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

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 ã c = 3.0 x 10 8 m/s300,000,000 m/s

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 Sufficient neutrons will create a chain reaction 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

Fission Reaction

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

Producing Electricity from Fission

U.S. Electrical Power Sources

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

Fusion and Energy ã Iron and nickel nuclei have the largest binding energies per nucleon of all nuclei and therefore are the most stable. ã The fusion of two nuclei lighter than iron or nickel generally releases energy. ã The fusion of nuclei heavier than them absorbs energy.

FUSION DEUTERIUM TRITIUM HELIUM NEUTRON

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

Every second, the sun converts 500 million metric tons of hydrogen to helium. Due to the process of fusion, 5 million metric tons of excess material is converted into energy in each second. This means that every year, 157,680,000,000,000 metric tons are converted into energy. THE SUN

Cold Fusion ã Efforts are being made to start and sustain a fusion reaction at lower temperatures, in other words with a lower amount of input 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. Review

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

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

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

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

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

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

Quiz ã Explain this equation: E = mc 2