Chapter 31. Caleb Pat FM Carrette

Introduction Formulas E-mc Strong nuclear force – The force that overcomes the mutual repulsion of the charged protons. Nucleons – the neutron and the proton. Binding energy - the energy required to separate particles from a molecule or atom or nucleus Mass defect - the mechanical energy required to disassemble a whole into separate parts Summary 31.1 – holding the nucleus together The strong force binds the nucleus together. The energy released in a nuclear reaction can be calculated by finding the mass defect, the difference in mass of the particles before and after the reaction. The binding energy is the energy equivalent of the mass defect.

31.2 * Artificial Radioactivity - a previously stable material has been made radioactive by exposure to specific radiation Fission – A division of a nucleus into two or more fragments Chain reaction – if one or more neutrons cause fission, that fission releases three more neutrons, each of which can cause more fission. Nuclear reactors - a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate Moderator - any substance used to slow down neutrons in nuclear reactors Control rods - a rod made of chemical elements capable of absorbing many neutrons without fissioning themselves Breeder reactors Nuclear fusion Fusion – nuclei with small masses combine to form a nucleus with a larger mass Thermonuclear reactions Controlled fusion Inertial confinement fusion

Summary 31.2 – using nuclear energy Bombardment can produce radioactive isotopes not found in nature. These are called artificial radioactive nuclei and are often used in medicine. In nuclear fission, the uranium nucleus is split into two smaller nuclei with a release of neutrons and energy Nuclear reactors use the energy released in fission to generate electrical energy The fusion of hydrogen nuclei into a helium nucleus releases the energy that causes stars to shine. Development of a process for controlling fusion for use on earth might provide large amounts of energy safely.

Nuclear reactions deal with interactions between the nuclei of atoms Nuclear reactions deal with interactions between the nuclei of atoms The focus of this presentation are the processes of nuclear fission and nuclear fusion, The focus of this presentation are the processes of nuclear fission and nuclear fusion, E = mc 2, history of nuclear physics Both fission and fusion processes deal with matter and energy Both fission and fusion processes deal with matter and energy Introduction

Mass Matter can be changed into Energy Matter can be changed into Energy Einstein’s formula above tells us how the change occurs Einstein’s formula above tells us how the change occurs In the equation above: In the equation above: E = Energy m = Mass c = Speed of Light (Universal Constant) Energy Light Speed Light Speed E = mc 2

The equation may be read as follows: The equation may be read as follows: Energy (E) is equal to Mass (m) multiplied by the Speed of Light (c) squared This tells us that a small amount of mass can be converted into a very large amount of energy because the speed of light (c) is an extremely large number This tells us that a small amount of mass can be converted into a very large amount of energy because the speed of light (c) is an extremely large number

29.2 Binding Energy The total energy of the bound system (the nucleus) is less than the combined energy of the separated nucleons Binding Energy per Nucleon

binding energy This difference in energy is called the binding energy of the nucleus It can be thought of as the amount of energy you need to add to the nucleus to break it apart into separated protons and neutrons

Binding Energy Notes Except for light nuclei, the binding energy is about 8 MeV per nucleon The curve peaks in the vicinity of A = 60 Nuclei with mass numbers greater than or less than 60 are not as strongly bound as those near the middle of the periodic table The curve is slowly varying at A > 40 This suggests that the nuclear force saturates A particular nucleon can interact with only a limited number of other nucleons

Ex. Nuclear binding energy = Δmc^2 For the alpha particle Δm= u which gives a binding energy of 28.3 MeV.

Fission Fusion

Fission Fission may be defined as the process of splitting an atomic nucleus into fission fragments Fission may be defined as the process of splitting an atomic nucleus into fission fragments The fission fragments are generally in the form of smaller atomic nuclei and neutrons The fission fragments are generally in the form of smaller atomic nuclei and neutrons Large amounts of energy are produced by the fission process Large amounts of energy are produced by the fission process

Fission Fissile nuclei are generally heavy atoms with large numbers of nucleons Fissile nuclei are generally heavy atoms with large numbers of nucleons The nuclei of such heavy atoms are struck by neutrons initiating the fission process The nuclei of such heavy atoms are struck by neutrons initiating the fission process Fission occurs due to electrostatic repulsion created by large numbers of protons within the nuclei of heavy atoms Fission occurs due to electrostatic repulsion created by large numbers of protons within the nuclei of heavy atoms

A classic example of a fission reaction is that of U-235: A classic example of a fission reaction is that of U-235: U Neutron 2 Neutrons + Kr-92 + Ba Energy In this example, a stray neutron strikes an atom of U-235. It absorbs the neutron and becomes an unstable atom of U-236. It then undergoes fission. Notice that more neutrons are released in the reaction. These neutrons can strike other U-235 atoms to initiate their fission. In this example, a stray neutron strikes an atom of U-235. It absorbs the neutron and becomes an unstable atom of U-236. It then undergoes fission. Notice that more neutrons are released in the reaction. These neutrons can strike other U-235 atoms to initiate their fission. Fission

The fission process is an a natural one as a French researcher found a natural uranium reactor in Gabon, West Africa; it has been estimated to be over 2 billion years old The fission process is an a natural one as a French researcher found a natural uranium reactor in Gabon, West Africa; it has been estimated to be over 2 billion years old Fission produces large amounts of heat energy and it is this heat that is captured by nuclear power plants to produce electricity Fission produces large amounts of heat energy and it is this heat that is captured by nuclear power plants to produce electricity

Fusion is a nuclear reaction whereby two light atomic nuclei fuse or combine to form a single larger, heavier nucleus Fusion is a nuclear reaction whereby two light atomic nuclei fuse or combine to form a single larger, heavier nucleus The fusion process generates tremendous amounts of energy; refer back to Einstein’s equation The fusion process generates tremendous amounts of energy; refer back to Einstein’s equation For fusion to occur, a large amount of energy is needed to overcome the electrical charges of the nuclei and fuse them together For fusion to occur, a large amount of energy is needed to overcome the electrical charges of the nuclei and fuse them together Fusion

Fusion reactions do not occur naturally on our planet but are the principal type of reaction found in stars Fusion reactions do not occur naturally on our planet but are the principal type of reaction found in stars The large masses, densities, and high temperatures of stars provide the initial energies needed to fuel fusion reactions The large masses, densities, and high temperatures of stars provide the initial energies needed to fuel fusion reactions The sun fuses hydrogen atoms to produce helium, subatomic particles, and vast amounts of energy The sun fuses hydrogen atoms to produce helium, subatomic particles, and vast amounts of energy

Difference between controlled and uncontrolled reactions

1. The operators

Uncontrolled reactions

History

Fallout from Chernobyl

Three-Mile Island, PA 1979

Plants near TMI -lack of chlorophyll -deformed leaf patterns -thick, flat, hollow stems -missing reproductive parts -abnormally large TMI dandelion leaf at right

States with nuclear power plant(s)

Nuclear Reactor Process 3% enriched Uranium pellets formed into rods, which are formed into bundles Bundles submerged in water coolant inside pressure vessel, with control rods. Bundles must be SUPERCRITICAL; will overheat and melt if no control rods. Reaction converts water to steam, which powers steam turbine

Yucca Mountain

Introduction: Development of Nuclear Physics 1896 – the birth of nuclear physics Becquerel discovered radioactivity in uranium compounds Rutherford showed the radiation had three types Alpha (He nucleus) Beta (electrons) Gamma (high-energy photons) 1911 Rutherford, Geiger and Marsden performed scattering experiments Established the point mass nature of the nucleus Nuclear force was a new type of force

1919 Rutherford and coworkers first observed nuclear reactions in which naturally occurring alpha particles bombarded nitrogen nuclei to produce oxygen 1932 Cockcroft and Walton first used artificially accelerated protons to produce nuclear reactions 1932 Chadwick discovered the neutron 1933 the Curies discovered artificial radioactivity 1938 Hahn and Strassman discovered nuclear fission 1942 Fermi achieved the first controlled nuclear fission reactor