Kate Shoup - Particle Physics

Published in 2019 by Cavendish Square Publishing, LLC 243 5th Avenue, Suite 136, New York, NY 10016

Copyright 2019 by Cavendish Square Publishing, LLC First Edition

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Library of Congress Cataloging-in-Publication Data

Names: Shoup, Kate, 1972- author.

Title: Particle physics / Kate Shoup.

Description: First edition. | New York, NY : Cavendish Square Publishing,

LLC, [2019] | Series: Great discoveries in science | Includes bibliographical references and index. |

Audience: 9 to 12. Identifiers: LCCN 2018013135 (print) | LCCN 2018026077 (ebook) |

ISBN 9781502643711 (ebook) ISBN 9781502643810 (library bound) | ISBN 9781502643933 (pbk.)

Subjects: LCSH: Particles (Nuclear physics)--Juvenile literature. | Particles (Nuclear physics)--Histor--Juvenile literature. Classification: LCC QC793.27 (ebook) | LCC QC793.27 .S56 2019 (print) | DDC 539.7/2--dc23 LC record available at https://lccn.loc.gov/2018013135

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Contents

I n 1803, a British scientist named John Daltonbuilding on work by earlier scientists, such as Robert Boyle, Sir Isaac Newton, Gottfried Leibniz, and Ruder Boskovicput forth a theory on the nature of matter. Small particles called atoms exist and compose all matter, Dalton wrote. These atoms, he claimed, were indivisible and indestructible. Finally, Dalton concluded that Atoms of the same chemical element have the same chemical properties and do not transmute or change into different elements.

For more than ninety years, scientists believed Daltons model represented the final word on the nature of the atom. Two scientific discoveries during the 1890s, however, proved that aspects of Daltons model were either wrong or incomplete. The first of these discoveries occurred in 1896, when a French scientist named Henri Becquerel observed a phenomenon we now call radioactive decay. Further study by Becquerel, Marie and Pierre Curie, and Ernest Rutherford would prove that radioactive decay resulted in the transmutation of one element into another. In other words, said Rutherford, Radioactivity is shown to be accompanied by chemical changes in which new types of matter are being continually produced.

The second discovery to challenge Daltons atomic model was made by British scientist J. J. Thomson. In 1897, while conducting an experiment involving cathode rays, Thomson determined that atoms contained even smaller parts, meaning they were not in fact indivisible. Indeed, these parts, which Thomson called corpuscles, but scientists later renamed electrons, were much smaller than atomsone hundred million times smaller. Thomson also determined that electrons carried a negative electric charge. This discovery turned the disciplines of chemistry and physics inside out.

Further scientific advancements during the early twentieth century led to a revision of Daltons atomic model. The most notable of these advancements was the development of an entirely new scientific discipline called quantum physics. This field emerged in 1900 after a German scientist named Max Planck solved a problem, called the blackbody radiation problem, which had bedeviled scientists for decades. Although scientists had hypothesized (and experiments seemed to support) that atoms inside a blackbody should emit energy in a certain way, they had been unable to prove this hypothesis mathematically using the rules of classical physics. Planck discovered that if the equation restricted the amount of energy in these atoms to values of a certain range (rather than all possible values), it could be verified mathematically. From this, Planck and other scientists deduced that rather than being emitted in a gradual manner as had previously been assumed, all energy was emitted in tiny and instantaneous bursts. Moreover, they determined that this energy existed only in unified bundles, which they called quanta (the plural of quantum) and that particles like electrons were types of quanta.