Calculating your own natural radiation dose in context

26 06 2012

 

Traditional Radiation Trefoil Hazard Symbol. (Image credit: ORAU)

A Dose of Radiation Information

How much radiation is normal?

In light of Fukushima, sensationalized media, political fear-stoking, and rampant misinformation regarding radioactivity, consider this post an easy-to-reference tool/resource.  With it, you can be armed to understand and quickly make sense of this over-mystified, natural aspect of reality when it comes up.

For starters, here’s the simple reality about how much radiation you receive in a year just for standing on Planet Earth:

The average natural annual radiation dose for a U.S. resident is about 300 millirem, and when including man-made commercial products and medical procedures (MRI scans, etc.), the average dose jumps up to 600 millirem per year.  This is what we all get every year and bears no known, measured relationship to developing cancer.

  • Note: For the international units, divide all “millirem” numbers by 100, (i.e. 3.6 millisieverts.)  Or, an online converter can be found here.

However, what does that mean?  I’m completely aware that unless you’re a professional in the field of health physics, (as I am,) this number has no context.  So, allow me to explain just what this really means using things we can all identify with.

Hold on to your hats.

So, What’s My Dose?

For context, below is a list of the amount of radioactivity you receive in a year from very familiar items/sources:

  • Cosmic radiation  = 26-96 millirem (higher with altitude)
  • From standing on the Earth itself (geology) = 20-90 millirem (higher nearer igneous mountains)
  • From your own brick/stone/concrete building = 7 millirem
  • From your own body (food/water!) = 40 millirem
  • From breathing (naturally-produced radon) = 200+ millirem
  • For flying 1,000 miles in an airplane = 1 millirem
  • From having a dental/chest/normal x-ray = 50 millirem each
  • From having an annual mammogram = 75 millirem
  • From having a single CT scan = 150 millirem
  • From smoking a pack of cigarettes a week (polonium) = 200 millirem
  • From consumer goods = 10 millirem

Just add these up to produce your own, custom average annual radiation dose.

Wait.  My house/food/body/atmosphere is radioactive?

Yes.  Not to fear.  Just like the small amounts of chemicals that we can reliably tolerate, (e.g., trace arsenic, lead, etc.,) so too are trace amounts of radioactivity completely tolerable.

Fukushima in Context

Now, as you can see in the above plot of the radioactivity measured at the entrance of Fukushima nuclear powerplant as the disaster happened, it looks pretty dramatic.

  • (Note: The numbers are reported in “micro”sieverts per hour, which are admittedly reading a much smaller span of time, (hours versus years,) but are in units 1,000 times smaller than the “milli”sievert international units described above.  This is important.)

However, instead of running for the hills just yet, let’s take a look at what the numbers actually say.

The March 15th hydrogen explosion at the plant, which occured roughly 84 hours after the earthquake, shows the largest spike of activity: for a brief period upwards of nearly 12,000 microsieverts per hour.

But let’s take this apart.  What does that mean?  12,000 microsieverts is the same as 12 millisieverts.  12 millisieverts is the same as 1,200 millirem.

Now, compare this to the above list of natural radiation values, with an eye toward the annual average does of 360 millirem.

Yes, if reading correctly, this implies that simply standing on planet Earth every year nets everyone the same external radiation dose that would have been received if standing at the gates of the Fukushima Daichi powerplant during the worst part of the disaster for a full 15 minutes.

With these, even worst-case numbers, it becomes obvious that one could stand at the entrance to Fukushima during the worst period of the disaster for a full three minutes and have earned only the equivalent radiation dose of… an average chest x-ray.

Granted, this isn’t something one would necessarily want.  This is upwards of 15% of your natural average dose.  -But your biology wouldn’t ever notice the difference.  And one could go many orders of magnitude more than that before there would be any reasonable expectation of an acute health effect.

More realistically, even standing at the Fukushima gates during the unprecedented event of external venting from the internal containment of reactor number 2, (with an exposure rate of 0.5 millisievert per hour), it’s a full hour of loitering there before one would rack up the external exposure of simple set of dental x-rays.

Funny how the perception and the reality differ, eh?

Unwanted radioactive material is serious, just as a leak from underground gasoline storage tanks that could contaminate drinking water is serious.  But that seriousness must be given honest context.

Take-home

Hopefully this has provided a window into the reality of radiation protection, and it is my sincere wish that this was and will continue to be a useful go-to when radiation numbers come up in the media.

Feedback is welcome, and if desired, I would be happy to put other radiation values in context… (Chernobyl, Three Mile Island, going to the Moon, etc.)

Go forth and combat radiation misinformation!

[Sources for the above information: American Nuclear Society, the National Council on Radiation Protection and Measurement, the U.S. Department of Energy.]


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4 responses

19 11 2012
Joffan (@Joffan7)

Oops, unit conversion error. The dose-rate of 12000 microsieverts/hr , 12millisieverts/hr is actually 1200millirem/hr = 1.2 rem/hr

That’s not going to kill you either, but it’s going to get above your normal background dose rather quickly.

However there is really no need to go to the peak of the graph; the integrated dose is clearly going to work out at a far lower mSv/hr figure. And the doses away from the plant, through distance and natural dispersion, were far lower again.

The long-term evacuation of the area ignored the value of communities and economies and imposed life-altering decisions on people without proper information. To pretend there is no downside to such an action was wanton dictatorship.

7 01 2013
astrowright

Caught it! Thanks for the second pair of eyes – looks like I blazed through the segment too quickly; The scenario has been updated to reflect the correct conversion factor.

And you’re right about using the peak activity – I was just choosing it to illustrate an extreme worst-case (even worse than the actual worst-case we actually experienced there).

I agree that we need much more accurate representation of the risks of radiation dose in context with ordinary dose as well as the risks (economic, stress, environmental), as you mention, involved with hasty and perhaps inappropriate reactions.

Thanks for reading!

Cheers,
Ben

16 09 2013
kintaman

One vital point you are not accounting for is “internal contamination”. This is the real danger. If you were, as in your example, standing at the gates of Fukushima Daiichi when it was being vented or exploded you would have inhaled a large amount of material if you were not wearing adequate safety gear.

The same applies to the fallout beyond this area. If people simply walk by hotspots it is a brief exposure with no real impact. However, if people inhale contaminants via the air or ingest contaminated food/water the impact becomes much greater as it is now an much longer exposure (permanent in some cases).

17 09 2013
astrowright

Kintaman –

Correct you are, in all respects. Internal contamination was simply not addressed in my post. -And this is the problem in attempting to communicate radiation exposure facts and processes to a lay-audience who have been chronically confused by media misuse of health physics terminology. “Contamination” events, as you mention, are those where one has to worry about internalizing radionuclides, yet much of the public concern is in specific regard to “radiation” exposure. My post was targeted specifically to address those concerns and provide some context. In contrast, what you’re describing is not exposure so much as it is “uptake,” which is a different animal entirely. So, you’re right in that this post deserves a follow-up — (one would have only inhaled a large quantity of airborne radioactive material if you’d been down-wind of the release) — but this again deserves a context in terms of the quantities of radioactive material internalized during the course of a year, (with special note given to iodine, radium, and strontium isotopes), e.g., radon… a hazard that in my opinion, for all of the hype that radioactive material receives, is maddeningly *underplayed* by the public. -Still haven’t figured that one out.

In any event, thanks so much for taking the time to offer your thoughts! Perhaps with enough information, we can produce a laity that is well-informed enough about the ubiquity of radioactive material and radiation exposure to adopt a reason-based as opposed to fear-based stance on the intelligent use of nuclear energy.

Cheers,
Ben

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