Science strikes back at terrorism.

Ever since last summer's crash of TWA Flight 800, people have been talking about high-tech ways to keep bombs off planes.

Imagine a sniffing wand that smells out the vapors of bomb chemicals and flashes a red light when a culprit chemical is found. Or a precision X-ray machine that scrutinizes suitcases with the same imaging tools doctors use to find tumors in people. Or a tool that zaps a bin of luggage with enough energy to create "chemical fingerprints" of all the items inside.

These devices and others aim to reveal the tools of terrorism before they ignite the skies. The main goal: to detect "plastic" explosives (see box, p. 12. Last summer, investigators found traces of PETN, a chemical ingredient in some plastic explosives, on debris from TWA Flight 800. Unlike metal objects, plastic explosives can pass undetected through standard airport X-ray machines.

But travelers will surely foot the bill for improved detectors. The cost: higher ticket prices and long airport delays. Using even the fastest new technology, it would likely take more than two hours to survey all the luggage for a single jumbo jet, experts say.

Since 1982, 548 people - an average of 39 a year - have lost their lives in U.S. plane crashes blamed on sabotage. President Clinton recently asked Congress to spend nearly $250 million on new equipment and other measures to improve airline security. Is it worth the price? Or will current baggage scanners suffice? Check out the latest technologies, then decide.

SUITCASE SCANNER

One major flaw with current airport X-ray machines is their view, says Rick Muntz of InVision, a California technology company that builds luggage scanners. When X-rays (penetrating beams of invisible energy) pass through a suitcase, metal and other hard materials inside absorb the rays, casting shadows on a screen. Three-dimensional objects appear flat, so it can be difficult to distinguish one object from another.

Another problem is that soft, nonmetallic objects like plastic explosives don't absorb X-rays as well as hard, metallic objects. These "soft" objects cast only fuzzy shadows, so they're difficult to distinguish on the screen.

To get a better and more complete view, InVision engineers found a new use for Computed Axial Tomography (CT or CAT scans), a medical imaging device (see SW 10/20/95, p. 8). Doctors use CAT scans to look at cross-sections of a patient's body to search for abnormalities like tumors. InVision engineers overhauled CAT scanners to search for bombs.

"If I take a bag, slice it up like a loaf of bread, and pull out a slice, I can see a whole cross-section of the bag,, explains Muntz. "I can see each individual object inside."

Of course, InVision's machine doesn't actually cut up suitcases. Instead, the CTX 5000 passes X-rays through the bag at many angles. computer uses the flat 2-D images to create a single 3-D image. Objects that show up on X-rays can be easier to spot in 3-D.

To solve the problem of objects that are invisible to X-rays, the CTX MM also measures the density (mass per unit volume) of aH the materials in each bag. Every material - including explosives-has a unique density, Muntz explains. So, plastic explosives have different densities than, say, a pair of sneakers.

InVision engineers program the CTX 5000 to recognize the densities of particular explosives, including plastics, dynamite, and ammonium nitrate (the "fertilizer" material used in the bomb that blew up the Murrah federal building in Oklahoma City in April 1995). Potential explosives appear red on the screen, warning human operators to inspect the suitcase more carefully.

Today, 23 CTX 5000 machines are in use at airports around the globe. In the United States, Atlanta has two; San Francisco has one. New York's Kennedy Airport-where Flight 800 began its ill-fated journey-received its first CTX 5000 this fall.

But the machines cost about $1 million each. A busy airport like Kennedy would need at least 32 machines to scan carry-on luggage, and dozens more to search checked suitcases and cargo. So far, Muntz says, the CTX 5000 can scan up to 300 bags per hour-only half the luggage on a fully loaded 747 aircraft.

SUPER SNIFFER

A slightly quicker and cheaper detective is the "super sniffer" - a device that inhales, vapors on the outside of a suitcase to determine whether explosives are concealed inside. Sniffers report results in just 6 to 18 seconds per bag, manufacturers say. They cost anywhere from $50,000 to $165,000. So an airline could buy several super sniffers for the price of one CTX 5000.

To "sniff" a sample, an operator grazes the suitcase with a 25-centimeter (10-inch) wand. The wand sucks in an airstream filled with vapors and particles released by the suitcase's contents. Some models require the operator to wipe the suitcase's with a cloth to collect a sample.

A computer then analyzes the sample and compares it with a library of chemical explosives. If the computer finds a match flashes and security personnel are called in.

A super sniffer made by Thermedics Inc., of Massachusetts, can detect aas little as one-billionth of a gram of plastic explosives, says Joanne Kern, a company spokeswoman. In fact, the machine detected traces of explosives on about 10 pieces of debris from Flight SM.

Sometimes, though, the machines make mistakes. One falsely signalled explosives after sniffing perfume. But sniffer makers say they've ironed out these problems.

Only a few super sniffers have been installed at U.S. airports. But hundreds are in use at airports around the world.

X-RAY VISION 

An even faster scanner is still on the drawing boards. This device would scan an entire cargo bin at once, using high energy X-rays, says William Bertozzi, a professor of physics at Massachusetts Institute of Technology. Bertozzi says a workable model could be built within two years.

Unlike today's X-ray scanners, this machine wouldn't display just the shadowy image of items in a suitcase. It would also look at the chemical makeup of everything packed inside.

When high energy X-rays zap the luggage, each type of chemical building block, or atom, in each packed item would absorb and emit different amounts of energy. The energy emitted is like a fingerprint of an element," Bertozzi says. He plans to link the X-ray device with a computer programmed with the "chemical fingerprints" of explosive materials like PETN. The computer would alert airport security if the device detected danger.

GO FOR IT?

With all this new technology, you might say, Let's use it all!" But are you and your parents prepared for longer lines, tax hikes, or a jump in airline ticket prices to pay for safer skies? Some people say safety comes first-at all costs. Others prefer to take their chances and spare the expense. What do you think?