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Astronauts on spacewalks are subjected to high doses of
radiation; a spacesuit does not offer as much protection as
a spacecraft. A Canadian Space Agency experiment
enables researchers to measure the levels of radiation astronauts are exposed
to during a spacewalk. This radiation monitoring experiment
is called EVARM and it was conducted in 2002 and 2003. It
was led by
Dr. Ian Thomson of Thomson Nielsen in Ottawa,
Ontario
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American astronaut David Wolf wears the EVARM dosimeter
on a spacewalk, October 10, 2002. He is being moved by Canadarm.
(Photo: NASA) |
Measuring radiation: A question of survival
The EVARM experiment measured the radiation delivered to
the most sensitive organs: the skin, eyes, bone marrow, and lymphatic organs. Spacesuit
shielding influences the quantity and type of radiation absorbed by astronauts. Overexposure may
burn the skin, cause cataracts in the lens of the eye and
the immediate depletion of blood cells, as well as increase
the risk of cancer.
We can compare the internationally recognized limits of
radiation exposure for workers and the maximum allowed doses
for astronauts.
Table comparing internationally established annual limits
for workers and the doses astronauts are exposed to.
(Source: International Commission on Radiological Protection, 1977)
The table shows that radiation exposure for astronauts to the skin is six times higher, to their eyes, 13 times higher, and to their blood-forming organs, 25 times higher.
In the EVARM experiment, radiation was measured by means of three dosimeters in the form of small badges. These dosimeters, which are actually MOSFETs (metal-oxide semiconductor field effect transistors), were carried in pockets inside the astronaut's spacesuit. Data recorded by these
badges were then transferred to a laptop computer and sent to researchers.
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A badge was placed on the lower left leg in a
pocket of the astronaut's liquid cooling garment.
Two other badges were placed on the torso.
(Photo: NASA)
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The EVARM equipment had to be compact and light to be
carried to space, where there is a limited room for storage.
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Improving spacesuits
Measurements taken over a number of spacewalks (EVAs
or extravehicular activities) are now being studied.
The analyses must take various factors into account: the time and place of the EVA as well as the orbit and altitude of the International Space Station. Another factor to be considered is the proximity of the station, which may block radiation and influence the results of the experiment.
Researchers predict that at certain
times, they may be about ten times higher
than levels inside the space station. The
information gathered will help determine which
parts of the body are exposed to the highest
levels of radiation, in order to improve spacesuit
shielding.
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A promising technology for cancer treatment
The space industry will not be the only one to benefit from the technology
and results of the EVARM experiment. Similar devices are already being used in cancer treatment. They are small enough to be placed on any part of the body during a radiotherapy session, helping doctors to target malignant
tumours by providing real-time data on the radiation doses reaching the organs.
The shielding designed for this experiment can also be used to protect
people working in areas exposed to high levels of radiation, such as nuclear power plants.
The EVARM reader
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The EVARM reader conveys data gathered
by the EVARM badges
to the Control Centre.
During flight, badges are stowed in the lid. |
EVARM badges
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