Understanding radiation


The Bradbury Science Museum in Los Alamos, New Mexico contains a bunch of exhibits about the history of Los Alamos National Laboratory and its science and research work. And with alarm bells continuing to sound around the world in light of Japan’s troubled efforts to contain a nuclear contamination crisis at its Fukushima Daiichi plant, (and folks on the West Coast and beyond stockpiling potassium iodide for fear of exposure to drift) I found myself drawn to the “Understanding Radiation” display during a recent visit to the museum, which includes a chart to help folks calculate their annual radiation dose (scroll down to the end of this post to figure out your own personal annual dose.)

The display notes that the three main sources of radiation for folks in the United States are from outer space, fallout from past nuclear testing and nuclear power plants.

“Exposure doesn’t make you radioactive but can cause biological harm measured in units called rems,” the display stated, noting that our exposure to ionizing radiation is measured by a unit called a rem.
“On average, each of us receives a total dose of about one-third of a rem (362 millirem) per year, from all sources,” the display notes.

The average American receives about 360 millirems in one year, according to the Bradbury Science Museum, and the display includes a pie chart that shows that the biggest slice of our annual dose comes from natural sources, starting with radon gas, which is present in most rocks and soil and building materials, is produced in small amounts in buildings, and can build up indoors, especially in basements and tightly sealed buildings.

The second highest source is a combination of natural cosmic radiation (the dose you receive from the sun and outer space) and terrestrial radiation (the dose you receive from the ground).

The third largest dose comes from medical and dental procedures, including X-rays.

That’s followed by internal radiation (what comes from our bodies), consumer products, other sources, and lastly, an average annual but very small dose from Los Alamos National laboratory activities.

UPDATE: A spokesperson for the Los Alamos National Laboratory clarified that the small dose from the lab's activities opnly applies to folks living in the immediate area. “Our exhibit notes that Laboratory activities contribute about 1/10 millirem to the public - to a person who lives in Los Alamos year-round,” they clarified. “ It doesn't apply to someone living in say, the Bay Area, let alone a person who lives in the Bay Area and doesn't visit Los Alamos (or the nearby Lawrence Livermore National Laboratory for that matter)." [So, my apologies for my misinterpretation, and thanks for the clarification!]

Now, maybe, like me, you did not pay attention/or did not retain the information from your chemistry classes on nuclear fission, fusion and fallout. If so, what follows could be of interest to you.

And if you did pay attention, rest assured that I’m trying to figure out if folks will need to start factoring in a new annual dose level related to leaks from the Fukushima Daiichi plant. (Today’s news is all about how marine life faces a threat from the runoff: high levels of radioactive cesium have been detected in seawater near the damaged nuclear reactors, and this is raising the disturbing prospect that radiation could enter the food chain. Cesium 137 levels have been detected at 20 times the normal level at 1,000 ft from the effluent at the plant. These levels are far less than the iodine 131, which has been found spilling from the plant at concentrations of more than 1,150 times the maximum allowable levels. But the problem is that unlike iodine 131 which degrades relatively quickly, (it becomes half as potent every 8 days), cesium 137 has a half life of 30 years and is absorbed by marine plants, which are eaten by fish, and tends to bioaccumulate (become more concentrated) as it moves up the food chain (as big fish eat smaller fish).

Anyways, I’ll update this post, when we get more information about the size and nature of the leaks, which are thought to have occurred when seawater was dumped on the overheating reactors. (The idea is that the seawater picked up the radiation before it washed back out to sea, but other sources are also thought to be possible).

In the meantime, read on if you want to brush up your understanding of radiation/or better understand the sources of your annual personal radiation dose:

“Radiation is energy in the form of waves or particles,” the BSM display observes. “Radiation is energy traveling at the speed of light. It makes up familiar parts of our world, such as visible light, ultraviolet light and infrared light, radio and television waves, X-rays and microwaves.”

That said, the display goes on to explain that the problem is with ionizing radiation.

“Is radiation harmful?” the display asks. “Most radiation is not, but some radiation carries enough energy to separate molecules or remove electrons from atoms and this can damage living tissue. This type of radiation is called ionizing radiation. It includes particles and energy emitted from radioactive elements and the X-rays used in medicine or at airports. A less energetic form of radiation, ultraviolet rays from the sun, can burn our skin.”

So, how can we protect ourselves from ionizing radiation?
“We can protect ourselves from the effect of ionizing radiation by applying three principles: time, distance and shielding,” the display states.

“We use time to allow a radioactive material to decay and thus decrease its radioactivity. Or we limit the amount of time we are exposed to the source of radiation.”

“We use distance between us and the source to decrease the likelihood it will reach us.”

“We use shielding between us and the source of radiation to absorb or stop radiation before it reaches us.”

“We can protect ourselves from the effects of ionizing radiation from internal hazards (inhaling or ingesting radioactive material) through the use of engineered controls (like containment and ventilation) and personal protective equipment (like anti-contamination clothing and respirators).

Ionizing radiation comes in two forms: a) Waves or rays and b) particles.

One type is similar to visible light and occurs as waves or rays, e.g. gamma rays, X-rays. And, as the museum explains, gamma radiation and X-rays can easily penetrate our bodies and so are external hazards. They can be stopped by dense material such as lead, concrete and steel. Examples of gamma-emitting radionuclides are cesium-137 and cobalt-60, uranium-235 and plutonium-239, in addition to being alpha-emitters, also emit gamma radiation.

The other type of ionizing radiation is known as alpha, beta and neutron radiation and is produced by energetically charged particles.

Alpha radiation
Alpha particles (two protons and two neutrons) can be stopped by a single sheet of paper and cannot penetrate clothing or the outer layer of skin. So externally, alpha radiation is not a hazard. But if alpha particles enter your body by breathing and eating, then they can be an internal hazard. [Examples of alpha-emitting radionuclides are Uranium-235 and plutonium-239. And as recent reports from Japan have explained, plutonium has been found at the Fukushima Daiichi plant. While the source is currently not clear, the reactors could be a source, as could tests of tests of nuclear weapons in the atmosphere, because even though these ended in 1980, they left trace amounts of plutonium around the world. This is worrying because Plutonium-239 has a half-life of 24,000 years and can cause healthy tissue to turn cancerous if it gets deep inside the body.)

Beta radiation:
Most beta particles are negatively charged and have a short range in air and cannot penetrate other substances very deeply. But if beta radiation has enough energy, it can penetrate your skin, so it’s considered an external hazard. It can be stopped by plastic, aluminum, wood, and clothing. Examples are phosphorous-32 and hydrogen-3 (tritium) which is deemed to be a very low hazard.

Neutron radiation
Neutrons are neutrally charged, subatomic particles emitted during a nuclear reaction in radiation-generating devices like accelerators and nuclear power plants.
They are also emitted by special radionuclides like californium-252 or by ionization of materials like plutonium plus berrylium. Highly penetrating, water, concrete and hydrogen-rich materials make effective shields.”

How to measure your exposure
Our exposure to ionizing radiation is measured by a unit called a rem.
“On average, each of us receives a total dose of about one-third of a rem (362 millirem) per year, from all sources,” the museum display notes.

How to calculate your personal annual radiation dose.

1.    Calculate your Cosmic radiation level
The level of cosmic radiation depends on your altitude:
If you live at sea level, you receive 26 millirem, a year.
If you live at 0-1,000 ft above sea level, it’s 28 millirem.
If you live at 1,001-2,000 ft, it’s 31 millirem.
If you live at 2,001-3000 ft,  it’s 35 millirem.
If you live at 3,001-4,000 ft, it’s 41 millirem.
If you live at 4,001-5,000 ft, it’s 47 millirem.
If you live at 5,001-6,000 ft, it’s 52 millirem.
If you live at 6,001-7,000 ft, it’s 66 millirem.
If you live at 7,001-8.000 ft, it’s 79 millirem.
If you live at 8,001 ft and plus, it’s 96 millirem.

2.    Now add the terrestrial radiation, the dose you receive from the ground:
If you live closest to the Atlantic Coast, add 23 mrem.
If you live closest to the Gulf of Mexico, add 23 mrem.
If you live closest to Colorado Plateau (AZ, Utah, Colorado, New Mexico) add 90 mrem.
If you live closest to the MidWest, add 46 mrem.
If you live closest to the Pacific Coast, add 46 mrem.
If you live closest to Alaska, add 46 mrem.
If you live closest to Hawaii, add 46 mrem.

3.    Add your radon gas dose
Add 200 mrem (the U.S. Average) for radon gas we breathe.

4.    Add natural radiation dose for food and water
Add 40 mrem for average natural radiation from food we eat and water we drink.

5.    Fallout from past atmospheric testing of nuclear devices
Add 0.5 mrem for fallout from past atmospheric testing of nuclear devices.

6.    Occupational exposure
Add 44 mrem if you work at the Los Alamos National Laboratory as a radiation worker, or your occupational dose from your job.

7.    Radiation from different medical treatments
If you have X-rays of the arm, hand, foot, or leg, add 1 mrem.
If you have Xrays of the chest, add 6 mrem.
If you have X-rays of the pelvis/hip, add 65 mrem.
If you have X-rays of the skull/neck, add 20 mrem.
If you have barium enemas, add 405 mrem.
If you have upper gastrointestinal tract radiography,    add 245 mrem.
If you have dental X-rays, add 2 mrem.
If you have CT (computed tomography) scans, add 110 mrem.
If you have a plutonium-powered pacemaker, add 100 mrem.
If you have a thyroid scan, add 14 mrem.
If you have porcelain crowns or false teeth, add 0.07 mrem.

8.    Depending on your lifestyle, place of residence, here are more factors to add:

If you travel by air plane, add 0.5 mrem per hour in air.
If your luggage is inspected, add 0.002 mrem.
If you live within 50 miles of a coal-fired electric utility plant, add 0.03 mrem.
If you live within 50 miles of a nuclear reactor, add 0.01 mrem (not counting Japan).
If you smoke 1/2 pack of cigarettes per day, add 500 mrem.
If you smoke 1 pack of cigarettes per day, add 1,000 mrem.
If you smoke 11/2 packs per day, add 1,500 mrem.
If you smoke 2 packs per day, add 2,000 mrem.
If you have a smoke detector, add 0.008 mrem.
If you live in a stone, adobe, brick, or concrete building, add 7 mrem.
If you wear a luminous wristwatch, add 0.06 mrem.
If you use a gas compression lantern, add 6.2 mrem.

9.    Average annual dose from the Los Alamos National Laboratory, add O.1 mrem.
The museum notes that this dose is, “a small fraction of the amount the public receives from some consumer products and our natural environment.” And it clarifies that a mrem, or millirem, is one thousandth of a rem.

So, you’ve added up your annual dose, but what does this mean in terms of health?

“Radioactive materials give off ionizing radiation that can alter the chemical makeup of human tissue,” the museum display notes. ‘The amount of damage depends  on the amount of radioactivity.” (And the time, distance and shielding involved, see above).

‘It’s clear that very high exposures such as those experienced at Chernobyl can be fatal,” the display continues, noting that 31 people died within the first few weeks at Chernobyl after receiving radiation doses in excess of 1,000 rems, and that many others, who were exposed to doses of 100 rems, have a 1 in 100 chance of developing cancer.

“It’s very difficult to determine at exactly what level exposure to radioactivity becomes dangerous,” the display states, noting that worldwide the number of fatalities over the next 50 years were estimated to be as high as 17,000. (Again, this was before the March 2011 triple disaster in Japan.)

The display observes that a 1991 study by the International Atomic Energy Agency measured no increase in any radiation-related illnesses in villages near the site.
“But the study did not look at the highest-risk populations closest to the site,” the display added, noting that there were no fatalities in 1979 at Three Mile Island, when reactor failure allowed “small amounts of radioactive water and steam to be released from the containment structure.”

“Exposure levels to folks nearby were less than 100 millirem per year, which is about one third of the normal background yearly dose,” the display observed.

It also noted that strontium and radium are biologically active, which means they can migrate to bone tissue and stay there a long time. And that radioactive iodine can replace the stable iodine which is very important to human health. “Radioactive iodine is taken up by the thyroid and can pose a significant health risk.” (Hence the rush on potassium iodine, even though radioactive iodine degrades fairly fast, and the radioactive risk can be combated by banning fishing and the consumption of seafood for a period of time as Japan is already doing.)

The display clarifies that exposure doesn’t make you radioactive, but it can cause biological harm, and that medical X-rays are by far the largest artificial source of radiation for the average American.

For more information, you can also check this chart from the Public Domain here