High resolution monochromators for spectroscopy at high-energy Mössbauer transitions at the Dynamics Beamline P01

Monochromatization of x-rays with high energy resolution is a vital demand for several structure and dynamics investigation techniques in condensed matter. High-efficient monochromatization is a key point for experiments with nuclear resonant scattering of synchrotron radiation since such experiments rely on high narrow band photon flux. Particularly, the monochromatization becomes more challenging for the studies of Mössbauer transitions with the energies 30-80 keV when the spectral reflectivity of silicon crystals becomes low.A free choice of the selected energy together with high energy resolution can be achieved by backscattering from a low symmetry crystal, in particular, from an Al2O3 sapphire crystal [1]. Due to the lower crystal symmetry and higher Debye-Waller factor of Al2O3 as compared to silicon, sapphire crystals provide a wide choice of energies and higher spectral reflectivity at high photon energies. In backscattering geometry the temperature of the crystal defines the interplanar distances in the crystal and the energy of the reflected photons. The dynamical theory of x-ray scattering predicts the energy width of the back-reflections, ~0.1-3 meV, in an ideal sapphire single crystal in the 5-100 keV energy range. Thus, in order to maintain such high resolution the temperature of the crystal should be tuned with a relative precision of 0.1-1 mK in the 120-400 K temperature range, respectively [2,3,4]. Here, we present the backscattering monochromator developed and installed at the Dynamics Beamline P01 at PETRA III. The monochromator consists of a flow cryostat with sub-mK temperature stability hosting a high-quality sapphire crystal. The efficiency of the monochromator has been tested with nuclear resonance scattering on 119Sn at 23.88 keV. An energy resolution of 1.4 meV has been obtained. The monochromator is suitable for nuclear inelastic scattering experiments at transitions energies from 20 to 50 keV , e.g., 151Eu at 21.5 keV, 125Te at 35.5 keV, 121Sb at 37.1 keV 129Xe at 39.6 keV.The nuclear resonances with transitions at 60-80 keV can be studied by other techniques which profits from the lower x-ray absorption of silicon detectors in this energy range [5]. By means of this technique we report on the first observation of nuclear resonance scattering on 193Ir at 73.04 keV and discuss first scientific applications on iridate compounds.[1] Yu. V. Shvyd’ko, X-Ray Optics, Springer Ser. Optical Science, V.98 (2004)[2] M. Lucht, M. Lerche, H.-C. Wille et al., J. Appl. Cryst. V.36 (2003), p. 1075[3] I. Sergueev, H.-C. Wille, R.P. Hermann et al., J. Synch. Rad. V.18 (2011), p.802[4] B. Klobes, A. Desmedt, I. Sergueev et al., Europhys. Lett., V.103 (2013), p.36001[5] D. Bessas, D.G. Merkel, A.I. Chumakov et al. Phys. Rev. Lett. 113 (2014), p.14760

Notes for genera – Ascomycota

Knowledge of the relationships and thus the classification of fungi, has developed rapidly with increasingly widespread use of molecular techniques, over the past 10--15 years, and continues to accelerate. Several genera have been found to be polyphyletic, and their generic concepts have subsequently been emended. New names have thus been introduced for species which are phylogenetically distinct from the type species of particular genera. The ending of the separate naming of morphs of the same species in 2011, has also caused changes in fungal generic names. In order to facilitate access to all important changes, it was desirable to compile these in a single document. The present article provides a list of generic names of Ascomycota (approximately 6500 accepted names published to the end of 2016), including those which are lichen-forming. Notes and summaries of the changes since the last edition of `Ainsworth Bisby's Dictionary of the Fungi' in 2008 are provided. The notes include the number of accepted species, classification, type species (with location of the type material), culture availability, life-styles, distribution, and selected publications that have appeared since 2008. This work is intended to provide the foundation for updating the ascomycete component of the ``Without prejudice list of generic names of Fungi'' published in 2013, which will be developed into a list of protected generic names. This will be subjected to the XIXth International Botanical Congress in Shenzhen in July 2017 agreeing to a modification in the rules relating to protected lists, and scrutiny by procedures determined by the Nomenclature Committee for Fungi (NCF). The previously invalidly published generic names Barriopsis, Collophora (as Collophorina), Cryomyces, Dematiopleospora, Heterospora (as Heterosporicola), Lithophila, Palmomyces (as Palmaria) and Saxomyces are validated, as are two previously invalid family names, Bartaliniaceae and Wiesneriomycetaceae. Four species of Lalaria, which were invalidly published are transferred to Taphrina and validated as new combinations. Catenomycopsis Tibell Constant. is reduced under Chaenothecopsis Vain., while Dichomera Cooke is reduced under Botryosphaeria Ces. De Not. (Art. 59)