Particle Induced X Ray Emission and Mars Exploration Rovers

1. Particle Induced X Ray Emission and Mars Exploration Rovers

2. 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 http://www.seds.org/spaceviews/pathfinder/images.html

3. 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

4. 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

5. 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.

6. Particle Induced X-Ray Emission • Energy emitted is characteristic of an element • E = Energy difference between shells • Λ= 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

7. 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)

8. 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