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Stability Requirements

XAS at NSLS-II. Stability Requirements. Paul Northrup April 19, 2007. Environmental Research and Technology Division. EXAFS data requirements. 1000 eV scan range Data can be influenced by 0.1% change in signal. Ravel. EXAFS experiment. Ravel.

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Stability Requirements

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  1. XAS at NSLS-II Stability Requirements Paul Northrup April 19, 2007 Environmental Research and Technology Division

  2. EXAFS data requirements 1000 eV scan range Data can be influenced by 0.1% change in signal Ravel

  3. EXAFS experiment Ravel • Ideal experiment not sensitive to stability • Uniform sample, energy calibration reference • Challenging real-world experiment sensitive to stability • Non-uniform sample, no transmitted beam, etc.

  4. Non-uniform samples Low-concentration heterogeneous samples: • Beam motion changes signal due to variations in • composition • matrix • particle distribution • surface irregularities

  5. Maximum tolerable beam motion? For random distribution of particles: • Function of particle size, • Number of particles in beam spot for a given concentration • Probability that a certain degree of motion will result in a 0.1% change in signal • For 1x1mm beam spot at low concentration: 5 microns

  6. Positional stability requires… 1) Aperture close to sample, overfilled by 10% 2) Source stability within 10% of source size and divergence 3) Monochromator (and optics) output position and angle must be stable over 1000 eV scan

  7. Energy stability (repeatability) requirements XANES Data: • High-resolution XANES requires stability within 0.05-0.1 eV • K edges: P, Cl, Cr, Mn, As, Se… • L edges: Cd, Sb, Mo… • M edges: Yb, Au, Hg, U… P K-edge XANES

  8. Energy stability/repeatability Is a function of: • Source angular stability (vertical) incident to mono • requires 1 microrad • Monochromator repeatability and angular stability • fixed exit position and angle Can be achieved by: • Beamline monochromator design • Appropriate for each source type (Damping Wiggler, 3-pole, Soft Bend) • Beamline feedback system (vertical angle/position) • For example, NSLS X15B achieves 0.1 eV, 10 micron stability on less-stable source

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