Why are there so many different ways of measuring radiation?

Slate has an interesting look at what's up with all the different ways of measuring radiation exposure. Sieverts, rems, grays—what's the difference? It is boils down to two issues. First, some units measure specific things. Sieverts, for instance, are different from grays because sieverts are a measure of the effect of radiation on human tissue, while grays are more about radiation absorbed by any object.

And the second issue: It's a case of the Metrics.

As with distance, weight, and temperature, doses of radiation can be expressed in either SI units (sieverts) or U.S. customary units (rem). U.S. scientists and engineers in most fields had switched to metric units by 1964, when the National Bureau of Standards (now the National Institute of Standards and Technology) officially adopted the international system. But nuclear physicists never made the full switcheroo. That's because a wholesale change in measurement could lead to mistakes, at least during the transition--and even a small mistake can be very dangerous when it comes to radiation exposure. (There is an historical argument for being cautious: In 1999, NASA lost contact with the Mars Climate Orbiter because of a mix-up between metric and customary units [PDF].)

Via Chris Pasco-Pranger

• [Anonymous]

  Forget about some unmanned probe. Stubborn adherence to customary units and resulting jet fueling error very nearly killed 69 people in the Gimli Glider incident, http://en.wikipedia.org/wiki/Gimli_Glider .

• [coop]

  More science than CNN. I miss Mr. Wizard.

• [Camp Freddie]

  I see 3 problems.

  1) There are 4 different types of radiation. Each of these has very different effects depending on how it is distributed/absorbed (e.g. alpha is absorbed by dead skin, but if you ingest an alpha emmiter then you’re in trouble). Also, for at least gamma radiation (and maybe some of the others) there are lots of different energies involved, so not all gamma photons are equally dangerous.

  2) Switching from rems to sieverts, and to a lesser extent grays to curies. The propensity of lay people to focus on the number rather than the unit prefix (micro- being 1000 times less than milli-). Most people don’t use micro- units in their everyday lives.

  3) Dosage vs. rate of dosage. I keep hearing about X sieverts in a pool of water. Is that sieverts per hour, per day, per year. Or is is total sieverts, assuming full decay over an infinite duration of exposure (not a sensible measurement for plutonium, but probably a useful way of measuring the total exposure from iodine). Also, do you have to be in the puddle to get this reading, or is it the reading from a nearby walkway, or is it assuming you drink water from the puddle?

  Its similar to the problems people have with computer memory (e.g. bits vs bytes, quantity vs. rate and 2^10 vs 10^3). Journalists are mostly humanities graduates, so they get this stuff wrong (this is not a dig at humanities, science grads generally aren’t good at writing stories!).

• [Anonymous]

  Has a programming geek written a conversion script out of the calculation tables and put it up on a web page yet?

• [Lexicat]

  The video is missing neutron radiation (free moving neutrons) which results from certain nuclear reactions. It’s not particularly common—except in reactors and accelerators. Neutron radiation has the nasty possibility of making other substances radioactive not by polluting them with alpha, beta or gamma emitters, but by actually changing the nuclear composition of the atom of material exposed to neutron radiation.

• [Nadreck]

  Like the difference between Canadian and US gallons didn’t cause more than one pipeline to blow up.

• [millrick]

  quibble!
  the article states: “Once the radiation has cleared the source and is floating ominously through the air…”

  correct me if i’m wrong, but…
  the author is confusing radiation with radioactivity.
  radiation does indeed travel through air, and anything else that doesn’t block it, but it doesn’t float. radioactive particles can float through the air and be ingested by humans & everything else that eats and breathes. once you’ve ingested a radioactive particle, you now have a source of radiation in your body. that’s why iodine pills work. if your body’s full up on non-radioative iodine, then radioactive iodine can’t lodge in your thyroid gland. iodine pills do not protect you from radiation, they protect you from a specific type of radioactive particle that you ate or breathed in.

  the Japanese nuclear reactors are emitting radiation as well as creating radioactive particles that can be carried by the winds.

  my apologies if the wording isn’t clear. high school physics was a long time ago for me.

  btw. another bad result from the switch to metric…
  http://en.wikipedia.org/wiki/Gimli_glider

• [anansi133]

  Y’know, I would be much more interested in a science-based scale to measure exaggerations, half-truths, and outright lies of omission and commission.

  Comparing this crisis to Chernobyl or 3 mile island seems to make sense, but I really want to compare it to the Deepwater Horizon and the Unocal pipeline in Afghanistan.

  Although when it comes to public deception, I suppose it would also make sense to compare the fallout from this crisis to the fallout from nuclear testing. Yeah, different particles, different wavelengths and chemical profiles. But how does the long term impact compare for the down-winders?

  TEPCO is no more ethically reliable than Goldman Sachs. If you were to invent a metric for corruption, how might these apples and oranges weigh out?

  As long as the crisis comes one at a time, it can turn into last weeks news to be forgotten until a worse one comes along. I want to connect the dots!

• [emmdeeaych]

  That’s because a wholesale change in measurement could lead to mistakes, at least during the transition–and even a small mistake can be very dangerous when it comes to radiation exposure.

  Yet, somehow, nobody thought the backup could use a second backup.

  We have every right to complain when failsafe mechanisms only exist to the extent they’re easy (safer to keep the old units) but not when they’re pricey (build away from the coast, build a large reservoir and provide for emergency gravity powered cooling, have a waterproof generator building capable of withstanding massive damage, etc…)

• [teapot]

  The world laughs at the imperial system. How come Americans typically dislike everything British but fight tooth-and-nail to hang onto their system of measuring stuff?

  Weird.

• [TEKNA2007]

  TEPCO is no more ethically reliable than Goldman Sachs. If you were to invent a metric for corruption, how might these apples and oranges weigh out?

  Yeah, this NYT article makes them look pretty bad:

  http://www.nytimes.com/2011/03/27/world/asia/27nuke.html?partner=rss&emc=rss

  Perhaps the saddest observation by scientists outside Japan is that, even through the narrow lens of recorded tsunamis, the potential for easily overtopping the anti-tsunami safeguards at Fukushima should have been recognized. In 1993 a magnitude 7.8 quake produced tsunamis with heights greater than 30 feet off Japan’s western coast, spreading wide devastation, according to scientific studies and reports at the time.

• [Anonymous]

  “There is an historical argument for being cautious [with a a wholesale change in measurement units]: In 1999, NASA lost contact with the Mars Climate Orbiter because of a mix-up between metric and customary units.”

  I think you’ll actually find that is a historical argument for why for critical and life-threatening measuremnts you should make sure you always use the standard (scientific/metric) units for something.

• [Anonymous]

  You also didn’t mention an even more basic fact, that the different forms of radiation are fundamentally different particles. Gamma radiation is made of photons but alpha radiation is effectively a stream of helium nuclei. Beta radiation is electrons. Depending on what’s radiating as well as how much, one will need to measure fundamentally different things (ie, ‘energy particles’, or leptons, or ‘matter particles’ or baryons), hence requiring fundamentally different apparati (and basic units as well).
  Most nuclear radiation consists of all the above, so the optimal method is context dependent.

• [PaulR]

  Before I forget: the link
  http://ftp/ftp.hq.nasa.gov/pub/pao/reports/1999/MCO_report.pdf
  is bad.

  Let me see if I’ve got this right:

  Since Alpha particles can be blocked by paper, put newspaper on your windows, and are relatively harmless. But Alpha particles aren’t safe, because they’re absorbed by human tissue (just like the paper is doing).
  Especially if you breath in Alpha particle-emitting substances.
  http://en.wikipedia.org/wiki/Alpha_particle#Biological_effects
  (Remember to not lick the inside of your smoke detector, eh!)

  So, what about Beta particles? The can pass through paper, but given enough paper, er, wood, they can be stopped. So, they’re safer? Or, since we’re thicker than a piece of wood, we would absorb them, no?
  http://en.wikipedia.org/wiki/Beta_particle#Health
  (Like beer, it can be the cause and solution to your cancer.)

  So, on to Gamma rays: They would pass right through us, so no damage anything, no? (Thus they’re safer than Alpha particles.)
  Well, it depends:
  http://en.wikipedia.org/wiki/Gamma_ray#Health_effects
  and:
  http://www-pub.iaea.org/MTCD/publications/PDF/Pub1124_scr.pdf
  Three junkyard workers died within two months as a result of their two week work-day exposure to some Cobalt-60 (that is Gamma rays).

  From the Slate article:
  Once the radiation has cleared the source and is floating ominously through the air, we need a new set of units.”

  Radiation floating around the air?
  Generalist columnists shouldn’t try to write sciencey articles.

  I have to admit a prejudice: I suspect that most journalist go to Journalism School because they hope that they won’t have to do math and science.

• [Kaden]

  Why does the link take me to http://rumba.microfocus.com/ ?

  I’m sure Rumba is a *fine* bit of code, but I wanna read about Orbiter

• [KC]

  “That’s because a wholesale change in measurement could lead to mistakes, at least during the transition”

  It seems like running two parallel measurement systems side by side for decades, requiring frequent error-prone conversions between them, has a lot more opportunity for accidents than a brief transition period during which people are extra vigilant. This is the first time I’ve seen the Mars Orbiter used as an example of the dangers of the metric system rather than an argument for getting on board with the international system.

• [cratermoon]

  Regarding the Mars Climate Orbiter. While it’s commonly repeated that it was a mixup in SI vs. customary units that caused the loss, the reality is a much more complicated people problem.

  As respected space writer (and former spaceflight engineer) James Oberg notes at Why the Mars probe went off course, it was really a project management failure. Engineers tracking the flight knew well in advance that the probe was off course and urged a course-correction that would have returned the MCO to a safe trajectory.

  Yes, an error in unit conversion was part of what put the probe too close to Mars, but it was really management improperly denying the navigation engineers’ request for a burn their figures showed them was needed that doomed MCO.

• [Anonymous]

  You damn Merkans are just sentimentally attached to those English Imperial units! Lawsy! ;)

  (2nd what KC said)

  At least medicine is mostly metric.

• [Anonymous]

  Am I alone in expecting to be told to “Write that down in my copybook?”