Nuclear Bragg scattering of synchrotron radiation with strong speedup of coherent decay, measured on antiferromagnetic57FeBO3

A strongly speeded-up decay of a collective nuclear excitation has been observed in pure nuclear resonance diffraction of synchrotron-radiation pulses by a perfect single crystal of antiferromagnetic ${}_{}{}^{57}{}_{}{}^{}\mathrm{FeBo}_3^{}{}_{}{}^{}$. Superimposed appeared a quantum-beat spectrum exhibiting the interference of four hyperfine transitions. The angular dependence of the time spectrum was verified with measurements above, below, and at the exact Bragg position. The off-Bragg measurements reveal sensitively the weak quadrupole interaction in ${}_{}{}^{57}{}_{}{}^{}\mathrm{FeBO}_3^{}{}_{}{}^{}$. .AE