Radi-N Neutron Field Study

Beyond the shelter of the Earth's atmosphere and magnetosphere, highly charged particles are in the midst of a cosmic dance. These particles—atoms stripped of their electrons—are extremely energetic and move at nearly the speed of light.

Liquid droplets are dispersed throughout the clear polymer gel of the bubble detectors. (Courtesy: Bubble Technology Industries)

Collectively known as space radiation, some come from the deepest regions of the universe as galactic cosmic rays, others as solar particles emitted in sun flares, and some as particles trapped in the Earth's magnetic field.

The astronauts of the International Space Station (ISS) travel in low-Earth orbit, thus our planet's atmosphere and magnetosphere provides them some measure of protection. Unfortunately, they still receive much higher doses of radiation than we do on Earth.

Neutron radiation has been shown to make up 10-30% of this exposure. In space, neutrons are produced when primary radiation particles collide with physical matter, such as the ISS, and scatter. Since neutrons do not carry an electric charge, they can penetrate deeply into living tissue. These unstable particles have the potential to damage or mutate DNA—this can cause cataracts, and cancer. With that in mind, it's crucial we learn more about them.

Dosimeter Reader

Radi-N Bubble Detector

The Radi-N Neutron Field Study, a collaboration of the Canadian Space Agency and RSC-Energia, was created to do just that.

Radi-N used bubble detectors produced by a Canadian company, Bubble Technology Industries, as neutron monitors. They were designed to detect only neutrons to the exclusion of all other radiation. Bubble detectors first started being used for space in 1989, and have since become popular because of their accuracy and convenience.

During Expedition 20/21, Canadian Space Agency (CSA) Astronaut Bob Thirsk placed six of these finger-sized instruments around various modules on the ISS. Each detector was filled with a clear polymer gel. Inside the polymer were liquid droplets. When a neutron made contact with the test tube portion, a droplet was vaporized. This created a visible gas bubble in the polymer. Each bubble, which represents neutron radiation, was counted by an automatic reader.

Bubbles are counted by the BDR-III automatic reader. (Courtesy: Bubble Technology Industries)

Radi-N is a follow-up to the Matroshka-R experiment. Matroshka-R used a "phantom", a spherical dummy to simulate a person's body, and bubble detectors placed in and around it, to record the neutron exposure that tissues and organs receive in low-Earth orbit. The results indicated that the internal organs absorbed more neutron radiation than scientists expected. They hypothesize that cosmic rays were interacting with the phantom itself, creating a secondary source of neutrons.

Radi-N has contributed more data to Matroshka-R's results by monitoring the incidence and energy range of neutron radiation throughout the ISS. More specifically, Radi-N measured the neutron spectrum for the first time and results showed that 40% of the neutron dose was due to high-energy neutrons. Also, measurements from various ISS modules revealed that some areas offered more shielding against neutrons than others. These results will help scientists and researchers make better risk assessments of human exposure to neutron radiation in space.

In 2012-2013, a sequel called Radi-N2 will be performed on board the ISS. It will duplicate its predecessor, but because it will occur during a different solar cycle (solar maximum), it will provide scientists with new insights regarding neutron radiation in low-Earth orbit.