CHEM 1120 1st Edition Lecture 11 Outline of Last Lecture 1 Nuclear stability continued 2 Nuclear transmutation 3 Rates of radioactive decay 4 Detection of radioactivity 5 Applications of radioactivity Outline of Current Lecture Current Lecture 21 6 Energy Changes in Nuclear Reactions Radioactive decay o Nucleus emits one or a few small particles or photons to become a slightly lighter nucleus Nuclear Fission Fusion two other processes that cause much greater changes They both release enormous quantities of energy o Fission Heavy nucleus splits into two much lighter nuclei emitting sever small particles at the same time o Fusion Two lighter nuclei combine to form a heavier one Mass defect o Mass and energy are interconvertible total quantity of mass and energy is constant o Einstein equation E mc 2 E energy M mass C speed of light 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 o Nuclear reaction are accompanied by a loss or gain of mass o mass is conserved in chemical reactions o The much larger mass change for nuclear processes is related to the enormous energy required to bind the nucleus together or break it apart o see slide 52 for reaction energy and mass change exercise Nuclear binding enegies o Nuclear masses are always less than the sum of the masses of their nucleons i e protons and neutrons o Mass defect mass difference between nucleus and its individual nucleons Nuclear binding energy o Energy required to separate a nucleus into its individual nucleons o Nucleus nuclear binding energy nucleons o Nuclear binding energy mass defect x c 2 o Slide 53 54 for nuclear binding energy exercise Nuclear binding energy in Mev o Joules is to large of a unit to express the binding energy of a single nucleus o Electron volt Energy an electron acquires when it moves through a potential diffence of 1 volt 1eV 1 602 19 J Mega electron volts MeV 10 6 eV 1 602x10 13 o Useful conversion factor 1 amu 931 5x10 6 eV 931 5 MeV o Slides 54 56 for MeV exercise s 21 7 Nuclear Power Fission Most beneficial application is production of large amount of energy Must utilize this energy source safely and efficiently Subcritical and supercritical fission o Critical mass Mass required to achieve a chain reaction o Supercritical mass Mass in excess of the critical mass Controlled vs uncontrolled fission o Controlled fission nuclear energy reactors Electric power can be produced more cleanly than coal A nuclear power plant generates heat to produce steam which turns a turbine attached to an electric generator s Safe disposal of nuclear waste is a serious problem o Uncontrolled chain reaction can create a powerful explosive Manhattan project 1941 Scientific effort to develop a bomb based on nuclear fission Lead to A bomb Nuclear Power Plant o In nuclear reactors heat generated by the reaction us used to produce steam that turns a turbine connected to a generator 21 8 Nuclear Power Fusion Energy from sun results from series of nuclear fusion reactions Very appealing energy source Fuels are virtually limitless For most part waste is not radioactive High temps are required around 100 000 000 K At these high temps matter exists as plasma neutral mixture of positive nuclei and electrons Must be confined in a manner that does not destroy its container Enclose plasma within a magnetic field tokamak magnetic bottle see slide 68 for picture Smoke detectors o See slide 71 Energy of transmuting collisions o Neutrons require minimal kinetic energy in order to collide with nucleus o A proton required very high kinetic energy in order to overcome repulsion from the nucleus o Particles with such kinetic energy produced in particle accelerators linear accelerators and cyclotrons Nuclear isotope dating o Carbon 14 half life of 5730 years o Used to date objects up to 36 000 years old