Greg Roza - Plutonium

For Allen

Published in 2009 by The Rosen Publishing Group, Inc.

29 East 21st Street, New York, NY 10010

Copyright 2009 by The Rosen Publishing Group, Inc.

First Edition

All rights reserved. No part of this book may be reproduced in any form without permission in writing from the publisher, except by a reviewer.

Library of Congress Cataloging-in-Publication Data

Roza, Greg.

Plutonium / Greg Roza.1st ed.

p. cm.(Understanding the elements of the periodic table)

Includes bibliographical references and index.

ISBN-13: 978-1-4042-1781-2 (lib. bdg.)

1. Plutonium. 2. Periodic lawTables. 3. Radioactivity. I. Title.

QD181.P9R69 2009

546.434dc22

2007047903

Manufactured in Malaysia

On the cover: Plutoniums square on the periodic table of elements. Inset: The atomic structure of plutonium.

Contents

L ike all elements up to fermium (Fm), plutonium (Pu) appears to be created when stars explode. Because plutonium breaks down into lighter elements over the course of millions of years, most of the natural plutonium on Earth decayed long ago. Therefore, essentially all of the plutonium on Earth has been created in laboratories during the past sixty years.

As the age of space exploration blossomed in the mid-1900s, scientists recognized plutoniums potential as a fuel for spaceships journeying into the depths of space. Over the years, it was used to power numerous manned and unmanned space explorations. In 1997, scientists from the United States and Europe launched the Cassini-Huygens space probe. Cassini-Huygens traveled 2.2 billion miles (3.5 billion kilometers) in just under seven years to reach Saturn. The Huygens probe separated from the Cassini orbiter and landed on the surface of Saturns moon Titan. Since July 2004, Cassini has been exploring Saturn and its many moons from orbit.

The Cassini orbiter contains 72.3 pounds (32.8 kilograms) of plutonium dioxide (PuO2) fuelthe most plutonium launched into space at the time.

This launch was strongly protested by antinuclear activists. Many people were afraid that an accident during the launch could be disastrous. Scientists provided extensive evidence and testing data to prove that the chances of an accident occurring were incredibly slim. They went ahead with the launch despite some continued objections.

The Cassini-Huygens space probe is being prepared for its mission at the Kennedy Space Center, Florida, on August 22, 1997.

Cassini has sent back abundant information about Saturn. Scientists planned for Cassini to function until 2008, but they now think it may last and be able to transmit data until 2012. This feat would not have been possible without plutonium fuel.

Plutonium plays a special role in the exploration of space. It is also used to create energy in nuclear power plants. Despite these useful abilities, plutonium is known to be a highly dangerous and controversial element because it can also be used to make nuclear weaponry. Sufficient exposure to plutonium can make people deadly sick. Despite the dangers, more than 2,000 tons (1,800 metric tons) of the element have been created over the past seventy years. Plutonium can be handled safely with the appropriate skills and equipment.

I t is difficult to discuss plutonium without first mentioning uranium (U), the element from which plutonium is made. In the eighteenth century, German silver miners discovered a black mineral they called pitchblende. Today it is called uraninite or uranium dioxide (UO2). In 1789, German chemist Martin Heinrich Klaproth analyzed pitchblende and identified that it contained a new element. He named it uranium after the planet Uranus.

In 1896, quite by accident, the French physicist Henri Becquerel discovered that uranium emitted strange rays. In 1903, Becquerel and Polish-French physicist Marie Curie received the Nobel Prize for Physics for the discovery and study of this radiation. Their work was just the beginning of the exploration of radioactive chemical elements.

Shown here is a sample of pitchblende, which today is more commonly called uranium dioxide.

The Search for Plutonium

With the discovery of uranium and radiation, scientists began to wonder if there were ways to use them to make even heavier elements. No element heavier than uranium had been discovered in nature, but many scientists thought it would be possible to make them in a laboratory. By the 1930s, many scientists began searching for the elusive transuranic elements, or those elements that come after uranium on the periodic table. They used a new technique of bombarding atoms with nuclear particles, which had been recently discovered. It had been proven that this could turn one type of atom into a different one. Attempts to form plutonium in this way did not appear to be successful.

Some scientists thought that the particles required to synthesize heavier elements needed to be different from neutrons. Some also thought the particles did not travel fast enough to create the reactions they wanted with the technique they had been using. Scientists at the University of California at Berkeley under the direction of Ernest O. Lawrence developed a groundbreaking invention that addressed the apparent problem. This invention, called a cyclotron, accelerates charged particles such as protons by spinning them in a spiral, where they repeatedly encounter alternating voltages that continually increase their speed and energy.

In the 1940s, Ernest Lawrence examines the cyclotron he invented in a University of California laboratory.

In this photo from 1946, Glenn Seaborg records meter readings on the cyclotron at the University of California. Seaborg was the primary discoverer or codiscoverer of ten chemical elements, including plutonium.

Plutonium Is Born

On December 14, 1940, American chemists Glenn T. Seaborg, Arthur C. Wahl, and Joseph W. Kennedy created plutonium for the first time by bombarding uranium-238 with deuterons (a proton and a neutron) in the cyclotron following the inspiration of Edwin M. McMillan. This created an isotope of an element called neptunium (Np) that had recently been discovered. The team of scientists noticed that the new element emitted radiation in the form of beta particles, which are electrons. This form of radiation had not yet been discovered. On February 23, 1941, they were able to prove that the experiment had produced chemical element 94plutonium. They decided to name the element for Pluto, the dwarf planet. This followed the naming of uranium and neptunium after the planets Uranus and Neptune.

By August 1942, Burris B. Cunningham and Louis B. Werner at the University of Chicago had created enough plutonium to see with the naked eye. Soon, they had enough to weigh (3 micrograms). The room in which this happenedroom 405 of the George Herbert Jones Laboratorywas declared a National Historic Landmark in 1967.