Nuclear Chemistry Nuclear Radiation • Marie Curie – Radioactivity • Radiation – penetrating rays & particles • Radioisotopes – nuclei of unstable isotopes Nuclear Radiation (cont’d) • Chemical reaction vs. Nuclear reaction • Radioactive decay – unstable nucleus releases energy through radiation Types of Radiation • Radioactive decay • Alpha Particle – 2 protons, 2 neutrons, double positive charge (not shown) • Beta Particle – electron • Gamma radiation – no significant mass, no charge Alpha Particle • Stopped by a sheet of paper 4 2 He 238 234 4 92 U 90Th 2 He Beta Particle • Results from breaking apart a neutron • Stopped by metal foil or layers of wood • Less mass, less charge – penetrates more 1 1 0 0 n 1H -1e 14 14 0 6 C 7 N -1e Gamma Radiation • High energy photon • Very penetrating • Stopped by meters of concrete or cm of lead 230 226 4 90Th 88Ra 2 He Nuclear Transformations • Unstable nuclei • Neutron (N) to proton (Z) ratio – Atomic # < 20: N/Z = 1 – Atomic # > 20: N/Z > 1 Nuclear Stability – Rules 1. Most stable nuclei have a # of neutrons = or > # of protons 2. A nucleus with N/Z too large or too small is unstable (N= neutron, Z = proton) 3. Nuclei with even #’s of neutrons & protons are more stable 4. Certain nuclei are more stable than others – atomic #’s 2, 8, 20, 28, 50, 82, 126 5. Atomic # > 83, Mass # >209 = unstable Types of decay • Depend upon N/Z ratio 1.Beta emission – N/Z too high (too many neutrons per proton) 2.Electron capture – N/Z too low (too many protons) 3.Positron emission – proton changes to neutron 4.Alpha emission – increases N/Z ratio Half-life • Time required for half of nuclei to decay to products (t1/2) • Ranges from fractions of a second to several years • Short-lived isotopes useful in medicine • Long-lived isotopes useful in dating artifacts Transmutation Reactions • Conversion of an atom of 1 element to an atom of another element • Radioactive decay or nucleus bombardment (particle accelerators) • Atomic # > 92 = transuranium elements – all undergo transmutation Transmutation • Rutherford – earliest artificial transmutation 14 4 18 7 N 2 He 9 F 18 17 1 9 F 8 O 1H • Chadwick – discovery of neutron 9 4 12 1 4 Be 2 He 6 C 0 n Fission • Nuclear Fission – splitting of nucleus into smaller fragments • Chain reaction – neutrons strike nucleus releasing more neutrons • Critical mass – minimum quantity of radioactive material needed to continue chain reaction More Fission • Neutron moderation – Slows down neutrons for capture – Water, graphite • Neutron Absorption – Decreases # of slow-moving neutrons – Prevents chain reaction from going too fast • Nuclear Waste – Water tanks used to cool spent fuel rods from power plants Fusion • Nuclear Fusion – combination of nuclei to produce nucleus of greater mass • Release more energy than fission reactions • Occur only @ extremely high temps. (40,000,000°C) • Desirable as energy source • Chernobyl Radiation in Your Life • Ionizing radiation – has enough energy to produce ions – Knocks electrons off of atoms of a bombarded substance Detecting Radiation • Geiger Counter – detects , , • Scintillation Counter – detects all ionizing radiation • Film Badge – monitors degree of exposure Using Radiation • Nuclear Activation Analysis – detects trace amounts of elements in substances – Used for art forgeries, gun powder residue detection • Radioisotope tracers – Used in agriculture • Radioisotopes in medicine – Diagnosis & treatment of disease Using Radiation • Medicine – Radiation Therapy – Teletherapy – Pharmaceuticals • Industry – Smoke Detectors .