Is it possible to run a nuclear test without producing radioactive fallout?

Let's start with a quick look at what happens to produce a nuclear explosion. It occurs when a radioactive atom -- usually either uranium-235 or plutonium-239 -- comes into contact with free-moving neutrons.

What makes these atoms different from most others is that they're fissile and can sustain a chain reaction. Both of these characteristics hinge on the atom absorbing one of those free neutrons. With the addition of this neutron, the atom splits into several pieces, including multiple neutrons.

With more and more free neutrons available, more and more atoms start fissioning. Under ideal circumstances, or "critical mass," the fissioning atoms can double the number of neutrons in a contained environment more than 80 times in one microsecond, causing the device to expand with tremendous force.

The result is not only a massive explosion but also the release of tremendous amounts of radioactive particles that can spread hundreds of miles, depending on the size of the device.

So we return to the question: Under what circumstances can you detonate an atomic bomb without causing damage to the surrounding area? For our answer, we'll look to methods that have been used in the past and find out what kind of harm, if any, these nuclear-weapon tests have produced.

There are four primary methods of testing nuclear weapons: high-altitude, underground, underwater and atmospheric.

Atmospheric nuclear tests release all the radioactive fallout of a nuclear bomb exploding in mid-air or on the surface of the ground. In these tests, the nuclear device may be fixed atop a tower, dropped from a plane or carried into the atmosphere by a balloon.

Tremendous amounts of fallout result from these tests, and the safety measures in place to prevent damage to humans, animals, crops, buildings, ecosystems and everything else within a radius of hundreds of miles involves clearing the area, pure and simple.

Nuclear tests are normally carried out in desolate areas like the Nevada desert, where damage from the fallout can be reduced because there is so little life in the area.

Still, the biggest nuclear-testing disaster in U.S. history was an atmospheric test in which engineers had taken all necessary precautions. Unfortunately, it turns out they took all the necessary precautions for a much smaller-yield bomb.

In 1954, the United States conducted the Castle Bravo test on a man-made island in the Pacific Bikini Atoll. The explosion was twice the size the U.S. had expected, and the radioactive fallout was far greater than predicted.

When weather patterns changed, the wind carried this mass of radioactive particles into areas that had not been evacuated before the test. Island populations that were not supposed to be subject to any damage at all ended up with radiation burns, high cancer rates and next-generation birth defects that most experts attribute to Castle Bravo.

In broader terms, the high number of atmospheric tests performed by France in the 1960s and '70s appears to have led to three times the rate of thyroid cancer and four times the rate of acute myeloid leukemia in French Polynesia than in other comparable populations not in the vicinity of extensive nuclear testing.

Underwater tests carry a lot of the same risks at atmospheric testing, since the nuclear explosions rise well out of the water. But the amount of radioactive fallout in the atmosphere is decreased because a good portion of it is contained in the water. This causes its own problems, of course.

While effects of underwater testing on sea life have been surprisingly absent from most literature, environmental groups document complete destruction of coral reefs and death and contamination of other marine life as resulting from these tests.

By extension, fishing villages and their seafood-subsisting populations can be severely affected by underwater nuclear tests conducted hundreds miles from their shores.

Read on to learn about two more types of nuclear testing.

If you weigh all the nuclear testing options, you'll no doubt discover that the underground method considered the safest. Though to be clear, nuclear weapons testing is never truly safe.

Underground testing provides the possibility of containment, but containing a nuclear blast is no simple task. The smallest nuclear bomb imaginable will break through 20 meters (65 feet) of earth as if it were a tissue paper. A 1-kiloton-yield bomb needs to be at least 90 meters (300 feet) underground in order for its explosion to be fully contained.

For comparison, the Castle Bravo accident involved a 15 megaton yield. And these depths are just estimates; it's unlikely to know exactly how a new nuclear technology is going to react until you test it.

Even under the most tightly controlled conditions, underground nuclear tests can break through into the atmosphere, which is a worst-case scenario because an underground nuclear explosion irradiates tons of soil that then rains down on everything in the surrounding area.

Ground contact can be the most damaging aspect of a nuclear explosion, so if an underground nuclear detonation does break through the surface, you're looking at fairly serious fallout.

The final nuclear-testing method falls under the "Are you kidding? What were they thinking?" category: detonating a nuclear bomb in outer space. Both the United States and Russia performed these high-altitude tests during the Cold War, sending up the devices by way of rockets, for the purpose of testing the efficacy of the weapons in decommissioning enemy satellites.

While radioactive fallout on Earth was not a problem (the radiation gets deflected by Earth's atmosphere), they stopped performing these tests when several things became apparent:

Besides the most far-reaching effects of nuclear testing, there are also significant dangers to those involved in carrying out the test. More than 4,000 workers at a former French testing facility have filed suits against the government alleging that radiation exposure has compromised their health. Many of those workers have been diagnosed with serious cancers. France conducted nuclear tests until 1996, long after most other countries has stopped.

For more information on nuclear testing and related topics, explore the links on the next page.