O. Leupold

Energy Dependence of Nuclear Recoil Measured with Incoherent Nuclear Scattering of Synchrotron Radiation

The energy dependences of nuclear forward scattering and nuclear 4π scattering of 14.4 keV synchrotron radiation were studied with an energy resolution of 6 meV. Nuclear 4π scattering resulted from internal conversion and therefore represents the energy dependence of resonant nuclear absorption. In the case of the [57Fe(bpp)2][BF4]2 sample the energy dependence of nuclear 4π scattering revealed a 13 meV inelastic broadening of the absorption line. This indicates an excitation of lattice motions in the nuclear absorption process. The technique allows the direct measurement of the energy distribution of nuclear recoil.

Broad-Band Nuclear Resonant Filters for Synchrotron Radiation: a New Source for Nuclear Diffraction Experiments

A grazing incidence antireflection film (GIAR film) containing 57Fe has been used as a broad-band filter in a nuclear-diffraction experiment with synchrotron radiation. A band of 0.5 μeV width has been reflected by the GIAR film consisting of a 57Fe5B4C-layer on a Ta-backing. The electronic reflectivity was reduced to 0.04. The diffracted beam was analysed by the (333) pure nuclear reflection of 57FeBO3. A counting rate of delayed quanta of 8 Hz was obtained. The experiment proves that coherent excitation of hyperfine split nuclear levels took place after a GIAR film reflection.

Fast Switching of Nuclear Bragg Scattering of Synchrotron Radiation by a Pulsed Magnetic Field

The time dependence of perturbed nuclear Bragg scattering of synchrotron radiation by a 57FeBO3 crystal was studied. The perturbation was an abrupt rotation by 90° of the hyperfine fields in the crystal effectuated by fast switching of an external magnetic field. This perturbation did not destroy the coherence. It transformed the nuclear transitions and caused, therefore, dramatic changes in the time evolution. A new quantum beat pattern of different frequency was immediately established after switching. The intensity and decay rate of the re-emitted radiation sensitively depended on the moment of switching. The frequency of the original beat pattern was restored by switching back.

Nuclear Bragg Diffraction of Synchrotron Radiation in the Presence of Acoustic Vibrations

The time evolution of nuclear Bragg diffraction of 14.4 keV synchrotron radiation in a 57FeBO3 crystal was studied when the crystal was excited to magnetoelastic vibrations by a r.f. field of 2.93 MHz. The vibrations did not modify the time evolution of the diffraction. This result is due to the fact that after the excitation by the SR pulse the nuclear vibrations cause only a phase modulation of the re-emitted radiation. Energy spectra, by contrast, are extremely sensitive to vibrations. Thus the present case is an instructive example of complementarity between energy and time domain Mossbauer spectroscopy. Time domain spectroscopy, in particular, will allow to reveal phenomena, which are blurred in the energy spectra by vibrations.

Ultrasound-induced echoes and quantum beats observed in the nuclear exciton decay utilizing synchrotron radiation

Abstract The time evolution of the free decay of the nuclear exciton induced by E = 14.413 keV synchrotron radiation pulses was observed with a system of two stainless-steel absorbers containing 57 Fe. In between these foils the radiation was Bragg scattered from a vibrating quartz crystal. The ultrasound modulated radiation field leads to echo-spikes or echo-dips in the decay of the nuclear exciton. In case of relative Doppler motion between both foils with a constant velocity we observe quantum beats that are concentrated in the echoes.