小中大需要精修峰形不对称 see third figure - single peak。
S/L = Axial Divergence S term H/L = Axial Divergence H term
typical value 0.020 depend on instrument
reference
cuturl('http://www.aps.anl.gov/Xray_Scie') ... rametersRecipes.pdf
cuturl('https://wiki-ext.aps.anl.gov/ug11bm/index.php/GSAS_Profile_Terms')
For more info see: "Typical values of Rietveld instrument profile coefficients" Kaduk J, Reid J. Powder Diffraction (2011) vol. 26 pp. 88