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 1. Name of Experiment:
    ------------------
    Leakage Neutron and Gamma Spectra from 40 cm diameter Tungsten Sphere
    Pile With 14 MeV Neutrons (July 1987)   


 2. Purpose and Phenomena Tested:
    ----------------------------
    The leakage current spectrum from the outer surface of the sphere pile
    with 14 MeV neutrons normalized per source neutron was measured ([1], [2],
    [3], [4]). The gamma-rays were produced from (n,xg) reactions.


 3. Description of Source and Experimental Configuration:
    ----------------------------------------------------
    The pulsed beam line of the intense 14 MeV neutron source facility
    OKTAVIAN [5] at Osaka University was used. Neutrons were produced
    by bombarding a 370 GBq tritium target with 250 keV deuteron beam.
    The energy spectrum of the neutron source was measured using the same
    detection system as for the leakage spectrum measurement. The spatial
    distribution of the emitted neutrons was measured for the target
    assembly, but for the purpose of the analysis an isotropic neutron
    source distribution is assumed. The neutron source spectrum is 
    given in Table 1. More information about the neutrons emission is
    given in [6].

    The neutron spectra were measured with the time-of-flight (TOF)
    technique. A tritium neutron producing target was placed at the
    center of the pile. A cylindrical liquid organic scintillator NE-218
    was used as a neutron detector, which was located about 11 m from the
    tritium target and at 55 deg. with respect to the deuteron beam axis.
    A pre-collimator made of polyethylene-iron multi-layers was set between
    the pile and the detector in order to reduce the background neutrons.
    The aperture size of this collimator was determined so that the whole
    surface of the pile facing the detector could be viewed. The details of
    the experimental set-up are shown in Figure 1.

    Gamma-rays were detected with a cylindrical NaI crystal and the
    energy spectra were obtained from the unfolding process of the
    gamma-ray pulse-height spectra, using a response matrix of the
    NaI detector. The detector was located at 5.8 m distance from the
    neutron source and counted the gamma-rays emitted from the sphere.
    The energy spectrum of gamma-rays at the source is shown in Table 2,
    and Figures 4 and 5. Time spectra of neutrons and gamma-rays from the
    sphere were measured simultaneously with the pulse-height spectra by
    means of a TOF technique.

    The pile was made by filling a spherical vessels with tungsten metal
    powder. The stainless steel (JIS SUS-304) vessel with 39.9 cm outer
    diameter was equipped with a 20 cm inner diameter void at its center
    and a 11 cm diameter reentrant hole for the  target beam duct. The
    vessel thickness was 0.2 cm everywhere. The details of the pile
    geometry are given in Figure 2.

    Tungsten metal powder was at least 99.97% pure, with density of 
    4.43 g/cm3.

    The assumed composition of stainless steel is 18.5 % chromium,
    70.4 % iron and 11.1 % nickel, with density of 7.86 g/cm3.


 4. Measurement System:
    ------------------
    A cylindrical liquid organic scintillator NE-218 (12.7 cm-diameter,
    5.1 cm-long) was used as a neutron detector. The detector efficiency
    was determined by combining:
    1) Monte Carlo calculation,
    2) measured efficiency derived from the TOF measurement of Cf-252
       spontaneous fission spectrum and the Watt's spectrum, and
    3) measured efficiency from the leakage spectrum from a graphite
       sphere, 30 cm in diameter with the similar detection system.

    To monitor the absolute neutron spectrum per source neutron, a
    cylindrical niobium foil was set in front of the tritium target and
    irradiated during the TOF experiment. From the gamma-ray intensity
    of the induced activity, Nb-92m and the integrated counts of the
    source neutron spectrum, the absolute neutron leakage spectrum can
    be obtained. The formulation of this procedure is described in the
    Oktavian Report [7].

    To measure the gamma spectra, OKTAVIAN was run in the pulsed mode
    with a repetition frequency of 500 kHz. The pulse width was 3 ns in
    FWHM and the difference in flight times between the 14 MeV neutrons
    and the prompt gamma-rays was about 90 ns from the sphere to the
    detector. Since those were enough to separate the gamma-rays from
    the neutron background in the TOF spectra, the desired gamma-rays
    could be discriminated from a neutron background.

    The gamma emission spectra were dominated by the gamma-rays from
    (n,n') and (n,2n) reactions rather than the gamma-rays from
    (n,xg) reaction. The data are therefore available to the assessment
    in the nuclear data for energy distributions of gamma-rays from
    non-elastic scattering by high energy neutrons.


 5. Description of Results and Analysis:
    -----------------------------------
    The measured neutron leakage spectrum from a 40 cm diameter tungsten
    pile is given in Table 3 and in Figure 6. Numerical data for the
    gamma-ray leakage spectra, measured from a 40 cm diameter tungsten
    pile is given in Table 4 and in Figure 8.

    The energy integrated data taken from the ref. [9] are given in 4
    energy groups in Table 5.

    Error Assessment:

    The experimental errors in the measured neutron spectra include only
    statistical deviation (1 s). The relative error to measure the niobium
    activation foils is less than 1 % (0.4 to 1 %), which is not included.

    In the measured gamma spectra the following sources were included
    in the errors:
    (a) Uncertainty in monitoring absolute fluxes of the source neutrons,
    (b) Errors of the response matrix,
    (c) Statistical deviation (1 s).

    Example of Experiment Analysis:

    Three sets of inputs are provided:
    - two older 1–dimensional (1D) MCNP-4B input models, one model
     (mcnp4b-n.inp) for neutron, and the second (mcnp4b-g.inp) for gamma
      transport calculations.
    - two routine MCNPX(5) (semi) 2–D models in which the neutron source or
      the gamma source is specified (W2dns.i, W2dgs.i).
    - Detailed 3–dimensional MCNPX(5) model including the full experimental
      information for neutron spectra (W3dn.i).
    - Detailed 3–dimensional MCNPX(5) model including the full experimental
      information and explicit D-T source for gamma spectra analysis (W3dg.i).
      The D-T source routine (DT_MCNP5.TXT) is needed to run this input.

    Results using the recommended 2-D and 3-D models are discussed in [11].

    Older benchmark calculations performed with the simple (obsolete) 1D MCNP
    model and the FSXLIB-J3 and ENDL-85 libraries are described in ref. [8].
    Ref. [9] presents the benchmark calculation performed by the 1D MCNP-4A
    model and the JENDL-3.1, JENDL-3.2, JENDL-FF, FENDL-1, EFF and BMCCS
    libraries.
    Ref. [10] presents the calculations performed at the OECD/NEA DB using
    the simple 1D MCNP inputs with the FENDL-2 (=JENDL-FF) and ENDF/B-VI.8
    evaluations. The calculated and measured spectra for the 40 cm diameter
    tungsten pile are shown in Fig. 6 and Fig. 7. It is also shown that the
    fine neutron source spectra given in the MCNP input reproduces better
    the fusion peak spectra then the one given in Table 2.
    The gamma spectra shown in Fig. 8 indicate good agreement between the
    experiment and the calculation using the ENDF/B-VI.3 data.

 6. Quality assessment:
    -----------------
    The OKTAVIAN SILICON 40 CM and 60 CM experiments seems to be of sufficient
    quality for nuclear data validation purposes.
    However, in order to use this benchmark for the validation of modern cross-
    section evaluations, supplementary experimental information would be needed
    on:
    – the neutron realistic effects below 0.5 MeV (background subtraction
      method in particular)
    – the gamma source measurements
    – the gamma detector response function

    For detailed evaluation see [11].



 7. Author/Organizer:
    ----------------
    Chihiro Ichihara, Katsuhei Kobayashi:
    Research Reactor Institute, Kyoto University
    Noda, Sennan-gun, Osaka 590-04, Japan

    Shu A. Hayashi:
    Institute for Atomic Energy, Rikkyo University
    2-5-1 Nagasaka, Yokosukas Kanagawa 240-01, Japan

    Itsuro Kimura:
    Department of Nuclear engineering, Faculty of Engineering,
    Kyoto University
    Yoshida-honmachi, Sakyo-ku, Kyoto 606, Japan

    Junji Yamamoto, Akito Takahashi, T. Kanaoka, I. Murata, K. Sumita:
    Department of Nuclear Engineering, Faculty of Engineering,
    Osaka University
    2-1, Yamada-oka, Suita, Osaka 565, Japan
    
    Compiler of data for Sinbad:
    S. Kitsos
    OECD/NEA, 12 bd des Iles, 92130 Issy les Moulineaux, France
    
    Quality assessment:
    A. Milocco, Institut Jožef Stefan, Jamova 39, Ljubljana, Slovenia

    Reviewer of compiled data:
    I. Kodeli
    OECD/NEA, 12 bd des Iles, 92130 Issy les Moulineaux, France


 8. Availability:
    ------------
    Unrestricted


 9. References:
    ----------
    [1] Ichihara C., et al.: Proc. Int. Conf. on Nucl. Data for Sci.
        and Technol., Mito, Japan, pp.319-322 (1988).
    [2] Ichihara C., et al.: Proc. Second Specialists' Meeting on Nucl.
        Data for Fusion Reactors (1991), JAERI-M 91-062 (1991).
    [3] Yamamoto J. et al.: "Gamma-Ray Emission Spectra from Spheres with
        14 MeV Neutron Source", JAERI-M 89-026, 232 (1989).
    [4] Yamamoto J. et al.: "Integral Experiment on Gamma-Ray Production
        at OKTAVIAN", JAERI-M 91-062, 118 (1991).
    [5] Sumita K., et al.: Proc. 12th SOFT, Vol. 1 (1982)
    [6] Yamamoto J. et al.: "Numerical Tables and Graphs of Leakage Neutron
        Spectra from Slabs of Typical Shielding Material with D-T Neutron
        Source", OKTAVIAN-Report A-8305, Dept. of Nuclear Eng.,
        Osaka University (1983).
    [7] Takahashi A., et el.: OKTAVIAN Report, C-83-02 (1983).
    [8] Sub Working Group of Fusion Reactor Physics Subcommittee:
        Collection of Experimental Data for Fusion Neutronics Benchmark,
        JAERI-M-94-014, Feb. 1994.
    [9] F. Maekawa, M. Wada, C. Ichihara, Y. Makita, A. Takahashi, Y. Oyama:
        Compilation of Benchmark Results for Fusion Related Nuclear Data,
        JAERI-Data/Code 98-024, Nov. 1998.
   [10] I. Kodeli, Recent Progress in the SINBAD Project, EFFDOC-866, EFF
        Meeting, Issy-les-Moulinaux (April 2003)
   [11] A. Milocco, Quality Assessment of the OKTAVIAN Benchmark Experiments,
        IJS-DP-10214, April 2009
   [12] A. Milocco, A. Trkov, MCNPX/MCNP5 Routine for Simulating D–T Neutron
        Source in Ti-T Targets, IJS-DP-9988, July 2008
   [13] A. Milocco, A. Trkov, I. Kodeli: "The OKTAVIAN TOF Experiments in SINBAD:
        Evaluation of the Experimental Uncertainties",
        Annals of Nuclear Energy 37 (2010) pp. 443-449


10. Data and Format:
    ---------------

    DETAILED FILE DESCRIPTIONS
    --------------------------
        Filename     Size[bytes]   Content
    ---------------- ----------- -------------
  1 okw-abs.htm     13,563 This information file
  2 okw-exp.htm     17,860 Description of experiment
  3 Oktavian.pdf 2,934,763 Document describing quality assessment of OKTAVIAN experiments
  4 W2dns.i          5,066 Routine (~2D) MCNP5(X) input with neutron source
  5 W2dgs.i          4,085 Routine (~2D) MCNP5(X) input with gamma source
  6 W3dn.i           7,238 Detailed 3D MCNP5(X) input for neutron spectrum analysis
  7 W3dg.i           7,229 Detailed 3D MCNP5(X) input with DT source -gamma analysis
  8 DT_MCNP5.TXT    51,672 patch with the source subroutines for MCNP5
                           to calculate 14-MeV D-T source (new revised version)
  9 source.F        29,688 source.F subroutine for MCNPX version 2.6f
                           to calculate 14-MeV D-T source (new revised version)
 10 srcdx.F         12,709 srcdx.F subroutine for MCNPX version 2.6f
                           containing also subroutines for numerics
                           to calculate 14-MeV D-T source (new revised version)
 11 D-T.pdf        493,108 Document describing D–T source routine for MCNPX/MCNP5
 12 mcnp4b-n.inp     6,799 MCNP4B input for neutron calculation (W 40 cm) (OBSOLETE)
 13 mcnp4b-g.inp     1.921 MCNP4B input for gamma calculation (W 40 cm) (OBSOLETE)
 14 okw-f1.gif      13.827 Fig. 1: Experimental arrangement of the OKTAVIAN Facility
 15 okw-f2.gif      10.292 Fig. 2: 40 cm diameter vessel (Type-II)
 16 okw-f3.jpg      39.858 Fig. 3: Comparison of neutron source spectrum from MCNP
                                   input and Table 1
 17 okw-f4.gif       9,224 Fig. 4: Gamma-ray emission spectrum from neutron source
 18 okw-f5.jpg      30,851 Fig. 5: Comparison of gamma-ray source spectrum from MCNP
                                   input and Table 2
 19 okw-f6.jpg      39,030 Fig. 6: Measured and calculated neutron spectra (lethargy
                                   scale) (from ref. [10])
 20 okw-f7.jpg      41,045 Fig. 7: Measured and calculated neutron spectra (energy
                                   scale) [10]
 21 okw-f8.jpg      41,162 Fig. 8: Measured and calculated gamma-ray spectra [10]
 22 j94-014.pdf 22,068,530 Reference
 23 j98-024.pdf 10,339,840 Reference
 24 ane-10.pdf     585,384 Reference


    File okw-exp.htm contains the following tables:

      Table 1:  Neutron source spectrum for tungsten
      Table 2:  Gamma-ray energy spectrum at the source
      Table 3:  Measured neutron leakage spectrum from a W sphere of 40 cm diameter
      Table 4:  Measured gamma-ray leakage spectrum from a W sphere of 40 cm diameter
      Table 5:  Integrated neutron flux from W sphere of 40 cm diameter

   Figures are included in GIF and JPG formats.

SINBAD Benchmark Generation Date: 05/2003
SINBAD Benchmark Last Update: 02/2010