03/25/2013 01:52 pm ET Updated May 25, 2013

Radiation: What It Is and What You Need to Know About It

By Robert Peter Gale, MD and Eric Lax

We all fear radiation yet life depends on it. We each are radioactive, living on a radioactive planet, in a radioactive solar system, in a radioactive universe, in a radioactive galaxy. We, and all living creatures, exist because plants and other organism use photosynthesis to capture photons, a basic unit radiation energy (light), produced by thermonuclear fusion within the Sun, and convert it chemical energy which drives our world. Carbon dioxide and water are turned into the oxygen we breathe, the sugars we eat and the carbon the makes up our bodies. Think of photosynthesis as a giant power facility producing the equivalent of about 130 terawatts of energy each year, six times more than the total annual power consumption of mankind. Without radiation life as we know it would not exist.

What do you mean by "We are all radioactive"?

Radioactivity is in our food and our water, even in our bodies. It is part of our makeup and causes no known harm. There are several radioactive elements in each of us, among them naturally occurring radioactive forms of potassium (potassium--40) and carbon (carbon--14), as well as man-made isotopes like cesium--137 that result from nuclear fission. Each second, thousands of radioactive atoms in our bodies decay; sleep next to someone, and your bedmate will get a dose of radiation from you. Potassium--40, which to the body looks like normal nonradioactive potassium, is taken up by all cells but especially muscle cells. Men, who usually have more muscle mass than women, are on the whole more radioactive than women because they have more potassium -- 40.

How am I exposed to radiation?

About half of the radiation we normally receive comes from natural sources called background radiation. There are two major sources of background radiation: cosmic radiation, which comes from the universe, including our Sun (cosmic radiation increases when there are solar flares) and supernovas (that fling out particles when they explode); and terrestrial radiation, which comes from radionuclides in the Earth's crust. An additional component comes from radiation in our body. We live in a sea of radiation.

The other half of the radiation we receive is from man-made sources such as consumer products and the nuclear fuel cycle. What might come as a shock is that these account for about 2 percent of our man-made radiation. The rest comes from medical tests and treatments. This is a six-fold increase from the early 1980s. Estimated numbers of diagnostic imaging studies in the U.S. in 2012 exceeds 80 million and nuclear medicine procedures exceed 20 million.

Computed tomography (CT) scans are the major contributor to our man-made radiation dose; they deliver about two times our normal annual natural and man-made radiation (often more for whole body scans). And the number of CT scans is rapidly rising. There were about 50 CTs per 1,000 US residents in 1996 versus about 150 in 2010, a three-fold increase. In many parts of the country it is virtually impossible to leave the emergency department without a CT scan; some call it the new physical exam. We call unnecessary CTs a danger. Yet many people will demand a CT scan but worry about backscatter radiation they might receive courtesy of the TSA at the airport that delivers exposure to a radiation dose thousands of times smaller. Ask your physician why he/she is recommending a test and about the balance of risk and benefit and the dose of radiation you will receive. (This caution applies to all medical tests and procedures, not just radiation.)

What are some ways radiation makes daily life safer?

Radiation can both kill us and cure us. A small amount of radioactive iodine-131 can cause thyroid cancer but a larger amount of it properly administered can cure that cancer. In fact, radiation saves lives every day. Americium-241 makes many smoke detectors work; tritium stimulates the phosphors that illuminate some exit signs; gamma rays test the structural integrity of airplanes, bridges, and skyscrapers; and cobalt-60 and other sources of radiation are used to diagnose and treat cancers.

Should I be afraid of backscatter radiation from airport security checks?

First, most peoples' fear of radiation is disproportionate to the real risk. We are all normally exposed to very different doses of background radiation depending on where we live and work. Within this range, however, few data suggest adverse health effects. We should also not worry, as individuals, about backscatter X‑ray screening at airports and other very low level radiation exposures. If you are worried about radiation from airport screening, don't fly. You will receive much more radiation in the first few minutes of your flight from natural cosmic radiation than from an airport screening device. (This does not mean that society should disregard the potential risks of exposing millions of people to even very small doses of radiation such as these.)

What about microwaves and radio waves from cell phones?

Many forms of radiation, like microwaves or radio waves from cell phones, are called non-ionizing because they have insufficient energy to cause important changes in the cells they strike. Other, more energetic forms can alter the structure of atoms they hit, forcing electrons out of their normal position in the atom and producing a charged particle--an ion. These high-energy forms of radiation are termed ionizing radiations and they are everywhere. Some are produced by the natural decay of radionuclides (atoms that are radioactive) remaining from the creation of the universe. Others are man-made or man-caused, coming from exploding nuclear weapons, burning coal (which releases naturally occurring radionuclides locked inside raw coal), fissioning uranium in nuclear power facilities, and many other sources. Ionizing radiation in sufficient quantities can be a life changer. An X-ray delivers about 10 million times more energy than a radio wave, which gives a sense of why radio waves don't hurt us but X-rays can.

If there is so much radiation, what is one major source I may not know about?

Radon-222, an odorless, colorless gas, is a decay product of radium. It is everywhere on Earth (though unevenly concentrated), and it and its decay products (called radon daughters) account for between half and two--thirds of our annual background radiation dose. Because radon-222 is a gas, it can be inhaled, and the radioactive alpha particles it releases can be highly damaging to the lungs. Radon is commonly trapped in unventilated basements. In areas with high concentrations of radium in the soil, the gas also enters the groundwater and evaporates (especially in hot water), so we inhale it when we shower. Radon--222 and related radionuclides are estimated to be the most common cause of lung cancer deaths in nonsmokers. (Some lung cancer in nonsmokers is attributed to so-called passive smoking, secondhand exposure to cigarette smoke.) The Environmental Protection Agency estimates that radon causes about 21,000 of the approximately 160,000 lung cancer deaths in the United States each year. Smoking is of course the largest cause overall, and radon gas and smoking may interact to increase lung cancer risk. (Among the many poisons in cigarette smoke is radioactive polonium-210. Smoking in some regards is like deliberately inhaling a small nuclear weapon into your lungs.)

The greater the concentration of radon in the air and water at your home, the greater the potential danger. Some areas in the United States, such as the Colorado plateau, have high levels because of the composition of radionuclides in the soil, whereas other areas, such as Texas and other states along the Gulf Coast have lower levels. People living in areas of high radon concentration should consider home radon testing. For information on how to test your home for radon, go to the Environmental Protection Agency website. For a map showing concentration of radon in the United States, go here.

Can I calculate how much radiation I receive?

Yes. The Environmental Protection Agency has an easy way to do it. Go here.

Bonus question: Where would you be subject to more radiation, in Grand Central Terminal or in a nuclear power facility?

You will receive a higher immediate radiation dose standing at the information booth in Grand Central Terminal -- or standing in front of U.S. Capitol building -- than you will being inside a nuclear power facility. The marble and granite in these buildings release radiation at levels higher than permissible in the public areas of a nuclear power facility.

Robert Peter Gale, MD and Eric Lax are the authors of RADIATION: What It Is, What You Need to Know

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