The new NASA Mars Science Laboratory (MSL) mission to Mars is scheduled to be launched in the Fall of 2009 with the aim to determine the planet’s habitability. This new Mars rover will carry a total of 10 scientific instruments.

 

 

 

The CANBERRA Detectors will be incorporated in the Radiation Assessment Detector (RAD)

About the size of a small toaster, the Radiation Assessment Detector will look skyward and use a stack of silicon detectors and a crystal of cesium iodide to measure galactic cosmic rays and solar particles that pass through the Martian atmosphere. ( Image credit: NASA/JPL-Caltech/SwRI)

The RAD will be one of the first instruments sent to Mars specifically to prepare for future human exploration. RAD will measure and identify all high-energy radiation on the Martian surface, such as protons, energetic ions of various elements, neutrons, and gamma rays. That includes not only direct radiation from space, but also secondary radiation produced by the interaction of space radiation with the Martian atmosphere and surface rocks and soils. The detector consists of a stack of 300 micron thick silicon detectors and detectors coupled to cesium iodide scintillator acting as a calorimeter. As the particles pass through the detectors, they lose energy, producing electron or light pulses. An internal signal processor analyzes the pulses to identify each high-energy particle and determine its energy. Three specific tasks needed to be accomplished in manufacturing the Silicon detectors.

• One of the restrictions is the weight and space within the instrument and therefore some detectors are read-out using no more than a Kapton flex board.
• The read-out of the scintillator light (565nm) requires an anti-reflective coating (ARC) on the detectors and a very thin entrance window for a good light efficiency.
• The CO2 Martian atmosphere is highly conducive to electrical discharge. Therefore all interconnects needed to be passivated and able to withstand from -70 to +60 degrees Centigrade (the normal Martian climate).

CANBERRA produced a total of 4 different models to go aboard and a total of 72 devices. The model called ABC Detector has 1200mm² active area segmented into 6 junctions. The models called D, E and F are single-junction detectors with 200 to 300mm² active areas and specific shapes. The devices showed extremely good leakage currents. Less then 100pA at room temperature for the 300mm² devices. The applied anti-reflective coating proved a quantum efficiency above 80%. At this very moment the first flight detectors are being tested.

This type of instrument and/or detectors is also envisaged to be used on the NASA mission “The Great Escape” and for the Ionizing Radiation Sensor (IRAS) on ESA’s ExoMars mission.