nd fractional masses.

        Parameters
        ----------
        name : `str`
            Name of the meterial
        fractional_masses : `dict`
            The element and fractional masses of the material e.g. `{&#39;H&#39;: 0.031, &#39;O&#39;: 0.969}`
        thickness : `astropy.units.Quantity`
            Thickness of the material
        density : `astropy.units.Quantity`
            Density of the material

        Returns
        -------
        `roentgen.absorption.material.Material`
         