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Plutonium-239 (Pu-239)
Plutonium-239 is an isotope of plutonium. Plutonium-239 (Pu-239) is one of the three
fissile isotopes used for the production of nuclear weapons and in nuclear reactors as a
source of energy. Other fissile isotopes used are uranium-235 and uranium-233.
Plutonium-239 has a half-life of 24,110 years. The nuclear properties of plutonium-239,
as well as the ability to produce large amounts of nearly pure plutonium-239, led to its
use in nuclear weapons and nuclear power. The fissioning of an atom of uranium-235 in
the reactor of a nuclear power plant produces two to three neutrons, and these neutrons
can be absorbed by uranium-238 to produce plutonium-239 and other isotopes. Plutonium
fissions provide about one-third of the total energy produced in a typical commercial
nuclear power plant. The use of plutonium-239 in power plants occurs without it ever
being removed from the nuclear reactor fuel, i.e., it is fissioned in the same fuel rods in
which it is produced.
Weapons Grade
Weapons-grade means that a substance is pure enough to be used to make a weapon or has properties that make it suitable for weapons use. Weapons-grade plutonium and uranium are the most common examples, but it is also be used to refer to chemical and biological weapons. Weapons-grade nuclear material causes the most concern, but plutonium and uranium have other categorizations based on their purity.
Pu-239 is produced artificially in nuclear reactors when a neutron is absorbed by U-238. Pu-240 has a high rate of spontaneous fission, which can cause a nuclear weapon to predetonate, and its concentration must be less than 7% for the plutonium to be weapons-grade. It is produced when Pu-239 absorbs a neutron. To avoid this the uranium fuel in a reactor must typically be replaced four to six times per year. This is necessary because the concentration of Pu-240 rises over time and its mass and chemical properties are too similar for it to be separated from Pu-239. With any reactor, plutonium is separated from the nuclear fuel, U-235 and U-238, chemically in a nuclear reprocessing plant.
Nuclear Weapons
The first "atomic bombs" were developed in the United States during World War II, at
which point two were dropped on Japan. The Soviet Union started development shortly
thereafter with their own atomic bomb project, and not long after that both countries
developed even more powerful fusion weapons also called, "hydrogen bombs". During
the Cold War, the U.S. and U.S.S.R. each acquired nuclear weapons arsenals numbering
in the thousands, placing many of them onto rockets which could hit targets anywhere in
the world. Currently there are at least nine countries with functional nuclear weapons.
There have been (at least) four major false alarms, the most recent in 1995, that almost
resulted in the U.S. or Russia launching its weapons in retaliation for a supposed attack.
See an interactive Timeline of the Nuclear Age.
Source: Wikipedia.com
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