The tables are from the article
X-Ray Interactions: Photoabsorption, Scattering, Transmission, and Reflection at E=50-30.000eV, Z=1-92
B.L.Henke, E.M.Gullikson and J.C.Davis
Center for X-Ray optics, lawrence Berkeley Laboratory, California 94720
At the time of writing, three materials are used in SynRad, and their respective tables are included here:
Aluminium:
Aluminium Oxide:
Copper: