The decay rate of 57 Fe nuclei in an 57 FeBO 3 crystal excited by 14.4 keV synchrotron radiation pulses was controlled by switching the direction of the crystal magnetization. Abrupt switching some nanoseconds after excitation suppresses the coherent nuclear decay. Switching back at later times restores it, starting with an intense radiation spike. The enhanced delayed reemission is due to the release of the energy stored during the period of suppression. Suppression and restoration originate from drastic changes of the nuclear states and of the interference within the nuclear transitions.
PACS.76.80 + y -Mossbauer effect; other gamma-ray spectroscopy.
PACS.07.85-m -Xand gamma-ray instruments and techniques. PACS. 63.20-e -Phonons and vibrations in crystal lattices.
Asymmetric nuclear-resonance broadening, as originating, e.g., from magnetic-hyperfine-field distributions in magnetic alloys, has strong effects on the time evolution of nuclear forward scattering of synchrotron radiation. In thin samples of an Invar alloy, resonance broadening and the resulting dephasing in time cause a fast decay of the coherent scattering signal. In thick samples, the asymmetry of the broadening strongly affects dynamical scattering. Quantum beat and dynamical beat blend into a fast hybrid beat with thickness dependent period and field distribution sensitive modulation.
Our diffraction enhanced images represent the first radiographic detection of the structural orientation in cartilage. Our data are in line with previous studies on the structural organization of joint cartilage. They confirm the model of a vaulting system of collagen fiber bundles interrupted by proteoglycan aggregates.
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