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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _spectrum(self, photon_energy):
 """Compute differential bremsstrahlung spectrum for energies in ``photon_energy``. Parameters photon_energy : :class:`~astropy.units.Quantity` instance Photon energy array. """


        Eph = _validate_ene(photon_energy)

        spec = self.n0 * (
            self.weight_ee * self._emiss_ee(Eph)
            + self.weight_ep * self._emiss_ep(Eph)
        )

        return spec