Calculating your own natural radiation dose in context

 

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.

Image source: http://www.tepco.co.jp/cc/press/betu11_j/images/110316e.pdf

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.]

Proposing an Antimatter Hazard Symbol

Proposed Antimatter Hazard Symbol. Credit: Me

As the most potent potential fuel we are familiar with at this stage in our development as a civilization, I think it’s time we talk about getting serious about Antimatter.

For those unfamiliar, Antimatter is atomically identical to normal matter, but electrically (and subatomically) backward.  Electrons become positrons, and protons become anti-protons, particles with opposite electrical charges.  (Think of flipping over the batteries in your remote control, so the “plus” side is now the “minus.”)  Anyway, when matter and antimatter interact, they are both completely anihillated and converted to pure energy in a release that makes nuclear warheads quake in their boots.  (Gene Roddenberry had it right 40 years ago when he powered his fictional interstellar craft with it.)

To this day, Antimatter is the only thing we know of that could power inter-star-system or galactic space transportation technology, real or imagined, and get the job done in a practical amount of time, (read: a single human lifetime).

This brings us to the present, where I currently find myself buried in 10 CFR 835 federal regulations for work.  They’re the regulations our government has put into place to protect workers and the public from sources of radiation and properly warn them of areas of radiation and radioactive contamination.  These rules relate heavily to symbology and the implementation of the familiar yellow-and-black radiation symbol.

You can see where this is going.  Should we decide to seriously consider Antimatter as the fuel (read: energy storage) source that it has the potential to be, we are going to need to seriously consider warning people about it.  The first step is creating a hazard identity.

There have been a couple of attempts at an Antimatter Hazard Symbol floating around the web, but I haven’t found that they adequately address the risks nor do they necessarily coincide with accepted symbology.  Why not start with something familiar?  I think the radiation tre-foil is panic-inducing enough to serve as an acceptable starting point…

So, the thought evolution of my proposed antimatter symbol is simple:

• The trefoil already represents radiative energy from a point, so why not start there?  It’s already internationally recognizable.
• Instead of one point in the symbol center, use two overlapping inverted-color circles, representing the interaction of matter and antimatter.
• Instead of solid trefoil blades, bisect them to provide the visual appearance of even more energy released than radioactive matter.
• Instead of yellow, a warning color, use red, a color associated with grave danger or death.  The background color doesn’t matter so much, as long as it provides a high contrast with the red.  I like navy, violet, or black.

And there you go.  People will get it, even if they aren’t specifically familiar.  It immediately looks like a radiation symbol, only worse.  Stay away.  Find someone who has proper instrumentation and knowhow before you start messing with whatever you’ve got in your hands with this symbol on it.

UPDATE 04/2012: For more info and subsequent uses of the symbol, click here!

Thoughts, anyone?

Better in black? (reader-suggested)

Second, modified example: (feel free to use any of these in your own projects/work!)

Credit: Ben McGee