CHEM 1120 1st Edition Lecture 10 Outline of Last Lecture I Hypothesis vs Theory II Six Principles of Scientific Thinking a Ruling out rival hypotheses b Correlation vs causation c Falsifiability d Replicability e Extraordinary Claims f Occam s Razor III Typical Scientific Methods in Psychology a Natural Observation b Case Study Designs c Self Report d Correlational Designs e Experimental Designs Outline of Current Lecture I Detection of Radioactivity a Scintillation couter b Radiotracers c PET imaging d Applications of Ionizing Radiation II Energy Changes in Nuclear Reactions a Radioactive decay b Nuclear fission c Nuclear fussion d The mass defect These 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 energies f Fission and Fusion g MeV III Nuclear Power Fission a Subcritical b Critical mass c Supercritical d Controlled vs uncontrolled IV V Nuclear Power Fusion Radiation in the Environment and Living Systems a Excitation b Ionization Current Lecture I Detection of Radioactivity a Oldest method of detection is photographic film b More modern Geiger counter c Scintillation counter i Components ii Scintillator substance that emits light pulses when struck by radiation iii Photomultiplier a device that coverts light pulses into electric current and amplifies this current d Radiotracers i Small amount of radioisotope mixed with a stable isotope can act as a tracer that emits nonionizing radiation that signals its present ii Used in medicine e Positron Emission Tomography PET imaging i Used in observing brain structure and function ii Biological substance is synthesized with one of its atoms replaced by an isotope that emits positrons iii Substance is injected into a patient s blood stream and taken up to brain iv Photons are emitted which are detected by an array of detectors around patients head f II Applications of Ionizing radiation i Some radioisotopes use high energy ionizing radiation 1 Cancer cells diviede more rapidly than normal cells so radioisotopes that interfere with cell division kill more cancer cells than normal cells 2 Irradiation of food increases the shelf life by killing microorganisms that cause food to spoil Energy Changes in Nuclear Reactions a Radioactive decay nucleus emits one or a few small particles or photons to become a slightly lighter nucleus b Nuclear fission heavy nucleus splits into two much lighter nuclei emitting several small particles at the same time c Nuclear fusion 2 lighter nuclei combine to form a heavier one i Both release enormous amounts of energy d The mass Defect i Mass and energy are interconvertible total quantity of mass energy is constant 1 E mc 2 2 E energy 3 M mass 4 C speed of light ii Nuclear reactions Change in E c 2 x change in m iii Check out book to see good examples e Nuclear binding energies i Mass defect mass difference between a nucleus and its individual nucleons ii Nuclear binding energy energy required to separate a nucleus into its individual nucleons 1 Mass defect x c 2 iii Larger nuclear binding energy more stable nucleus f Fission and Fusion i Fission 1 Product nuclei have greater binding energy per nucleon are more stable than the reactant and the difference in energy is released 2 Nuclear power plant atomic bombs ii Fusion 1 Sun and other stars hydrogen bombs g Nuclear binding Energy in MeV i Joules too large to talk about energy of single nucleus ii Electron volt energy an electron acquires when it moves through a potential difference of 1 volt 1 1 eV 1 602 x 10 19 J III IV V 2 Mega electron volts MeV 10 6 eV 3 1 amu 931 5 MeV Nuclear Power Fission a Most beneficial application production of large amounts of energy b Must utilize this energy source safely and efficiently c Splitting of an atomic nucleus into 2 or more parts d Chain reaction i Shoot in one neutron produces 3 neutrons e Subcritical chain reaction stops f Critical mass mass required to achieve a chain reaction g Supercritical chain reaction accelerates a mass in excess of the critical mass h Controlled vs Uncontrolled Fission i Controlled 1 Electric power can be produced more cleanly than coal 2 Safe disposal is a serious problem 3 Nuclear power plant generates heat to produce steam which turns a turbine attached to an electric generator ii Uncontrolled 1 Manhattan project scientific effort to develop a bomb based on nuclear fission Nuclear Power Fusion a Very appealing energy source b Fuels are virtually limitless c For the most part the waste is not radioactive d But high temperatures are required for fusion e 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 container i Enclose plasma within a magnetic field tokamak magnetic bottle ii A doughnut shaped magnetic containment vessel for suspending plasma Radiation in the Environment and Living Systems a Nuclear changes cause chemical changes in surrounding matter i Emissions do affect electrons of nearby atoms b Excitation nonionizing radiation of relatively low energy interacts with an atom of a substance which absorbs some of the energy and then re emits it c Ionization ionizing radiation collides with an atom energetically enough to dislodge an election i Ionizing radiation rays can eject valence electrons and create ions in biological tissues ii Free radicals can initiate a chain of reactions producing damaged biomolecules iii Gamma and x rays can penetrate human tissue beta rays can penetrate 1 cm alpha rays stopped by skin