Nuclear Reactions: AN INTRODUCTION TO FISSION & FUSION Farley Visitors Center

Chemical vs. Nuclear Reactions Chemical ReactionsNuclear Reactions Occur when bonds are brokenOccur when nuclei emit particles and/or rays Atoms remain unchanged, although they may be rearranged Atoms often converted into atoms of another element Involve only valence electronsMay involve protons, neutrons, and electrons Associated with small energy changes Associated with large energy changes Reaction rate influenced by temperature, particle size, concentration, etc. Reaction rate is not influenced by temperature, particle size, concentration, etc.

ã Nuclear reactions deal with interactions between the nuclei of atoms ã The focus of this presentation are the processes of nuclear fission and nuclear fusion ã Both fission and fusion processes deal with matter and energy Introduction

Matter and Energy ã Previous studies have taught us that “matter and energy cannot be created nor destroyed” ã We now need to understand that Matter and Energy are two forms of the same thing

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

ã The equation may be read as follows: Energy (E) is equal to Mass (m) multiplied by the Speed of Light (c) squared ã 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

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

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

ã A classic example of a fission reaction is that of U-235: U Neutron 2 Neutrons + Kr-92 + Ba Energy ã 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

ã 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 ã Fission produces large amounts of heat energy and it is this heat that is captured by nuclear power plants to produce electricity

Nuclear Fission Neutron induced in U 235 Fission is Exothermic The sum of the masses of the resulting nuclei is less than the original mass (about 0.1% less) The “missing mass” is converted to energy according to E=mc 2

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

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

ã Mass and Energy are two forms of the same thing; neither can be created nor destroyed but mass can be converted into energy (E = mc 2 ) ã Fission is a nuclear reaction in which a heavy atomic nucleus is split into lighter atomic nuclei ã Fusion is a nuclear reaction in which 2 light atomic nuclei are combined into a single, heavier atomic nucleus Review

Nuclear fission: A large nucleus splits into several small nuclei when impacted by a neutron, and energy is released in this process Nuclear fusion: Several small nuclei fuse together and release energy.

Quiz ã 1. Which nuclear process produces large amounts of energy? A. Fission B. Fusion C. Both fission & fusion D. Neither fission nor fusion

Quiz ã 2. Fission is the process that _________ atomic nuclei. A. Combines B. Burns up C. Stores D. Splits

Quiz ã 3. Mass may be converted into energy. A. True B. False

Quiz ã 4. The fission process requires heavy atomic nuclei. A. True B. False

Quiz ã 5. Name a nuclear reaction that occurs within the sun:

Quiz ã 6. Fission is a natural process that occurs on the planet Earth. A. True B. False

Quiz ã 7. Explain this equation: E = mc 2