Two programs with calculate attenuation lengths of various materials using NIST data. And when I say it uses NIST data, it actually scrapes the data from the NIST XCom database with every update so it will need internet access to work. The densities for all elements are held in densities.dat, a pickle file using densities I took from Wikipedia ages ago, so if you're using it for precision work you might want to check they're accurate enough for you. Required Libraries: - pygtk - matplotlib - numpy Tested on python 2.6.5 There are two seperate programs, each using the included nistxcom.py library. ./simple_att_calc.py: A simple program which can be used to calculate single values for attenuation length, absorption efficiency and absorption length (how much material is needed to reduce the X-ray flux by X%) ./attenuation_calc.py: A plotting tool to see how attenuation length changes with respect to incident energies