太空旅行比预想的稍微安全

Analysis of data from the MATROSHKA experiment, the first comprehensive measurements of long-term exposure of astronauts to cosmic radiation, has now been completed. This experiment, carried out on board and outside of the International Space Station, showed that the cosmos may be less hostile to space travellers than expected. Among the many life-threatening hazards to the space traveller, cosmic radiation is a major one, considerably limiting the time astronauts may spend in space without incurring excessive risk to their health from too high a dose of this ionizing radiation. To determine the actual doses of radiation which astronauts undergoing long-term space travel 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 phantom closely mimicking the human body was fitted with several thousand detectors, most of which were manufactured at the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN) in Kraków, Poland. These detectors recorded the doses from cosmic radiation inside the International Space Station and outside -- in open space -- over a few years. The painstaking analysis of the MATROSHKA data has just been completed, yielding somewhat unexpected results.

"One may say that we found open space to be a bit less hostile to humans than expected. The effective doses, related to the health risk of the astronauts and calculated from measurements with our detectors, were lower than those indicated by dosimeters worn by the astronauts", says Dr. Paweł Bilski, an Associate Professor at IFJ PAN.

A specially adapted humanoid phantom used in medical research, in which real human bones were placed inside a plastic "body" simulating the shapes and densities of soft tissues or lungs in the human body, was used to measure doses of cosmic radiation. The mannequin (a torso without legs) consisted of 33 slices of 2.5 cm thickness each. The 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 phantom by six thousand thermoluminescent detectors. Over three thousands of these detectors were manufactured at the IFJ PAN. This experimental design enabled the researchers to accurately determine the spatial distribution of dose inside the phantom, to evaluate doses absorbed in particular organs of the human body, and finally to establish the value of the so-called effective dose, which is considered to be an estimate of the radiation hazard to humans.

"Our thermoluminescent detectors are thin white pellets of 4.5 mm diameter. We produce them out of lithium fluoride, adding some carefully selected dopants", explains Prof. Paweł Olko, Scientific Director of IFJ PAN.