CHEM 106 1nd Edition Lecture 17Outline of Last Lecture I. NucleosynthesisII. Beta DecayIII. Radioactive DecayIV. Nuclear Binding EnergyOutline of Current Lecture II. Belt of StabilityIII. Decay (Radioactive, Alpha, and Beta)IV. Natural Decay SeriesV. Nuclear Fissiona. Nuclear FuelsCurrent LectureChapters 2 & 21: Nuclear and Radiochemistry (continued)Catalyst Demo:C4H4O62-(aq) + 5H2O2(aq) → CO32-(aq) + 3CO2(g) + H2O(l)Catalysts: Co 2+ and 2Cl- (Oxidation of Tartrate by H2O2 with and without Co2+ catalyst)21.4 Belt of StabilityLight, stable nuclei: protonsneutrons equals about 1Heavier, stable nuclei:protonsneutrons < 1 (neutrons in excess)Radioactive Decay- change in nuclear structure that frequently alters protonsneutronsBeta Decay-Electron emission (negatron)Underlying nuclear change is neutron → protonPositron emission (positron)Underlying nuclear change is proton → neutronElectron capture (external electron)C611+ e−10→ B511proton → neutronThese can bring a molecule closer to the belt of stabilityFor lighter nuclei, you can predict decay modes from protonsneutrons ratioC610 – proton rich, electron capture or β+1019Ne – 10 protons, proton rich, electron capture or β+1053Ti – 22 protons, 21 neutrons, neutron rich, β−10Alpha Decay (α emission ¿U92238→ Th90234+ α24t12 = 4.46 e6 yearsFig. 21.6 pg. 1008How decay modes result in change shown on a chart of nuclidesNatural Radioactive Decay Series Thorium decay series-232Th parentUranium decay series-238U parentActinium decay series-235U parentThese have been decaying since they were formedFig. 21.7 pg. 1009, uranium decay series8 α decays6 β particles emitted206Pb final productExtinct Natural Decay SeriesEx: neptunium decay series237Np present; t12 = 2.16 * 106 yearsEarth’s formation was about 4.7 * 109 years ago209Bi final productNote belt of stability for heaviest nuclei-Neutron: proton is about 1.5 to 1 (for heavy isotopes)What is the net result of α decay?Losing an α ↑ neutron: proton ratioCreates neutron-rich isotopesBeta decay (negatron emission) converts neutrons to protons21.5 Synthesizing IsotopesArtificial nuclear reactions since around 1919Ex: N714+ α24→ O817+ p11Al1327+ α24→ p1530+ n01α’s form accelerators or spontaneous α decayReactions only occur if collisional energy is correct.Ex: U92238+ n01→ Pu94239+2 β−10Cf98249+ O818→ Sg106263+ 4 n0121.6 Nuclear Fission, Chain ReactionFig. 21.9 pg. 1013U92235+ n01→ Ba56144+ Kr3692+3 n01Or→ Te52137+ Zr4097+2 n01Or→ Cs55138+ Rb3796+2 n01And much moreSignificant energy is released. More neutrons are released than consumed.For subsequent neutron-induced fission, neutron energy must be moderated.Typical moderators: water, graphite, berylliumChain reaction can be stopped completely by absorbing the neutrons.Typical neutron absorbers: Cd, Gd, B, Ag, In Nuclear Fuels:235U (U.S. civilian reactors), 238U, 239Pu, 238Pu (nuclear batteries), 232ThNatural U is: 99.27% 238U, 0.72% 235U, and 0.005% 234UOklo reactors: naturally occurring nuclear reactorsEnrichment of 235UU3O8 → UF6 = volatile solid, sublimes at 57°C235U vs. 238UF6Centrifugation or gaseous diffusion to separate 235UF6