B. H. Fields - Understanding Neutrinos

To my classmate, friend, and world-class neutrino-catcher, Professor Lawrence R. Sulak

Published in 2016 by Cavendish Square Publishing, LLC
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Copyright 2016 by Cavendish Square Publishing, LLC

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Library of Congress Cataloging-in-Publication Data

Fields, B. H.

Understanding neutrinos / by B. H. Fields and Fred Bortz.

p. cm. (Exploring the subatomic world)

Includes index.

ISBN 978-1-50260-540-5 (hardcover) ISBN 978-1-50260-541-2 (ebook)

1. Neutrinos Juvenile literature. 2. Particles (Nuclear physics) Juvenile literature. I. Fields,

B. H. II. Title.

QC793.5.N42 F48 2016

539.7215d23

Editorial Director: David McNamara

Editor: Andrew Coddington

Copy Editor: Cynthia Roby

Art Director: Jeffrey Talbot

Designer: Stephanie Flecha

Senior Production Manager: Jennifer Ryder-Talbot

Production Editor: Renni Johnson

Photo Research: J8 Media

The photographs in this book are used by permission and through the courtesy of: DeAgostini/ Getty Images, cover; maralova/Shutterstock.com, throughout; By Loon, J. van (Johannes), ca. 1611-1686. (http://nla.gov.au/nla.map-nk10241) Public domain, via Wikimedia Commons, 7; Dr. Longs copy of Cassini/File:Cassini apparent.jpg/Wikimedia Commons, 8; Nicku/ Shutterstock.com, 9; Thomas Forget, 10; Paul Nadar, Public domain/File:Portrait of Antoine-Henri Becquerel.jpg via Wikimedia Commons, 15; SSPL/Getty Images, 17; By Bain News Service, publisher, Public domain/File:Ernest Rutherford 1908.jpg via Wikimedia Commons, 20; Thomas Forget, 22, 23; Encyclopaedia Britannica/UIG/Getty Images, 24; Science & Society Picture Library/Getty Images, 26; Ann Ronan Pictures/Print Collector/Getty Images, 29; Thomas Forget, 30, 33; Fermi National Accelerator Laboratory/Science Source/ Getty Images, 35; Max-Planck Institute, courtesy AIP Emilio Segre Visual Archives, 36; Jiu/ Imaginechina/AP Images, 38; Research Laboratory of Electronics/Greg Hren Photography, 41; Thomas Forget, 42; Science Source, 45; AIP Emilio Segre Visual Archives, 48; Thomas Forget, 50; Courtesy of the SNO+ Collaboration, 51; Thomas Forget, 52; NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University) File:CL0024+17.jpg/Wikimedia Commons, 54.

Printed in the United States of America

Contents

Matter and the Forces of Nature

Neutrinos Save the Day

Neutrino Number Two and the Particle Zoo

A Universe of Neutrinos

T his is the story of a kind of subatomic particle that you have probably never heard about. Yet it is more numerous by far than the ones you probably know. It is called the neutrino, Italian for little neutral one. Neutrinos speed through space, pass through matter, and rarely leave a trace. Still, on the rare occasions that we dectect them, they tell a remarkable story.

That story begins with facts you probably have learned in school. Every substance is made of atoms, and atoms are made of smaller subatomic particles called protons, neutrons, and electrons. Protons and neutrons carry most of the atoms mass and make up its central region, called the nucleus. Electrons are much lighter. You may have been told that the electrons orbit the nucleus like planets orbit the sun. Thats a useful way to view an atom, but, as you will discover, it is not exactly correct. And that is only the beginning of the story.

Besides those three kinds of subatomic particles, there are many others that are not found in matter as you are used to thinking about it. The neutrino is one of those other particles. In the chapters ahead, you will discover that neutrinos carry no electric charge, have very little mass, and are very hard to detect. Yet understanding neutrinos is essential to make sense of the entire subatomic world.

Although neutrinos are not contained within atoms, they are created within them. They come out of a nucleus during one kind of radioactive decay. They also emerge when heavy subatomic particles transform into lighter ones, or when nuclei merge together in a process called fusion. Fusion fuels the stars. Stars not only produce light and heat, but they also send vast numbers of neutrinos streaming outward.

Billions of neutrinos zip through your body every second without affecting it at all. In fact most neutrinos that reach Earth pass through without interacting with even a single atom. It takes careful scientific work to detect those few that do. In fact, it took about twenty-five years from the time physicists (scientists who study matter and energy) first realized that neutrinos were necessary in natures scheme of things until a team of researchers identified them in a nuclear reactor.

To understand neutrinos, you first need to understand atoms and their parts, especially the nucleus and the phenomenon of radioactivity. The nucleus was discovered little more than a century ago, and physicists are still exploring the forces within it. This book follows the path of discovery from the nucleus to the modern limits of particle physicswhere nearly massless, uncharged, barely detectable sprites known as neutrinos turn out to reveal the deepest secrets of the universe.

MATTER
and the Forces of Nature

P hysics is a mathematical science. When people hear or read that, they immediately think about equations or formulas. Those formulas often arise from patterns that physicists see in natural phenomena. Then they look for fundamental principles underlying those patterns.

The process often goes like this: At first, a pattern seems complex. Then someone discovers a new viewpoint from which things appears to be simpler. That viewpoint often leads to important discoveries about the laws that govern nature. Although this book will eventually take you to unfamiliar forces deep within atoms, it begins with a force you experience all the time: gravity.

The Universe According to Ptolemy. The second-century Greek-born Egyptian mathematician and astronomer Ptolemy observed and described the motion of the Sun, Moon, stars, and planets in several important texts. It was natural, though incorrect, for people of that time to view Earth as the center of all motion, as shown in this illustration based on Ptolemys writings.