Nuclear Bragg diffraction of synchrotron radiation in yttrium iron garnet

Abstract

Monochromatizationof synchrotron radiation down to about 10 eV at an energy of 14.4 keV has been achieved by double nuclear Bragg diffraction from "Fe-yttrium iron garnet single-crystal films set for the electronically forbidden (200) reflection. The monochromatized y quanta have been analyzed with respect to time delay and capability of resonance absorption. By setting of appropriate energy and time windows a pure beam of resonant y quanta at a rate of about 1 Hz is available.PACS numbers: 76.80.+y, 07.85.+ n, 61.10.Fr y quanta with an energy width of 10 6 to 10 s eV, which is typical for low-lying nuclear states, have a coherence length of 0.2 to 20 m. Thus a highly brilliant beam of such quanta would open new perspectives to experimental y optics. Unfortunately, the usual radioactive sources are monochromatic but not brilliant whereas synchrotron radiation is very brilliant but white.Resonant nuclear diffraction of synchrotron radiation as has been first pointed out by Ruby' is a suitable method to achieve the desired beam, which in addition would have a well-defined time structure and polarization pattern. A first attempt to observe resonant nuclear excitation in Fe has been published by Cohen, Miller, and West.In order to maintain the outstanding brilliance of the synchrotron radiation only coherent reflections come into consideration, i.e. , either grazing-incidence reflec-tions3 or nuclear Bragg and Laue diffraction. 4 5 Obviously the 14.4-keV resonance of Fe is a good choice because the excitation energy is easily available from any synchrotron radiation source which covers the xray range and because the mean life v = 140 ns of the excited state allows the application of delayedcoincidence techniques. Furthermore, the chemistry and crystallography of iron compounds is well known, so that the needed large-size single crystals can be made.While present experience with grazing-incidence antireflection films indicates that four sequential reflections are required in order to obtain the desired suppression of the nonresonant prompt radiation, only two nuclear Bragg reflections will be sufficient if pure nuclear reflections are used. The greatest progress with this technique has been published by Chechin et al. , who reported an enhancement of delayed counts behind an o. -Fe203 single crystal positioned for the I777) pure nuclear reflection.

An X-ray scattering beamline for studying dynamics

“…More recently an IXS instrument at APS has begun to provide results [9,10], and a second beamline for these measurements has been built at ESRF [11]. In the field of nuclear resonant scattering of synchrotron radiation, first work was also done at HASYLAB [12]. However, during the period between this first work and the operation of the NRS beamline at ESRF, pioneering experiments were carried out by many groups working in facilities in Europe, the US and Japan [13].…”

Condensed Matter Physics Using Nuclear Resonant Scattering

“…3) Attempts to observe nuclear resonant excitation with SR were reported in 1978, [4][5][6] and Gerdau et al reported the clear observation of the nuclear Bragg scattering of SR by 57 Fe in a single crystal in 1985. 7) In 1991, nuclear resonant forward scattering by 57 Fe in iron foil in the time domain was observed. 8) This showed that examining polycrystalline samples is meaningful with this method.…”

Synchrotron-radiation-based perturbed angular correlations used in the investigation of rotational dynamics in soft matter

“…18͒ was verified only years later. Here the intense channels of collective, spatially coherent scattering have been investigated first: nuclear Bragg scattering ͑NBS͒ 19 and nuclear forward scattering ͑NFS͒. 20 Both channels rely on recoil-free scattering and break down for f LM ϳ 0.…”