Chem 1120 1st Edition Lecture 11Outline of Last Lecture I. RadioactivityA. Chemical vs Nuclear ReactionsB. Definitions and Review of the nucleus II. Equations, Terms and Notation III. Balancing Nuclear ReactionsA. Modes of Radioactive DecayOutline of Current Lecture I. Detecting RadioactivityII. Energy Changes in Nuclear ReactionsIII. Fission and FusionA. Controlled vs Uncontrolled Fission IV. Radiation in the Environment and Living MatterCurrent LectureI. There are a few methods to detect radioactivity: Geiger counter, Scintillation counter, radiotracers, PET imagingScintillation ——> scintillator is a substance that emits light pulses when struck by radiation, photomultiplier is a device that converts light pulses into electric current and amplifies this currentRadiotracers ——> give us the ability to detect small amounts of radioisotopes -a small amount of radioisotope mixed with a stable one can act as a tracer that emits non ionizing radiation that signals its presence -largest use of these is in medicine 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.Positron Emission Testing (PET) ——> powerful imaging method for observingbrain structure and function where a biological substance is synthesized withone of its atoms replaced by an isotope that emits positrons, then the substance is injected into a patients bloodstream and taken to the brain, where photons are emitted and detected by an array of detectors around thepatients head II. Some radioisotopes use high energy ionizing radiation (cancer cells divide more rapidly than normal cells so radioisotopes that interfere with cell division kill more cancer cells than normal cells ——> used to treat brain tumors for exampleRadioactive Decay ——> nucleus emits one or a few particles or photons to become a slightly lighter nucleusTwo other processes cause much greater changes: nuclear fission and nuclear fusion; both release enormous quantities of energyThe Mass Defect ——> mass and energy are interconvertible, the total quantity of mass-energy is constantThe Einstein EquationNuclear reactions are accompanied by a loss or a gain of massThe much larger mass change that accompanies a nuclear process is related to the enormous energy required to bind the nucleus together or break it apartExample: What is the energy associated with the alpha decay of 1.00 gram of 238U?Solution:Nuclear masses are always less than the sum of their nucleons (protons and neutrons)Mass Defect = the mass difference between a nucleus and its individual nucleonsNuclear Binding Energy = energy required to separate a nucleus into its individual nucleons (nuclear binding energy = mass defect X c2)The larger the nuclear binding energy, the more stable the nucleus III. Fission = heavier nucleus splits into lighter ones by undergoing fission-product nuclei have greater binding energy per nucleon (they’re more stable) than the reactant and the difference in energy is released -nuclear power plants, atomic bombsFusion = lighter nuclei can combine to form a heavier one by undergoing fusion -sun, stars, hydrogen bombsJoules is too large of a unit to express the binding energy of a single nucleus Electron volt = energy an electron acquires when it moves through a potential difference of 1 volt- 1 eV = 1.602 X 10-19J - Mega-electron volts (MeV) = 106 eV = 1.602 X 10-13J- 1 amu = 931.5 X 106 eV = 931.5 MeVNuclear Fission ——> splitting of an atomic nucleus into 2 or more partsNuclear Fusion ——> two light nuclei are merged into one heavier nucleus*this is ideal, but it has to be completed at unreasonably high temperatures (matter exists as plasma at these temperatures)A. Uncontrolled fission leads to an uncontrolled chain reaction and can create a powerful explosive (Manhattan Project and atomic bombs) Controlled fission is usually shown in the form of nuclear energy reactors; a nuclear power plant generates heat to produce steam, which turns a turbine attached to an electric generatorNuclear waste is becoming the main problem with these, reactors must be stopped periodically to replace or reprocess nuclear fuel IV. Nuclear changes causechemical changes in surroundingmatter Radioactive emissions interactwith matter in two ways: Excitation = nonionizingradiation of relatively low energyinteract with an atom of asubstance which absorbs some ofthe energy and then re-emits itIonization = ionizingradiation collides with an atomenergetically enough to dislodgean electron•gamma and x-rays canpenetrate human tissue•beta rays can penetrate only about 1 cm•alpha rays are stopped by the skin, but can be dangerous within the body•1 gray (Gy) = 1 J/kg of tissue1 rad = 0.01 J/kg of