  The possibility to control the coherent decay of resonant excitations in
nuclear forward scattering is investigated. By changing abruptly the direction
of the nuclear hyperfine magnetic field, the coherent scattering of photons can
be manipulated and even completely suppressed via quantum interference effects
between the nuclear transition currents. The efficiency of the coherent decay
suppression and the dependence of the scattered light polarization on the
specific switching parameters is analyzed in detail. Using a sophisticated
magnetic switching sequence involving four rotations of the hyperfine magnetic
field, two correlated coherent decay pulses with different polarizations can be
generated out of one excitation, providing single-photon entanglement in the
keV regime. The verification of the generated entanglement by testing a
single-particle version of Bell's inequality in an x-ray optics experimental
setup is put forward.
