Murphy’s Law of radioactivity measurement

If you’re like me, you’ve been following with great concern the latest radioactivity measurements in various places, from Japan to the US West Coast. What an utterly hopeless task:

  • sieverts
  • grays
  • rads
  • rems
  • Roentgens
  • becquerels

Is this a joke? How are you supposed to understand anything at all from this gibberish?

Well, yes it is a joke, of course, in the same way the entire universe is a joke (and a rather sick one!), as the apocryphal sage Murphy first observed:

Anything that can go wrong, will go wrong.

I once saw a booklet of addenda to Murphy’s Law. This week, I suddenly remembered one that seems germane:

Measurements will always be given in the least useful unit: Thus speed will be given as furlongs per fortnight.

Fortunately we have Mr Crotchety, who sent me this chart which, if correct, puts it all in some perspective.

35 thoughts on “Murphy’s Law of radioactivity measurement

    • I wish I could, Gordon. It was a “toilet read” — ie, I literally saw it in a guest bathroom, and it was circa 1990.

      That’s how you can tell that the measurement quote rocks — it stayed with me all these years.

      Mind you, I’m sure I corrupted it in some way.

  1. I always liked the X-ray techs who tell you there is nothing to worry about, that it’s perfectly safe, and then scurries back behind the leaded shield. And no one ever keeps track of the number of X-rays you’ve had.

    I am waiting for the tumors to appear on my feet from all the times my feet were X-rayed at shoe stores in the early 50’s.

    The reason they use almost nonsensical and inconsistent terms is either to (a) keep you off kilter and afraid or (b) so you will eventually give up trying to figure out if there is any real danger and lapse into apathy.

  2. Thank you, Mr. Crotchety, for putting it all in “layman’s” terms.

    Andreas, doesn’t the chart put things in perspective, even (especially?) if it’s not correct?

  3. Per this one:

    “Measurements will always be given in the least useful unit….”

    That is certainly true if you live in the U.S.A., the most technologically advanced society on the planet, yet clinging to an antique system of weights and measures that is comically complex and frighteningly prone to error. I wonder, has anyone tallied the human and business costs of my country’s infantile refusal to join the modern world in this regard?

    • The human cost, Martha M, is largely borne by my children, since I (a quasi-European) cannot properly convert American measurements (food, height, weight — for food portions, Roller-Coaster ride limits and such) into the comprehensible (metric) units….

  4. I think part of the confusion regarding the units of measure in this instance is attributable to the fact that we group a lot of things in the category of radiation. Daylight is radiation, but it is not ionizing. The ionizing radiation has different hazards depending on the wavelength (or frequency). X-ray is different from gamma ray, etc. Therefore the safe doses vary. I think all of the xkcd chart is about ionizing radiation, but the different frequencies are a more subtle part of the information. Sorry, (yawn) I know..

    The official, SI (international system of units) definition for ionizing dose is the becquerel (Bq). Henri Becquerel made the first solar cell from selenium, but he also got a Nobel prize for something else (photographic film?), neither of which has anything to do with nuclear reactions. If I were playing Jeopardy, I would have guessed that the Curie was the official unit.

    I also recommend the page that introduces the xkcd chart:

    • Mr. C.

      while you are in the area… how about a link to “the math of skyscrapers”?

      my sixth grader is doing a math fair project and there is precious little laymen resource dealing with the math. this loosely relates, since buildings are built to withstand, well…

      it’s all math really, after all.

      a skyscraper is a delicately balance equation whose variables include; load, mass, wind force, gravity forces, and probably many other SE equations that we don’t need to entirely understand but at least cut and paste into the project.

    • Mr C, would you (as the only expert in sight) be tempted to explain to us, in simple Mr C style, what frequency (as opposed to amplitude etc) is all about, why it seems to matter so much which “particle” (eg cesium) these “waves” show up in, and so forth?

      Ie, a Mr C 101 of radiation?

      I say with confidence that the rest of us haven’t the foggiest notion of what we’re talking about.

  5. I don’t know anything about skyscrapers other than that they are tall. But, since there is a child’s education at stake, I have to be earnest for a moment. There are some interactive simulations at a website that was originated by Carl Wieman with his Nobel prize money. The simulations are kinda clunky compared to video game, but something to play with.

    The variables you mention, except for mass, are vectors and forces.

    And for those of you still wondering about radiation!
    (What’s with the gun?)

    • aw shucks…

      doesn’t everyone carry ’round a neutron shootin’ nuclear fission gun in their back pocket?

      thanks for the links Mr. C.

      here’s another one – specifically for you andreas about units of measurements from the Nuclear Information and Resources Service.

      looks like they agree with Mr. C. that the unit of measurement should be a “curie” as the other units are measurements that attempt to measure the impact of the “curie” on human tissue – something that is basically “immeasurable”.

      excerpted from link; “A single alpha particle, acting on a single cell, may damage that cell to the same degree as if a thousand x-rays had hit it.”

  6. As near as I can see, the degree, gray, and sievert all describe the transformative effect that the absorption of energy has on an object, but they each reflect the respective concerns of different scientific disciplines:

    – the degree concerns physics and radiation’s effect on the object’s temperature.

    – the gray concerns chemistry and radiation’s ionization of the object (that is to say, its knocking loose of that object’s electrons).

    – the sievert assumes the object to be human, concerns medicine, and radiation’s damage to human tissue.

    Strangely, despite their different meanings, these terms are expressed in identical units, energy per mass (e.g., “joules per kilogram”). They justify their existence by forming a progression from the impersonal to the ever more personal.

    The sievert is the newest term and, presumably, is of the most interest to the public. It is explained here:

    When anything absorbs radiation, energy is deposited in it, and the amount of energy deposited can be measured. The amount of energy deposited in tissue by an exposure to ionizing radiation (“a dose”) can be expressed in joules per kilogram. Health physicists give 1 joule per kilogram a special name, a gray.

    Simply measuring the amount of energy tissue has absorbed from a dose of ionizing radiation is not enough to predict the amount of harm done. There are different kinds of ionizing radiation, including alpha, beta and gamma rays. Experience has shown that a 1-gray dose of alpha rays, for example, is about 10 to 20 times more harmful than a 1-gray dose of gamma rays, depending on the energy of the gamma ray…

    To express the size of an exposure in terms of biological damage, which is what health physicists need to do, a measurement of the absorbed dose in joules per kilogram (hence in grays) is multiplied by a “quality factor” for that kind of radiation. The quality factor is in part determined experimentally and in part based on expert judgment…

    The quality factors are chosen so that 1 sievert of radiation is the amount of any kind of radiation which would cause the same amount of biological damage in a human being as would result from absorbing 1 gray of X rays… It is intended to be used at the sort of radiation levels encountered in medicine or the workplace…


    As it turns out, none of these metrics directly reflect the extent to which cumulative low-level radiation exposure shortens human life — the most personal measurement of all — but the sievert comes closest. With a few additional assumptions one could estimate the life-shortening effect of one sievert, but such estimates tend to be controversial, not least because they have legal and financial implications, while sometimes being impossible to verify by observation or experiment.

    DISCLAIMER: This is an inordinately tricky area (to me at least), so don’t take my inexpert explanation as more than a rough guide.

    A tip of the hat to Mr. C.

    • As I say so often: blessed is he who has sophisticated readers.

      I actually understand this explanation, Jim M!

      Wow! I should ask dumb questions more often here on the HB.

  7. Per AK’s request for radiation 101:

    In the case of photons (any radiation), the wavelength refers to the distance traveled during a single oscillation while moving at the speed of light.

    As I said before, everything and everyone is an oscillator made up of lesser oscillators. Some oscillators have mass (matter, electrons, e.g.) and others don’t (radiation, photons, e.g.). The interaction of radiation and matter is the extent to which the oscillators resonate.

    I propose a metaphor for the interaction of radiation and matter. Behold. Mr. C’s playground physics:

    Imagine that a lump of matter is a swing set populated by our beloved children. Imagine that the radiation is us (photons), trying to run past (under) a swing. Whether you have a plump teenager or a skinny toddler doesn’t matter – until you collide.

    The Matter:
    The swing set has big swings and kiddie swings (long and short swings; different swings amount to different sorts of particles, atoms, electrons, nucleus, etc.). Short swings oscillate faster than long swings.

    The Radiation:
    As photons, we must all move at the same speed (the speed of light), but we must walk funny. To oscillate, we bow (like bend at the waist) up and down as we walk. Some of us bend more frequently than others, but we’re always in the process of bowing. Each of us must bow to what amounts to the same change in height. High-energy (ionizing) parents bow more frequently.

    Our goal: walk under a swing without knocking someone off (or getting kicked in the face).

    Those who bow frequently are going to collide with a swing more frequently, especially with the short swings.

    By analogy, high energy (fast oscillating, short wavelength) photons are more likely to get tangled in the swings. Thus, high energy photons will disrupt the organization of matter – like damage DNA, or turn nitrogen into carbon 14.

    Disclaimer: I do claim to be an expert. If you disagree, just be polite.

    • This is, if I may say so, poetic, Mr C! You give Brian Greene a run for his money.

      (Who knows? Maybe you are Brian Greene.)

      Let me soak up this metaphor in its entirety.

      But one thing seems apparent: amplitude (of the parents or the swingers) seems to play no part here.

      Would “ionization” = knocking a toddler of the swing?

    • wow… that was amazing! you should consider making a contribution to the knowledge base at Khan Academy . it is very similar, but more fleshed out than the site Wieman created.

    • Don’t tell me this is just about physics. Parents as radiation, ionizing (or lionizing) their children and knocking them off swings.

      Mr. C takes on Amy Chua.

      Colleges all over the country complain about moms and dads who oscillate too much and disrupt the organization of matter. I like “high energy photons” as a replacement for the hackneyed and inelegant phrase “helicopter parent”.

      The power of poetry!

  8. In lieu of amplitude, you could think of a high dose as being alot of the same. That is, a high number of photons per area at an instant. Using a different metaphor: low dose = sprinkle. High dose = downpour. Ionization would be knocking a toddler off his swing. Lionization would be to confuse me with Brian Greene.

    • ie, higher amplitude would be not one parent but both parents and some uncles and aunts ducking up and down under the swing.

      Your metaphors is withstanding more and more tests. We must think about popularizing it….

  9. The chart is horseshit. Weasel assumptions and misleading twists. Radioactivity is easy, if nor expressed in :”crapies”- units of Govt.propaganda. Same for radiation,if not expressed in weasel terms of: “goverts”. Let the reader beware.

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