Radiation Chart

Randall Munroe, who draws the geekerrific xkcd webcomic, has created a really good chart showing relative radiation doses absorbed by humans doing various activities.

I’ve put a piece of it here, the section with the lowest doses. I like this! A lot of folks don’t understand what radiation is — light is radiation, for example — or that just by existing on the surface of our planet you absorb a certain amount all the time: from the ground, from space, from things you eat. Wikipedia actually has an excellent rundown of what radiation is, and the critical distinction between ionizing and non-ionizing radiation (there’s also electromagnetic versus subatomic particle radiation, but that’s less of a concern here).

In the chart, Russel deals with doses from ionizing radiation. This is the kind that can cause damage… but only in sufficiently high doses. For example, bananas are a natural source of gamma rays due to the decay of an isotope of potassium (40K). It’s a pretty weak source — a few years back I had access to a gamma-ray detector and we could barely detect a banana’s emission — and it doesn’t affect you in any real way. Potassium iodide is a common salt that’s also a gamma-ray emitter, but again you’d need a lot of it for it to be dangerous… and if you ate that much you’d have worse issues!

The average amount of radiation you absorb in a year is about 3 – 4 milliSieverts, depending on where you live. At higher elevations — like, say, Boulder, where I live — cosmic radiation puts you on the higher end of that scale. I’ll note that cancer risk is not really higher living up here than at sea level(lung cancer rates are lower than average here, probably due to the healthy lifestyles most people follow in Boulder, but skin cancer rates are slightly higher than average, probably due to a combination of people being outside more than average together with the thinner air blocking less UV).

In general, you can actually absorb a much higher than usual radiation dose (up to a point, of course) without ill effects, since your body can heal some amount of damage (just like it heals from a cut). Too many such doses too close together, or too big a dose all at once, can do too much tissue damage and be fatal (I guess, again, like a cut). For example, I like to point out that the Apollo astronauts got roughly a year’s worth of radiation absorption in their tissue while voyaging to the Moon and back, but didn’t suffer any ill effects.

Obviously, this is a complicated issue, but the xkcd chart looks like a pretty good way to eyeball where things fall on a scale of “nothing to worry about” to “AIEEEEPANICPANICPANIC”.

Source: Bad Astronomy

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  1. #1 by pauls on March 25, 2011 - 00:44

    This article and chart make the misleading claim that extra radiation in the form of fallout — that is the kind of extra radiation the Japanese are experiencing from the damaged reactors at Fukushima — is the same as a small innocuous addition to background radiation.

    What’s wrong with the claim is that ALL of the new radiation the Japanese are now seeing is from radioactive fallout (=radioactive dust). The fallout can be inhaled directly from the air or ingested when it contaminates the food supply. Since radioactive decay inside the body (‘internal’ radiation) is potentially more damaging than exposure to the same radiation products from the outside the body (‘external’ or ‘background’ radiation), fallout as a radiation source is potentially more dangerous than the same level of radiation added to the background.

    The takeaway from this post should not be that concern about the fallout the Japanese are seeing is unwarranted. Rather, today in Japan: 1) people are not going to start falling over dead from exposure, so panic is not warranted, but 2) people should be cautious about what they feed themselves and especially what they feed their children. At this time, they should NOT be drinking dairy products from areas hit by the fallout. Likewise, pregnant women should avoid fallout areas and should not eat or drink foods produced in the fallout areas

  2. #2 by pauls on March 25, 2011 - 01:18

    From the chart:

    “Extra dose from one day in an average town near Fukushima plant (~3.5 uSv as of March 17, varies quite a bit).”

    From the reference cited in the source page for the chart for March 17:

    http://www.facebook.com/notes/international-atomic-energy-agency-iaea/iaea-briefing-on-fukushima-nuclear-emergency-17-march-2011-1400-utc/202624509767343

    “Dose rates to the north-west of the nuclear power plants, were observed in the range 3 to 170 microsievert per hour, with the higher levels observed around 30 km from the plant.

    You know, taking the lowest value from a range where the highest value is larger than the lowest by 50X and calling this ‘the average’ is just dishonest. Calling a dosage ‘daily’ when in fact it is hourly is 24 X dishonest.

    • #3 by 0infinity on March 27, 2011 - 03:08

      Thanks for this information, i do like the chart (at least the way it is designed), furthermore i believe the author of this image has made it informative, but not that one would know exactly know how radiation works, as stated on the bottom of the image: I’m sure I’ve added in lots of mistakes; it’s for general information only., but your replies adds some in-depth info, of which I do thank you.

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