To participate in the RaDI-N2 & You action project in the 2018-2019 school year, click here!
Earth is under attack from outer space! We are constantly being bombarded by radiation that comes from space, but the Earth’s natural defences shield us from most of its effects. As Julie Burtt, a Radiation and Health Sciences Officer from the Canadian Nuclear Safety Commission (CNSC), explains, “radiation is all around us in many forms.” Some of the most dangerous radiation comes from outer space in the form of cosmic rays (also known as cosmic radiation), high-energy particles that come from our Sun and outer space. When this cosmic radiation strikes matter, this can lead to the formation of secondary cosmic radiation (including neutron radiation) through radioactive decay. These free neutrons, because they have both high mass and high velocity, can cause serious damage to plant and animal cells that could lead to mutations (you can learn more about radiation and its effects on humans here, here, and here).
Fortunately for us, the Earth’s magnetosphere and our atmosphere protect us from much of this harmful radiation. For Canadian astronaut Chris Hadfield and other astronauts on board the International Space Station (ISS), however, it’s a different story. Dr. Martin Smith, a scientist at Bubble Technology Industries who studies cosmic radiation, explains: “The Earth has different layers of protection. Earth’s atmosphere stops a lot of radiation, and so does its magnetic field. The ISS (which orbits the Earth at an average altitude of 370 km) is outside the atmosphere but inside the magnetic field. We are inside both. Beyond the ISS orbit, the radiation is different.” When astronauts move beyond Earth’s orbit to go back to the Moon, to Mars, or an asteroid, they will be at even greater risk from cosmic radiation. Scientists are very interested in learning more about cosmic radiation in space and how it affects living matter.
One of the experiments that Chris Hadfield conducted while he was on board the ISS from December 2012 until May 2013 was RaDI-N2, a Canadian Space Agency experiment designed to gather data on neutron radiation exposure in space to better understand the cosmic radiation environment. Information from RaDI-N2 and other experiments will help scientists develop ways to protect astronauts from neutron radiation as they move out of Earth orbit and away from any of the protection that Earth offers towards destinations such as Mars or an asteroid. You can see Chris Hadfield explain the experiment here.
Chris Hadfield with bubble detectors on board the International Space Station. Photo credit: NASA
The device used in RaDI-N2 is called a Bubble Detector – Personal Neutron Dosimeter (BD-PND or ‘bubble detector’), a unique piece of Canadian technology developed by Bubble Technology Industries in Chalk River, Ontario. The bubble detector has a clear plastic tube containing a polymer gel that has small drops of superheated liquid in it. If a high-speed neutron passes through the bubble detector and hits one of the drops of superheated liquid, that drop will vapourize, forming a bubble. Figuring out your neutron radiation exposure is as simple as counting bubbles (well, that and multiplying the number of bubbles by the bubble detector’s sensitivity to determine your exposure in millirems or microsieverts).
While RaDI-N2 was going on 370 km above the Earth’s surface, over 7 500 students in 310 classrooms across Canada were collecting data on Earth using the same bubble detectors that were on board the ISS, participating in Let’s Talk Science’s RaDI-N2 & You action project right here on CurioCity (you can see the participating locations here). Data was collected using the same types of bubble detectors as were in space during the same week-long collection periods in February and March 2013 when Commander Hadfield was conducting RaDI-N2. Additionally, pilots from Jazz Aviation took bubble detectors in the air on their regularly scheduled flights during these weeks, providing another different set of data to compare.
Former astronaut Dr. Robert Thirsk hosted a live downlink between Chris Hadfield and students participating in the RaDI-N2 & You action project at Bert Church High School in Airdrie, Alberta on March 10, 2013. Photo credit: Let’s Talk Science
Looking at the data, one can see a lot of variation between locations. There are many factors that could affect the data collected at different sites, including altitude above sea level, cloud cover on data collection dates, the materials used to construct the building the bubble detector was inside, and more. Dr. Robert Thirsk, who conducted RaDI-N on board the ISS in 2009, pointed out that the Earth’s magnetic field “is weakest near the north and south polar regions,” so people in Nunavut, for instance, can expect to “receive a bit higher (but not dangerous) level of radiation.”
One particular aspect that the scientists conducting RaDI-N2 were interested in was to see whether the increased solar activity in 2013 would lead to higher radiation levels on board the ISS. Dr. Smith was rather surprised, however: “so far, we don’t see a big difference between the 2009 and 2013 results. We think this is because the ISS is quite close to Earth, where solar activity has relatively little effect. The difference in solar activity would be more noticeable out in deep space, on the way to Mars for example.”
Jazz Aviation pilots flew both turboprops, like the Bombardier Dash 8 at top, and regional jets, like the Bombardier CRJ below, while collecting RaDI-N2 & You data. Photo credit: Scott Taylor<
The results from the Jazz Aviation pilots clearly showed that there is much higher exposure to neutron radiation at high altitudes compared to ground level – something I noticed myself when I took a flight from London to Saskatoon recently and brought along my bubble detector. However, Julie Burtt from the CNSC reassures us that the amount of radiation we receive on a long flight is no more than we get from a single medical X-ray, and that even for frequent flyers and aircrew this does not pose a health risk.
The data gathered by experiments like RaDI-N2 will help scientists to better understand radiation in space, but this is only the first step towards protecting astronauts in space. Dr. Thirsk summarizes: “there are many challenging issues regarding radiation protection that still need to be solved: characterizing the radiation environment of interplanetary space, developing spacecraft shielding methods, predicting solar flares, and treating astronauts who have been exposed to high doses of radiation.” The issue of spacecraft shielding is particularly important, as Dr. Smith, who is also one of the lead researchers for RaDI-N2, explains: “spacecraft shielding is a complicated problem because there are different types of radiation requiring different shielding. For example, gamma and x-rays are shielded well by heavy metal such as lead, but charged particles can produce other radiation (such as neutron radiation) when they hit metal shielding, so no one material can do the job required.”
A bubble detector after a 5 ½ hour flight from London, Ontario, to Saskatoon via Calgary (top), compared to the same bubble detector after a 24-hour reading on the ground in London (bottom). Photo credit: Scott Taylor
While he was on board the ISS in 2009, Dr. Thirsk did some experimenting of his own to investigate shielding. “Near the end of the original RaDI-N experiment, I asked the scientists on the ground if I could place the bubble tubes inside large bags of water. I wondered whether water would be a good shield against ionizing radiation. The result was ‘Yes!’ The radiation dose inside the water shield was 72% (i.e., 28% less) of the dose outside.” While there is much work to do, solving the problems posed by cosmic radiation is essential if we are to send astronauts to explore other worlds, and RaDI-N2 is part of that work. As Chris Hadfield commented while on board the ISS, “Thanks to RaDI-N2, future spaceships will be safer, as we head deeper and deeper into the cosmos.”
Although Chris Hadfield is back on Earth now, astronauts on the ISS will continue collecting RaDI-N2 data until 2015, and the data from RaDI-N2 & You is available for all to explore on CurioCity.
A big thanks to everybody who participated in the RaDI-N2 & You project, including the thousands of students, teachers, volunteers, Jazz Aviation pilots, and of course Chris Hadfield for collecting data in this project. Thanks also to the folks at the Canadian Space Agency, the Canadian Nuclear Safety Commission, Bubble Technology Industries, Jazz Aviation, MDA, 3M, and the Trottier Family Foundation for generously supporting this project.