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Skin and Bones -- what the 'beta burns' story means

This came in to me from the pseudonymous author of the Worlds Only Rational Man blog.  He's an experienced radiation tech and has some useful information for the most recent panic story.

Skin and Bones

The Fukushima events have inspired three world-wide responses:  concern, fear, and terror.  Japan’s 28,000 dead and missing weigh less, in millions of minds, than the slightest change in that nuclear facility.

This, despite no deaths or injuries due to radiation.  With one possible exception:  recently it was believed that workers had taken “beta burns” to their feet and legs.

The claim has since been put in doubt.

But what does it mean, exactly?  What are beta burns?  How do they compare to all these other worries tossed at you en masse?

Think of sunburn.  What the sun does with ultraviolet light, radioactive materials can do with beta radiation.

(For an introduction to types of radiation, see this PJM primer.)

Which is worse, sunburn or beta burn?  We assume beta.  It goes deeper into the skin, and is ionizing radiation.  But prolonged UV light is certainly carcinogenic.  So there’s not much qualitative difference in the harm each does.

Given this, how dangerous is beta burn?  As dangerous as sunburn, ranging from “distracting” up to “lethal”.  Your skin is your largest organ.  Destroy enough of it by any means—sunlight, beta particles, fire—and you will die.

Besides skin damage, the only external threat beta poses is to the eye.  Doses large enough to cause skin damage can also trigger cataracts.  There’s no reason to suspect the workers received doses in this range, but it’s mildly surprising that media didn’t raise this fear as well.

So how did the incident occur?  An account is here (14th and 15th paragraphs).

In brief:  three workers laid cable while standing in 6” of extraordinarily radioactive water, ignoring alarms for 40-50 minutes while doing so.

(An aside:  if you must ignore safety alarms, you’re likelier to survive a radiation warning than, say, the “oxygen deficient” one.  But better still, don’t ignore any of them.)

Because of their unwise decision the workers picked up “whole-body” gamma doses of 173 to 180 mSv, “milli-Sieverts” (17.3 -18 rem).  The single worker wearing high boots was apparently not assigned a large beta dose.  But the others had their feet soaked in that water for an extended time.  They were believed to have gotten 2 to 6 Sv (200-600 rem) beta dose to their feet and lower legs.

The rough equivalent to this would be a very mild (2 Sv) to moderate (6 Sv) sunburn.  But again, beta exposure is assumed to be worse than UV exposure (though no precise ratio is known).

At this point, communication is less than ideal.  When both gamma and beta radiation are concerns, obviously two sets of readings are needed.  We’re not seeing those.  And when beta doses are given in Sv rather than Gy (a Gray, equal to 100 rad), confusion is possible.

However, contextual analysis lets us be confident the dose rates we’re seeing are gamma, the “whole body” dose.  And if you had to guess (I’m not permitted to), you’d want to assume it is.

Why?  Well, as the worker with the high boots showed, beta radiation can be eliminated by shielding.  In fact, there’s no excuse for anyone to ever get a “beta burn”.  As for the other reason, gamma is the “whole-body” dose.

So what is “whole-body” dose?  It’s what the name implies: radiation that sluices throughout your entire body, from skin down into the bones.  You’ll pick up a lethal dose of gamma long before it even slightly reddens your skin.

That’s why the Fukushima Fifty’s emergency dose limit is 250 mSv (25 rem).  It is well below where even the most radiosensitive would suffer acute injury.

Throughout this crisis, the media’s reporting of radiological matters has been dreadful.  To name but a few mistakes:  misplaced decimals, “micro/milli” transpositions, confusion between doses and dose rates, and an apparent institutional inability to distinguish radiation from contamination.

So if you’re concerned over radiological news, I’d recommend “vetting” media reports prior to accepting them.

(“wormme” is a radiation safety technician with over twenty years’ experience in nuclear plants and research facilities.  His blog is here.)