America on alert. (Bacteria/Irradiation).

Since the terrorist attacks last September 11, the U.S. government has been on the highest level of alert since World War II. Now, terror tactics are under the microscope as scientists brainstorm new ways to protect airports, buildings, the food supply, even your mail. Last December, President George W. Bush convened a first-ever panel of science advisers to recommend ways to counter terrorism: "Science and technology have never been more essential to the defense of the nation," the President says. Read on to find out how the latest high-tech tools can help keep our homeland safe.

FOOD SUPPLY

WHY IT'S VULNERABLE:

Each year, the U.S. imports nearly 3.7 million shipments of food--and just 1 percent is inspected for disease-causing germs, according to Congress's General Accounting Office. Two of the biggest threats to the nation's food supply: Salmonella and Escherichia coli (E. coli), microscopic single-celled bacteria. If slipped into salad bars or sprayed onto produce-then eaten--the microbes can infect the lower intestines, a long, coiled tube that digests and absorbs food. There the microbes feed on cells and release toxins that can cause diarrhea, fever, vomiting, and death. Even without the aid of terrorists, the Centers for Disease Control (CDC) estimates that accidental food poisoning kills 5,000 Americans annually and sickens millions more.

HOW TO PROTECT IT:

In October, President Bush requested $61 billion from Congress to help protect America's food supply. One food-processing technique already in place can help thwart in tentional contamination of meat, poultry, and fruits and vegetables. It's called irradiation, a process that uses low levels of radiation (high-energy particles) to kill germs. Many irradiation machines rely on X-rays, a type of energy wave strong enough to penetrate soft tissues like human flesh or a hamburger patty up to a depth of several feet. As rays pass through food, their heat energy kills living cells. But since prolonged exposure to X-rays can damage living cells in humans (thick lead shields are used to protect machine operators), the process is controversial.

Still, experts of the technology believe its benefits outweigh potential hazards. Says Rhona Applebaum of the National Food Processors Association: "Food irradiation is a safe and simple process for destroying harmful pathogens in many foods."

BIO-MENACE

E. coli 0157:H7 is a potentially lethal bacterium that thrives in undercooked meat. But scientists say it makes a poor bioweapon, thanks to dozens of food safety procedures.

X-RAY VISION

In five seconds the EXACT[TM] CT machine (above right) takes 250 rotational X-rays of a bag to create a 3-D image of its contents. If the computer detects an object with a density that matches the density of a known weapon, like an explosive, it signals an alarm. A steel handgun, for example, has a density of around 7.8 grams per cubic centimeter (g/cc). Clothing: 0.1 to 0.2 g/cc.

AIRPORTS

WHY THEY'RE VULNERABLE:

In 2000, more than 9 million commercial jets took off and landed, transporting 630 million people and their luggage, according to the Bureau of Transportation Statistics. While all bags boarded on international flights are currently screened for weapons-like knives, guns, and explosives--less than 10 percent of baggage loaded onto domestic U.S. flights undergoes such scrutiny.

HOW TO PROTECT THEM:

Landmark legislation signed into law on November 19, 2001, now requires federal agents to screen all baggage on domestic flights. By the end of 2002, all baggage must be screened with weapons-detection machines.

How can a machine detect lethal weapons? One device called a computer tomography (CT) scanner rotates pencil-thin high-energy X-ray beams around a piece of luggage. As X-rays penetrate luggage, the rays' energy is absorbed by dense, metallic materials with a high atomic number, or the number of protons (positively charged particles) found in an atom's nucleus. "The effect is called photoelectric absorption," says engineer Dave Schafer at the Analogic Corporation in Peabody, Mass. which makes the EXACT[TM] CT scanner.

For example:: If a gun contains the metallic element iron (atomic number 26), energy in passing X-rays collides with atoms inside the iron. An array of detectors lined up below the luggage detects the quantity of X-rays absorbed by iron in the gun. "A computer then converts the information into a measurable electronic signal and forms an image of the gun on the screen," says Schafer (see images, above).

POSTAL SYSTEM

WHY IT'S VULNERABLE:

Before October 2001, few people ever imagined a simple envelope could become a prime vehicle for terrorism. But since then, 23 Americans have become infected with the letter-borne bacteria Bacillus anthracis, or anthrax, according to a November 2 CDC report. And as of late December, five people have died. What makes mailed anthrax so deadly?

Many other toxic germs die when exposed to oxygen in the air. But anthrax's tough outer coat, called a spore, allows it to sit dormant (inactive) without food or water for a century or more--until the spore finds a warm, moist environment to spawn in, such as human lung tissue. More disturbing: A standard envelope contains microscopic holes about twice the size of an average anthrax spore (see photo, below), which means the spores can easily slip out of a sealed envelope to crosscontaminate other letters, or people handling them.

HOW TO PROTECT IT:

In October, the U.S. postal system invested $200 million in a hightech germ-killing technology called electron-beamirradiation (see diagram, above).

Electron-beam sterilizing machines will be installed at a small number of undisclosed mail centers around the U.S.

Cross-Curricular Connection

History: Research U.S. government protection measures taken after the Japanese attacked Pearl Harbor on December 7, 1941. How are they similar to actions taken after the September 11, 2001 terrorist attacks? How are they different?

Did You Know?

* According to the Centers for Disease Control and Prevention, the irradiation process does not reduce the nutritional value of food, although some treated foods may taste slightly different.

* After the September 11, 2001, terrorist attacks, U.S. fighter pilots provided 24hour surveillance over airspace in major cities.

* Microwaves will not kill anthrax spores: the waves work by exciting water molecules, of which there are very few in the deadly bacteria spores.

[CHART OMITTED]

America on Alert

Directions: Circle the correct word in the parentheses.

1. One food-processing technique to thwart disease-causing germs: (irradiation, radiation, microwave). The machines rely on (X-rays, ultraviolet rays, gamma rays), using the energy to kill living cells.

2. E. coli thrives in undercooked meat. Heat over (73.8[degrees] C, 98.6[degrees] C, 100[degrees] C) destroys bacterial DNA.

3: A (shell, spore, pore) is anthrax's tough outer coat.

4. Negatively charged particles are called (protons, electrons, ions).

5. An atomic number is the number of (protons, electrons, ions), or the number of (positively, negatively, neutrally) charged particles found in an atom's nucleus.

America on Alert

1. irradiation, X-rays 2. 73.8[degrees] C 3. spore 4. electrons

5. protons, positively

National Science Education Standards 

Grades 5-8: transfer of energy * structure and function in living systems * risks and benefits * science and technology in society

Grades 9-12: structure and properties'of matter * chemical reactions * interactions of energy and matter * the cell * natural and human-induced hazards

Resources

"Protecting America," by Sharon Begley, Newsweek, Nov. 5, 2001.

The University of Wisconsin Food Irradiation Education Web site:

uw-food-irradiation.engr.wisc.edu

Johns Hopkins University Center for Civilian Biodefense Studies Web site:

www.hopkins.biodefense.org