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Would your head glow in the dark if you got 100 dental x-rays?

Posted Jun 27 2011 12:00am

These are the questions that keep me up at night.  Strange, I know.

But with all the talk about Japan’s nuclear power plant mishap and with everything I am reading about radiation in cell phone use, I thought I would do some extensive research on the subject.  (hmm…I wonder if sitting in front of my computer is radiating me….)

Radioactivity. What is it?

There is radioactivity all around us and even inside our own bodies.  Our blood and bones contain Potassium 40, Carbon 14, and Radium 226.   Ever hear of “carbon 14 testing” on bones found in an archeological site?  They are measuring the amount of radioactive Carbon 14 in the bones which has a half-life (the amount of time it takes for half of the substance to degrade) of 5730 years.  (And just in case you ever make it to Final Jeopardy, the half life of Uranium 238 is 4.5 billion years.)

There is also radiation that comes naturally from the soil and the air, which finds its way into our food.

Non-ionizing radiation refers to waves that travel through the air, but do not have enough energy to damage atoms, and ultimately, living cells.  Some types of non-ionizing radiation include the sun, microwaves, radio waves and infa-red waves.  That’s why the sun feels hot.  This form of radiation can do damage, but it is in the form of heat damage (burns), not cell destruction and cancer.

Ionizing Radiation is what we think of when we think of nuclear radiation.  This is the kind that can cause damage to the body’s cells and can cause cancer.  We aren’t aware of exposure to these types of rays.  This type of radiation is cumulative, that is, exposure adds up over your lifetime.  Ionizing radiation can be found in x-rays and nuclear radiation exposure.  It is also all around us in the environment.

So how much is too much?

When we talk about “damage” and “harmful radiation” we want to know how much can I get and still be sure I won’t grow another pinky finger.  The answers on safety will vary.

There are many ways of measuring radiation.  For this post, I used units called sieverts (Sv). For the purpose of discussing radiation to humans we have to make the unit smaller.  Milliverts (mSv) are 1/1000 of a sievert (don’t worry, there’s no test on this).  For example, one chest x-ray gives you 0.1 mSv.  You may also hear of “rems” or “rads”, but we will use the international standard of sieverts for this post.

We know, from Japanese victims of Hiroshima, unfortunately, that sudden exposure (all at once, not over the course of a lifetime) to levels of radiation produce the following effects:

  • 500 mSv – nausea
  • 700 mSv – vomiting
  • 750 mSv – hair loss in 1 – 2 weeks
  • 900 mSv – diarrhea
  • 1000 mSv – internal bleeding
  • 4000 mSv – death within 2 months
  • 10,000 mSv – death in 1 – 2 weeks
  • 20,000 mSv – death within hours
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