W. Sturhahn

Nuclear Bragg Diffraction of Synchrotron Radiation at the 8.41 keV Resonance of Thulium

For the first time nuclear Bragg diffraction of synchrotron radiation at the 8.41 keV resonance of 169Tm was observed. Time differential measurements were performed with the pure nuclear (424) reflection of a thulium iron garnet single crystal. The dynamical theory of Mossbauer optics is applied to evaluate the time spectra. The measurements reveal information about the hyperfine fields which has not been accessible before by conventional Mossbauer spectroscopy with polycrystalline samples.

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.

A high resolution spectrometer using nuclear Bragg diffraction

A high resolution spectrometer for synchrotron radiation using nuclear Bragg diffraction has been constructed at a DORIS beamline (DESY, Hamburg). This spectrometer provides a γ-ray beam for hyperfine spectroscopy and for other application which need high resolution in energy and/or time.

Nuclear Bragg diffraction using synchrotron radiation A new method for hyperfine spectroscopy

Abstract Nuclear Bragg diffraction with synchrotron radiation as source will become a powerful new X-ray source in the A region. The brilliance of conventional Mossbauer sources is already exceeded; giving hyperfine spectroscopy a further impulse. As examples applications to yttrium iron garnet (YIG) and iron borate will be discussed.

Nuclear Resonant Filtering of Synchrotron Radiation by Grazing-Incidence Antireflection Films

Coherent nuclear diffraction of synchrotron radiation has been observed from grazing-incidence antireflection films (GIAR films) containing 57Fe. These films, which consisted of polycrystalline 57FeCrNi on a Pd backing, reduced the electronic reflectivity to 710-4. Nuclear reflection of the resonant photons led to a counting rate of ≈ 0.05 Hz of delayed quanta. The measurements show that nuclear resonant filtering of synchrotron radiation by GIAR films is possible.

Nuclear Bragg diffraction using synchrotron radiation — A new method for hyperfine spectroscopy

Nuclear Bragg diffraction with synchrotron radiation as source will become a powerful new X-ray source in the Å-region. This source exceeds by now the brilliance of conventional Mössbauer sources giving hyperfine spectroscopy further momentum. As examples applications to yttrium iron garnel (YIG) and iron horate will be discussed.

Dependence of nuclear diffraction on the azimuthal angle: (002)- and (0010)-reflections of YIG

Nuclear diffraction of synchrotron radiation has been investigated using YIG single crystals in different scattering geometries. Time resolved quantum beat spectra of pure nuclear (002) and (0010) Bragg reflections were observed in a set-up where the hyperfine interaction was kept constant, while the azimuthal angle in the (001) surface between the [100] axis and the scattering plane (kin,kout) was varied. The time spectra were analyzed by means of the dynamical theory for coherent nuclear scattering. The results revealed the high sensitivity of this experimental technique on the complete set of hyperfine interaction parameters and on the specific geometrical conditions for nuclear diffraction of polarized γ-rays.

Determination of directions of internal fields in BaFe12O19

Mössbauer-absorption measurements were carried out on single crystals and polycrystalline samples of BaFe12O19 (BaM). This material has an easy axis of magnetization along the c axis. At the iron 12k site a deviation of the directions of the internal fields from the c axis is shown. Both the EFGs and the magnetic dipole fields at the iron 12k site form an ‘umbrella’ around the c axis.

Shaping of Nuclear Bragg Reflected SR-Pulses by Broad Resonance Absorbers

Time and energy spectra have been studied of Mossbauer filter systems consisting of a pure nuclear reflection 3FeBO57(333) in connection with a broad resonance absorber. The energy spectra show how much of each line of the multiplet has been absorbed. The corresponding time spectra show the modified quantum beats to be expected from this, and also display risetime effects revealing the absorbers action. Part of the motivation is to produce simpler wave packets suitable for subsequent analysis of 57Fe-containing materials.

Magnetic interaction in Tm3Fe5O12 studied by means of169Tm and57Fe Mössbauer spectroscopy

The temperature dependence of the hyperfine parameters of thulium iron garnet (Tm3Fe5O12) powder was studied from 90 to 550 K using169Tm and57Fe Mössbauer spectroscopy (MB). The spectra were analyzed by least mean square fits to the transmission function. The temperature dependence of the magnetic fields of the thulium nuclei is well described by the mean field model. The coupling constants between the magnetic lattice occupied by the thulium atoms and the magnetic lattices occupied by the iron atoms were derived.