CHEM 1120 1st Edition Lecture 10 Outline of Last Lecture I. Hypothesis vs. TheoryII. Six Principles of Scientific Thinkinga. Ruling out rival hypothesesb. Correlation vs. causationc. Falsifiabilityd. Replicabilitye. Extraordinary Claimsf. Occam’s RazorIII. Typical Scientific Methods in Psychologya. Natural Observationb. Case Study Designsc. Self-Reportd. Correlational Designse. Experimental DesignsOutline of Current Lecture I. Detection of Radioactivitya. Scintillation couterb. Radiotracersc. PET imagingd. Applications of Ionizing RadiationII. Energy Changes in Nuclear Reactionsa. Radioactive decayb. Nuclear fissionc. Nuclear fussiond. The mass defectThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.e. Nuclear binding energiesf. Fission and Fusiong. MeVIII. Nuclear Power: Fissiona. Subcriticalb. Critical massc. Supercriticald. Controlled vs uncontrolledIV. Nuclear Power FusionV. Radiation in the Environment and Living Systemsa. Excitationb. IonizationCurrent LectureI. Detection of Radioactivitya. Oldest method of detection is photographic filmb. More modern: Geiger counterc. Scintillation counteri. Components:ii. Scintillator: substance that emits light pulses when struck by radiationiii. Photomultiplier: a device that coverts light pulses into electric current and amplifies this currentd. Radiotracersi. Small amount of radioisotope mixed with a stable isotope can act as a tracer that emits nonionizing radiation that signals its presentii. Used in medicinee. Positron Emission Tomography (PET imaging)i. Used in observing brain structure and functionii. Biological substance is synthesized with one of its atoms replaced by an isotope that emits positronsiii. Substance is injected into a patient’s blood stream and taken up to brainiv. Photons are emitted which are detected by an array of detectors around patients headf. Applications of Ionizing radiationi. Some radioisotopes use high-energy ionizing radiation1. Cancer cells diviede more rapidly than normal cells so radioisotopes that interfere with cell division kill more cancer cellsthan normal cells2. Irradiation of food increases the shelf life by killing microorganisms that cause food to spoilII. Energy Changes in Nuclear Reactionsa. Radioactive decay: nucleus emits one or a few small particles or photons to become a slightly lighter nucleusb. Nuclear fission: heavy nucleus splits into two much lighter nuclei emitting severalsmall particles at the same timec. Nuclear fusion: 2 lighter nuclei combine to form a heavier onei. Both release enormous amounts of energyd. The mass Defecti. Mass and energy are interconvertible-total quantity of mass-energy is constant1. E=mc^22. E: energy3. M: mass4. C: speed of lightii. Nuclear reactions: Change in E=c^2 x (change in m)iii. Check out book to see good examplese. Nuclear binding energiesi. Mass defect: mass difference between a nucleus and its individual nucleonsii. Nuclear binding energy: energy required to separate a nucleus into its individual nucleons1. Mass defect x c^2iii. Larger nuclear binding energy = more stable nucleusf. Fission and Fusioni. Fission1. Product nuclei have greater binding energy per nucleon (are more stable) than the reactant and the difference in energy is released2. Nuclear power plant, atomic bombsii. Fusion1. Sun and other stars, hydrogen bombsg. Nuclear binding Energy in MeVi. Joules too large to talk about energy of single nucleusii. Electron volt- energy an electron acquires when it moves through a potential difference of 1 volt1. 1 eV= 1.602 x 10^-19 J2. Mega-electron volts (MeV)= 10^6 eV3. 1 amu= 931.5 MeVIII. Nuclear Power: Fissiona. Most beneficial application: production of large amounts of energyb. Must utilize this energy source safely and efficientlyc. Splitting of an atomic nucleus into 2 or more partsd. Chain reactioni. Shoot in one neutron, produces 3 neutronse. Subcritical: chain reaction stops,f. Critical mass: mass required to achieve a chain reactiong. Supercritical: chain reaction accelerates, a mass in excess of the critical massh. Controlled vs Uncontrolled Fissioni. Controlled1. Electric power can be produced more cleanly than coal2. Safe disposal is a serious problem3. Nuclear power plant generates heat to produce steam, which turns a turbine attached to an electric generatorii. Uncontrolled1. Manhattan project-scientific effort to develop a bomb based on nuclear fissionIV. Nuclear Power: Fusiona. Very appealing energy sourceb. Fuels are virtually limitlessc. For the most part the waste is not radioactived. But high temperatures are required for fusione. At these high temperatures, matter exists as plasma ( a neutral mixture of positive nuclei and electrons) which must be confined in a manner that does not destroy its containeri. Enclose plasma within a magnetic field-tokamak-magnetic bottleii. A doughnut shaped magnetic containment vessel for suspending plasmaV. Radiation in the Environment and Living Systemsa. Nuclear changes cause chemical changes in surrounding matteri. Emissions do affect electrons of nearby atomsb. Excitation: nonionizing radiation of relatively low energy interacts with an atom of a substance which absorbs some of the energy and then re-emits itc. Ionization: ionizing radiation collides with an atom energetically enough to dislodge an electioni. Ionizing radiation: rays can eject valence electrons and create ions in biological tissuesii. Free radicals can initiate a chain of reactions producing damaged biomoleculesiii. Gamma and x rays can penetrate human tissue, beta rays can penetrate 1 cm, alpha rays stopped by