Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Nuclide which is unstable. It emits radiation & changes into another kind of atom. Radioactive Nuclide An atom with a specific number of protons and a specific number of neutrons. 14C 6 12C 6 14N 7 are all nuclides Nuclide Two atoms with the same atomic number but different mass numbers. Isotopes A change in the identity of a nucleus as a result of a change in the number of its protons. Transmutation Reaction As stability , energy . Relationship between stability and energy Attractive force between all nucleons. Holds the nucleus together. But it is a very short-range force. Nuclear Strong Force Occur between like charges. Occur between protons in the nucleus. Longer-range force. Electrostatic repulsive forces - Can be assessed by neutron to proton ratio. - A certain number of neutrons are needed to increase the strong nuclear force (the attractive force) enough to hold the nucleus together. - Small atoms, a stable N/P ratio is 1:1 - Large atoms: 1.5:1 Stability of nuclide All the elements with atomic number > 83 (or beyond Bismuth) That’s all nuclides 84! Which elements are unstable? Alpha, Beta, Gamma Separated by electric or magnetic fields. Opposites attract. Rays are pure energy. No charge so they are not deflected by an electric field. Types of Radiation Alpha radiation. Shielding can be paper or cloth. Least penetration power Gamma radiation. Requires lead/concrete shielding. Most penetration power Symbol for alpha radiation Same as the nucleus of a helium atom Mass = 4 amu Charge = +2 4 2He 4 or 2 Symbol for beta particle Fast moving electron originating from nucleus Mass = “zero” Charge = -1 0 -1e or 0 -1 or - or Symbol for positron. Mass = “zero.” Charge = +1. Positive electron 0 +1e or 0 +1 or + Symbol for gamma radiation. Pure Energy 0 mass 0 charge 0 0 or Symbol for neutron 1 0n or n Symbol for proton 1 1H or 1 1p Have mass numbers & atomic numbers Describes changes in the nucleus of an atom Nuclear Equations Unstable nucleus emits an alpha particle. Atomic # by 2. Mass # by 4. Alpha Decay Alpha Decay Atomic # by 2. Mass # by 4. 220Fr 87 4 + 216At 2 85 Equation represents natural transmutation. 1 term on reactant side. 220Fr 87 4 + 216At 2 85 Balance nuclear equations using conservation of atomic number & conservation of mass number. 220 220Fr 87 87 = 4 + 216 4 + 216At 2 = 85 2 + 85 Use a nuclide chart! For elements 1-20: If the n/p ratio is too high, beta emission happens. If the n/p ratio is too low, positron emission happens. Predicting Decay Modes Beta Decay Atomic # by 1. Mass # stays the same. 42K 19 0e -1 + 42Ca 20 Positron Emission Atomic # by 1. Mass # stays the same. 19Ne 10 0e + 19F +1 9 Elapsed time Length of H.L. # of Half-Lives = Fraction = 1/2n where n = # of half-lives Fraction Remaining 1 Half-Life Map Amount (mass) Initial Mass Elapsed Time 0 # of Half Lives 0 ½ 1 X H.L. 1 ¼ 2 X H.L. 2 1/8 3 X H.L. 3 1/16 4 X H.L. 4 Same as type of particle emitted Decay Mode Weighted average of the masses of the naturally occurring isotopes. Average Atomic Mass Cl has 2 isotopes: 25% Cl-37 & 75% Cl-35 1) Convert percent abundances to decimal format 2) Multiply each abundance factor by the appropriate isotopic mass 3) Sum 4) Do a reality check. 0.25(37) + (0.75)(35) = 9.25 + 26.25 = 35.5 35.5 is in between the high & the low, and it is closer to the more abundant isotopic mass. How to calculate the Average Atomic Mass of Cl Particle “bullet” hits target nucleus & new isotope is produced. 2 terms on reactant side. Artificial Transmutation Artificial Transmutation target 32S 16 bullet 1 + n 0 32P 15 + 1H 1 Particle “bullet” may be proton or alpha particle. To react with a nucleus, must overcome + + repulsive forces by accelerating bullet to high speeds. Particle “bullet” may be a neutron. Neutrons have no charge, so no repulsive forces to overcome. No acceleration necessary. Target can be anything from PT. Artificial Transmutation Fission is division. Large nucleus (U-235 or Pu-239) is split into 2 medium sized nuclei by a neutron bullet. Excess neutrons & a great deal of energy are also produced. Fission Fission 239Pu 94 147Ba + 3 1n + 01n 90 Sr + 38 56 0 Fusion: U for unite and U for sun. Very small nuclei (H & He) are jammed together. Huge amounts of energy are released. Fusion Fusion 1H 1 + 21H 3He 2 a) b) 1n 0 + 235U 92 59Co 27 c) 3He 2 d) 14C 6 142Ba 56 + 01n 60Co 27 + 91Kr 36 14N 7 + -10e 0 fission Artificial transmutation + 11H 4He + 0e 2 + 3 1n + energy +1 fusion Natural transmutation Identify each of the rxns The difference between the mass of a specific atom and the sum of the masses of its protons, neutrons, & electrons. Can be expressed in amu or kg. In nuclear reactions, a small amount of mass is converted to a huge amount of energy. Mass Defect, m The energy released when a nucleus is formed from its nucleons. Often expressed per nucleon. Nuclear Binding Energy 4He Potential Energy of System 2 + energy 2 protons + 2 neutrons Reference level Separate Nucleons Yellow arrow shows the binding energy! Stable Nucleus r, distance between nucleons Potential Well Diagram Represents potential energy changes during a process Einstein’s Equation relating energy and mass! Recall that to use this equation, the mass needs to be in kilograms, not amu’s. E = mc2 or E = mc2 1. Count up protons, neutrons, & electrons. 2. Multiply the number of particles X the mass of the particles. 3. Sum the terms. 4. Subtract the isotopic mass. This is m in amu’s. 5. Convert to kg. 6. Plug into Einstein’s famous equation, E = mc2 or E = mc2. 7. Divide by the number of nucleons to get BE per nucleon. 8. Multiply by Avogadro’s number to get binding energy per nucleon for 1 mole of substance. STEPS TO CALCULATE BINDING ENERGY Curve of Binding Energy Fe and Ni have the highest binding energies. The higher the binding energy, the more energy is released when the nucleus is formed. So the nucleus is in a deeper potential well, and it is MORE stable. Binding Energy & Stability Protons and Neutrons Mass # = # of nucleons Nucleon Fuel Control rods Containment or shielding Coolant Moderator Parts of a nuclear reactor Substance that slows down fast neutrons. Increases the efficiency of the fission process. Sometimes the moderator is also the coolant. Sometimes it is in the fuel rods. 1n 0 + 235U 92 Slow neutrons work better! 142Ba 56 + 91Kr 36 + 3 01n + energy But fast neutrons come off here! Moderator Contain a substance that absorbs neutrons, removing them from the reaction. On days with high electrical demand, the control rods would be removed from the core. Control Rods One of the products is also one of the reactants Neutron products Neutron reactant Chain Reaction The minimum amount of U-235 or Pu-239 that will undergo a selfsustaining chain reaction. Critical Mass Radioactive Dating: C-14 to C-12 for organic material. U-238 to Pb-206 for rocks. Killing bacteria/spores in food and mail. Chemical tracers: follow the path of material in a system. Used to study organic reaction mechanisms. Medical uses: I-131, Tc-99 Uses of radioisotopes