How Terahertz Waves Tear Apart DNA

KentuckyFC writes "Great things are expected of terahertz waves, the radiation in the electromagnetic spectrum between microwaves and the infrared. Terahertz waves pass through non-conducting materials such as clothes, paper, wood and brick and so cameras sensitive to them can peer inside envelopes, into living rooms and 'frisk' people at distance. That's not to mention the great potential they have in medical imaging. Because terahertz photons are not energetic enough to break chemical bonds or ionize electrons, it's easy to dismiss fears over their health effects. And yet the evidence is mixed: some studies have reported significant genetic damage while others, although similar, have reported none. Now a team led by Los Alamos National Labs thinks it knows why. They say that although the forces that terahertz waves exert on double-stranded DNA are tiny, in certain circumstances resonant effects can unzip the DNA strands, tearing them apart. This creates bubbles in the strands that can significantly interfere with processes such as gene expression and DNA replication. With terahertz scanners already appearing in airports and hospitals, the question that now urgently needs answering is what level of exposure is safe."

Comments

The airport scanners are passive

[Anonymous Coward]

If you follow the link provided about the airport scanners you find that they are passive devices meaning they don't emit terahertz waves they only recieve the waves coming off of everything around us.
There are some devices out there that using terahertz radiation to inspect packages much like x-ray today.

Re:The airport scanners are passive

[Gadgetfreak]

For now. But the last paragraph of the MIT article indicates newer cameras will have their own emitters.

Re:The airport scanners are passive

[Shrike82]

If you follow the link provided about the airport scanners you find that they are passive devices meaning they don't emit terahertz waves they only recieve the waves coming off of everything around us. There are some devices out there that using terahertz radiation to inspect packages much like x-ray today.

Thankyou. The summary implies that scanning using T-waves in airports might cause you to have your DNA scrambled, which is just plain wrong. Passive scanning (which we are told is what the airport scanners are) don't expose you to any more radiation than you get in a normal day.

Re:The airport scanners are passive

[natehoy]

The MIT article has no citations to any models coming out that use active scanning. Meanwhile, the article summary clearly implies, no, actually STATES, that they are being introduced already into airports. Which is patently false. Active scanners ARE being introduced, but they are milliwave body scanners, and these passive t-wave scanners appear to be a more effective and safer alternative.

"With terahertz scanners already appearing in airports and hospitals, the question that now urgently needs answering is what level of exposure is safe."

The "terahertz scanners already appearing in airports", like the cited ThruVision T5000, are passive units. There is no discussion about "what level of exposure is safe" because there is no exposure to terahertz radiation. It's detecting what your body and possessions are already emitting.

The t-band scanners are being tested for two reasons that seem to make sense to me, at least:

1. Their imagery can detect materials more accurately whilst simultaneously not getting as accurate a picture of the actual body. This is better scanning with better privacy.
2. The new scanners are passive t-ray detectors as opposed to active milliwave detector.

Better scanning, less violation of privacy, no active emitter. If true, this sounds like a trifecta to me. I'd much rather pass through one of these than a milliwave unit.

If and when ACTIVE t-band scanners start being introduced into general airport use, I'll share your concern and be right there with you in the pat-down line.

Re:The airport scanners are passive

[Anonymous Coward]

Disclaimer: I am an expert in millimeter-wave and terahertz imaging systems.

I wanted to emphasize to everyone reading this is that the parent is exactly right. ThruVision (the only commercial terahertz imaging system currently in airports) is passive, in that it detects the blackbody radiation being emitted by your body, clothes, and other objects, and compares it to the blackbody radiation of the background. The apparent difference in radiometric temperature is what constitutes the final image. There is no emission of terahertz radiation by this system.

On the other hand, the active microwave systems, which operate around 35 GHz (there are variations on this, of course) are essentially an active radar system. You are exposed to some non-ionizing radiation, and its reflection from your body, clothes, and other objects is received and compiled to create an image. In terms of radiation, then, the active microwave systems are irradiating you, but at a level far below your cell phone. I can give citations if you like (or refer to the SPIE conference publications by the Pacific Northwest National Lab group who pioneered the system that is currently in airports.)

Or we can talk about privacy. The active microwave systems have far better spatial resolution than the passive terahertz systems, since they take full advantage of phase in the imaging, and have a great SNR due to transmitting their own microwave power. (the passive systems mostly use direct detectors, which are really only sensitive to the magnitude of the radiation. ThruVision's, though, uses a heterodyne receiver, and thus is quite sensitive, but since it is very narrow-band [340 GHz, +/- 5 GHz], its sensitivity is similar to a direct detector) Fancy radar algorithms give you spatial resolution far better than the diffraction-limited optics definition you are probably used to hearing about. On the other hand, the passive terahertz systems are limited by the diffraction limit, and thus their operational wavelength gives you a good idea of their spatial resolution.

You would then say that a passive terahertz system operating at 1 THz would give you much better images than a passive system at 340 GHz, and in terms of spatial resolution you are right. However, it is commonly known that clothing transmittance drops off quickly as frequency increases from 100 to 1000 GHz (and of course even more at higher frequencies, which is why you don't see thermal IR cameras being used to detect ceramic knives under your clothes). So, somewhere between 100 and 1000 GHz is a happy medium in terms of spatial resolution AND being able to see through multiple layers of clothing.

And yes the parent was also right that the passive terahertz systems are very bad at gathering an image of the body, since it is essentially isothermal. No radiometric temperature contrast? No image.

One thing that everyone has missed is the amount of power needed to "unzip" DNA with terahertz frequencies. (TFS poses this question, actually. The answer is in the arxiv article.) It's actually quite high, and it is very difficult to find a source that can emit this level of power. Yes, there are terahertz lasers (at the several microwatt level), but you should be more afraid of a 10 micron CO2 laser that will punch a hole through your chest, and is also quite invisible.

Re:The airport scanners are passive

[Anonymous Coward]

I replied to the parent as AC also, just so you get an idea of who this is.

I wanted to clarify again: the microwave systems are NOT passive. If it looks like this, it is an active microwave system, basically a radar. (I have to question their sanity in that the URL contains "xray"... real smart guys, real smart.) These systems produce images like this.

Passive narrowband terahertz systems produce images like this. (this is actually one of ThruVision's... it's in an SPIE conference paper from a few years back.) Passive broadband terahertz systems produce images like this. As the parent said, passive terahertz is the way to go, but IMHO, only broadband actually works very well.

Re:Ethical use of panic...

[oldspewey]

Hasn't it always been the case that you have the option to decline to use "the machine" and be hand-searched instead?

Until this issue gets resolved, that's what I plan to do anyhow.

In most cases, airport scanners are still optional

[MadCow42]

The times I've encountered the terahertz scanners at airports, they've always been optional (although they don't make it clear to you that it is). If directed to one, I've always simply asked if I must use it or if I had a choice of a "normal" metal detector. EVERY time they've allowed me to choose (and I travel a LOT). Most times they take a note of it or ask me to sign a sheet to indicate my declination - I assume so they can figure out if people object or not.

Asking the quesiton never hurts. It also sends the message that this intrusion isn't accepted by the public. Don't surrender to these things willingly.

Structural explanation

[damn_registrars]

The summary mentions that the terahertz waves "tear apart" strands of DNA. For those who might not remember their undergraduate biology, DNA strands are held together by hydrogen bonds - not covalent bonds. So the total amount of force to "tear apart" two strands is not as great as you might imagine. For that matter, strands have to be "torn apart" in order to be replicated for cell division.

Re:Structural explanation

[Sockatume]

The authors aren't concerned about it unzipping the entire DNA strand like string cheese. The process creates local regions of unzipping, which your DNA gains and loses as a matter of course. These unexpectedly-open regions interfere with replication and translation, but your DNA can cope with the the "normal amount", so the question is whether these additional regions are enough to be a problem.

Grossly simplified, but...

[Sockatume]

Single-stranded DNA has its information-encoding side exposed and flops around kind of pathetically. Double-stranded DNA sticks the two information-encoding sides together so that they're hidden and inactive, and helps you wind up and store the DNA. However the double strand can "unzip" along a small part of its length to expose two single strands which can go to work.

You can get triple-stranded DNA, but it's not traditionally been thought of as important. Normally the groove for the third strand would be occupied by proteins involved in the function and maintainence of the DNA instead. However it now seems that forming a triple strand in some regions might be important in DNA's control mechanisms too.

Re:Not just peeking

[Anonymous Coward]

They produce a 3-dimensional model of your body that is accurate down to the pores of your skin.

Ha! No, they don't. In theory you could do this, but not quickly. The data volume alone should make it obvious they aren't doing this. The model you describe would be terabytes in size. On top of that, creating the model would require a huge amount of supercomputer time. There's just no way they are doing this quickly in a line at an airport. I *wish* it was that easy, since my job involves radar imaging.