Alpha-particle X-ray spectrometer

All Mars rovers to date have carried alpha-particle X-ray spectrometer (APXS) instruments for chemical analyses of rocks and soils (see Fig. 13.16). The source consists of radioactive curium, which decays with a short half-life to produce a-particles, which then irradiate the sample. Secondary X-rays characteristic of specific elements are then released and measured by a silicon drift detector. The Mars Pathfinder APXS also measured the backscattered a-particles, for detection of light elements, but the Mars Exploration Rovers measured only the X-rays. 

---

MIMOS lla is an advanced version of the MER instruments (Klingelhofer et al. 2003) operating continuously since landing in January 2004. A new detector system has been implemented, inherited from the Alpha Particle X-ray Spectrometer (APXS), also part of the MER payload. This Si Drift Detector system provides higher energy resolution and increased... 

Ming, D.W. et al. 2008. Geochemical Properties of Rocks and Soils in Gusev crater, Mars Results of the Alpha Particle X-ray Spectrometer from Cumberland Ridge to Home Plate. Journal of Geophysical Research, 113, E12S39,... 

The Mars Pathfinder rover carried an Alpha Proton X-ray Spectrometer (APXS), and the two Mars Exploration Rovers (MER - Spirit and Opportunity) carried Alpha Particle X-ray Spectrometers (also called APXS, but in this case more precise versions of the Pathfinder instrument, though without the ability to monitor protons for light element analyses). These instruments contained radioactive curium sources (Fig. 13.16) whose decay produced a-particles, which irradiated target rocks and soils. The resulting characteristic X-rays provided measurements of major and minor element abundances. The MER rovers also carried Mossbauer spectrometers, which yielded information on iron oxidation state. 

Gellert, R., Rieder, R., Briickner, J. et al. (2006) The Alpha Particle X-Ray Spectrometer (APXS) results from Gusev crater and calibration report. Journal of Geophysical Research, 111, E02S05, doi 10.1029/2005JE002555. 

Rieder, R., Gellert, R., Anderson, R. C. et al. (2004) Chemistry of rocks and soils at Meridiani Planum from the alpha particle X-ray spectrometer. Science, 306, 1746-1749. 

Figure 12.16 Alpha particle X-ray spectrometer (APXS). To determine the elemental composition of rocks and soils of Martian surface, the rovers, which landed in 2004 on Mars, carry a deployment device that could be in contact with the rocks. The sensor head contains six Cm radioactive sources, six alpha detectors and one X-ray detector in the centre. The accumulation time is a few hours per sample analysed.

X-rays can be emitted from a sample by bombarding it with electrons, alpha particles, or with other X-rays. When electrons or alpha particles are used as the excitation source, the process is called X-ray emission or particle-induced X-ray emission (PIXE). This is the basis of X-ray microanalysis using an electron microprobe (Chapter 14) or an SEM. An alpha particle X-ray spectrometer (APXS) is currently on the Mars Curiosity rover collecting data on Martian rock composition. 

Fig. 2.47 The scientific payioad of the Mars Expioration Rovers consists of the remote sensing Panoramic Camera (Pancam) and the Miniature Thermai Emission Spectrometer Mini-TES) the in situ or contact instruments Microscopic Imager (Ml), Alpha Particle X-ray Spectrometer (APXS), Mossbauer spectrometer (MB), and the Rock Abrasion Tool (RAT) the Magnetic Properties Experiment (NASA/JPL/Comeii) [77]...

RGURE 12-13 Energy-dispersive X-ray fluorescence spectrometer. Excitation by X-rays from (a) an X-ray tube and (b) a radioactive substance (curium-244, a 5.81 MeV alpha particle and X-ray source) as shown in the sensor head for the Mars alpha proton X-ray spectrometer. The X-ray detector is a new room-temperature type. (Reprinted with permission from R. Gellert et al., J. Geophys. Res. 2006. 111. E02S05.)... 

RBS can provide absolute quantitative analysis of elemental composition with an accuracy of about 5%. It can provide depth-profile information from surface layers and thin films to a thickness of about 1 pm. In some cases, however, the high-energy beam can damage the surface. This is particularly a problem with insulating materials, such as polymers, alkali halides, and oxides. The Mars Pathfinder mission in 1997 contained an alpha proton X-ray spectrometer (APXS). In its RBS mode, the spectrometer bombarded samples with alpha particles and determined elemental composition via energy analysis of the backscattered particles. In addition to RBS, the APXS instrument was designed to carry out proton emission and particle-induced X-ray emission (PIXE) experiments. Soil and rock compositions were measured and compared to those from the earlier Viking mission. 

Curium may be used as a thermoelectric power source (a never-ending battery) for space flights. Curium was also the alpha particle source for the Alpha Proton X-Ray Spectrometer on Mars. 

Microscopic Imager Alpha Particle X-ray Spectr. Mossbauer Spectrometer Rock Abrasion Tool... 

The Curiosity rover has a whole suite of chemistry tools on board. The laser-induced breakdown spectroscopy (LIBS) tool is probably the coolest. This instrument breaks down rocks and bits of soil by firing a (freaking) laser at the target. The elements that made up that rock are then detected by atomic emission spectroscopy. Curiosity also contains an alpha particle (He + ion) X-ray spectrometer (APXS), which is also used to measure what elements make up a sample. If the NASA scientists want to know more... 

---