Archive for April 2011
I’m not a physicist and, as such, would appreciate comments/emails alerting me to any errors! And yes, I did feel like I had to write this whole thing up before approaching radiation ecology. Welcome to my brain.
White Sands, New Mexico, 1954. An FBI agent, a police sergeant, and two scientists venture into a sandstorm, goggles pressed to their eyes, with one goal in mind: to find an odd footprint that they suspect is connected to recent area deaths. The scientists exchange knowing glances when they find it. “Something incredible has happened in this desert,” Dr. Graham says.
A minute later, the air swells with alien screams and the blinding sand clears to reveal their source: a giant ant, nearly 8 feet long. The agent and sergeant shoot frantically — “get the antennae! get the other antenna!” Graham yells. With its senses disabled, the ant collapses into machine gun fire. The team looks on in wonder: what is this thing and where did it come from? “It appears to be from the family Formicidae: an ant,” says Graham. “A fantastic mutation probably caused by lingering radiation from the first atomic bomb.”
This is a scene from the 1954 film Them!, one of many horror movies inspired by the first atomic bomb tests in the southwest United States. (And a great one, at that!) This idea seems preposterous now: radiation causing mutations that cause ants to grow to enormous sizes and feast on humans. Or atomic waste dumped into the ocean landing upon a human skull, creating a murderous zombie. Or a woman’s irradiated brain causing her grow to 50-feet — “incredibly huge, with incredible desires for love and vengeance!”
But is it really so preposterous? Radiation has taken on its own character, not only because of the immediate fears represented in film and books to the present day, but also because it is so hard to describe. It’s simultaneously envisioned as vats of poisonous waste, particles streaming from the sky — fallout — that can burn human skin, and atoms suspended in the air or water that can be incorporated into living tissue, festering there for decades and causing miniscule damage to DNA.
When I spoke to Tim Jannik of the Savannah River National Laboratory for The Scientist, he had to remind me what radiation really is. “What people often forget is that radiation is simply just energy,” he said. “When you get exposed to radiation, your body is absorbing energy.”
Ward Whicker, a radioecologist at Colorado State University whom I also interviewed for The Scientist, pushed it further: not only is radiation a simpler idea than that held in the public mindset, but it is also omnipresent in our lives. “People in general have a hard time understanding that we live in a very radioactive environment naturally,” he said. “Life has evolved in a radiation environment.”
Of course, we mostly think about radiation during times of crisis, whether it’s concern about nuclear weapons or, more recently, the flooding and subsequent breakdown of the Fukushima nuclear power plant. After discussing radiation for several days in terms of its hazard and then having these conversations of its basic nature in our environment, I realized that I really couldn’t remember very much about what radiation actually is! One thing led to another — or, rather, one wikipedia page led to another — and, after a few days of research, I felt I actually understood, on a basic level, how radiation works.
It felt wonderful to have radiation demystified! So, in case some of you are also struggling to think back to high school physics, I thought I’d write up what I learned.
The split nucleus
Radiation is a broad term that has taken on a very specific meaning for those of us who aren’t physicists. Radiation, from the same root as “ray,” describes something that travels in waves — and if you can think back to high school physics, remember that if something is a wave, it is also a particle. So sunlight — a form of radiation — is a wave, but is also composed of particles, photons. The same goes for UV and radio waves: Also particles. What we call “energy,” some amorphous force, is actually matter. Henceforth, when I mention “radiation” I will be referring to nuclear radiation: the waves/energy/particles that radiate from a nucleus.
As long as we’re on the subject of words that have taken on their own mythology, I may as well add another to the mix: nuclear. For some reason, I have two compartments for the word “nuclear” in my brain. One describes those tightly packed balls in the center of atoms, the nucleus, around which race electrons in various configurations. The other is more conceptual: a word that describes a great power, much like the One Ring, that can be used for good hypothetically, but is also dangerous.
But, of course, the actual meanings of nuclear in each case is one and the same, as nuclear power and all its gifts and danger are the product of activity at the nucleus of atoms — in particular, its breaking apart.
It takes a great deal of energy to compact neutrons and protons together into a tight ball and hold them there. So you can probably imagine that, if the nucleus does manage to break, energy is released. And this energy release, my friends, is nuclear radiation. (Its actual movement is also called radiation, but I’m referring to radiation as the actual energy.) There are different kinds of nuclear radiation — alpha particles, beta particles, gamma particles, neutrons, and others — that differ in what materials they are able to penetrate and the strength of the energy they carry. There are two ways a nucleus can break:
- It is unstable enough to disintegrate on its own.
- If it collides with another particle or nucleus with enough force.
A nucleus that is unstable enough to break apart on its own is an isotope, meaning it’s picked up a neutron or two that fly through the air constantly. This heavier nucleus cannot be held together by the same amount of energy, and thus it typically splits into smaller elements, a neutron or few, and energy. There are around 340 naturally-occurring isotopes that we know of that are radioactive in this way, but that’s leaving out some that (a) split so quickly that we can’t recognize their existence in the first place or (b) haven’t split yet since the formation of the earth, but they may still.
The second way for a nucleus to split is to be struck with another particle, a neutron for example, with enough force that the energy holding the nucleus together is disrupted and it breaks into smaller parts. This is the reaction that scientists organize in particle colliders to try and identify all the little particles released at the breaking point.
There really isn’t a huge distinction between these two methods: In both cases, a neutron strikes a nucleus, disrupting the energy holding it together, and causing it to break. It’s just a matter of time — either it happens immediately, or the neutron joins the nucleus for a little and, eventually, causes its demise.
This is the reaction that occurs in nuclear power plants. Many of these plants use Uranium-235, the only naturally occurring isotope that can sustain a nuclear chain reaction. A nuclear chain reaction is when one nuclear reaction leads to one or more — like knocking the first domino in a row. When Uranium-235 is struck with a neutron, it can release 3 more neutrons during its breakdown. If just one of these three manages to strike another atom of Uranium-235, another reaction occurs, ad infinitum.
And the main point: When any of these reactions or related ones occur, a bit of radiation (energy/waves/particles) is released with it, the extra energy that once was part of the nucleus and held it together. This energy is collected in nuclear power plants to generate electricity by heating water, for example. And it’s this energy that can do damage to our cells.
The danger of radiation
Most forms of radiation in our day-to-day lives are relatively benign — visible light, microwaves and radio waves, for example — and can’t do much harm, with their energy simply causing heat, if that.
But some radiation, such as alpha particles or UV rays, are tough little buggers that can interact and change other molecules that they run into by pulling off electrons. And it’s these resulting molecules — the oft advertised free radicals — that can damage DNA, causing mutations. With enough DNA damage, the cells commit suicide (apoptosis), and large amounts of cells dying quickly is what makes people exposed to large amounts of radiation to become sick.
If you’re in the vicinity of a large amount of radiation — such as when nuclear power plant cooling is disrupted, nuclear fuel is ignited, as at Chernobyl, or a nuclear bomb explodes — a lot of energy is reaching your body, both in the form of heat, which can cause burns, and nuclear radiation.
Cells in your body that divide very rapidly are the first to cause illness, as losing a group of these can quickly effect the total number due to their exponential growth. These are blood-forming bone marrow cells, and their damage can cause anemia due to a drop in red blood cells and a weakened immune system from a drop in white blood cells. Intestinal cells divide quickly, but not as rapidly as bone marrow cells, so they’re the next to be affected, causing symptoms such as nausea and vomiting, dehydration, and digestion trouble. At very high radiation doses, the cells that don’t divide are affected, in particular nerve cells, causing neurological problems from headache to coma. And these problems combined can kill.
If the radiation manages to damage DNA without killing the cells, this damage could still cause problems that could potentially lead to cancer later in life. Another concern for cancer-causing radiation is when radioactive isotopes accumulate in tissue, decaying and releasing energy within the body. (Read on! I dare you.)
Bioaccumulation of radioactive isotopes
Much of the concern in the aftermath of the Fukushima reactor accident has been about various radioactive isotopes: Iodine-131, Cesium-137, and Strontium-90, to name a few. These are isotopes that are taken up by the body when eaten and are incorporated into tissues because their biochemistry is similar to iodine, potassium, and calcium, respectively.
Non-radioactive iodine is necessary for proper thyroid function, but when Iodine-131 is taken up by the thyroid instead, the isotope is stored in the thyroid, slowly able to release its radioactive energy and particles over time. This long-term exposure in a very small area can lead to thyroid cancer. However, Iodine-131 decays relatively quickly: In just 8 days, a sample of Iodine-131 will be half the size it began. In other words: on average, half of the nuclei in the sample will have decayed after 8 days, proportional to but not an exact measure of the decay rate of a single nucleus (Thanks, Liz!). However, it releases alpha radiation, a stronger form of radiation that creates free radicals more easily and quickly, so it’s best to avoid it despite its short lifespan.
Cesium-137 and Strontium-90, however, take around 30 years each to halve in size, slowly releasing radiation over that period of time. Cesium-137 imitates potassium and is taken up into muscle tissue where it can remain for half a year before it is recycled out by proper potassium, giving it a fair bit of time to release radiation. Strontium-90 takes the place of calcium, building up in bone and bone marrow. Unfortunately, this isotope gets stuck there and isn’t cycled out like Cesium-137, and can cause bone cancers and leukemia.
These latter two — with 30 year half-lives — can accumulate in plants or animals and, when humans ingest them, become incorporated into our bodies. That is the fear behind much of the environmental impact talk: Will Strontium-90 enter the food chain? How far from the reactor will it spread? And how long do we have to wait before the food is safe again?
The answers to these questions are mostly unknown because we simply don’t have enough experience with them. As I will elaborate on in my next post, very little work has been done studying the ecosystems at Chernobyl, giving us little insight into how these isotopes remain in the environment.
Congratulations! You made it through. I hope I was able to successfully explain radiation and its basic effects to you. Please leave any questions, comments and corrections in the comments or send me an email.
Post edited 4/10/11 to clarify explanation of a radionuclide half-life
Right now there are over 150,000 people watching a Bald Eagle nest in Decorah, IO with me over webcam.
Isn’t the internet wonderful?
Join the cool club and look at some cute/ugly baby birds (or just the momma eagle nesting) with us on ustream
UPDATE: According to Wired, there is still another chick that hasn’t hatched yet! And it will probably hatch within the next 48 hours! You know what that means: NO SLEEPING. NO GOING OUTSIDE. I hope it doesn’t hatch during my commute…