Plutonium


Plutonium is a radioactive metallic element. Although it is occasionally
found in nature, mostly all of our plutonium is produced artificially in a lab.
The official chemical symbol for plutonium is Pu, coming from its first and
third letters. Its atomic number is ninety-four. Plutonium is able to maintain
its solid state until very high temperatures, melting at six hundred and forty
degrees Celsius, and boiling at three thousand four hundred and sixty degrees.
The density of Plutonium, at twenty degrees centigrade, is 19.86 grams per cubic
centimeter.
Plutonium was discovered, in the laboratory, by Glenn Theodore Seaborg,
and his associate Edward M. McMillan. The two shared the Nobel prize in 1951
for their discoveries of Plutonium, Americium (Am), Curium (Cm), Berkelium (Bk),
and Californium (Cf). In addition, Seaborg later contributed to the discovery
of three more radioactive elements, Einsteinium (Es), Mendelevium (Md), and
Nobelium (No). Plutonium was Seaborg’s first discovery. Its name came from
Pluto, the planet after Neptune for which Neptunium was named. In 1940, at the
University of California at Berkeley, he bombarded a sample of Uranium with
deuterons, the nuclei in atoms of deuterium, transmuting it into plutonium.
Shortly after, Seaborg was able to isolate plutonium 239, an isotope used in
atomic bombs.
Plutonium is a highly dangerous and poisonous element because it rapidly
gives off radiation in the form of alpha particles. Alpha particles, which are
identical to the nucleus of a helium atom, consist of two protons and two
neutrons tightly bound together. Although the particles can only travel about
five centimeters in the air, they can cause great damage when the enter the body,
causing cancer and other serious health problems. Beyond the danger of their
radiation, Plutonium will spontaneously explode when a certain amount, called
critical mass, is kept together. Soon after the discovery of Plutonium, it was
discovered that at least two oxidation states existed. It is now known to exist
in oxidation states of +3, +4, +5, and +6.
Currently, there are fifteen known isotopes of Plutonium, with mass
numbers ranging between 232 and 246. The most important isotope is plutonium 239,
or Pu-239. When struck by a neutron, this isotope undergoes a process called
fission. In fission, When struck by a neutron, the nucleus of the plutonium atom
is split into two nearly equal parts, and energy is released. Although the
energy released by one atom is not much, the splitting of the nucleus releases
more neutrons, which strike more plutonium atoms. This process, called a chain-
reaction, produces enormous amounts of energy. This energy is often used to
power nuclear reactors, or to provide the energy for nuclear weapons. Although
Pu-239 is such an efficient use for energy, disposing of its waste has become a
major problem. When uranium is converted to Pu-239, a waste with a half-life of
around 24,100 years is produced.
Another large problem for scientists creating power with plutonium is
actually getting the chain-reaction to work. Often, only the first few atoms
struck by the deuterons convert to Plutonium. Unfortunately for the scientists,
the whole problem is a matter of probabilities and chance. There are four
factors that determine whether the reaction occurs. They are 1) escape, 2) non-
fission capture by uranium, 3) non-fission capture by impurities, and 4) fission
capture. The first three factors cause the uranium to lose neutrons, the last
is what causes the reaction. If the loss of neutrons is less than that of those
produced, by fission capture, the reaction occurs. Otherwise, plutonium is not
made, and the chain-reaction stops immediately.
Using the chain-reaction system, the first operating nuclear reactor of
a reasonable amount of power was built in 1943. It was called the X-10 reactor.
The core of the reactor was a twenty- four foot cube of graphite blocks, with
1248 fuel channels each 1.75 inches square. Each hole was fueled with four inch
long uranium rod, jacketed in aluminum to protect against oxidation. The entire
core was surrounded by a seven-foot thick concrete shield, with openings at one
end to replace the uranium rods. At a cost of $1,000,000 for the building and
$2,000,000 each for the graphite and uranium, this plant produce about 190 Mevs
per fission.
In addition to its uses as fuel for a reactor or in a bomb, plutonium
has some practical, everyday uses as well. For example, the original plutonium
isotope, Pu-238, is used today to power pacemakers for people with deficient
hearts. Also, isotopes Pu-242 and Pu-244, which occurs naturally, are used in
studying chemicals and metals.
The half-life of atoms of plutonium was very important to seaborg and
his assistants back in 1940. In fact, all of his