Transcript Slide 1
1. Gravity – Range of gravity is unlimited - every object in the universe exerts a gravitational force on everything else, but…. – Weakest of the four fundamental forces – Only attractive (not repulsive) – Most important to our understand of the universe. 2. The Electromagnetic Force – Long range force responsible for electric and magnetic effects such as the repulsion between like electrical charges or the interaction of bar magnets Nuclear Forces 3. The Weak Force - Short range force that is responsible for radioactive decay and neutrino interactions 4. The Strong Force – Short range force which can hold a nucleus together against the enormous forces of repulsion of the protons. This binding of neutrons and protons into nuclei is the strongest force known. Matter and Energy Previous studies have taught us that “matter and energy cannot be created nor destroyed” We now need to understand that Matter and Energy are two forms of the same thing E = mc2 Energy Mass Light Speed Matter can be changed into Energy In the equation above: E = Energy m = Mass c = Speed of Light .993 kg Helium 1kg Hydrogen This tells us that a small amount of mass can be converted into a very large amount of energy because the speed of light (c) is an extremely large number Matter can be converted into energy through Nuclear Reactions • Scientists can use a special machine called a particle accelerator to bombard particles and atoms in order to achieve fusion and fission reactions. The big circle marks the location of the Large Hadron Collider (LHC) Fission Fission may be defined as the process of splitting an atomic nucleus into smaller atomic nuclei and neutrons Large amounts of energy are produced by the fission process A classic example of a fission reaction is that of U-235: U-235 + 1 Neutron 2 Neutrons + Kr-92 + Ba-142 + Energy Fusion Fusion is a nuclear reaction whereby two light atomic nuclei fuse or combine to form a single larger, heavier nucleus For fusion to occur, a large amount of energy is needed to overcome the electrical charges of the nuclei and fuse them together Fusion reactions do not occur naturally on our planet but are the principal type of reaction found in stars All Stars undergo Nuclear Fusion converting mass into energy THE SUN Fusion Changes Mass to Energy : E=mc2 .993 kg Helium 1kg Hydrogen mass difference ~ 0.019 u ~ 30 me energy gain ~ 20,000,000 chemical bonds!!! ***A nuclear chain reaction occurs when one nuclear reaction causes an average of one or more nuclear reactions, thus leading to a self-propagating number of these reactions. Ping pong NUCLEAR POWER PLANTS GENERATE ELECTRICITY Most power plants burn fuel to produce electricity, but not nuclear power plants. Instead, nuclear plants use the heat given off during fission of uranium as fuel. Unlike fusion, fission produces radioactive waste that must be disposed of FAR from populated areas and water sources since it causes mutations in living organisms. Fission Fission Fusion vs Fusion Requires less energy but yields less energy Produces Radioactive waste byproducts Requires more energy but yields more energy Doesn’t produce radioactive waste The nucleus of an atom changes into a new element – The proton number (atomic number) must change – A neutron changes into a proton 14 14 6 7 Atoms with the same number of protons but a different number of neutrons are called isotopes. Most of the isotopes which occur naturally are stable. A few naturally occurring isotopes and all of the man-made isotopes are unstable. Unstable isotopes can become stable by releasing different types of particles. This process is called radioactive decay and the elements which undergo this process are called radioisotopes/radionuclides. Elements with atomic numbers at or above 83 are radioactive. Other elements may have radioactive isotopes depending on the isotopes neutron to proton ratio. Radioactive Decay Radioactive decay results in the emission of either: • an alpha particle (a), • a beta particle (b), • or a gamma ray(g). Alpha Decayunstable atom emits an alpha particle A Z X A-4 Z-2 4 2 Y + He unstable atom alpha particle more stable atom 226 88 Ra 222 Rn 86 4 He 2 An alpha particle is identical to that of a helium nucleus. Simulation Beta Decay A beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay. Beta decay occurs when the neutron ratio is too high for the atom to be stable. 218 84 Po to proton 218 At 85 b 0 -1 Simulation Gamma Decay Gamma rays are electromagnetic radiation with high frequency. When atoms decay by emitting a or b particles to form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable. This excess energy is emitted as gamma rays (gamma ray photons have energies of ~ 1 x 10-12 J). Radioactive isotopes have predictable rates of decay. ***Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing radioactive decay to decrease by half. Half-Life For example, suppose we had 20,000 atoms of a radioactive substance. If the half-life is 1 hour, how many atoms of that substance would be left after: Time #atoms remaining % of atoms remaining 1 hour (one lifetime) ? 10,000 (50%) 2 hours (two lifetimes) ? 5,000 (25%) 3 hours (three lifetimes) ? 2,500 (12.5%) Radioisotopes are used in Medicine •Over 10,000 hospitals worldwide use radioisotopes in medicine •Isotopes must have a short half-life (time it takes to decay) because the body will flush it out quickly. Review Nuclear fission: A large nucleus splits into several small nuclei when impacted by a neutron, and energy is released in this process . Fission is easier to attain but radioactive waste is produced. Nuclear fusion: Several small nuclei fuse together and release energy. More energy is produced than fission but high temperatures are required. Question 1 Which nuclear process produces the largest amount of energy? A. Fission B. Fusion C. Both fission & fusion D. Neither fission nor fusion Question 2 Fission is the process that _________ atomic nuclei. A. Combines B. Burns up C. Stores D. Splits Question 3 Which force is the strongest? A. Gravitational B. Electromagnetic C. Weak D. Strong Quiz 4 Radioactive decay occurs naturally in elements that are unstable and depend on: A. Where the element is located on the periodic table B. How many electrons are in the atom’s energy levels C. The ratio of protons and neutrons in the nucleus of the atom Quiz 5 When the ratio of proton to neutrons is too high to be stable, a ________ decay is most likely. A. Alpha B. Beta C. Gamma Ray D. All of the above Video links US store nuclear waste 2013 US nuc waste US storage vid Without Humans video section