RDX is what the Soviets stole from us to use in their first nuclear weapons. Their other conventional explosives had a nasty habit of pre-detonating due to the exposure to radiation.
Posted on 10/19/2004 5:38:28 PM PDT by EvilOverlord
Photoluminescent method detects explosives at a distance
By R. Colin Johnson EE Times October 18, 2004 (9:31 AM EDT)
Portland, Ore. — Experience in photoluminescent spectroscopy has helped university researchers bring to light a method by which explosives can be detected at a distance.
In contrast, to detect the presence of explosives today, airport and other screeners must swab an object like a suitcase or clothing, use a dog to sniff it, or blast puffs of air across a filter that traps airborne explosive particles.
The advantages of the photoluminescence-based explosive detection method are that it can be remotely applied and that it requires neither time-consuming and expensive machines nor trained dogs. All you do is shine a laser on an object and watch for the photoluminescent "signature" distinctive of explosives. Whether it's an approaching ship, a suitcase, a moving car or a pile of trash half a mile up the road, if you can shine a green laser on it, professor Rolf Hummel at the University of Florida (Gainesville) says he can tell you whether it's an explosive device.
Hummel, an engineering professor emeritus specializing in materials science, was intrigued by a U.S. Army Research Office challenge to universities to find an inexpensive, quick and reliable explosive-detection system. With his lab's high-resolution photoluminescent meter, one of his students performed a simple test that no major lab had thought to perform before: Shine a green laser on an explosive and see if it glows like a white shirt under a black light, but in the infrared. When Hummel's assistant at the Nanoscale Devices and Novel Engineered Materials center at the University of Florida performed the test, it worked the first time, the second time and every time thereafter. No false alarms yet.
Hummel performed the work with University of Florida professor Paul Holloway and doctoral candidates Anna Fuller and Kwanghoon Kim.
The novelty of Hummel's discovery stems from the fact that no one knew explosives were photoluminescent in the infrared — let alone that the vapors forced out of them by their very reactive nature could be made to glow from a distance with a laser.
No false positives Although photoluminescence is a well-known field — that's how fluorescent tubes work — no one thought to check to see if explosives glowed in the infrared when zapped with a green laser. Hummel said his years of experience suggested this combination when he started thinking about what a lifesaver such a device might be.
Chuck Schau, a scientist at Raytheon Missile System's Radiation Technology Laboratory, actually had conducted experiments on detecting explosives using photoluminescence before Hummel's discovery. He did not have the specialized detectors present in the Nanoscale Devices and Novel Engineered Materials center at the University of Florida, however, so he missed observing the distinctive infrared peak that enables Hummel's claim of freedom from false positives. Raytheon is now considering licensing the technology for military use.
"This discovery is very exciting for the field of remote detection," Schau said.
The researchers have proven that the effect works with TNT, nitroglycerin and the plastic explosives trinitrofenil-Nmetilnitramina (Tetryl), hexahydro-trinitro-triazine (RDX), octahydro-tetranitrotetrazocine (HMX) and pentaerythrol tetranitrate (PETN).
Photoluminescence works by adding energy to a molecule with a high-energy wavelength of light, then allowing that molecule to fall back into its ground state by emitting a photon of a different, distinctive wavelength. For instance, the ultraviolet rays from the mercury vapor in a fluorescent bulb bump the phosphor coating on the inside of the tube into a higher energy state. When the coating molecules drop back into their ground state, they emit a visible photon, thereby making a light bulb.
Similarly, in Hummel's approach a high-energy green laser (325- to 532-nanometer wavelength) adds energy to molecules floating in the air and on the surface of anything, including people, luggage and approaching vehicles. If explosives are involved in any way, Hummel claims, his detector will set off an alarm triggered by a glow that has a unique signature.
Over the past year Hummel has tested his technique on everything he can image might end up in a suitcase, from benzene, naphthalene, nail polish, perfume, lighter fluid, rubber cement, acetone, toluene, fertilizer on golf shoes, sugar, baking soda, polyvinyl pyrrolidone (PVP), paint thinner and more — with no false positives yet.
"It turns out that all explosives use groups of nitrogen molecules bonded to two oxygen molecules, which makes them very reactive — they can't help but seep out into the air around anything concealing them. When our green laser hits these molecules they photoluminesce at the 705-nm wavelength. Anything else that radiates at that frequency also radiates at nearby frequencies. Only explosives emit in this very narrow band," said Hummel.
As a consequence, Hummel's detector could theoretically sense a single molecule from an explosive's "aroma" without fear of false positives, by using two sensors — one for explosives and one to prevent false positives. The primary sensor has a filter so it only senses exactly 705-nm wavelengths, thus "arming" the alarm. But the alarm is only set off if a second, "fail-safe" sensor verifies that there is no equally strong radiation at wavelengths adjacent to 705 nm, thus preventing false positives, according to Hummel.
"This invention is almost a year old now, because at first people here did not believe us — that no one had thought of this before. But when they checked the literature and found we were right, they told us we couldn't tell anybody until they got a patent on it," said Hummel.
In the ensuing year, Hummel's group at the University at Florida built several successful prototypes. Even without special equipment, the researchers were able to trigger the effect by merely donning a soldier's night-vision goggles and shining a green presentation laser on an explosive.
Eventually, Hummel envisions sensors mounted outside doors at airports, to scan people and vehicles before they even get close to the terminal. By doing so at a distance, automatic door closers, blast barriers and police units could be automatically deployed before bombers get close to secure areas.
Pun intended, I assume?
Why isn't this deployed in Iraq right now....?
I agree. This should be expedited.
We need them all over Iraq now.
Look at this.
Why isn't this deployed in our airports right now?
This technology has been sitting around for a year without implementation?
All sensitive areas should have these scanners set up and running at major events..
It falls under the classification of "national security"...
Then get these units on the next plane to Iraq, Afghan, and U.S. Airport terminals, as well as high security facilities throughout the nation.. ( Nuclear reactors, arms depots, railroad terminals, major business districts, border crossings, etc.. )
Because it takes a great deal of research, engineering, time, and money to reduce what is essentially a quick and dirty science experiment into a rugged, reliable, portable, instrument. Designing such things is what I do for a living, and it is complex and time consuming.
The article is full of "golly-gee", "gee-whiz", "look how neat and all the other scientists missed it", when in fact the technique is well-known and used for other things. The thing that made this possible is that the group who observed it had a new, more sensitive detector that previous groups who had looked at the effect did not have. Very probably that detector requires liquid nitrogen (or helium) cooling, and is nicely practical for use in a research lab. Getting it to work in the Iraqi desert at midsummer is a whole other animal.
I agree with most of what you say, except for the part about the detector. The article states that the standard issue night vision goggles is enough to detect the effect.
The only question is how expensive/rugged is the green laser.
Bingo!
You just rendered the device useless.
That "might" work under highly artificial conditions (like shining the laser over an open bottle of the explosive, and exciting the concentrated vapors) but I guarantee you that "standard issue night vision goggles" will NOT be sensitive enough to detect explosive vapors in the real world at the much lower concentrations under which they will be present in the field.
"The only question is how expensive/rugged is the green laser."
No, the real question is how expensive and rugged the detector is. Believe me, I "know" about this stuff. We were attempting to do infrared fluorescence (the proper term for "photoluminescence")when I was in grad school back in the late seventies. The detectors back then were just not sensitive enough.
RDX is what the Soviets stole from us to use in their first nuclear weapons. Their other conventional explosives had a nasty habit of pre-detonating due to the exposure to radiation.
Well, they described how to defeat it...that's always useful. /sarcasm
How about chlorates? Potassium perchlorate and chlorate are also explosive.
>Very probably that detector requires liquid nitrogen (or helium) cooling
Sensitive detection of 705nm may require some cooling, but not that much.
Iraq? Can you imagine the Palestinians horror at being on the wrong end of beeber stuned like that?
Great, now thats what I'm talking about.
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