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(NASA)

The Invisible Killers

We have the technology to send astronauts to Mars. But can we return them safely to Earth?

Other forms of radiation populate deep space and may pose a danger to astronauts: X-rays, alpha-rays, beta-particles, gamma-rays, and neutrons. All contain excess energy and, in an attempt to stabilize themselves, throw off mass or energy. The high energy of these particles enables them not only to travel at or near light speed but also to penetrate shields and burrow deep into human tissue.

Sim City
In the space between here and Mars, the distribution of cosmic rays is not dense enough to induce acute radiation sickness. But what if the exposure consisted of a low, steady level of ionizing radiation over a two- or three-year mission in deep space? Would that cause subtler health problems? Scientists estimate that an astronaut in a conventional spacecraft on a 900-day Mars mission might encounter as much as 130,000 millirem—a dose equivalent to what you’d be exposed to living 370 years on Earth.

To help build a database that relates levels of radiation exposure with adverse effects, NASA runs the Space Radiation Laboratory at the Department of Energy’s Brookhaven National Laboratory in New York. Adam Rusek oversees the daily operations of the new $34 million facility, which is the only one in the United States devoted exclusively to studying the effects of radiation on living creatures.

The NSRL is housed in an unimpressive low gray building in the woodlands of central Long Island. Here, Rusek and his team of physicists operate a particle accelerator that can replicate deep space’s highly charged subatomic particles, accelerate them to nearly the speed of light, and then slam them into vials of tissue and cells, laboratory animals, and various shielding materials.

Rusek also runs a “summer camp” for biologists to learn the rudiments of particle physics. Sitting in the NSRL’s cramped kitchen, which serves as an informal command center, Rusek comments with a wry grin: “You’d be surprised how many biologists don’t know what a Gaussian wave is.” (It’s a phenomenon of quantum physics.)

To simulate particles found in space, Rusek and his colleagues begin with ordinary materials, such as iron and carbon. They energize the particles by heating them until they are dangerously unstable. During experiments, Rusek mans a computer near the large steel door that marks the opening to the accelerator. From here he operates a Sony webcam that provides views of the 400-square-foot room where the speeding particles end up. Because of the danger involved in the experiments, opening the door can take up to five minutes, requiring an iris scan (to confirm the researchers’ identities), a sign-off from an operator watching on a video camera in another building, and a series of key insertions into a bank of instruments.

Once the door opens, the white-painted cinderblock hallway cuts left, then right, then left again, a precaution against errant particles escaping. The hallway ends at the chamber, which contains a 30-foot track of parallel stainless steel bars; the bars follow the path of the particles and disappear into a hatch in the wall. As the particles travel down the track toward this room, a series of powerful magnets attached to the bars accelerates them and focuses their path.

Marcelo Vasquez, an energetic Argentinian-born biologist and physician, is chief of medical research at NSRL. Presently, he is using mice to look at the effect of ionizing radiation on cognitive function. Vasquez and his colleagues built a three- by three-foot plexiglass pool with a small platform within. They trained mice to swim to the platform and climb on it. After the mice grew proficient at the task, the scientists recorded their times.

Vasquez then strapped three trained mice at a time to a small block of Lucite and irradiated them in the accelerator chamber. Next, he put them back into the water and found that it took the mice longer to find the platform than it had before. The radiation exposure, says Vasquez, caused the animals to lose brain cells quickly. He does acknowledge, however, that in his experiments he administers high doses of radiation, and one can’t necessarily extrapolate directly from the mouse results to what humans will experience.

Vasquez brings up on a computer screen a series of slides showing mouse brain cells exposed to increasing levels of ionizing radiation. The network of axons and dendrites, the structures that enable cells to communicate with one another, first appears as a field densely packed with shapes and fibers. By slide four, the picture is sparsely filled: Cell nuclei look like they have exploded, their contents spread randomly. The image is reminiscent of a block in World War II-era Dresden after a bombing run. The radiation, explains Vasquez, doesn’t kill all the cells, but it severely disrupts the flow of signals. Vasquez’s colleague, Derek Lowenstein, chairman of Brookhaven’s collider accelerator program, has given voice to deep fears among scientists by asking: “Will astronauts come back blithering idiots or not?”

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