Nuclear
Band of Stability n = p Number of neutrons Number of protons 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 Band of Stability n = p Number of neutrons The band of black squares, which shows the stable nuclides, is known as the band of stability. In general, the further a nuclide is from the band of stability, the shorter the half-life of the nuclide. No stable isotopes are known for elements with atomic numbers higher than 83 (bismuth). Stable nuclides Naturally occurring radioactive nuclides Other known nuclides 10 20 30 40 50 60 70 80 90 100 110 Number of protons
Nuclear Decay Why nuclides decay… b a need stable ratio of neutrons to protons 120 100 80 60 40 20 Neutrons (A-Z) Protons (Z) P = N b stable nuclei a e-capture or e+ emission Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem DECAY SERIES TRANSPARENCY
Nuclear Decay Why nuclides decay… b a need stable ratio of neutrons to protons stable nuclei P = N b stable nuclei a P = N 120 120 e-capture or e+ emission 100 100 80 80 60 60 Neutrons (A-Z) Neutrons (A-Z) 40 40 20 20 20 40 60 80 100 120 20 40 60 80 100 120 Protons (Z) Protons (Z)
Discovery of the Neutron + + Chadwick is credited with the discovery of the neutron as a result of this transmutation experiment. James Chadwick bombarded beryllium-9 with alpha particles, carbon-12 atoms were formed, and neutrons were emitted. Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 764
Types of Radiation Type Symbol Charge Mass (amu) Alpha particle 2+ 4.015062 Beta particle 1- 0.0005486 Positron 1+ Gamma ray
Alpha, Beta, Gamma Rays b rays g rays a rays Lead block (+) (-) (negative charge) Aligning slot (no charge) g rays a rays Radioactive substance (positive charge) Photographic plate Electrically charged plates (detecting screen)
Alpha, Beta, Positron Emission Examples of Nuclear Decay Processes a emission (alpha) b- emission (beta) b+ emission (positron) Although beta emission involves electrons, those electrons come from the nucleus. Within the nucleus, a neutron decays into a proton and an electron. The electron is emitted, leaving behind a proton to replace the neutron, thus transforming the element. (A neutrino is also produced and emitted in the process.) Herron, Frank, Sarquis, Sarquis, Schrader, Kulka, Chemistry, Heath Publishing,1996, page 275
Nuclear Decay Numbers must balance!! Alpha Emission parent nuclide daughter nuclide alpha particle Numbers must balance!! Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Nuclear Decay Beta Emission electron Positron Emission positron Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Nuclear Decay Electron Capture electron Gamma Emission Transmutation Usually follows other types of decay. Transmutation One element becomes another. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Half-Lives of Isotopes Half-Lives and Radiation of Some Naturally Occurring Radioisotopes Isotope Half-Live Radiation emitted Carbon-14 5.73 x 103 years b Potassium-40 1.25 x 109 years b, g Radon-222 3.8 days a Radium-226 1.6 x 103 years a, g Thorium-230 7.54 x 104 years a, g Thorium-234 24.1 days b, g Uranium-235 7.0 x 108 years a, g Uranium-238 4.46 x 109 years a
Half-Life Plot Half-life of iodine-131 is 8 days 20 Half-life of iodine-131 is 8 days 15 1 half-life Amount of odine-131 (g) 10 16 2 half-lives 5 24 3 half-lives 32 4 half-lives etc… 40 48 56 8 Time (days) Timberlake, Chemistry 7th Edition, page 104
Half-Life Half-life (t½) Time required for half the atoms of a radioactive nuclide to decay. Shorter half-life = less stable. 1/1 Newly formed rock Potassium Argon Calcium Ratio of Remaining Potassium-40 Atoms to Original Potassium-40 Atoms 1/2 1/4 1/8 1/16 1 half-life 1.3 1 half-lives 2.6 3 half-lives 3.9 1 half-lives 5.2 Time (billions of years)
Half-Life Half-life (t½) Time required for half the atoms of a radioactive nuclide to decay. Shorter half-life = less stable. 1/1 1/2 1/4 1/8 1/16 Ratio of Remaining Potassium-40 Atoms to Original Potassium-40 Atoms 1 half-life 1.3 1 half-lives 2.6 3 half-lives 3.9 5.2 Time (billions of years) Newly formed rock Potassium Argon Calcium
Nuclear Fusion + + + Sun Energy Four hydrogen nuclei (protons) Two beta particles (electrons) One helium nucleus
Conservation of Mass …mass is converted into energy Hydrogen (H2) H = 1.008 amu Helium (He) He = 4.004 amu FUSION 2 H2 1 He + ENERGY 1.008 amu x 4 4.0032 amu = 4.004 amu + 0.028 amu This relationship was discovered by Albert Einstein E = mc2 Energy= (mass) (speed of light)2
Mass Defect Difference between the mass of an atom and the mass of its individual particles. 4.00260 amu 4.03298 amu Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
The Energy of Fusion The fusion reaction releases an enormous amount of energy relative to the mass of the nuclei that are joined in the reaction. Such an enormous amount of energy is released because some of the mass of the original nuclei is con- verted to energy. The amount of energy that is released by this conversion can be calculated using Einstein's relativity equation E = mc2. Suppose that, at some point in the future, controlled nuclear fusion becomes possible. You are a scientist experimenting with fusion and you want to determine the energy yield in joules produced by the fusion of one mole of deuterium (H-2) with one mole of tritium (H-3), as shown in the following equation:
2.01345 amu 3.01550 amu 4.00150 amu 1.00867 amu 5.02895 amu 5.02895 amu 5.01017 amu 5.01017 amu First, you must calculate the mass that is "lost" in the fusion reaction. The atomic masses of the reactants and products are as follows: deuterium (2.01345 amu), tritium (3.01550 amu), helium-4 (4.00150 amu), and a neutron (1.00867 amu). Mass defect: - 0.01878 amu