Radiation Exposure in the Real World

Japan’s nuclear threats have us all thinking about radiation exposure; and I have an added interest since I was the medical director for 10 years at the Palo Verde Nuclear Generating Station, the largest nuclear plant in the nation.

But my first introduction to the hazards of radiation was as an elementary student. We, like all children around the U.S., were instructed to hide under our desks in the event of nuclear war. That seems a bit naive in retrospect.

Radiation is everywhere. The sun emits radiation, as does the earth, and probably the moon. The stars definitely do. Medical procedures like X-rays and CT scans involve radiation, as do TSA scanners. There is even a little radiation in the food we eat and the air we breathe. Like so many other things, radiation is all about dose.

Radiation is counted in millisievert (mSv), a word which keeps the non-PhDs like myself out of their field. Normally we are exposed to a background radiation total of 2.40 mSv per year. This is an additive scale. It’s like getting less than a penny’s worth of radiation per day and end up with $2.40 at the end of the year. This comes from solar radiation predominantly, and a small amount from man-made sources. Man-made sources range from the luminous hands on your watch, a chest X-ray, or nuclear testing from 60 years ago.

Some locations have higher normal background radiation due to more radioactive materials in the bedrock or simply high elevation like Denver. The normal range of background radiation is from 1 to 100, so a hundred-fold increase could still be in the normal range.

So why worry about radiation?

Radiation is bad because it can cause breaks in your DNA – the chain of life so to speak. You don’t go far with a broken chain. The body attempts to repair these breaks and is pretty successful, but nothing is 100%. Those few poorly repaired DNA chains may self-destruct and cause no mischief, or can code for unfriendly cells, like cancer.

Scientists have studied radiation exposure and calculated that normal background radiation will cause 1 person out of 100 to get cancer in his or her lifetime. Additional radiation exposure increases the risk.

There is also danger from large exposures to radiation that occur acutely, as opposed to 20 years of exposure. This is called radiation sickness. Here we are talking about nuclear accidents. Radiation sickness causes the most active cells to die first. The lining of your stomach and intestine are usually affected first, causing nausea, vomiting and bloody diarrhea. This might take 24 hours to develop in exposures of 3,500 mSv or 1 hour in more extreme exposures of 5,500 mSv. At 8,000 mSv acute exposure, the mortality rate is 50%. The cardiovascular system breaks down in high-level radiation exposure. If you survive those, the blood system is the next likely victim. Radiation can kill your blood-making cells. You would miss them.

These are the kind of dangers emergency workers who stayed at the damaged nuclear plant face.

What about people in Tokyo or the world?

“Dilution is the solution to pollution” was my organic chemistry’s professor’s favorite expression. The closer you are to the source, the higher the radiation exposure. Radiation goes down with distance. This assumes the radiation source doesn’t move.

The levels measured at the plant in recent days are high enough to cause radiation sickness. These are potentially dangerous in the short term as well as the long term. The levels measured 120 miles away in Tokyo are 10 times higher than normal, but you would get just as much radiation moving to Denver. Moving to Denver with its higher level of solar radiation (due to elevation) doesn’t seem like a particularly foolhardy thing to do.

But life gets more complicated if the radiation source moves around. Radioactive elements are rather dense and don’t move around too easily. All solids can be made liquid or gas, just like water. The fuel rods in the reactor are solids. They release huge amounts of heat energy because they are radioactive. If not cooled, this heat can build up to the point of making the uranium rods melt and become a liquid. This liquid is so dense and hot, it can melt though almost anything (picture trying to keep lava in a container).

The next step is going from liquid to gas. Uranium can be vaporized by explosion or intense heat. Now we have a cloud of highly radioactive material floating about. That is exactly what happened at Chernobyl 20 years ago. One of the radioactive elements to spread was radioactive iodine. Potassium iodide keeps your thyroid full and stops you from absorbing the radioactive variety. This helps prevent thyroid cancer, but nothing else.

So this triple (quadruple) meltdown is unprecedented in history, but the science is very well understood. Simply keeping distance between you and trouble, like so many other times in life, is all it takes. Today, you will get more radiation in Denver than in Tokyo.

Take care,

Dr. B


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