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.
Collectively known as space radiation, some come from the deepest regions of the universe as galactic cosmic rays, some as solar particles emitted in sun flares, and others as particles trapped in the Earth's magnetic field.
The astronauts of the International Space Station (ISS) travel along a low-Earth orbit; this provides them modest protection via the Earth's atmosphere and magnetosphere. Unfortunately, they still receive much higher doses of radiation than we do down 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 this in mind, it's crucial we learn more about them.
The RaDI-N Neutron Field Study, a collaboration of the Canadian Space Agency and RSC-Energia, has been designed to do just that. Bob Thirsk measured the neutron radiation levels on the station while onboard the ISS for Expedition 20/21.
RaDI-N uses bubble detectors produced by a Canadian company, Bubble Technology Industries, as neutron monitors. They have been designed to only detect neutrons and ignore all other radiation. Bubble detectors first started being used for space in 1989, and have since become popular because of their accuracy and convenience.
Bob Thirsk placed six of these finger-sized instruments around various modules on the ISS. Each detector is filled with a clear polymer gel. Inside the polymer are liquid droplets. When a neutron strikes the test tube portion, a droplet is vaporized. This creates a visible gas bubble in the polymer. Each bubble, which represents neutron radiation, is counted by an automatic reader.
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 will add more data to Matroshka-R's results by monitoring the incidence and energy range of neutron radiation throughout the ISS. The RaDI-N team is confident that their findings will provide an invaluable resource for accurate risk assessment of neutron radiation in space. This could help reduce astronauts' exposure to radiation during future missions.