Induced X Ray Emission
- APXS uses a variety of radiation techniques to determine
- Alpha particle
- Radioactive Currium is used as the alpha particle source
Photo of Mars Pathfinder
with APXS highlighted in red
- Alpha particles (4He) are emitted from Curim source
- Using Rutherford’s laws for backscattering, the atomic mass of
nuclei can be determined
- Lighter elements absorb energy of alpha particle
- Heavier elements reflect energy of alpha particle of the same
- Most useful in determining lighter elemental composition of a
- Alpha particles are absorbed by atomic nuclei producing protons
- Sodium, magnesium, silicon, aluminum, and sulfur detection
*Used only by Mars Pathfinder, subsequent Mar Exploration Rovers did
- Alpha particles ejected electrons from
the inner electron shell (K or L
- K series: ejection from K shell
- L series: ejection from L shell
- Outer shell electrons drop down to
fill vacancies emitting
- Only certain
transitions are allowed.
- Energy emitted is characteristic of an element:
where E is the energy emitted & K
is a constant = 1.9865 x 10-16 nm
- The number and energy of X ray emitted are measured
- Rock sample from Barnacle Bill in Ares Vallis on Mars
- Unexpectedly high in silica and potassium; low in magnesium
martian soils and martian meteorites.
- Analysis indicates that sample rocks are andesitic
Barnacle Bill on Mars exhibiting a
diverse chemical composition (Reider 1997).
A. Turkevich, J. Crisp, J.
Brückner, G. Dreibus, H. Y. McSween Jr. "The
of Martian Soil and Rocks Returned by the Mobile Alpha Proton X-ray
Spectrometer: Preliminary Results from the X-ray Mode."