def _sigma_ee_rel(self, gam, eps):
        """
        Eq. A1, A4 of Baring et al. (1999)
        Use for Ee > 2 MeV
        """
        A = 1 - 8 / 3 * (gam - 1) ** 0.2 / (gam + 1) * (eps / gam) ** (
            1.0 / 3.0
        )

        return (self._sigma_1(gam, eps) + self._sigma_2(gam, eps)) * A