Plutonium Essay, Research Paper

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 other radioactive discoveries

were based on the finding of Pu-238. For example, Pu-241 decays with a half-life

of about thirteen years emitting negatively charged beta particles, or electrons.

It then converts to Am-241, an isotope of americium, which emits alpha particles

for 470 years, before turning into Am-242, which converts to Cm-242, an isotope

of curium, in only sixteen hours. The Cm-242 emits alpha particles for about 162

days before ending the decay of Plutonium 241.

Chemical Equation for Producing Plutonium: 92U-238 —-> 92U-

-239 —-> 93Np-239 —-> 94Pu-239