Speaker
Description
Clathrate hydrates are are crystalline water-based solids (similar to ice), which form cages that are able to host guest molecules. The guests are trapped in cavities of the hosts, that are composed of hydrogen-bonded water molecules. Tetrahydrofuran (THF) clathrate hydrates (fully or partially deuterated) seem particularly well suited as a moderation medium for neutron, as they possess low-energy modes with sufficiently large inelastic neutron scattering cross sections [1].
Since THF only occupies the large cages in the clathrate structure, the twice more abundant smaller cages can still be filled with other molecules. This allows a binary clathrate, consisting of two guest molecules within the water structure to be constituted [2]. Of particular interest is oxygen as a second guest molecule. It offers an additional path for moderation via a cooling cascade mechanism that exploits the zero-field splitting of the magnetic triplet ground state of molecular oxygen [3].
In the context of the European project HighNESS [4, 5], whose main mission is the "Development of an High Intensity Neutron Sources at the European Spallation Source (ESS)", we present the first results of measurements of the neutron scattering function $S(q, \omega)$ for clathrate hydrates in absolute units. Both the simple and the binary structure are investigated on the time-of-flight (TOF) spectrometer Panther and IN5 at the ILL. The results include measurements with neutron-wavelengths from 0,1 nm to 0,3 nm, for fully and partially deuterated clathrate samples. With this variation contrast we show the contribution of the different constituents.
References
[1] H Conrad, W. F Kuhs, K N ̈unighoff, C Pohl, M Prager, and W Schweika. Inelastic scattering and spectralmeasurements of advanced cold moderator media.Physica B: Condensed Matter, 350(1, Supplement):E647–E650, July 2004.
[2] Hongjun Yang, Shuanshi Fan, Xuemei Lang, and Yanhong Wang. Phase equilibria of mixed gas hydrates ofoxygen + tetrahydrofuran, nitrogen + tetrahydrofuran, and air + tetrahydrofuran.Journal of Chemical &Engineering Data, 56, 10 2011.
[3] Oliver Zimmer. Neutron conversion and cascaded cooling in paramagnetic systems for a high-flux source of verycold neutrons.Physical Review C, 93(3):035503, March 2016. Publisher: American Physical Society.
[4] HighNESS. Project Description.https://highnessproject.eu/mission-and-ojbectives/, 2020. [Online].
[5] V Santoro, KH Andersen, DD DiJulio, Esben Bryndt Klinkby, TM Miller, David Milstead, G Muhrer, M Strobl,A Takibayev, L Zanini, et al. Development of high intensity neutron source at the European Spallation Source.Journal of Neutron Research, (Preprint):1–11, 2020.
