NASA Space Radiobiology Research Takes Off
at New Brookhaven Facility

SPACE RADIATION

Given the low risk to public health on Earth and the limited time that astronauts have been spending in space, little research has been performed until recently on the consequences to human beings of exposure to ionizing radiation in space.

The profile of a heavy-ion beam (yellow spot) is shown on one of four fluorescing “flags” within the NSRL beam line. After tuning the beam, these flags are retracted so that the beam can be delivered unimpeded to experiments. Heavy ions were first sent down the NSRL beam line in winter 2002.

Radiation, in this sense, is a stream of particles, such as alpha and beta particles, electrons, neutrons, protons, heavy ions, x- and gamma rays, etc. Ionizing radiation is a stream of such particles that, when passing through a body like that of a human being, has enough energy to cause the atoms and molecules within that substance to lose or gain electrons, thereby acquiring a charge and becoming an ion. The higher the energy of ionizing radiation, the farther it will penetrate within the body.

By directly or indirectly ionizing and thus damaging the components of living cells, including the genetic material called DNA, ionizing radiation may cause changes in cells’ ability to carry out repair and reproduction. Such radiation-induced changes may lead to mutations, which, in turn, may result in tumors, cancer, genetic defects in offspring, or death. If a dose of ionizing radiation is received over a shorter time period, then the more damage that it can cause.

Earth-bound human beings are shielded from harmful exposure to ionizing space radiation by the Earth’s atmosphere and magnetic field. But astronauts on the Space Shuttle and the International Space Station fly above the magnetosphere. Although the spacecraft itself somewhat reduces radiation exposure, it does not completely shield astronauts from galactic cosmic rays, which are highly energetic heavy ions, or from solar particles, which primarily are energetic protons. By one NASA estimate, for each year that astronauts spend in deep space, about one-third of their DNA will be hit directly by heavy ions.

Astronauts such as this Shuttle mission specialist will be the beneficiaries of the radiobiology research now ongoing at the NASA Space Radiation Laboratory.

Since astronauts are spending longer and longer time in space on the International Space Station, they are receiving more exposure to ionizing radiation than astronauts on previous missions. If future space travelers venture beyond low-Earth orbit for new journeys to the Moon or Mars, for example, then they will be exposed to even higher space radiation doses.

ACCELERATING HEAVY IONS

Because one type of radiation, such as cosmic rays, can be reproduced by another type, such as iron, silicon, and gold heavy ions of the same energy, two of Brookhaven’s accelerators — first the AGS and now the Booster — can serve as ground-based suppliers of particle beam for controlled radiobiological experiments.

From 1995 until this July, the AGS was the only accelerator in the United States capable of providing heavy ion beams at energies useful for space radiobiology research. So, for the past eight years, NASA-sponsored scientists have conducted experiments once or twice annually at the AGS, studying model organisms, cell and tissue cultures, and various materials bombarded with beams of iron, silicon, and gold ions at energies ranging from 0.6 to 10 billion electron volts (GeV) per nucleon.

Their goal has been to develop accurate estimates of radiation-associated risks to human beings in space, and to identify effective countermeasures for reducing those risks. So far, these studies have advanced the understanding of the molecular mechanisms by which radiation causes damage to the central nervous system. In quantifying these effects, radiobiology researchers have elucidated, for example, which types of damage to DNA are the most harmful.

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