The types of radiation referred to in last week´s column (alpha, beta, gamma and neutron) are called ionizing radiation because of what they do to living tissue or other matter.

A gamma ray or one of the particles (alpha, beta, neutron) has enough energy to strike atoms at the cellular level and remove an electron from an atom. When this happens the atom changes chemically and can react with other atoms in a way to damage a living cell. If this happens to enough atoms in enough cells, there will be symptoms of damage such as burns and hemorrhaging.

Because alpha and beta particles are so easily stopped they usually do not present a danger to humans. However, they can be dangerous if the emitting substance is inhaled or ingested. If the material lodges in the body, the particles are stopped by the tissue´s cells and damage can be continuous.

On the other hand, scientists can take advantage of this fact to treat such problems as an overactive thyroid gland. Radioactive iodine can be injected into the patient. The iodine naturally travels to the thyroid gland and lodges there. While there, the radioactive emissions destroy cells in the gland and reduce hormone production. The iodine quickly decays to a stable state, loses its radioactive properties and is eliminated by the body.

Cancer is caused by radiation when the nuclear particles or rays damage the DNA of a cell and then, when the cell divides, the damaging change is passed on. Sometimes the change does no harm because the body naturally deals with it. At other times, the signals get scrambled and cancers and tumors grow.

The more radiation an element emits during a certain time, the more radioactive it is and the more dangerous. Scientists have developed several ways to measure radiation and turn it into meaningful numbers for comparing levels or amounts.

The rem is the most common unit used and is short for "Roentgen equivalent man." It is a way to measure radiation in terms of possible biological damage. Because most natural radiation emitters can only be measured in fractions of a rem, the millirem is a commonly seen unit of measure. It take one thousand millirems to equal one rem.

"Everyday all humans are subjected to radiation from naturally occurring radioactive materials. This is referred to as background radiation because it is everywhere and there is no way to escape it. The background radiation level for the United States varies from less than 100 to more than 200 millirems per year depending on where you live. Background in southern N.M. is about 190 millirems per year because of the mountains with their uranium and the high altitude.

Flying from coast to coast in a jet will give you a one-time dose of three to five millirems of exposure from cosmic radiation. Living in a brick house instead of a frame house will give you an additional 50 millirems of radiation per year. A visit to Trinity Site, where the first atomic bomb was exploded, will give you less than one millirem. Finally, living in Kerala, India will give you an average annual dosage of 1,300 millirems per year because of the radioactive sands in the area.

(NOTE: Follow this link to information on updated estimates on average radiation exposure in the U.S.)

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