The Facts About Depleted Uranium
The co-called controversy over bullets and armor plating made with Depleted Uranium (DU) has become the new rallying point for what I call the anti-nuclear coalition (ANC). The ANC is a loosely knit informal group of organizations that share several commonalities. Among these is a total rejection of anything nuclear.
The ANC consists primarily of left-wing, pseudoscientific environmental organizations whose core membership draws on the disaffected fringe elements of our society. Unfortunately, these organizations have large membership rolls made up of ordinary people who do not understand the nature of radioactivity, the greenhouse effect, atmospheric ozone, or the myriad of other causes championed by the ANC. Consequently, the members are duped into supporting with their dollars and their votes scientifically untenable positions staked out by the ANC.
The latest of these is the worldwide scare campaign against the use of Depleted Uranium for bullets and armor plating.
For a better understanding of the falsity of the anti-DU campaign, we need to review some basic physics.
Uranium is one of the more abundant materials in the Earth’s crust. It is present in most rocks and soils as well as in many rivers and seawater. Useable Uranium occurs naturally in nature as a pitchblende ore. Pitchblende is mildly radioactive, which means that it spontaneously emits alpha particles. The level of radioactivity is very low, however, so there is no threat from mining and transporting the ore, and in any case, alpha particles, which are nothing more than Helium atoms stripped of their two electrons, pose no threat outside the body.
The Uranium normally extracted from pitchblende typically takes two different forms, called isotopes: Uranium-235 (U235) and Uranium-238 (U238). About 99.3 percent of Uranium in the Earth’s crust is U238; only about 0.7 percent is U235, along with a vanishingly small percentage of four other isotopes. U235 is the basis of most current nuclear power generation.
Depleted Uranium results from the enriching of natural uranium found in pitchblende. Since most nuclear reactors use U235 to produce energy, natural uranium has to be enriched so the percentage of U235 is sufficiently high for a reaction to take place. Uranium is enriched to about 20 percent U235 for civilian reactors, but submarine power plants use Highly Enriched Uranium (HEU) with at least 50 percent U235, and weapons-grade HEU is 90 percent or more U235.
When the 0.7 percent of U235 is removed from natural Uranium, what remains is a silvery, very dense metal consisting of U238 plus a small percentage of U235 and a negligible percentage of the four other isotopes. We call this Depleted Uranium or DU.
Over the past decades, the ANC has conducted a vast public campaign to frighten people about radiation. Its efforts have been so successful that, for example, the Germans have given up their nuclear power generation option for the time being, and most Americans and Europeans will tell you, if asked, that nuclear power is too dangerous to justify its use.
Why? It boils down to fear of radiation and to the presumed danger it poses.
Let’s take a look at radiation.
Step outside on a nice day and feel the sun’s warmth – that’s radiation; so is the light. A body’s warmth is radiation. And radio waves. And television signals. And X-rays. And light from a glow worm’s tail.
Radiation is energy transfer. It can take several forms. One is tiny mass-less packets called photons. We experience photons most commonly as ordinary light. This radiation frequently is called electromagnetic radiation. Photons carry energy, and the more energetic they are, the higher their frequency, the more “dangerous” they can be. Harm results from radiation when energy is transferred to living cells in a damaging way.
Early atomic scientists identified a form of radiation they called “gamma-rays.” Ironically, this radiation turned out to be nothing more than high-energy photons, but the name still is frequently used. So when certain reactions produce high-energy photons, instead of referring to them as “high-energy photons,” scientists usually call them “gamma-rays,” but they are identical.
In 1895, William Roentgen discovered a form of radiation that has become known as the X-ray. Not very long thereafter, scientists determined that X-rays were photons in an energy range below gamma-rays but above ultraviolet light.
Early atomic scientists discovered another form of radiation they dubbed “beta particles” before they determined that it was only high-energy electrons in a range above ten thousand electron Volts. The name stuck. As sub-atomic particles go, the electron is not very large, but it carries a full negative electric charge.
Let’s conduct a mind experiment: Remember the little black and white Scottie Terrier magnets from your childhood? Nose to nose they repelled each other.
Imagine a pool table with balls that consist of only the noses of these Scottie Terrier magnets. Now place them around the table in any configuration you wish. Once you have this picture firmly in mind, imagine rolling one of these “Terrier nose” balls across the table. As it moves through your arrangement, other “Terrier nose” balls are repelled in all directions, and these repelled balls further repel other balls, so by the time your ball reaches the far side of the table, you will have disrupted most of the balls you originally placed on the table.
This is exactly what happens when a beta particle – a high energy electron – speeds through matter. It disrupts every electron it passes near, and these in turn disrupt others. An atom containing too few or too many electrons is called an ion, and the process of creating ions is called ionization. A beta particle leaves an ionized trail of damage in its wake.
Neutrons carry energy as radiation much like electrons, except that neutrons are much heavier, and so can cause more direct damage for a given speed. Imagine the cue ball on a pool table smashing into the array of racked billiard balls. They scatter everywhere, and whatever structure they once had is lost. Since neutrons have no electric charge, they cannot be deflected by a magnetic field like electrons. But the particles released when a neutron collides with an atom often carry significant energy, and leave ionized trails of destruction behind them. So neutrons do double-duty damage, directly like a billiard ball, and indirectly like the “Terrier nose” balls discussed earlier.
A helium atom stripped of its electrons is capable of causing significant ionizing damage. Early atomic scientists called this an “alpha particle” before realizing what it actually was – they still use the name. Because an alpha particle has a positive electric charge twice as large as the negative electric charge of an electron, for a given distance of travel it can actually cause significantly more ionizing damage. Fortunately, alpha particles typically have very low electron Volt energy levels. Almost anything will stop them: skin, a piece of paper, a half inch of air, almost anything at all. Beta particles are a bit more energetic. They can actually penetrate a centimeter of skin and tissue.
A particular hazard exists when a substance that emits either alpha or beta particles is ingested. In this case, the ionizing damage happens directly in possibly vital organs. Another hazard is created when we try to stop beta particles by using a dense material such a lead. In the process of slowing down, the beta particles interact with the dense nuclei of the damping material, creating X-rays.
Because of how ionizing radiation damages tissue, small amounts of radiation damage are easily repaired by the body. Even small dosages over an extended period have no long-term effect. Similarly, a larger dose taken all at once may cause temporary sickness, although its long-term effect is negligible. Taking a larger dose repeatedly over a short period can, of course, have serious consequences. Taking a really large dose can be deadly, since so much tissue is damaged that the body cannot repair it.
We continuously experience a relatively constant level of background radiation. In the United States, radiation dosage is measured in rems, or more typically in millirems (one thousandth of a rem). The typical annual background radiation dose for a human is 360 millirems, or about a third of a rem. The internationally established radiation limit for adult workers in the nuclear industry is 5 rem above the normally occurring background.
Now let’s apply these basic facts to the DU debate:
From actual measurements, a hypothetical tank crewman who stays continuously inside a “heavy armor” tank (a model using DU armor panels), fully loaded with only DU ammunition with the gun pointed to the rear (which maximizes the exposure) – 24 hours a day, 365 days a year – would receive a total dose of approximately 1.14 rem, less than 25 percent of the permitted annual dose. Actual exposures based on realistic times spent in the tanks (904 hours per training year) are likely to be less than 0.1 rem in a year, which is about the same dosage you might receive from cosmic radiation on a round-trip between New York and Los Angeles.
Bottom line: Depleted Uranium simply is not a problem – except for the other guy whose armor is pierced by a DU bullet.
Robert G. Williscroft is DefenseWatch Navy Editor