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The article demonstrates a new method of performing synchrotron Mössbauer spectroscopy (SMS) that involves using a high-speed periodic shutter near the focal spot of a microfocused X-ray beam. It discusses the time-domain measurement of results that prove the principle of the method and improvements to deliver a pure beam of photons with unavailable spectral brightness. It also notes that the method improves signal rates and suppress electronic scattering by orders of magnitude.

We have built a high-energy-resolution monochromator for nuclear resonant scattering from the 9.4 keV nuclear transition of [sup 83]Kr. The monochromator consists of two highly asymmetric silicon single crystals arranged in a dispersive geometry and produces an energy bandwidth of 2.3 meV. This monochromator has been successfully used for a study of nuclear forward scattering and nuclear resonant inelastic scattering from a [sup 83]Kr sample that was solidified in a diamond anvil cell at 2.15 GPa and room temperature. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The time response of resonant nuclei in a rotating sample coherently excited by synchrotron radiation pulses maps to an angular scale. At sufficiently high rotational speeds, the temporal evolution of the nuclear decay can be recorded with a position sensitive detector. This has been demonstrated by nuclear resonant scattering of synchrotron radiation from a [sup 57]Fe metal foil rotating at 10 kHz. The method has the potential to yield time resolutions of a few 10 ps, thus overcoming principal limits of existing techniques. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The 57Fe phonon partial density of states (PDOS) in L12-ordered Pd3Fe was studied at high pressures by nuclear resonant inelastic x-ray scattering (NRIXS) measurements and density functional theory (DFT) calculations. The NRIXS spectra showed that the stiffening of the 57Fe PDOS with decreasing volume was slower from 12 to 24 GPa owing to the pressure-induced Invar transition in Pd3Fe, with a change from a high-moment ferromagnetic (FM) state to a low-moment (LM) state observed by nuclear forward scattering. Force constants obtained from fitting to a Born-von Kármán model showed a relative softening of the first-nearest-neighbor (1NN) Fe-Pd longitudinal force constants at the magnetic transition. For the FM low-pressure state, the DFT calculations gave a PDOS and 1NN longitudinal force constants in good agreement with experiment, but discrepancies for the high-pressure LM state suggest the presence of short-range magnetic order. [ABSTRACT FROM AUTHOR]

In the first known kinetic application of the technique, synchrotron 57Fe-Mo¨ssbauer spectroscopy was used to follow the rate of heterogeneous electron transfer between aqueous reagents and a solid phase containing Fe. The solid, a synthetic 57Fe-enriched Fe(III)-bearing pyroaurite-like phase having terephthalate (TA) in the interlayer [Mg3Fe(OH)8(TA)0.5 · 2H2O], was reduced by Na2S2O4 and then reoxidized by K2Cr2O7 by means of a novel flow-through cell. Synchrotron Mo¨ssbauer spectra were collected in the time domain at 30-s intervals. Integration of the intensity obtained during a selected time interval in the spectra allowed sensitive determination of Fe(II) content as a function of reaction time. Analysis of reaction end member specimens by both the synchrotron technique and conventional Mo¨ssbauer spectroscopy yielded comparable values for Mo¨ssbauer parameters such as center shift and Fe(II)/Fe(III) area ratios. Slight differences in quadrupole splitting values were observed, however. A reactive diffusion model was developed that fit the experimental Fe(II) kinetic data well and allowed the extraction of second-order rate constants for each reaction. Thus, in addition to rapidly collecting high quality Mo¨ssbauer data, the synchrotron technique seems well suited for aqueous rate experiments as a result of the penetrating power of 14.4 keV X-rays and high sensitivity to Fe valence state. [Copyright &y& Elsevier]

We have observed coherent nuclear resonant scattering of synchrotron radiation at the 22.5-keV resonance of (149)Sm. High-speed rotational sample motion led to an angular deflection of the resonantly scattered radiation off the nonresonant primary beam. This allowed us to determine the resonance energy of the first excited nuclear level of (149)Sm to be 22496(4) eV. Because of the angular deflection of the resonant photons, time spectra of coherent nuclear resonant scattering can be recorded as a function of a spatial coordinate. Time resolutions of a few 10 ps can be expected, which are beyond the limits of existing x-ray detection schemes.

The wavelength of the 57Fe Mössbauer radiation is measured with a relative uncertainty of 0.19 ppm by using almost exact Bragg backscattering from a reference silicon crystal. Its value is determined as lambda(M) = 0.860 254 74(16)x10(-10) m. The corresponding Mössbauer photon energy is E(M) = 14 412.497(3) eV. The wavelength of the 57Fe Mössbauer radiation is easily reproducible with an accuracy of at least 10(-11)lambda(M) and could be used as a length standard of atomic dimensions.