Liquid hydrogen is a dense Bose fluid whose equilibrium properties are both calculable from first principles using various theoretical approaches and of interest for the understanding of a wide range of questions in many-body physics. . . .
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We gratefully acknowledge the support of the US Department of Energy Office of Nuclear Physics (including Grant No. DE-FG02-03ER41258), the National Science Foundation (including Grants No. PHY-1068712 and No. PHY-1205833), PAPIIT-UNAM (Grant No. IN111913), and the Indiana University Center for Spacetime Symmetries.
Grammer, K. B.; Alarcon, R.; Barrón-Palos, L.; Blyth, D.; Bowman, J. D.; Calarco, J.; Crawford, Christopher; Craycroft, K.; Evans, D.; Fomin, N.; Fry, J.; Gericke, M.; Gillis, R. C.; Greene, G. L.; Hamblen, J.; Hayes, C.; Kucuker, S.; Mahurin, R.; Maldonado-Velázquez, M.; Martin, E.; McCrea, M.; Mueller, P. E.; Musgrave, M.; Nann, H.; Penttilä, S. I.; Snow, W. M.; Tang, Z.; and Wilburn, W. S., "Measurement of the Scattering Cross Section of Slow Neutrons on Liquid Parahydrogen from Neutron Transmission" (2015). Physics and Astronomy Faculty Publications. 290.
Fig. 1: Parahydrogen and orthohydrogen scattering cross sections at 20 K from ENDF-VII and the absorption cross section.
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Fig. 2: Experimental setup showing the cesium iodide detector array, liquid hydrogen target, and beam monitors.
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Fig. 3: Diagram of circulation loop inside the hydrogen target system. Evaporated hydrogen is recondensed and is forced to flow through the OPC at a rate of a few millimoles per second. T3, T7, T8, and T10 determine the liquid hydrogen bulk temperature. T2 and T5 determine the temperature of the catalyst in the OPC.
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Fig. 4: Observed ortho-para conversion over time as a fraction of the asymptotic limit for 3.42 meV neutrons shortly after filling the target, with a time constant of approximately one day. Residuals from the exponential fit are shown at the bottom.
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Fig. 5: Transmission monitor signals (left axis) for empty (triangles) and hydrogen-filled (squares) aluminum target vessel. Dips in the spectra are at the aluminum Bragg edges. Transmission ratio (right axis, diamonds) depicts no transmission for energies above 14.5 meV spin-flip transition.
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Fig. 6: Total cross section from this work in b/atom (triangles); parahydrogen scattering cross section (squares). The upper error bar on the parahydrogen cross section comes from Table I and the lower error bar is given by the upper limit on the orthohydrogen contamination.
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Fig. 7: The scattering cross section extracted in this work (triangles), Squires (diamonds), Celli (stars, some points omitted), Seiffert (circles), ENDF-VII (black), and subtraction of a 0.5% admixture of orthohydrogen from Seiffert (squares).
Table 1.GIF (38 kB)
Table 1: Main uncertainties in the total cross section at 1.92 meV.