Added function to interpolate the mass attenuation coefficient from data from [NIST](https://dx.doi.org/10.18434/T4D01F). Also added documentation for density values. Commit: [4308cad](https://github.com/LIBRA-project/BABY-1L-run-6/pull/5/commits/4308cad7f087ceed991fa78bbf2b5ec824d7bca2) _Originally posted by @cdunn314 in https://github.com/LIBRA-project/BABY-1L-run-6/pull/5#discussion_r2224131812_
Added function to interpolate the mass attenuation coefficient from data from NIST. Also added documentation for density values. Commit: 4308cad
Originally posted by @cdunn314 in LIBRA-project/BABY-1L-run-6#5 (comment)