DATA BASES
NIST: National Institute of Standards and Technology
http://www.cstl.nist.gov/nist839/839.01/index.html
NIST: Scientific and Technical Databases
http://www.nist.gov/srd/
NIST: X-ray Attenuation Coefficients
http://physics.nist.gov/PhysRefData/XrayMassCoef/cover.html
X-Ray Periodic Tables
http://csrri.iit.edu/periodic-table.html