Friday, March 18, 2011

Too Much Radiation is Dangerous: Numbers and Background

"Factbox: How much radiation is dangerous?"
Richard Borsuk, Kim Coghill, Tan Ee Lyn, Edition: U.S., Reuters (March 15, 2011)

"Health experts urged governments in the Asia Pacific to monitor radioactivity levels after Japan's quake-damaged nuclear power plant exploded and sent radiation into the air.

"Radiation is measured using the unit sievert, which quantifies the amount of radiation absorbed by human tissues.

"One sievert is 1,000 millisieverts (mSv). One millisievert is 1,000 microsieverts...."

So far, so good. Particularly. in the Lemming's opinion, the refresher on decimal prefixes:
  • 1 sievert (Sv) =
    • 1,000 millisieverts (mSv)
      • 1,000,000 microsieverts
There's a somewhat more technical definition of the sievert and a short history of Rolf Sievert's research at:Back to that Reuters backgrounder:

"...* Japan's Chief Cabinet Secretary Yukio Edano had, at one point, said radiation levels near the stricken plant on the northeast coast reached as high as 400 millisieverts (mSv) an hour. That figure would be would be 20 times the annual exposure for some nuclear-industry employees and uranium miners.

"* People are exposed to natural radiation of 2-3 mSv a year.

"* In a CT scan, the organ being studied typically receives a radiation dose of 15 mSv in an adult to 30 mSv in a newborn infant.

"A typical chest X-ray involves exposure of about 0.02 mSv, while a dental one can be 0.01 mSv.

"* Exposure to 100 mSv a year is the lowest level at which any increase in cancer risk is clearly evident. A cumulative 1,000 mSv (1 sievert) would probably cause a fatal cancer many years later in five out of every 100 persons exposed to it.

"* There is documented evidence associating an accumulated dose of 90 mSv from two or three CT scans with an increased risk of cancer. The evidence is reasonably convincing for adults and very convincing for children.

"* Large doses of radiation or acute radiation exposure destroys the central nervous system, red and white blood cells, which compromises the immune system, leaving the victim unable to fight off infections.

"For example, a single one sievert (1,000 mSv) dose causes radiation sickness such as nausea, vomiting, hemorrhaging, but not death. A single dose of 5 sieverts would kill about half of those exposed to it within a month.

"* Exposure to 350 mSv was the criterion for relocating people after the Chernobyl accident, according to the World Nuclear Association...."

It's a pretty good article, in the Lemming's opinion, although the Reuters reporters could, again in the Lemming's opinion, made the idea of background radiation a little clearer.

"Background radiation?!"

Background radiation is the radiation we're exposed to, just by living on Earth. It isn't the fault of evil scientists, Big Oil, or shape-shifting, space-alien lizard men. In the Lemming's opinion.

Most of Earth's background radiation comes from radon gas, which comes from the natural decay of uranium. Which is an element that occurs naturally on this planet.

More about background radiation:
  • "Background Radiation"
    Emory University, Radiation Safety Office, Laboratory Worker Training Manual

What's the Big Deal With Radiation?

Japan's got a full plate of problems just now:
  • Towns knocked flat by an earthquake
    • And rearranged by a tsunami
  • Thousands of known deaths as a result
    • And upwards of ten thousand missing
  • Road and rail system out of service
  • Power and utilities gone for survivors
  • Fires
  • Badly-damaged reactors at a nuclear power plant
That last item is why the Lemming thought this post might be of interest. There's been quite a lot of talk about 'radiation' and 'danger' on the news: but precious few facts about just what the danger is, and how serious it is.

Aside, that is, from the recurring references to Chernobyl and THREE MILE ISLAND! THREE MILE ISLAND! (March 16, 2011)

Which is why the Lemming was glad to see that Reuters backgrounder.

Radiation: Godzilla, Killer Bees, and Reality

We can learn a lot from the movies. For example, the movies teach us that radiation makes gigantic fire-breathing lizards attack Tokyo.

That's the movies.

This isn't quite as entertaining, but the Lemming thinks it's a tad more firmly attached to reality than Godzilla and The Swarm:

"Radiation and Health"
Department of Health, New York State

"...Radiation is energy that moves through space or matter at a very high speed. This energy can be in the form of particles, such as alpha or beta particles, which are emitted from radioactive materials, or waves such as light, heat, radiowaves, microwaves, x-rays and gamma rays. Radioactive materials, also known as radionuclides or radioisotopes, are atoms that are unstable. In nature, there is a tendency for unstable atoms to change into a stable form. As they change form, they release radiation.

"Radiation that can produce ions when it interacts with matter is called ionizing radiation. Ions are the charged particles that are produced when electrons are removed from their positions in the atoms. Alpha particles, beta particles, x-rays and gamma rays are forms of ionizing radiation. On the other hand, radiation that is not capable of producing ions in matter is known as nonionizing radiation...."

Not the stuff of which box office hits are made: but the Lemming thinks it's interesting, anyway.

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