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derived from Walker [52]. The neutron scattering in the Al lattice is composed by an incoherent inelastic scattering part generated as Scattering Law Data S(α,β,T) file in ENDF-6 format and the coherent elastic part. In Fig. 28 the generalised frequency distribution ρ(ω) for polycrystalline Al is shown which is taken in harmonic approximation for calculating S(α,β,T). The contributions of the elastic and inelastic neutron scattering to the integral cross section is shown in Fig. 29. Comparisons of calculated and measured Al cross sections at 100K [50] showed good agreement, measurements at 20 K are not available (see also [51]). rho(omega) normalised 140 120 100 80 60 40 20 from Walker 1956 0 0.000 0.010 0.020 0.030 0.040 omega in eV Figure 28. Frequency distribution of polycrystalline aluminium Figure 29. Total cross sections for polycrystalline aluminium 34
6. TRANSPORT CALCULATIONS FOR COLD AND ULTRA COLD NEUTRONS The transport calculations based on the evaluated scattering laws can be performed with standard transport codes in multigroup approximation or by continuous Monte Carlo e.g. by the multigroup programs ANISN, DORT, TORT (SN theory) or MORSE (Monte Carlo) and by continuous Monte Carlo codes like MCNP. The data processing for these codes can be performed by NJOY, if the scattering law data are available in corresponding ENDF-6 format. However, difficulties arise if the energy range of interest is lower than 10 -5 eV. For the range of ultracold neutrons (some neV to about 500 neV) the present NJOY version cannot process data. Therefore, we tried to extend all corresponding limits in NJOY to produce cross section data for multigroup and continuous Monte Carlo applications for the UCN range. This attempt was quite successful, we could produce data for solid, liquid and gaseous D2 for various temperatures. For multigroup calculations no further changes in transport programs are necessary. The generated 277 group data with 79 groups below 0.01 meV, 33 groups up to 3 eV and 165 groups above 3 eV can be applied directly in standard SN codes like ANISN. Continuous Monte Carlo calculations e.g. by MCNP, however, must be splitted into two parts. First part treats the energy range above the standard cutoff of 0.01 meV. The spectrum calculated by this part is then used to calculate the scattering source for the UCN range. A direct approach in one calculation leads to completely insufficient statistical results for extreme low energies. The separate calculation of scattering source will be performed based on the S(α,β) scattering law data. This scattering source will be used then for a second run only for the UCN range. Using a biased source distribution the calculation for the UCN range results in spectra with sufficient statistical accuracy without extraordinary large computing time. As an example a simple model of a sphere was calculated to estimate the UCN production in a sphere filled by liquid and solid Deuterium of 20K and 10K, respectively. The sphere of 20 cm diameter was surrounded by a moderator of 293K. The outer diameter of the moderator was 150 cm. The problems were calculated by SN code ANISN and MCNP (two parts, the space dependency of the scattering source in the inner sphere was regarded by subdividing the sphere into 10 regions). The results are shown in Fig. 30. The ANISN and MCNP results are in good agreement. The only problem found for the first part of calculation was in the range from 0.01 to 0.1 meV. Here, probably the procedure for treating the thermal scattering based on S(α,β) tables should be improved. However, in the case of D2 (liquid or solid) this range contributes not significantly to the UCN source. Neutron flux density spectra 1.E-01 1.E-02 1.E-03 1.E-04 1.E-05 1.E-06 1.E-07 Solid D2 MCNP ANISN MCNP Liquid D2 1.E-08 1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 Energy (eV) Figure 30. Comparison of ANISN and MCNP calculations for solid and liquid D2 in a spherical container 35
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 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 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
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
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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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202
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210
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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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