Tuesday, December 28, 2010

The limits of (tangential) expertise


Photo credit: zazzle.com
As it is the holidays, I suspect that a non-zero portion of the Chemjobber readership went through the TSA's new backscatter X-ray scanners while traveling. I don't really have much to say about the political aspects of the issue. Government does what governments will do -- sigh.

But one aspect of the conversation is fairly interesting, which is the health effects of the backscatter X-ray technology. James Fallows is a well-known author who writes a pretty great blog; his readership has been debating the science of the issue in posted e-mails.

Here's a missive from a physics professor talking about the difference between millimeter wave and backscatter X-ray instruments:

"All microwave photons are far too weak to cause damage to molecules through their absorption. The energy level of a microwave photon is sufficient to cause a molecule to rotate or vibrate (this is how microwave ovens work) but not to cause it to disintegrate or modify its structure, and those are essential requirements for causing a DNA molecule to mutate into a malignant strand... Lesson? Cell phones do not cause cancer. Period."

This caused a biophysicist to write in to contradict*: "Microwave energies can cause beaucoup molecular change; hell, I've used (um, well, I told my undergrad to use) a microwave source in an organic synthesis, so I'm real sure the emailer doesn't know what he's talking about. I mean, it can't _ionize_ (easily). Big whoop; most of biology is acid/base chemistry."

Oh. No. You. Di-dn't. I guess the biophysicist hasn't heard about last year's experiment by Kappe, where a silicon-carbide (thus microwave-irradiation opaque) vessel was used to perform reaction chemistry that showed no difference from traditional heating. If I'm interpreting correctly, the experiment strongly suggests that microwaves do not have a microwave-specific effect and microwave chemistry is just about faster and better heating. Therefore, it's the heat that causes 'beaucoup molecular change' and not the microwaves.**

I have a few points here:

1. I have no idea who's right about backscatter X-ray technology. There are a lot of things to worry about: their operation, their calibration, the exposure that a passenger gets, the exposure that TSA officers get, etc.

2. Experts who step out of their area of direct expertise do so at their peril. There are plenty of people who seem to have deep but tangential experience; witness the above debate and also the UCSF X-ray crystallography professors who have written letters of protest to President Obama's science adviser.  Here are a couple radiologists and they seem to be fine with it. Huh. I'd really, really like to hear from a professor of medical physics or radiation dosimetry before I have any idea who's right.

3. What does that mean for Chemjobber? Well, I'm a chemist who covers labor economic issues -- draw your own conclusions. I try to be as humble as possible in my analyses and my predictions. Why? Because I'm an amateur, that's why. Thanks for reading anyway.

*Check out this bad dude's credentialing: "Who you're taking _this_ from is a biophysicist and enzymologist who did his Ph.D. thesis in a cyclotron and who has overseen diagnostic sections in a hospital and attended Biophysical Society." Oh, okay -- so what you're saying is that you're smart. Gotcha.

** The physics professor responds: "So does he know what the microwave source actually did? Reaction rates frequently have a strong temperature dependence and a microwave source could give you very fine control over temperature. However, in that case, the fact that it is a microwave source is inessential. You could (and in the days before microwave sources, often did) achieve the same effect with a simple flame."

1 comment:

  1. Government does what government will do: It reminds me this stanza from Auden

    The Ogre does what ogres can,
    Deeds quite impossible for Man,
    But one prize is beyond his reach:
    The Ogre cannot master speech.
    About a subjugated plain,
    Among it's desperate and slain,
    The Ogre stalks with hands on hips,
    While drivel gushes from his lips.

    Also microwave heating effect is not that innocuous. Long before microwave ovens, it has been known that military crews working near powerful radar dishes could develop infertility as a result of exposure - testicles happen to be particularly sensitive to heat damage

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