Astronauts working outside the International Space Station (ISS) are exposed to about 27 times as much radiation annually than people on Earth, but the levels are still very low for space, Canadian researchers announced Tuesday.
Preliminary results from a year-long study funded by the Canadian Space Agency (CSA) show that astronauts were subjected to lower than expected levels of high-energy proton and electron radiation sent from the Sun over the last five months. The Extravehicular Activity Radiation Monitor study (EVARM) began in February, with astronauts wearing radiation detectors as they worked in space.
"This is good news for the astronauts," said EVARM lead researcher Ian Thomson during a telephone interview. Thomson is also president of Thomson Nielsen Electronics, Ltd., an Ottawa company that manufactures radiation-measuring devices for medical uses. "It looks like we're at a lower end of the radiation sent by the 11-year [sunspot] cycle."
Radiation doses are measured in Sieverts (Sv), though levels are usually quite small and denoted as milliSieverts (mSv). On Earth, humans receive an annual dose of about 2 mSv from background radiation, though radiation workers, who deal with radioactive substances daily, are capped at a maximum exposure of 20 mSv a year.
The astronauts floating in low Earth orbit outside the ISS are bombarded by 54 mSv a year, nearly three times the amount of a professional radiation worker on Earth, Thomson said. But as the years wear on, he added, the levels should rise in conjunction with the Sun's sunspot activity.
The findings were announced during the July 16 meeting of the American Association of Medical Physics in Montreal.
Nine astronauts aboard the ISS have taken the detectors, tiny silicon dosimeters mounted on aluminum badges the size of matchboxes, along on spacewalks. One detector located near the head monitored the amount of radiation hitting the eyes, another measured radiation levels on the trunk of the body where spacesuit equipment offers some shielding, and a third on the leg, where there is little protection.
"Radiation exposure is a known risk for these astronauts, it's just space weather and you can't avoid it," Thomson said. "But you can try and minimize it, by measuring how much radiation an astronaut gets."
In general, the more radiation doses a person receives, the higher the risk of developing cancer or radiation sickness. By knowing the amount of radiation an astronaut has received, their risk could be lowered in the future by simply avoiding spacewalks. The knowledge of radiation doses could even lead to the development of better shielding techniques.
Thomson Nielsen Electronics Ltd. has also adapted the silicon dosimeters used in space to gauge radiation doses for cancer patients on Earth. More than 400 cancer clinics around the world are using the detectors, which could be used in the future for pediatric radiology and cardiology.
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