Sticky Tape Found To Emit Terahertz Radiation 96
An anonymous reader writes with this excerpt from New Scientist "'Peeling sticky tape has already been shown to produce X-rays, so Joseph Horvat and Roger Lewis of the University of Wollongong in New South Wales, Australia, tried to see if it could create lower-frequency terahertz radiation. "We were rather pleasantly surprised to obtain a clear signal in our first attempt," says Horvat. Strongly adhesive Scotch Magic 810 tape and weakly adhesive electrical tape both yielded strong terahertz signals, ranging from 0.1 to 10 terahertz, but only about a microwatt of power, too little for practical use (Optics Letters, vol 34, p 2195). Horvat says that refinements should increase the power by orders of magnitude.' It may be old news to Slashdot that [peeling clear tape] had been proved to produce X-rays, but watching the linked video where they use tape to expose X-ray film was pretty amazing."
Re:Duct tape? (Score:5, Informative)
So, does peeling duct tape emit gamma bursts?
Do you really honestly want to know the answer to that question?
I, for one, enjoy my duct-tape and don't want a surgeon general's warning and government taxes on it...
High Voltage Warnings! (Score:5, Informative)
This causes very high voltages and, where the tape is just being unrolled from the roll, extreme electric field as the distance is so small. (Remember, Electric field is measured in V/m!). Charges arc through the air easier than they can travel through the tape, so you get all sorts of emissions from this miniature lightning storm as the voltage drops back to a static level of 'only' about a kV.
Incidentally, this is why you should always use special ESD-approved tape when working anywhere around electrostatic-discharge-sensitive devices. My company's ESD training class had some quite interesting demonstrations where stuff was destroyed with a single piece of freshly unrolled tape. Unfortunately for me, I had yet to learn that lesson in graduate school, and so I ruined many a sensitive analog ASIC by taping a supposedly protective dust cover over the bare IC* (we were too cheap to pay for the black packaging that most people call a "chip").
*Note to all the pedants out there: Yes, a fabricated IC has its own natural shield of silicon dioxide (glass) on top of the deposited layers, however the tens-of-micron-thin wire bonds that connected the IC to my prototyping board were exposed to air, and could easily be broken--or worse, shorted--by errant dust particles.
Re:Practical application? (Score:5, Informative)
Re:High Voltage Warnings! (Score:4, Informative)
you get all sorts of emissions from this miniature lightning storm
Just to clarify my own post:
The emissions don't come from the electric field itself, but from the electrons, accelerated to a very high velocity, ramming into things like air molecules and the other strip of tape. The high energies imparted to the electrons on the receiving end of these collisions allows for emission of very low-wavelength photons (terahertz radiation, x-rays) as the electrons drop back to their natural states.
Re:Terahertz radiation (Score:5, Informative)
Its like infra-red in that its darn hard not to give off a signature of some kind. That's how you can use it in the airports for monitoring for hidden weapons without dousing people with all kinds of xrays.
Actually, terahertz radiation security monitoring works just like current x-ray monitoring at airports. In other words, they have a source on one side and a receiver on the other, and they look for anything blocking the radiation. THz radiation penetrates fabrics, plastics, and mostly flesh, but is non-ionizing (unlike x-rays), so it is an ideal choice to see what someone is carrying without asking them to strip down, first.
THz security systems do *not* rely on the natural emissions of objects. The power contained in this band is quite small and difficult to use. Additionally, the power radiated from an object is *not* dependent on density, but, like all thermal radiation, dependent on the heat of the object.
It is a silhouette based detection--like a photograph or an x-ray--not an emission based detection, such as a Geiger counter detecting radioactive material.
Re:So What? (Score:4, Informative)
You can test this yourself with a mass spectrometer. All farts are methane; that's why you can light 'em. Cow farts, cat farts, people farts, etc. That smell that shit produces is methane and bacteria.
Methane is odorless, so no. And that is not the only factual error in your post. Methane is uncommon in flatulence (most livestock methane emissions are from belching, not farting). Most flatulence is nitrogen, and carbon dioxide. The smell comes from volatile organic acids and reduced sulfur compounds produced in protein breakdown.
TLDR version: You're talking out of your ass, and it stinks because you eat too much meat.
Re:Terahertz radiation (Score:3, Informative)
Actually, the current detectors appear to be reflective rather than transmissive. Since human flesh is generally opaque to terahertz waves, and human bodies are full of little cavities that don't show up in silhouette, it would be pretty simple to hide something from a transmissive detector.
X-rays work as transmissive detectors because the majority of the body is mostly transparent to them. It decreases the noise when you are looking for metal objects.
Terahertz generation is an interesting problem (Score:5, Informative)
Generating terahertz radiation, especially coherent Terahertz radiation, is hard because the frequency (around 300GHz - 20THz) is too low for conventional solid-state laser technology and too high for conventional electronic antennas. And it is potentially useful for a range of applications such as nondestructive high-resolution imaging (for e.g. materials, medical, and security applications), spectroscopy, or opening up new communications bandwidths. (Google "terahertz applications" [google.com] and you'll find a lot of links.)
There are a number of terahertz sources that are becoming available, from optical rectification schemes to free-electron lasers, but they have a tendency to be bulky and inefficient, so a lot of researchers are looking for alternative generation schemes.
That being said, I suspect that the terahertz radiation produced by sticky tape is incoherent, which would severely limit its utility in practical applications. (Quite apart from the efficiency, which sounds like it is currently very low.) That doesn't mean that it isn't interesting from a basic science perspective, of course.
"Beg the question", an explanation. (Score:2, Informative)
Don't take this as a personal criticism, because it's not... For those who want to properly use the phrase "Beg the Question" though, here's a fun explanation:
http://www.qwantz.com/index.php?comic=693 [qwantz.com]