A silicon (840) channel-cut crystal with a large asymmetry is used to linearly polarize synchrotron radiation generated by an undulator source at the 14.413 keV nuclear resonance of 57Fe. The resulting σ̂-polarized radiation is then scattered from an 57Fe foil placed in a magnetic field that effects σ̂→π̂ polarization conversion within the resonant bandwidth. A second crystal of the same type is placed in a crossed position to suppress the nonresonant radiation while transmitting the π̂-polarized resonant radiation. A polarization suppression factor of 6×10−7 has been obtained. The suppression of the nonresonant radiation allowed monitoring the decay of the nuclear levels after 1 ns of their excitation.
A coherently excited nuclear state in a rotating sample acquires a phase shift during its time evolution that is proportional to its angular momentum and the rotation angle. As a consequence, the radiative decay of the excited state proceeds into the rotated direction, and the time spectrum of the nuclear decay is mapped onto an angular scale. This effect has been observed in nuclear resonant scattering of synchrotron radiation from a 57Fe metal foil rotating at 18 kHz.
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