Physics
NIST:
Tables of X-Ray Mass Attenuation Coefficients and Mass Energy-Absorption Coefficients from 1 keV to 20 MeV for Elements Z = 1 to 92
https://www.nist.gov/pml/x-ray-mass-attenuation-coefficients
http://physics.nist.gov/PhysRefData/XrayMassCoef/tab4.html