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3.2 Moderator performance The results obtained with JESSICA spallation neutron source mock-up are shown in Fig. 8. The data have to be considered preliminary, because no shape and size optimizations of the moderator vessel have been attempted so far. The only correction applied to the spectra in Fig. 8 is the normalization to the same mass densities of the moderator materials. However, increased intensity compared to ice for methane clathrate and mesitylene at energies below about 5 meV is evident. Compared to mesitylene, on the other hand, methane clathrate exhibits increased intensity in the thermal energy range as expected due to the existence of the ice host (compare section 1). Due to the low statistical accuracy of the present data for energies below about 3 meV and the missing geometrical moderator optimization a decision upon the superiority of either the clathrate or mesitylene can not be made at this point. 4. CONCLUSIONS Synthetic methane clathrate has been found to exhibit the rotational energy levels of solid methane rendering it the potentially optimum cold moderator material, because it combines the excellent slowing down properties of solid methane at the lowest energies with those from water ice at thermal energies. So far unknown energy levels close to those observed with methane have been detected in ice suggesting that they are responsible for the comparatively good slowing down properties of this material. The same energy levels as in ice have been found in THF clathrate as well as an additional line at 10 meV. Whether this line has any importance for an improved moderation behavior of THF clathrate is not known yet, because cold neutron spectra have not been measured so far. Figure 8. Energy distribution of cold neutrons emitted from ice, mesitylene and methane clathrate moderators, respectively, measured at the <strong>Jülich</strong> spallation source mock-up JESSICA. The enhancement of the intensity compared to ice at the lowest energies attributed to methane in the clathrate as well as the methyl groups in mesitylene is clearly seen. 120
The wealth of low lying energy levels of mesitylene may well explain the favorable spectra observed already in the past as well as in the present investigations. Due to the intriguing simplicity in handling the room temperature liquid, mesitylene has to be considered a serious candidate material for an advanced cold neutron source. Simplicity may play another important role with respect to heat deposition in any of these materials in a future multi megawatt spallation neutron source. Any of the materials investigated in this study have to be in granular form. Pellets can be easily produced from substances, which are liquid at room temperature like water, mesitylene or THF-clathrate. Methane clathrate has been produced as pellets for these experiments, and it does not seem to be impossible to extend the scheme used here to a real mass production. REFERENCES [1] see e.g. M. Utsuro, M. Sugimoto, Y. Fujita; Ann. Report Research Reactor Institute, Kyoto University, 8, 17 (1975) [2] K.Inoue, H.Iwasa, Y.Kiyanagi; Atomic Energy Soc. Japan, 21, 865 (1979) [3] J.M.Carpenter and T.L.Scott; ICANS-XI, KEK Report 90-25, Tsukuba, Japan (1991) [4] C.Gutt, B.Asmussen, W.Press, C.Merkl, H.Casalta, J.Greinert, G.Bohrmann, J.S.Tse and A.Hüller; Europhys. Lett., 48 (3), 269 (1999) [5] H.Kapulla and W.Gläser; Neutron Inelastic Scattering; IAEA-SM-155/G3; p 841 - 849 (1972) [6] E.Shabalin; this conference [7] D. Staykova, Th. Hansen, A. N. Salamatin, and W. F. Kuhs.; Proc. Fourth Intern. Conf. on Gas Hydrates, Yokohama, May 19-23, 2002, pp. 537-542. [8] I.Natkaniec, K.Holderna-Natkaniec; this conference [9] K.Nünighoff et al.; this conference [10] H.Stelzer, N.Bayer, H.K.Hinssen, T.Matzerath; this conference [11] I. Natkaniec, K.Holderna-Natkaniec, J.Kalus; private communication 121
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ACoM - 6 6th 6 International Worksh
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Forschungszentrum Jülich GmbH Inst
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Preface These are the Proceedings o
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List of participants, cont’d. Kü
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Pepe M. 43 Petriw S. 43 Picton D.J.
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Experimental background, results an
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• Light water ice as H(H2O) at T
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In Table 2 a survey is given about
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sigma-T in barns/molecule Figure 4.
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2.3 Liquid water Compared to the so
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presented. The corresponding experi
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3.2 Gaseous hydrogen and deuterium
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Rho(Omega) normalised 160 140 120 1
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elatively free and can also suffer
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Figure 16. Heat Capacity for Solid
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o-D2 and p-H2 at 5K for an ucn ener
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Figure 22. UCN Upscattering Rates i
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ho(omega) normalised 40 35 30 25 20
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derived from Walker [52]. The neutr
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Since there is only a small gain of
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7. CALCULATION OF SCATTERING LAW DA
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For the validation of these data se
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[36] Nielsen, M.: Phonons in Solid
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2. THE CASE OF MOLECULAR SOLIDS An
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γ r ( 0) ≅ 2 2 2 T erf e ( ) / 2
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4. PRELIMINARY APPLICATION Solid Me
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[5] Meeting on Moderator Concepts a
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state. Conversely, the monatomic hy
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Note that the equilibrium trihydrog
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para hydrogen system under irradiat
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[12] T. E. Fessler and J. W. Blue,
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tion of neutron intensities, partic
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varied between calculations but the
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5. THE OPTIMISATION OF MULTIPLY GRO
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Figure 7. A comparison of time dist
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4.8 cm hydrogen slab in front of a
Page 75 and 76: ACoM - 6 6 th Meeting of the Collab
Page 77 and 78: the moderator is annealed every 12
Page 79 and 80: The method requires two additional
Page 81 and 82: ABSTRACT ACoM - 6 6 th Meeting of t
Page 83 and 84: Heat transfer processes across phas
Page 85 and 86: 3. TWO-PHASE FLOW PATTERN IN THE MO
Page 87 and 88: continuous phase dominating, and a
Page 89 and 90: Also the velocity pattern has chang
Page 91 and 92: Figure 8. Methane pellets concentra
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Page 95 and 96: sample volume and the nominal densi
Page 97 and 98: The results presented in this paper
Page 99: Table 10. Summary of energy transfe
Page 102 and 103: 2. EXPERIMENTAL Methane hydrate was
Page 104 and 105: Figure 4. Energy levels of methane
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Page 108 and 109: phase transitions from phase II to
Page 110 and 111: After melting phase I in the cryost
Page 112 and 113: 4. SOLID PHASES OF MESITYLENE-D0 AN
Page 114 and 115: G(ν) [a.u.] 8 6 4 2 Phase II Phase
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Page 118 and 119: A not quite as perfect cold spectru
Page 120 and 121: 2.2 Inelastic neutron scattering Th
Page 122 and 123: Figure 4. Inelastic spectra at the
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Page 128 and 129: Figure 2. The methane pelletizer, m
Page 130 and 131: Figure 5. The cryogenic hopper fill
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Page 134 and 135: ture
Page 136 and 137: The charging device scheme could be
Page 138 and 139: Table 1. Data of irradiation of met
Page 140 and 141: 5. METHODS OF PROCESSING OF RAW EXP
Page 142 and 143: of radicals, that is, before a burp
Page 144 and 145: 6.2 Condition for thermally stimula
Page 146 and 147: Table 4. Estimated values of an ene
Page 148 and 149: • Nine spontaneous burps were obs
Page 150 and 151: APPENDIX Some useful relations and
Page 152 and 153: APPENDIX. Graphs of burps. 148
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Page 160 and 161: 2. EXPERIMENTAL SETUP Fig. 1 will g
Page 162 and 163: All these parameters are kept const
Page 164 and 165: 4. CONCLUSIONS We demonstrated that
Page 166 and 167: JESSICA (Juelich Experimental Spall
Page 168 and 169: The moderator system consists of th
Page 170 and 171: to change the temperatures and to p
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supplied from the high pressure bom
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10 9 10 8 10 7 10 6 Para35%[Experim
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174
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2. TIME OF FLIGHT SPECTRA AND ENERG
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When applying this transformation t
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data were analyzed in more detail.
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182
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First of all, we should conclude th
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The equation (a) may also describe
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Even at h=0.01 mm which is too smal
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model and some consequences of its
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methane and 0.7-1.5% for water ice
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case: the sample of infinite size.
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Phase Diagram of the CH4-H20 system
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Reaction Chamber for Hydrate Produc
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Analysis: X-ray diffraction pattern
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Comparison with non-hydrate forming
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Mechanical Tests: Apparatus 220
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Morphology of Indium Jacket 222
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Schriften des Forschungszentrums J
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Schriften des Forschungszentrums J
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