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Particle Induced X Ray Emission and Mars Exploration Rovers. Alpha Particle X-ray Spectrometry. APXS uses a variety of radiation techniques to determine atomic nuclei mass Alpha particle Protons X-Ray Radioactive Currium is used as the alpha particle source. Photo of Mars Pathfinder
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Alpha Particle X-ray Spectrometry • APXS uses a variety of radiation techniques to determine atomic nuclei mass • Alpha particle • Protons • X-Ray • Radioactive Currium is used as the alpha particle source Photo of Mars Pathfinder with APXS highlighted in red
Alpha Particles • Alpha particles (4He) are emitted from Curim source • Using Rutherford’s laws for backscattering, the atomic mass of the nuclei can be determined • Lighter elements absorb energy of alpha particle • Heavier elements reflect energy of alpha particle of the same energy • Most useful in determining lighter elemental composition of a sample
Protons • Alpha particles are absorbed by atomic nuclei producing protons of a defined energy • Sodium, magnesium, silicon, aluminum, and sulfur detection • Used only by Mars Pathfinder, subsequent Mar Exploration Rovers did not use
Particle Induced X-Ray Emission • Alpha particles ejected electrons from the inner electron shell (K or L shell) • K series: ejection from K shell • L series: ejection from L shell • Outer shell electrons drop down to fill vacancies, but only certain transitions are allowed. • Energy emitted.
Particle Induced X-Ray Emission • Energy emitted is characteristic of an element E = Energy difference between shells Wavelength= K/E where E is the energy emitted & K is a constant = 1.9865 x 10-16 nm J • The number and energy of X ray emitted are measured
Results • Rock sample from Barnacle Bill in Ares Vallis on Mars • Unexpectedly high in silica and potassium; low in magnesium compared tomartian soils and martian meteorites. • Analysis indicates that sample rocks are andesitic (volcanic)
Advantages • Compact • Low power • Non destructive to sample • High sensitivity • High resolution (especially for heavier elements) Disadvantages • Slower than other available methods • Use of radioactive material