Tammy Bruce: What is an Atom Bomb?

What is an Atom Bomb?

Maynard explains some basic physics

Since the Iranian pursuit of atomic technology has been in the news lately, it's worth taking a moment to make sure that everyone understands the basic facts about atomic energy and bomb materials.

The basic building block of chemistry is the element. There are 116 unique elements; examples are hydrogen and helium and carbon and iron and uranium. Each element has its own unique properties. The elements can themselves be broken down into atomic particles (neutrons, protons, electrons), but set that aside for the moment. The zillions of chemicals in the galaxy are all mixtures of these 116 fundamental elements. For example, a molecule of water (H2O) is composed of two parts (two atoms) of the element hydrogen combined with one part (one atom) of the element oxygen.

Generally speaking, the elements are unchanging things. The hydrogen in a molecule of water is still hydrogen. Only an atomic reaction can cause an element to change into another element.

Atomic reactions don't happen naturally on earth in any large degree (although they're always happening on a small scale). The elements on the planet are mostly stable. Hydrogen will stay hydrogen; iron will stay iron. Even uranium will stay uranium. A big atomic reaction won't happen here unless we make it. That's why we don't have natural atomic bombs blowing up on earth like wildfires.

There are two types of atomic reactions: Fission and fusion. Fission is when a big element (such as uranium) breaks down into smaller pieces. Fusion is when the atoms of a small element (such as hydrogen) combine (or "fuse") into a bigger element. The sun is a huge engine of fusion, with small hydrogen atoms continuously fusing into bigger helium atoms. In other words, the sun is a huge, ongoing hydrogen bomb. (Somebody tell Al Gore! It's got to be stopped!) Technologically, we achieved fission before fusion. The atom bombs of WWII were fission bombs. Later we developed the fusion (hydrogen) bomb. We don't yet have the technology to control a fusion reaction; all fusion is good for at this point is a bomb. The current atomic plants are fission plants, because we know how to maintain a controlled (that is, a slow) fission reaction. Fusion plants would be a great source of energy, if we can ever develop the technology to contain a fierce 10 million degree inferno. The goal is to put a hydrogen bomb into a box. You can see why it's a daunting task.

So our basic atomic technology is fission technology. The choice materials for fission are the heavy elements of uranium or plutonium. I'll focus on uranium, since it's a "natural" element; plutonium does not occur naturally and must be created by artificial atomic processes.

As I said earlier, each element has its own unique chemical properties. However, there is a very subtle variation of certain elements called "isotopes". Technically, an isotope is a variant of an element with a different number of neutral atomic particles (neutrons). The neutral particle doesn't affect the chemistry of the element, but it does affect the atomic stability of the atom. Some isotopes make very stable atoms, and others make very unstable atoms. An unstable atom is more easily broken up into pieces. That is to say, an unstable atom is ideal for fission. So you'll want to gather a lot of unstable atoms to make an atom (fission) bomb.

Uranium is a natural metal that can be mined. Most uranium is not dangerous. If you dig up natural uranium and analyze it, you'll find that more than 99% of it is the isotope called U-238, and less than 1% of it is the isotope called U-235. The U-238 is just another stable, heavy metal, and has no sinister use. The U-235 is unstable and fissionable. So the uranium you dig out of the ground is not useful for weapons, because the 99% of it that's stable neutralizes the dangerous 1%.

To make uranium fissionable, you must separate the U-235 from the U-238. This is the process known as "enrichment". It sounds conceptually easy, but in fact it's very difficult. U-235 and U-238 have identical chemical properties. There is a very slight difference between the weight of a U-235 atom and a U-238 atom. Therefore, the enrichment process consists of separating the heavier atoms from the lighter atoms.

This is where the centrifuges that you've heard about in the news come into play. A centrifuge will spin its contents under controlled conditions. This causes an artificial enhancement of gravity, like when you're spun around in a carnival ride. The heightened gravity speeds up the process of separating heavy atoms from light atoms. It's like separating milk from cream. Thus the centrifuge is an essential tool in enriching uranium. The enrichment is a slow and tedious process, which is why we think in terms of numerous centrifuges and several years.

There are degrees of uranium enrichment, depending upon the use to which the enriched uranium is to be put. For the peaceful use of atomic energy, a low-enriched uranium is adequate. This means that about 20% of the uranium is U-235. This can run a light-water reactor at a slow-burn, but isn't good enough for a bomb. To make a bomb, you'll want highly enriched uranium, meaning more than 85% U-235. The highly enriched uranium can fission more quickly, causing a chain reaction that builds upon itself and spins wildly out of control. As each unstable atom of U-235 breaks apart, its pieces fly away and trigger the next U-235 atom to likewise break apart. That's what an atomic bomb is.

The international inspectors know the difference between a project to create low-enriched uranium and one to create highly enriched uranium. The signs out of Iran are that the Iranians are doing the highly enriched stuff. This, combined with the Iranian stonewalling and deception, is why the international community is skeptical of Iran's statement that its pursuits are peaceful.

Posted by Maynard · September 2, 2006 10:15 PM · Permalink
Maynard Post | Science & Technology

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Well, somewhat correct.

Fission bombs can be built with U-233, bred from thorium. Soil commonly contains an average of around 6 parts per million (ppm) of thorium, and thorium's much more abundant than uranium. Yes, that's the thorium in Coleman lantern mantles. http://www.dangerouslaboratories.org/radscout.html is a cautionary tale which deserves attention, for thorium is really, really common, and proliferation controls do not adequately address thorium.

Fission bombs may also be made of plutonium. If you operate a nuclear reactor, either a research or a power reactor, you're making plutonium. Plutonium fission bombs must be much more complex than the simpler designs available for uranium bombs, but plutonium's extreme toxicity makes it valuable for dirty bombs (AKA radiological dispersal devices, first discussed in 1939 in Heinlein's SOLUTION UNSATISFACTORY).

Only one design of reactor doesn't result in weapons grade fission material; the fast-flux reactor, misnomered the 'breeder'. Fast-flux reactors can be run for far longer between fuel changes, and extracts the maximum possible from our limited amount of atomic fuel, more than two orders of magnitude higher than what conventional reactor designs can provide. I would suggest, if you're interested in atomic power, take a look at this article http://kiloseven.blogspot.com/2006/05/al-gores-fundamental-misunderstanding.html then look into the sources, and what they tell you.

Posted by: Clackablog at September 3, 2006 11:09 PM

Nice piece and easy to understand. A slight correction: "peaceful" uses only require three to five percent U235 so that this stuff is basically benign. The minimum for a "dirty bomb" is 20% U235, but the result would be an explosion that would only kill a few hundred people in a one city block area. The military requires 90% U235. Your centrifuge description is correct, but there is a different way to "enrich" the uranium, and that is through the use of so-called "heavy water."

Heavy water is not really water at all if you want to get really technichal. It's actually a substance called deuterium oxide, D2O or 2H2O, not the H2O of regular water. The usual way of building a bomb requires graphite in order to slow the speed of the neutrons necessary to create a chain reaction (Fermi's discovery that made the atomic bomb possible). Heavy water allows the use of UNENRICHED uranium to achieve a chain reaction so that sophisticated fuel enrichment facilities like P2 centrifuges are not necessary.

I don't know, but these obvious displays of both centrifugal opulence and the acquiring of heavy water sounds like all of the ingredients necessary to conduct a bluff to me.

Posted by: Duke at September 4, 2006 12:54 PM

Thanks for the clear explanation for someone that has not had a Chemisty class in over 25 years and is scientifically challenged:-)

Posted by: TB in Baltimore at September 4, 2006 06:36 PM

Interestingly enough, there used to be large-scale nuclear reactions taking place on earth. About 1.5 billion years ago, there were uranium beds in Oklo in Gabon, Africa, which were sufficiently concentrated for a natural fission reactor to form. Back then, the natural fraction of U-235 was high enough to support fission.

There's a nice article at Wikipedia
(http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor)
and
(http://en.wikipedia.org/wiki/Nuclear_reactor)

Posted by: Karl at September 7, 2006 06:45 PM

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