Plutonium is one of the most exotic substances known to man. In fact, there is much about this elements properties which remains poorly understood at best, and some behaviors exhibited by it that are barely understood at all. One reason for this is the fact that Plutonium is highly reactive chemically and very active atomically as well. Twenty-one isotopes of Plutonium have been identified to date, all of them being radioactive. The element also exists in a variety of allotropic forms and is readily amorphous, slowly changing form over time. The most stable forms of the element are Pu-244, Pu-242 and Pu239. Pu-239 along with Pu-240 are fissile.
Plutonium’s atomic number is 94, representative of the number of protons contained in its’ nucleus. The atomic mass number of its most stable isotope, Pu-244, reflects its’ nucleus containing 94 protons and 150 neutrons. Plutonium’s electron configurations indicate a minimum oxidation number of “0” and a maximum of “7.” The element belongs to the actinide series of rare earth elements on the periodic table. It reacts readily with Oxygen, Water, and the halogens to form compounds.
At room temperatures, Plutonium is a silvery metallic solid. Its’ melting point is roughly 1183 F (639 C), and it boils at 5842 F (3228 C). It is pretty dense and therefor heavy stuff. If you could hold a lump of the stuff the size of a baseball in your hand, in would be comparable by weight to a gallon of water. From a chemical perspective, Plutonium is toxic, but no more than other metals. It’s radioactive status makes it lethal however. For instance, if you did, hold a baseball sized quantity of it in your hand for just a few minutes, you would succumb to radiation poisoning resulting in death within a few weeks. Another thing you would notice is that the metal is warm to the touch as a result of alpha particle emissions. For this reason, Plutonium is stored in small quantities and usually submerged in water to preclude it from combusting with oxygen or igniting other materials in close proximity to it. Plutonium is often alloyed with other metals to lessen its volatility and increase its stability.
Plutonium is probably best known for its radioactive properties and use in atomic bombs. As I mentioned before, there are two fissile isotopes of the element, Pu-239 and Pu-240. The latter will fission spontaneously, and is therefore usually considered an unwanted contaminant. So Pu-239 is the predominant material used to produce critical mass chain reactions. U 235 is very difficult to obtain in pure form where as Pu -239 occurs in large quantities as a byproduct of certain other atomic reactions, like those which take place in nuclear reactors. In fact, the vast majority of the hundreds of tons of Plutonium in existence today is the byproduct of nuclear reactors used for power generation, but only small amounts of this waste is of the fissionable variety, and it is quite difficult to separate it out. Most weapons grade plutonium (Pu-239) is produced in breeder reactors where conditions are carefully controlled to produce high concentrations of the fissile material. Another advantage of Pu-239 over U-235, is that you need about a third as much of it to constitute a critical mass and thereby initiate a chain reaction.
PLUTONIUM AND THE ATOMIC BOMB
Pu-239 is the ideal and preferred material for manufacture of atomic bombs. Unlike U-235 it is readily available in large supply. The instability of Pu-239 makes it’s use in “gun-type” nuclear explosives unmanageable, but it works fine in implosion type bombs. While the workings of the atomic bomb are pretty textbook these days, the methods of synthesizing, refining and handling materials to produce bomb grade Plutonium are well guarded secrets. This is particularly true for the more sophisticated nuclear warheads called “hydrogen bombs.”
Atomic bombs are limited in capacity and destructive force, because you can only use a small amount of fissile material in the bomb – basically no more than would constitute a critical mass. The largest atomic bombs were in the 100-500 kiloton range. Famed physicist Edward Teller (father of the Hydrogen Bomb) figured a way to use an atomic bomb to initiate a fusion reaction – that which occurs at the center of the Sun. Basically, the atomic explosion is used to compress a volume of tritium to the point where fusion begins. The whole event takes place in just a fraction of a second, but the result is essentially an application of the atomic explosion releasing a tremendous amount of energy. Had hydrogen bombs instead of atomic bombs been dropped on Hiroshima and Nagasaki, there would not likely have been any survivors to suffer the after effects of radiation. According to former secretary of defense Robert McNamara, by the 1960’s the U.S. Had developed hydrogen bombs with an explosive capacity in excess of 100 million tons of TNT. Theoretically, it is possible to build a hydrogen bomb big enough to incinerate the entire planet, perhaps even vaporize it.
Prior to 1940, you could probably have put all the naturally occurring plutonium in the world in a five gallon bucket. Since then the proverbial lid has been ripped off the Pandora’s box of nuclear weapons proliferation. Mankind has increased the amount of this lethal substance on earth by millions of times, and we continue to add to the stockpiles already in existence. They say the cold war is over, but there remain in the American arsenal alone, enough hydrogen bombs to end human existence on this planet, and that of most other species of life as well. For this reason if none other, Plutonium must be considered the most important and dangerous element on the face of the earth today. Ironically the decision to use these bombs rests with just a few humans, and nuclear annihilation remains as present a threat to human existence as it ever has. No one has yet come up with a solution to this dilemma, but the more all humanity knows and understands about this most dangerous of the elements, the better opportunity we will have to learn to live with it, and to not allow the consequences of its’ most lethal attributes to be realized.
There seems to be an effort in recent years to downplay some of the dangers and implications of the element Plutonium. This is particularly true in Internet venues. Perhaps this is a subliminal effort on the part of the nuclear energy industry to lessen fears about nuclear power and gain support to construct new power generation plants. Maybe it’s just a case of complacency, and not wanting to deal with the perplexing issues and realities surrounding the prospects of nuclear war. I can remember, and most of my generation will attest to the regular duck and cover drills we practiced at school in the late fifties and early sixties. Later in life, I became all to familiar with the unthinkable scenarios which would be spawned by a nuclear holocaust, as I served in the Air Force, on a Strategic Air Command base which was as close as you could get to the front lines of the cold war. The necessity for future generations to have a clear understanding of the continuing threat and implication of nuclear annihilation is essential if our species is to survive this most awesome of threats to its continuance.
REFERENECES AND FURTHER READING
WIKIPEDIA Online: http://en.wikipedia.org/wiki/Plutonium
Robert McNamara, The Fog of War, Video, Sony, 2005: