Chem 1120 1st Edition Lecture 11 Outline of Last Lecture I Radioactivity A Chemical vs Nuclear Reactions B Definitions and Review of the nucleus II Equations Terms and Notation III Balancing Nuclear Reactions A Modes of Radioactive Decay Outline of Current Lecture I Detecting Radioactivity II Energy Changes in Nuclear Reactions III Fission and Fusion A Controlled vs Uncontrolled Fission IV Radiation in the Environment and Living Matter Current Lecture I There are a few methods to detect radioactivity Geiger counter Scintillation counter radiotracers PET imaging Scintillation 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 current Radiotracers 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 observing brain structure and function where a biological substance is synthesized with one 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 the patients 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 example Radioactive Decay nucleus emits one or a few particles or photons to become a slightly lighter nucleus Two other processes cause much greater changes nuclear fission and nuclear fusion both release enormous quantities of energy The Mass Defect mass and energy are interconvertible the total quantity of mass energy is constant The Einstein Equation Nuclear reactions are accompanied by a loss or a gain of mass The much larger mass change that accompanies a nuclear process is related to the enormous energy required to bind the nucleus together or break it apart Example What is the energy associated with the alpha decay of 1 00 gram of U 238 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 nucleons Nuclear 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 bombs Fusion lighter nuclei can combine to form a heavier one by undergoing fusion sun stars hydrogen bombs Joules 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 MeV Nuclear Fission splitting of an atomic nucleus into 2 or more parts Nuclear 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 generator Nuclear waste is becoming the main problem with these reactors must be stopped periodically to replace or reprocess nuclear fuel IV Nuclear changes cause chemical changes in surrounding matter Radioactive emissions interact with matter in two ways Excitation nonionizing radiation of relatively low energy interact with an atom of a substance which absorbs some of the energy and then re emits it Ionization ionizing radiation collides with an atom energetically enough to dislodge an electron gamma and x rays can penetrate 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 tissue 1 rad 0 01 J kg of tissue