Language of radiation at a glance

Sunday, Jan. 24, 1999 | 10:06 a.m.

While we live in a world bathed naturally in radiation, since the first atomic bomb exploded into the skies of Alamogordo, N.M., on July 16, 1945, scientists have warned about exposing people to too much extra radioactivity.

Nuclear-weapons testing worldwide and nuclear reactors, plus medical X-rays, add to radiation exposure above the amount received from the Earth and cosmic rays from space, which is considered natural background radiation.

Las Vegans receive a daily average dose of radiation from the sun of about 6 millirems. Exposure to an X-ray is about 10 millirems.

Atoms are the basic building blocks of all matter. Unstable atoms that decay within a fraction of a second to billions of years are called radionuclides. The rate of decay is known as a half-life, or the time it takes half the radioactive atoms to decay.

For example, plutonium has a half-life of 24,000 years; uranium-238 rates a half-life of 4.5 billion years; tritium has a half-life slightly of more than 12 years.

Nuclear bombs are designed to bring together a large amount of atoms together so they split, creating energy, in a process called fission. The fissionable materials create a chain reaction that rapidly consumes the material and explodes.

Radiation takes three forms:

* GAMMA: Has the greatest penetrating power of the three types. Humans must be shielded from it by lead or a thick concrete barrier. Exposure to gamma radiation can damage organs in the body. Most fission products emit both gamma and beta radiation. Cesium-137 is an example of a gamma-emitter.

* BETA: Can be blocked by wood or aluminium. Beta radiation causes the most damage if its particles are ingested or inhaled, or if the radioactive materials come in contact with skin. Tritium and strontium-90, which seeks the bones in the human body, emit beta radiation.

* ALPHA: The least penetrating type of radiation. It can be blocked by a sheet of paper and cannot penetrate or burn intact human skin. But it is harmful if swallowed or inhaled. Plutonium emits alpha radiation, which is why it is dangerous if inhaled or ingested.

The sun emits all three types of radiation.

The way scientists measure radiation is by a unit called a curie.

The curie is a traditional unit of radioactivity equal to the radioactivity of 1 gram of pure radium. The curie is named after Pierre and Marie Curie, who discovered radium in their Paris laboratory.

Sources: The League of Women Voters "Nuclear Waste Primer" and The Institute for Energy and Environmental Research's "Plutonium: Deadly Gold of the Nuclear Age."