The backup of the RAD instrument (Radiation Assessment Detector) on board Curiosity, the rover which has been moving around on the surface of Mars since August 2012, was tested this year at the IRSN. This clone of the instrument, kept on Earth to conduct tests relating to the processing of data from Curiosity, was calibrated to measure the activity concentration of radon (222 Rn) in the Baccara facility at the LPMA in Saclay. With this calibration, the RAD instrument will be able to accurately quantify the perturbations induced by radon and its progeny present in the Martian atmosphere, on the measurements of low-energy ionizing radiations (around 5MeV) performed at the surface of the planet. IRSN's Baccara bench, dedicated to studies on radon metrology, is the only facility in the world that offers the experimental conditions needed for these tests, that is to say, under a CO2 atmosphere and low-pressure (7 mbar).
This exchange between the IRSN and NASA was established following a thesis carried out at IRSN in 2004-2007, during which the doctoral student Pierre-Yves Meslin revealed the presence of polonium-210, and thus radon, on Mars. The Americans learned of the existence of the Baccara bench and the IRSN was able to provide this RAD instrument calibration service because Pierre-Yves Meslin has since continued to work on this subject1, regularly collaborating with NASA. During the testing, with the financial support of CNES, American teams (under the auspices of NASA) and French teams (IRSN and Irap) worked hand in hand, accompanied by German researchers (University of Kiel) who are also involved in the instrument design and the use of RAD results. Baccara's robust calibration procedure was only changed a little to fulfil this request.
The RAD instrument was developed by the
Southwest Research Institute (Boulder, Colorado, USA), with University of Kiel (Germany), and funded by NASA and the German national aeronautics and space research centre (DLR), within the framework of the Mars Science Laboratory (MSL) mission to explore Mars, which was launched in late 2011. It is used to detect and characterize all elementary particles, charged or not, over a very wide range of energies (0.2 MeV to 2 GeV). In-depth knowledge of the Martian radiation environment is indeed essential to prepare for future manned space missions to the red planet.
 At the
Astrophysics and Planetology Research Institute (Institut de recherche en astrophysique et planétologie, Irap), a joint research unit of the
CNRS and of the
Université de Toulouse III Paul Sabatier.