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.


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.]


Japanese lunar light farming

1 06 2011

Rendering of a solar array ring on the Moon's surface. (Credit: Shimizu Corporation)

Definition of mixed emotions: Reading an ambitious plan recently released by the Shimizu Corporation of Japan that effectively wields fear of radiation to incentivize lunar colonization for solar power generation. 

Wow.  While I abhor anything that preys upon the irrational fear of nuclear energy, I’m all for the use of solar power.  (I’d like to make the ironic point here that “solar power” is also nuclear energy – the result of a giant nuclear fusion reactor, albeit a natural one.)  I’m also certainly for anything that makes an extraterrestrial business case, and I further endorse any plan that leads us off-world so that we can begin developing the practical know-how to live there.  Throw in the fact that the endeavor would ease stress on the terrestrial ecosystem at the same time, and the idea seems like a home run.

Diagram depicting the lunar power delivery process. (Credit: Shimizu Corporation)

How does it work?  Quite simply.  Called the LUNA RING, solar arrays are to be installed across the lunar surface in an equatorial belt.  Panels on the sun-facing side of the Moon then deliver energy via circumferential transmission lines to laser and microwave transmitters on the Earth-facing side.  These transmitters then beam the energy to receiving stations on the Earth, providing power enough for all.

Sound too good to be true?  Well, it may be.  The problem, like many great ideas, is funding.  The technology is all but completely available to make an attempt, but the capital costs here are incomprehensible.  Yet-to-be-invented tele-robotics plays a major role in construction, (which as I’ve previously mentioned is a very smart move,) and when weighed in combination with untried lunar transport, operations, and manufacturing techniques, equates to a seriously steep R&D curve.

However, this sort of distance planning can demonstrate that the basic elements already exist, which may be exactly what we need to convince  governments and the power industry that the venture is possible.  And, if Japan suddenly puts the economic weight of the government behind a plan like this, e.g., by making a call to return to the Moon and by actually launching small-scale versions of this system, then we should all take note… and I believe we should all participate.

The International Space Station is an endeavor that has and will continue to benefit many.  An international effort to establish renewable lunar-terrestrial power production can benefit everyone, both immediately as well as by developing the skills we’ll need to expand into the cosmos.

Good on ya’, Shimizu Corporation, for thinking big.  Hopefully it’ll catch on.

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