code: def make_energies_hdu(self, extname="ENERGIES"):
          
          if self._evals is None:
              return None
          cols = [fits.Column("ENERGY", "1E", unit='MeV',
                              array=self._evals)]
          hdu = fits.BinTableHDU.from_columns(
              cols, self.make_header(), name=extname)
          return hdu
docs: Builds and returns a FITs HDU with the energy bin boundries
  
          extname   : The HDU extension name