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Space Travel Safer Than Thought?
March 31, 2015   
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Space may be less hostile to astronauts than previously thought, scientists have concluded after an experiment to measure cosmic radiation aboard the International Space Station.

Among the many life-threatening hazards to the space traveler, ionizing cosmic radiation is a major one, considerably limiting the time astronauts can safely spend in space. To determine the actual doses of radiation that astronauts undergoing long-term missions in space are exposed to, the European Space Agency (ESA), in collaboration with research institutions from Germany, Poland, Austria, Sweden and Russia, designed and carried out the Matroshka experiment. A dummy closely mimicking the human body was fitted with several thousand detectors, most of which were manufactured at the Polish Academy of Sciences’ Institute of Nuclear Physics in Cracow. The detectors recorded levels of cosmic radiation inside the International Space Station and outside—in open space—over several years.

Analysis of the Matroshka data has yielded somewhat unexpected results: that space is slightly less hostile to humans than expected, according to Paweł Bilski, an associate professor at the Institute of Nuclear Physics. “The effective doses calculated from measurements with our detectors were lower than those indicated by dosimeters worn by the astronauts”, says Bilski.

A specially adapted humanoid dummy, in which real human bones were placed inside a plastic “body” simulating the shape and density of soft tissues and lungs in the human body, was used to measure doses of cosmic radiation. The mannequin (a torso without legs) consisted of 33 slices, each 2.5 cm thick. Measuring equipment was located inside these slices and included sets of passive thermoluminescent detectors placed in plastic tubes. Thus, a three-dimensional rectangular grid of measurement points was created inside the dummy by 6,000 thermoluminescent detectors. Over 3,000 of these detectors were manufactured at the Institute of Nuclear Physics. Researchers were able to accurately determine the spatial distribution of radiation inside the dummy, to evaluate the dose absorbed by particular organs of the body, and finally to calculate the so-called effective dose, which is considered to be the most accurate estimate of the level of radiation hazard to humans.

Prof. PawełOlko of the Institute of Nuclear Physics, said, “Our thermoluminescent detectors are thin white pellets, 4.5 mm in diameter. We produce them out of lithium fluoride, adding some carefully selected dopants.”

The main hazard to an astronaut’s health due to exposure to cosmic radiation is the increased probability of developing cancer. Much, however, depends on the type of radiation the astronaut is exposed to. Most of the natural sources of ionizing radiation on Earth produce electromagnetic radiation of high energy—gamma rays. On the other hand, in cosmic rays, energetic protons or heavier ions dominate, which are much more effective in creating cancer cells. Thermoluminescent detectors are unable to distinguish between gamma rays and ions, therefore the dummy was also equipped with plastic track detectors in which tracks of protons or heavier ions could be measured.

The mannequin on board the International Space Station, with thermoluminescent and plastic detectors inside its “body,” was also fitted with additional, external detectors, simulating the personal dosimeters worn by astronauts. Thus, the doses recorded by individual dosimeters of the International Space Station crew could be compared with those actually absorbed inside their bodies.

From 2004 to 2009 the Matroshka mannequin was used in three experiments to measure cosmic radiation, each lasting over a year. Two of these experiments were conducted in the Russian modules of the space station, while during one experiment the dummy, in a container imitating the shielding properties of a spacesuit, was placed in open space outside the International Space Station. Such measurements had never been carried out before.

Back on Earth, the data gathered in the Matroshka experiment was analyzed by teams of scientists at the Polish Academy of Sciences’ Institute of Nuclear Physics in Cracow, the German Aerospace Center (DLR) in Cologne, and the Vienna University of Technology. Their overall conclusion was that the individual dosimeters worn by the crew of the International Space Station overestimated the actual dose measured inside the dummy by about 15 percent. However, in open space this overestimation exceeded 200 percent.

The results of the Matroshka experiment led the scientists to conclude that missions to the Moon or Mars may be somewhat safer in terms of the radiation danger than presumed so far. Nevertheless, the doses that astronauts would likely receive, though lower than earlier thought, would still be dangerously high.
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