Coherent and Incoherent Mössbauer Scattering Observed by Using a Newly Designed γ-Ray Diffractometer

Nakai, Yutaka; Hirano, Minoru; Ooi, Yoshiharu; Kunitomi, Nobuhiko

doi:10.1143/jpsj.51.929

Cited by 5 publications

(2 citation statements)

References 4 publications

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“…(The overall count rate doubled with the sample in position but with the incident beam blocked from entering the detector.) Our instrument differs from rocking curve diffractometers appropriate for single crystal work [6][7][8][9][10][11][12], or powder diffractometers designed to measure energy spectra [14][15][16]. An earlier version of this instrument was used to make the first measurements of diffraction patterns from polycrystalline bcc 57 Fe [17].…”

Section: Division Of Engineering and Applied Science Mail 138-78 Camentioning

confidence: 99%

Chemical Environment Selectivity in Mössbauer Diffraction from57Fe3Al

Stephens

Fultz

1997

Phys. Rev. Lett.

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Mössbauer diffraction was used to measure different autocorrelation functions for 57 Fe atoms in different chemical environments. The sample was polycrystalline 57 Fe 3 Al with the ordered DO 3 structure. Diffraction peaks from a fcc structure with a doubled unit cell were detected when the incident radiation was tuned to the Mössbauer resonance of the Wyckoff 4(b) Fe site, but not for tuning to the 8(c) site, thereby distinguishing the spatial arrangements of these two Fe sites.[S0031-9007(96)02020-0] PACS numbers: 76.80.+y, 07.85.Nc, 61.10.Eq Most of what we know about atomic arrangements in materials has been learned from diffraction experiments. Three coherent scattering processes have proved useful: scattering of x rays by atomic electrons, scattering of electrons from Coulombic interactions with the electronic and nuclear charge of the atom, and scattering of neutrons from nuclei or magnetic electrons. Some Mössbauer scattering processes are coherent and may be useful for diffraction experiments on materials. Coherent interference between x-ray and Mössbauer scattering was first identified in Mössbauer energy spectra [1,2]. Later experiments with high quality single crystals measured diffraction peaks directly [3][4][5]. These later studies showed that with strong dynamical diffraction there is a suppression of incoherent decay channels such as internal conversion processes, and a large lifetime broadening of peaks in the Mössbauer energy spectra [6][7][8][9][10][11][12].In this Letter, we show a new feature of Mössbauer diffraction that is useful for studies of atomic arrangements in materials-we show that Mössbauer diffraction can measure the autocorrelation function of 57 Fe atoms as a functional of their chemical environment. By working with polycrystalline materials near the kinematical limit of diffraction, the broadening of nuclear energy levels is not severe, so the spectroscopic capabilities of Mössbauer scattering are preserved. The structure of the bcc-based DO 3 structure is shown in Fig. 1. The two sites for the 57 Fe atoms, the Wyckoff 4(b) and 8(c) sites, differ in both their chemical environment (0 versus 4 Al neighbors) and in their spatial arrangement (face-centered cubic, fcc, with lattice parameter 2a 0 versus simple cubic, sc, with lattice parameter a 0 ). In the present experiment, we tuned the incident beam to the hyperfine magnetic field (HMF) of each chemical environment (0 Al and 4 Al), and detected diffraction peaks characteristic of their spatial arrangements (fcc and sc).Pieces of 57 Fe (95% isotopically enriched) and Al metal were arc melted under an argon atmosphere and remelted several times to ensure homogeneity. The 50 mg ingot was then induction melted and splat quenched in high vacuum to obtain a chemically disordered foil of 35 mm thickness. This foil was cold-rolled to a thickness of 3 mm. To obtain DO 3 chemical order, the samples were annealed in evacuated quartz ampoules at 773 K for 6 days, followed by 723 K for 40 days. Xray diffractometry showed ͑ 1 2 1 2 1 2 ͒...

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Section: Division Of Engineering and Applied Science Mail 138-78 Camentioning

confidence: 99%

Chemical Environment Selectivity in Mössbauer Diffraction from57Fe3Al

Stephens

Fultz

1997

Phys. Rev. Lett.

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“…[2][3][4][5][6][7][8][9] In almost all of these studies, a detector was placed at a few angles near a Bragg peak, and an energy spectrum was measured. This was the method used in experiments by Kovalenko et al 10 and Nakai et al 11,12 who measured interference effects between Mössbauer nuclei having different hyperfine fields.…”

Section: Introductionmentioning

confidence: 99%

Mössbauer diffractometry on polycrystalline57Fe3Al

et al. 2002

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A Mössbauer powder diffractometer was used to measure diffraction patterns from polycrystalline foils of 57 Fe 3 Al. The intensities of Bragg diffractions were measured as a function of the energy of the incident photon. The bcc fundamental diffractions showed large changes in intensity as the incident energy was tuned through the nuclear resonances. These variations of diffraction intensity with incident energy were calculated with reasonable success using a kinematical theory of diffraction that included effects of coherent interference between x-ray Rayleigh scattering and, more importantly for these samples, Mössbauer scattering from nuclei having different hyperfine magnetic fields.

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