In situ analysis of rock chemistry is a fundamental tool for exploration of planets. To meet this need, a high-spatial- resolution micro x-ray fluorescence (Micro-XRF) instrument was developed that is capable of determining the elemental composition of rocks (elements Na–U) with 100 μm spatial resolution, thus providing insight to the composition of features as small as sand grains and individual laminae. The resulting excitation beam is of sufficient intensity that high signal-to-noise punctual spectra are acquired in seconds to a few minutes using an Amptek Silicon Drift Detector (SDD).

Two views of the breadboard Micro-XRF Instrument, which includes a Peltier-cooled detector with electronics, Moxtek HVPS, and x-ray tube integrated with an XOS polycapillary optic, a camera, and a focused laser.
The instrument features a tightly focused x-ray tube and HVPS developed by Moxtek that provides up to 200 μA at 10 to 50 keV, with a custom polycapillary optic developed by XOS Inc. and integrated into a breadboard Micro-XRF (see figure). The total mass of the complete breadboard instrument is 2.76 kg, including mounting hardware, mounting plate, camera, laser, etc. A flight version of this instrument would require less than 5W nominal power and 1.5 kg mass.

The instrument includes an Amptek SDD that draws 2.5 W and has a resolution of 135 to 155 eV FWHM at 5.9 keV. It weighs 180 g, including the preamplifier, digital pulse processor, multichannel analyzer, detector and preamp power supplies, and packaging. Rock samples are positioned relative to the instrument by a three-axis arm whose position is controlled by closed-loop translators (mimicking the robotic arm of a rover). The distance from the source to the detector is calculated from the position of a focused laser beam on the sample as imaged by the camera. The instrument enables quick scans of major elements in only 1 second, and rapid acquisition (30 s) of data with excellent signal-to-noise and energy resolution for trace element analysis.

This work was done by Lawrence A. Wade, Robert P. Hodyss, and Abigail C. Allwood of Caltech; Ning Gao of XOS; and Kris Kozaczek of Moxtek for NASA’s Jet Propulsion Laboratory. NPO-48599