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NUCLEAR CHEMISTRY. nuclear chemistry/physics : processes that occur in the NUCLEUS—these are not chemical reactions!. Objectives. What is radiation? Understand the meaning of terminology related to radioactivity. Know the three main types of nuclear radiation.
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NUCLEAR CHEMISTRY nuclear chemistry/physics: processes that occur in the NUCLEUS—these are not chemical reactions!
Objectives • What is radiation? Understand the meaning of terminology related to radioactivity. • Know the three main types of nuclear radiation. • Be able to write correct nuclear equations.
Radioactivity • 1896: Henri Becquerel discovers that uranium affects photographic film. • Marie Curie calls it radioactivity: the process of materials emitting “rays” • radiation: the rays/particles given off by a radioactive source • radioisotope: unstable isotope that emits radiation
Three Types of Radiation • a: Alpha (helium nucleus emitted) Total charge (subscript) and mass (superscript) must be conserved. • b: Beta (electrons emitted as no → p++ e-) • g: Gamma (high energy EM radiation)
Objectives • Why do atoms decay? Understand the concept of nuclear stability. • Be able to determine the type of radioactive decay based on various circumstances. • Be able to determine the products of various transmutation reactions.
Nuclear Stability • Protons repel, but the nuclear strong force holds p+ and no together. • A stable p+ / no ratio is needed. • Elements “decay” to make a stable ratio. 1:1.5 1:1
Transmutations • transmutation: an atom is converted into a different atom (a different element) • occurs through radioactive decay *positron: positive electron (antimatter) *neutrino (v): may be massless (nucleus is too heavy) (too many neutrons) (too many protons)
Transmutations • bombardment: particles collides with the nucleus to cause transmutations (like bowling!) Rutherford The discovery of the p+ and the no were achieved using bombardment.
Objectives • How long does it take for a nucleus to decay? Understand the concept of half-life. • Simulate the radioactive decay of an imaginary radioisotope and determine the half-life of the isotope. • Be able to make simple half-life calculations.
Half-Life • half-life (T1/2): the time it takes for one-half of the nuclei of a radioisotope to decay to products • 64 nuclei → 32 → 16 → 8 → 4 → 2 → 1 • If T1/2 = 200 years, it takes six half-lives (1200 years) to decay from 64 to 1.
Measuring Nuclear Decay • Fermium has a half-life of 100.5 days. How much of a 5.2 mg sample of fermium will remain after 365 days?
Objectives • What is nuclear energy? Understand the processes of nuclear fission. • Be able to discuss how various technologies employ nuclear fission. • Be familiar with the process of nuclear fusion.
Nuclear Fission • fission: the splitting of a large nucleus • products have less mass than reactants • mass is converted into energy (E=mc2)
Nuclear Fission Power • Nuclear power plants use controlled nuclear fission to release energy slowly. • Heat creates steam that generates electricity.
The Fission A-Bomb • The WWII bombs used uncontrolled nuclear fission. • Material must have a critical mass to explode. • Test bomb/Nagasaki: implosion of Pu-239 • Hiroshima:gun-type with U-235
Nuclear Fusion • nuclear fusion: small nuclei combine and release much more energy than fission reactions. • occurs in the sun and nuclear weapons
Thermonuclear Weapons • Modern “nukes” use fission to start a fusion reaction. • 100 times more powerful than the A-bomb (1.2 megatons vs. 15 kilotons of TNT).