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. • Understand the concept of penetration power.
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 and be able to determine the type of radioactive decay for various isotopes. • Be able to determine the products of various transmutation reactions.
Nuclear Transformations • Protons repel, but the nuclear strong force can hold p+ and no together. • Neutrons are needed to supply this force, but a stable p+ to no ratio is necessary. • Elements “decay” to create a stable ratio.
Transmutations • transmutation: an atom is converted into a different atom (of a different element) • radioactive decay *positron: positive electron (antimatter) *neutrino (v): may be massless (nucleus is too heavy) (too many neutrons) (too many protons)
Transmutations • bombardment: particles collide 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.
Nuclear Fission • fission: the splitting of a large nucleus into smaller fragments • the products have less mass than the 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 more energy than fission reactions. • The energy (E=mc2) is mostly in the form gamma rays, positrons, and neutrinos.
Thermonuclear Weapons • Modern “nukes” use fission to start a fusion reaction. • These weapons are about 100 times more powerful than the A-bomb (1.2 megatons vs. 15 kilotons of TNT).