System of Fear: A Dose of Radiation Reality

14 10 2013

In line with last week’s post, please see the below infographic, which paints radiation doses in the visual context of a sort of system of planets according to size (click to enlarge):


As is plainly evident, it’s shocking how much the public perception of radiation doses and negative health effects differs from reality.

(For example, in today’s perceptual climate, who would believe that a person could live within a mile of a nuclear powerplant for a thousand years before receiving the radiation dose from a single medical CT scan?)

If feedback to this is positive, I think I’ll make this the first in a series of similar infographics.  (Perhaps people would find it interesting/useful to next have illustrated the relative magnitudes of nuclear disasters?)


If anyone doubts the numbers in the above diagram, please feel free to investigate the references for yourselves!

International Atomic Energy Agency:

U.S. Environmental Protection Agency:

U.S. Nuclear Regulatory Commission:

U.S. National Council on Radiological Protection (via the Health Physics Society):

U.S. Department of Energy:


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.]

Space radiation has Astronauts seeing stars

2 01 2011

View of Earth at night from the International Space Station. The thin atmosphere layer visible acts as a natural radiation shield. (Credit: NASA)

There are many astronauts experiences that are well understood.

Everyone knows about “weightlessness,” or floating in a microgravity environment, (which is actually perpetual free-fall around the Earth, but that’s a technicality for another post.)

Everyone has heard about the problem of space sickness that hits some astronauts and not others.   Disruptions in our sense of orientation (i.e., up and down,) are likely to blame.

However, what many do not know about are the strange “flashes” of light astronauts see while in space and what it might mean for their future heath.  With commercial space travel on the horizon and space tourists and commercial astronauts lining up to take part, the realities of space travel must be explored and disclosed.

The Earth’s atmosphere normally acts as a shielding layer, protecting the surface from cosmic and solar radiation.  However, when we travel beyond the atmosphere, (i.e., space,) we increase our exposure to such radiation.  In truth, these “flashes” reported by astronauts are actually electrochemical reactions occurring in astronauts’ eyes as a result of high-energy radiation striking their retinas.  A radiated particle passes through the lens of the eye, strikes the retina, and fakes out the optic nerve, which in turn interprets the signal as light.

So, aside from being strange, what are the potential effects of these flashes?

There appears to be a relationship between this radiation exposure and later development of cataracts, a disease characterized by a clouding of the lens of the eye.  According to a 2001 study, a total of 39 astronauts have developed cataracts later in life, and 36 of them flew on high-radiation missions, such as those to the Moon.

Scientists are currently working on nailing down the genetic link between radiation exposure and cataracts, but until then, it simply appears that exposure to space radiation increases your risk of cataracts later in life.  Advances in and the regularity of surgically-implanted interocular lenses make cataracts less of a concern, but effects like these are something for the aspiring casual spaceflight participant as well as for future planetary and deep space explorers to be aware of.

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