Radi-N2: Tracking space radiation and its risks

Health Science

Radi-N2 used bubble monitors, a Canadian-made technology which will lead to better protection of crews in Earth orbit and on deep-space missions.


From Earth, the Sun looks like a calm, unchanging source of light. But it is actually a highly active, constantly churning ball of gas. The Sun continuously releases not only heat and visible light, but also radiation in the form of massive streams of high-energy particles. Thankfully, Earth's atmosphere and magnetosphere largely shield us from this threat.

But space can be a potentially hazardous place to live and work. Astronauts aboard the International Space Station (ISS) are at higher risk of radiation exposure, and receive greater doses than they would here on Earth.

One of the most serious types is neutron radiation. It makes up about 30% of the radiation that astronauts receive on the Space Station, and can potentially cause cataracts, bone marrow damage, and even cancer over long-term exposure.

The Radi-N2 experiment measured neutron radiation using bubble monitors: finger-sized tubes filled with a clear polymer gel containing liquid droplets. When struck by a high-energy neutron particle, a droplet vaporized, leaving a visible bubble that could be counted.

Radi-N2: Detecting neutron radiation on the ISS

The Canadian Space Agency (CSA) astronaut Chris Hadfield explains the Canadian Radi-N2 experiment and displays the neutron bubble detectors used on the ISS. (Credits: CSA, NASA)


The Radi-N2 experiment is designed to:

Radi-N2 and You

The CSA partnered with Let's Talk Science to engage students in a unique project with Canadian astronaut David Saint-Jacques during his six-month mission on the ISS.

Students in classrooms across Canada participated in Radi-N2 & You. Students measured neutron radiation levels on Earth using bubble detectors and compared their results to David's measurements on the Station.

How it worked

There were two slightly different procedures for the Radi-N2 experiment. When a Canadian astronaut was aboard the Station, they were in charge of conducting a session according to the following steps:

  1. The astronaut retrieved a set of eight bubble detectors from storage on board the Station.
  2. These tubes were loaded into the automatic reader, and the number of bubbles was recorded for later comparison.
  3. The astronaut placed six bubble monitors in specific locations around the Station. One of the bubble monitors was worn by the astronaut to measure the dose their body received, and another was placed within their sleeping quarters. All of the monitors were left in place for one week.
  4. When seven days had passed, the monitors were collected and loaded into the automatic reader. The crewmember recorded the data, and scientists on the ground calculated how much neutron radiation the Station received.

When there were no Canadians on board the Station, an astronaut placed all eight bubble monitors around the Station.


Early results from Radi-N2 show that astronauts on the ISS typically receive doses of neutron radiation equivalent to 150 microsieverts per day, hundreds of times higher than we receive on Earth. The study has found that only minor differences in radiation dose exist between the seven modules of the US segment of the ISS, but astronauts typically receive lower doses of neutron radiation in their sleeping quarters than during their daily activities elsewhere on the Station.

Researchers anticipate that Radi-N2 data will contribute to future human exploration missions, including those to the Moon and Mars. Knowledge of the neutron field in space may influence future strategies to mitigate radiation exposure, including countermeasures in shielding and spacecraft design.

Improvements in measuring the doses of radiation that humans are exposed to in space will also impact radiation monitoring practices on Earth. For example, bubble detectors will continue to be used to monitor neutron radiation in many places on Earth, including nuclear power stations and medical facilities.

Did you know that the Sun has seasons? Our closest star goes through an 11-year cycle of activity, including a solar minimum and maximum.

During solar maximum, the Sun can release flares, powerful bursts of particles and gas that can contain high levels of radiation. Flares and other types of solar ejections produce spectacular displays of auroras in our skies, but they can also cause power outages, satellite malfunctions and even disruptions to GPS and other communications systems.


An earlier version of the experiment, Radi-N, took place during Robert Thirsk's Expedition 20/21 mission to the ISS in .

Radi-N2 began during Chris Hadfield's ISS Expedition 34/35 mission in and concluded in .


With support from the CSA, Bubble Technology Industries of Chalk River, Ontario, designed and manufactured the bubble monitors used in space.

The Radi-N2 study was a collaboration between the CSA and:

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