smoke detectors, and nuclear power as a source of energy. The radioactive elements are named after the first 3 letters of the Greek alphabet.A magnet can separate a the 3 radioactive elements. Alpha- a stream of aplha particles. (2 p, 2 n). Relatively low speed, not usually dangerous unless exposed to living tissue. Beta- an electron ejected from a nucleus. More dangerous, though cant penetrate very dense materials. Gsmms- more energy than visible light, penetrate most materials. No mass or electric charge.

15.3 Environmental Radiation Most radiation that we encounter originates in nature Common source of radiation is Radon-222. Radon is a heavy gas that accumulates in basements. Amounts depend on the local geology. About 20% of the radiation we encounter comes from outside of nature. Radiation is something that has always been around. It is something we must live with. You can have your house tested for radon.If amounts are high protective measures can be taken to seal the walls and floors. Medical procedures are the main cause of radiation outside of nature. Coal-burning power plants are actually a greater source of air-borne radiation than a nuclear power plant.

Radiation Damage to the Body Cells are able to repair most kinds of damage caused by radiation, if it is not too severe. -Can cause DNA mutation, which can lead to cancer or be passed down genetically if it affects reproductive cells. Usually the mutations are insignificant. We should avoid radiation when possible, but most of it is simply a part of nature.

15.4 Transmutation of Elements The changing of one element to another is transmutation The gain or loss of protons causes a change in atomic number, and therefore a change in what element it is. When transmutation occurs energy is released Most of the energy released is the alpha particle.

15.5 Half Life The half-life of a radioactive material is the time needed for half of the radioactive atoms to decay. Half-lives are constant and are not affected by external conditions.

Isotopic Dating All living things on Earth contain Carbon-14. All animals eat either plants or other animals, and therefore all animals, including us, have a little Carbon-14 in them. Carbon-14 dating measures current radioactivity to investigate the age of things that contain carbon. When a plant dies, replenishment of c-14 ends, and decays at a rate determined by it’s ½ life. The ½ life of c-14 is 5730 years. So every 5730 years there is half as many carbon atoms remaining.

15.6 Nuclear Fission Nuclear fission-the splitting of atomic nuclei. Involves the balance of 2 forces- a strong nuclear force, and a repulsive electric force. A chain reaction is a self-sustaining reaction in which the products of one reaction event stimulate further reaction events. Critical mass-the minimum mass chunk needed for a sustainable chain-reaction The strong nuclear force holds all nucleons together. If the nucleus is stretched to an elongated shape, the electrical forces may push on it, until elongation passes a critical point, and the nucleus splits. Releases an enormous amount of energy.

15.7 The Mass-Energy Relationship: E=mc2 In this equation, E= energy contained in any mass when at rest, m stands for mass, and c is the speed of light. -Helps us understand how energy is released in nuclear reactions.

15.8 Nuclear Fusion Nuclear fusion- the combining of 2 nuclei. After combination the mass decreases, because energy is released when fusion occurs. Thermonuclear fusion- fusion caused by high temperatures.