Druck-Materie 20b.qxd - JUWEL - Forschungszentrum Jülich

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5. THE OPTIMISATION OF MULTIPLY GROOVED MODERATORS One of the common ways to improve the flux from solid methane is to add a series of narrow grooves into the moderator. This presents us with a huge parameter space to study, so we have selected a few key points in this space to give us an idea about the possible performance. For the purposes of this study, we have added four horizontal grooves (Figure 5). In the initial configuration, the grooves extended half way into the moderator; the groove height was specified as 1.5 cm, with 1.5 cm of solid methane between the grooves. However, the enlargement of the grooves was found to be desirable, and later calculations used 2cm grooves separated by 1cm of moderator material. Similarly, the extension of the grooves further into the moderator proved to be advantageous, and later calculations all used grooves whose depth was 2/3 of the moderator thickness. Two options for the use of para-hydrogen in conjunction with a grooved methane moderator were explored: adding hydrogen inside the grooves, and/or an additional flat-faced hydrogen moderator in front of the grooves. Hydrogen Solid Methane Groove Groove Figure 5. The geometry of the multiply grooved moderators (vertical section). The moderator has lateral dimensions of 12 x 12 cm with four horizontal grooves. Various geometries have been run with different groove widths, separations and depths. Compound moderators incorporating a slab of hydrogen moderator in front of the grooves were also investigated. 64 Results for the time-integrated current are shown in Table 8 for selected cases. The best results appear to be from the case with hydrogen in front of empty grooves. However, this is only the case if the time integration is taken over the whole of the long tail. A more careful look at the peak shapes (figure 7) shows that for empty grooves the shape is double peaked and that adding hydrogen to the grooves adds height to the peak and produces a clean single shape with 10% extra flux in the 0 to 2000 µs region. Controlling the long time tail is obviously something that needs to be addressed, perhaps by adding a poisoning layer deep in the reflector. In Figure 6 the FWHM of these selected cases is shown as a function of thickness. One of the remarkable results is how the addition of hydrogen into the grooves sharpens up the pulse. From Figure 7 we can see that above 200µs the peak shapes for hydrogen in front of empty grooves and grooves filled with hydrogen are roughly the same (although the empty grooves are very slightly higher), but below 200µs there is a higher, sharper peak.
Figure 6. Plots of the FWHM pulse widths versus the moderator thickness for the multiply grooved moderators. There are four grooves, each 2cm high and separated by 1cm of solid methane. The methane moderator is 6cm thick with grooves 4cm deep and has lateral dimensions 12x12 cm. Table 8: A summary of calculated neutron intensities from multiply grooved moderators. The results are given relative to a 4.8cm flat-faced liquid hydrogen moderator. The lateral dimensions are 12 x 12 cm and the temperatures are 26K and 20K for the solid methane and hydrogen respectively. The time integration is from 0 to 30,000µs. Methane thickness 65 Hydrogen thickness Groove geometry Height (cm) Separation Fractional depth Groove material Relative intensity 8.0 0.0 1.5 1.5 0.5 void 1.621(9) 8.0 0.0 2.0 1.0 0.5 void 1.705(9) 8.0 0.0 1.5 1.5 0.67 void 1.692(9) 8.0 0.0 2.0 1.0 0.67 void 1.81(1) 2.0 0.0 2.0 1.0 0.5 void 1.307(8) 4.0 0.0 2.0 1.0 0.5 void 1.588(9) 6.0 0.0 2.0 1.0 0.5 void 1.644(9) 8.0 0.0 2.0 1.0 0.5 void 1.71(1) 10.0 0.0 2.0 1.0 0.5 void 1.72(1) 2.0 0.0 2.0 1.0 0.67 void 1.164(6) 4.0 0.0 2.0 1.0 0.67 void 1.623(9) 6.0 0.0 2.0 1.0 0.67 void 1.76(1) 8.0 0.0 2.0 1.0 0.67 void 1.81(1) 10.0 0.0 2.0 1.0 0.67 void 1.83(1) 2.0 0.0 2.0 1.0 0.67 H2 1.410(8) 4.0 0.0 2.0 1.0 0.67 H2 1.762(9) 6.0 0.0 2.0 1.0 0.67 H2 1.82(1) 8.0 0.0 2.0 1.0 0.67 H2 1.81(1) 10.0 0.0 2.0 1.0 0.67 H2 1.79(1) 6.0 1.6 2.0 1.0 0.67 void 2.01(1) 6.0 3.2 2.0 1.0 0.67 void 2.14(1) 6.0 4.8 2.0 1.0 0.67 void 2.21(1) 6.0 1.6 2.0 1.0 0.67 H2 1.98(1) 6.0 3.2 2.0 1.0 0.67 H2 2.05(1) 6.0 4.8 2.0 1.0 0.67 H2 2.12(1)
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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
Page 18 and 19: sigma-T in barns/molecule Figure 4.
Page 20 and 21: 2.3 Liquid water Compared to the so
Page 22 and 23: presented. The corresponding experi
Page 24 and 25: 3.2 Gaseous hydrogen and deuterium
Page 26 and 27: Rho(Omega) normalised 160 140 120 1
Page 28 and 29: elatively free and can also suffer
Page 30 and 31: Figure 16. Heat Capacity for Solid
Page 32 and 33: o-D2 and p-H2 at 5K for an ucn ener
Page 34 and 35: Figure 22. UCN Upscattering Rates i
Page 36 and 37: ho(omega) normalised 40 35 30 25 20
Page 38 and 39: derived from Walker [52]. The neutr
Page 40 and 41: Since there is only a small gain of
Page 42 and 43: 7. CALCULATION OF SCATTERING LAW DA
Page 44 and 45: For the validation of these data se
Page 46 and 47: [36] Nielsen, M.: Phonons in Solid
Page 48 and 49: 2. THE CASE OF MOLECULAR SOLIDS An
Page 50 and 51: γ r ( 0) ≅ 2 2 2 T erf e ( ) / 2
Page 52 and 53: 4. PRELIMINARY APPLICATION Solid Me
Page 54 and 55: [5] Meeting on Moderator Concepts a
Page 56 and 57: state. Conversely, the monatomic hy
Page 58 and 59: Note that the equilibrium trihydrog
Page 60 and 61: para hydrogen system under irradiat
Page 62 and 63: [12] T. E. Fessler and J. W. Blue,
Page 64 and 65: tion of neutron intensities, partic
Page 66 and 67: varied between calculations but the
Page 70 and 71: Figure 7. A comparison of time dist
Page 72 and 73: 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
Page 93 and 94: ACoM - 6 6 th Meeting of the Collab
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
Page 106 and 107: 102
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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A not quite as perfect cold spectru
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2.2 Inelastic neutron scattering Th
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Figure 4. Inelastic spectra at the
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3.2 Moderator performance The resul
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122
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Figure 2. The methane pelletizer, m
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Figure 5. The cryogenic hopper fill
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128
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ture
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The charging device scheme could be
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Table 1. Data of irradiation of met
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5. METHODS OF PROCESSING OF RAW EXP
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of radicals, that is, before a burp
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6.2 Condition for thermally stimula
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Table 4. Estimated values of an ene
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• Nine spontaneous burps were obs
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APPENDIX Some useful relations and
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APPENDIX. Graphs of burps. 148
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150
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2. EXPERIMENTAL SETUP Fig. 1 will g
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All these parameters are kept const
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4. CONCLUSIONS We demonstrated that
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JESSICA (Juelich Experimental Spall
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The moderator system consists of th
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to change the temperatures and to p
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168
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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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