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

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Figure 16. Heat Capacity for Solid hcp Deuterium Seiffert [40] has measured total neutron cross-sections for solid hydrogen and deuterium. To compare with the experiment, we must combine the partial cross sections for scattering (inelastic and elastic incoherent and coherent) with absorption for our two models. In Fig. 17 the result is shown for deuterium (probably n-D2). As it is clearly seen from the rotational peak around 10 meV, the rotations (and the oscillation) are not frozen. Therefore, the model 1 is not realistic for the solid moderators. The strong decrease of the measured crosssections around 2.3 meV may be caused by great single crystallic domains in the probe, whereas we calculated the coherent part for pure polycrystallic moderators. Figure 17. Total Neutron Cross-Sections for Solid Deuterium at a Temperature of 17K In Fig. 18 our results are presented for σT (E) of p-H2 ; but only for the model 2 calculations are done. As it is obvious, from the strong increase of the cross-section at E > ω rot (excitation of the rotator) , the neglecting of the optical modes in model 1 cannot lead to realistic cross-sections. 26
Over a wide energy range our data are in excellent agreement with the experiment. Therefore it is stated from the comparison for p-H2 (better than from deuterium), that the optical modes may be excited in the solid moderators under the conditions of working with cold neutron sources for the production of ultracold neutrons. Figure 18. Total Neutron Cross-Sections for Solid hcp p-Hydrogen at 5K 3.6 SOLID DEUTERIUM AS A COLD NEUTRON SOURCE PRODUCING ULTRA- COLD NEUTRONS (UCN) For design studies of existing [34] or planned [42] sources of ultracold neutrons extensive radiation transport calculations must be done. But determining the ucn density, nowadays no standard transport code is generally available to calculate realistic neutron spectrum data in the ultracold neutron energy range. Most of the known codes are restricted to energies greater than some 10 –5 eV from numerical aspects. Therefore, one must calculate the neutron flux spectrum for the cold neutron domain and then determine the production rate of ucn by the downscattering rate of the thermal and cold neutrons coming from the cold neutron source of the research reactor. Unfortunately, this method too delivers no spectral information for the loss rate of ucn, which essentially is the upscattering rate and the absorption rate. For our discussion, we therefore assume from our experience of studies with cold neutron sources in the liquid phase [29] that the neutron flux spectrum in a solid deuterium neutron source can be approximated as first guess by a maxwellian shape with a neutron temperature around 30K plus an 1/E slowing down flux with a cut-off around 40 meV. 3.7 UCN PRODUCTION RATE FROM DOWNSCATTERING OF COLD NEUTRONS The downscattering rate of cold and thermal neutrons to the ucn energy range from 10 –9 to 10 –6 eV generally describes the ucn production : PR (E-ucn) dE-ucn = N ∫ σ s ( Ei → E-ucn ) • Φ ( E i ) d Ei dE-ucn [ucn / cm 3 / s] The energy range for integration is dominated by the structure of the differential downscattering cross-section of the solid material. Cause in solid deuterium there may be some amount of hydrogen (normally around 0.2 wt%) in Fig. 19 this cross-section is plotted for 27
Page 1 and 2: ACoM - 6 6th 6 International Worksh
Page 3 and 4: Forschungszentrum Jülich GmbH Inst
Page 5: Preface These are the Proceedings o
Page 8 and 9: List of participants, cont’d. Kü
Page 10 and 11: Pepe M. 43 Petriw S. 43 Picton D.J.
Page 12 and 13: Experimental background, results an
Page 14 and 15: • Light water ice as H(H2O) at T
Page 16 and 17: 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 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 68 and 69: 5. THE OPTIMISATION OF MULTIPLY GRO
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
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ABSTRACT ACoM - 6 6 th Meeting of t
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Heat transfer processes across phas
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3. TWO-PHASE FLOW PATTERN IN THE MO
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continuous phase dominating, and a
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Also the velocity pattern has chang
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Figure 8. Methane pellets concentra
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ACoM - 6 6 th Meeting of the Collab
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sample volume and the nominal densi
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The results presented in this paper
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Table 10. Summary of energy transfe
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2. EXPERIMENTAL Methane hydrate was
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Figure 4. Energy levels of methane
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102
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phase transitions from phase II to
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After melting phase I in the cryost
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4. SOLID PHASES OF MESITYLENE-D0 AN
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G(ν) [a.u.] 8 6 4 2 Phase II Phase
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112
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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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152
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154
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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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196
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200
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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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