The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
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Nucleon is the term used to refer collectively to the particles that are found in the nucleus of an atom, the protons and the neutrons. The proton is a positively charged particle, while the neutron is neutral, but they have similar masses, the neutron being heavier than the proton by only one-thousandth of an atomic mass unit. An attractive force known as the strong nuclear force acts between the nucleons to hold the nucleus together. It acts between two neutrons, between two protons, or between a neutron and a proton, as long as they are no farther apart than a distance of one fermi (10-15 meters).
After developments in modern physics led to a proliferation of subatomic particles, by the 1960s physicists suggested a classification system that would group particles as either fermions or bosons. Fermions are the particles that exhibit half-integer spin and satisfy the Pauli exclusion principle, while bosons exhibit integer spin and are not limited by the exclusion principle. Therefore, nucleons are classified as fermions. A second classification divides particles into those that interact via the strong force, called hadrons, and those that do not, called leptons. Thus, nucleons are classified as hadrons. Hadrons that carry nucleon number one, as do both nucleons, are called baryons. In 1963 Murray Gell-Mann proposed that hadrons are made up of smaller charged particles which he called quarks, with each baryon containing three quarks. The only difference between the two nucleons is the number of each type of quark: protons have two "up" quarks and one "down" quark which give it a charge of +1, while neutrons have two down quarks and one up quark which give it a charge of 0. Gell-Mann was awarded the Nobel Prize in physics in 1969 for this work.