Adding method for processing isotxs cross sections to XML.

        return p.wait()

    def process_xs(self, overwrite=False, particle='neutron', cwd=None):

        """

        Runs ISOXML on the current set of cross sections

        Parameters

        ----------

        overwrite : bool

            Overwrite the current xs file if True (default False)

        particle : str

            Indicates what particle type the cross section data is.

            One of ('neutron', 'gamma', 'photon')

        Returns

        -------

            Path to the resulting ISOXML file

        """

        if str(self.xs).endswith('xml'):

            return self.xs

        cv.check_value('Particle data', particle, ('neutron', 'gamma', 'photon'))

        if particle in ('gamma', 'photon'):

            p_flag = '-p'

        else:

            p_flag = '-n'

        if cwd is not None:

            cwd = Path(cwd)

        else:

            cwd = Path('.')

        if cwd and not cwd.is_dir():

            msg = ("Specified working directory "

            "doesn't exist: {}".format(cwd))

            raise ValueError(msg)

        # run isoxml executable on the current xs file

        cmd = [self.config.isoxml_exec, p_flag, str(self.xs)]

        p = subprocess.Popen(cmd, universal_newlines=True, cwd=str(cwd))

        p.wait()

        # construct the name of the new xs file and return it

        name_parts = str(self.xs).split('.')

        name_parts[-1] = 'xml'

        xs_name = '.'.join(name_parts)

        return xs_name

    def generate_mesh(self, overwrite=False):

        """

        Generates the mesh for the griffin-problem if needed

        Parameters

        ----------

        overwrite : bool

            Overwrie the current mesh if needed (default False)

            Overwrite the current mesh if True (default False)

        Returns

        -------