Radicals and Oxidants Instrument (ROXI) for Mars surface analyses

摘要

Electron Paramagnetic Resonance (EPR) spectroscopy is likely the most sensitive technique for detection of elements and compounds with unpaired electrons. Typical analyses in the laboratory utilize a fixed microwave frequency and a scanning magnetic field to induce electron spin-state transitions in the sample. The location of the resonant absorption in the scan is a diagnostic property of the material, and the intensity of the signal is proportional to the concentration. We have developed a frequency scan EPR for planetary surface applications where a fixed magnetic field and tunable microwave sources are used to produce these characteristic resonant peaks. Our narrowband spectrometer covers 7.5 to 8.5 GHz at a field strength 2.8 kGauss and is specifically designed for the identification of organic radicals, minerals with radiation-induced defects, and reactive compounds in martian surface samples. Our wideband spectrometer covers 2.0 to 8.0 GHz at a field strength of 1.0 kGauss and is useful for the detection of paramagnetic cations. The detection limit of the narrowband and wideband spectrometers for species with unpaired electrons is 50 PPB and 1 PPM, respectively.