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Aluminium Sphere (OKTAVIAN)

1. Name of Experiment:
 Leakage Neutron and Gamma Spectra from Aluminium Sphere Pile
 With 14 MeV Neutrons (December 1988)

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.
 The gamma-rays were produced from (n,xgamma) reactions.

3. Description of Source and Experimental Configuration:
 The pulsed beam line of the intense 14 MeV neutron source facility
 OKTAVIAN [3] at Osaka University was used. Neutrons were produced
 by bombarding a 370 GBq tritium target with 250 keV deuteron beam.
 (Note: 243 keV is stated in [5] for the photon spectrum measurement,
 but the same neutron source spectrum is specified for the analysis).
 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 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.
 Time spectra of neutrons and gamma-rays from the sphere were measured
 simultaneously with the pulse-height spectra by means of a TOF

 The pile was made by filling a spherical vessels with aluminium 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.

 Aluminium powder was at least 99.7% pure with impurities consisting
 of less than 0.2% iron, less than 0.15% silicon and less than 0.01%

 The assumed composition of stainless steel is 18.5 % Chromium,
 70.4 % Iron and 11.1 % Nickel.

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

 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,xgamma) 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:
 Source of Information:
 The main source of information were references [5] and [6]. The
 information on the source neutron spectrum is ambuguous. Namely,
 the spectrum in the text is given on a different energy grid than
 the spectrum in the sample MCNP input in ref. [5] on pages 80 and 124,
 respectively. Furthermore, there is a trivial error in the exponent
 in the spectrum at about 0.5 MeV in the sample MCNP input, which is
 also evident as an unusual bump in the calculated neutron leakage
 spectrum below 0.5 MeV in Fig. 4.8 of the same document. The same
 error persist even in a more recent document [7]. By contacting the
 author it has been established that the recommended source spectrum
 for the calculation is the one from the sample MCNP input, corrected
 for the trivial error in the exponent. The energy grid in this
 spectrum is more refined around the 14 MeV peak and hence better
 suited for the calculations.

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

 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 (lcs)

 Example of Experiment Analysis:
 Three sets of inputs are provided
    - two older 1–dimensional (1D) MCNP models for any 55° line experiment.
      One model (file mcnp4b.inp) includes neutron, photon and electron
      transport with the neutron source term. The other (mcnp4b_g.inp)
      includes photon and electron transport with the gamma source term.
    - two routine MCNPX(5) (semi) 2–D models in which the neutron source or
      the gamma source is specified (AL2dns.i, AL2dgs.i).
    - Detailed 3–dimensional MCNPX(5) model including the full experimental
      information for both neutron and gamma spectra (AL3dn.i).
    - Detailed 3–dimensional MCNPX(5) model including the full experimental
      information and explicit D-T source for gamma spectra analysis.
      (AL3dg.i). The D-T source routine (patch_DT) is needed to run this input.

    The results obtained using the (obsolete) 1-D model and different cross-
    section evaluations (ENDF/B-VI.1, EFF-3) are compared in Figure 3 for
    neutron spectrum below 1 MeV and in Figure 4 for the high energy part of
    the neutron spectrum. Full energy range comparison is shown in Figure 5.
    Similarly, the gamma spectrum measurement results are compared in
    Figure 6, emphasizing the low energy spectrum and in Figure 7 for the high
    energy part of the spectrum.

    Results using more accurate 2-D and 3-D models are discussed in [9].

 6. Quality assessment:
    The OKTAVIAN ALUMINIUM experiment is ranked as benchmark quality experiment.
    However, in order to use this benchmark for the validation of modern cross-
    section evaluations, supplementary experimental information is advisable on:
    – the neutron flight path parameter
    – the neutron realistic effects below 1 MeV (especially background subtraction
    – the gamma source measurements
    – the gamma detector response function.

    For detailed evaluation see [9].

7. Author/Organizer:
 Experiment and analysis:
 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:
 A. Trkov
 Institute Jozef Stefan, Jamova 39, 1000 Ljubljana, Slovenia
 Quality assessment:
 A. Milocco, Institut Jožef Stefan, Jamova 39, Ljubljana, Slovenia

 Reviewer of compiled data:
 I. Kodeli
 Institute Jozef Stefan, Jamova 39, 1000 Ljubljana, Slovenia

 F. Maekawa
 JAERI, Tokai-mura, Naka-gun, Ibaraki-ken, 319-1195 JAPAN

8. Availability:

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] Sumita K., et al.: Proc. 12th SOFT, Vol. 1 (1982)
 [4] Takahashi A., et el.: OKTAVIAN Report, C-83-02 (1983).
 [5] Sub Working Group of Fusion Reactor Physics Subcommittee:
 Collection of Experimental Data for Fusion Neutronics Benchmark,
 JAERI-M-94-014, Feb. 1994.
 [6] International Atomic Energy Agency, Nuclear Data Section:
 Compilation for FENDL benchmarks,
 [7] Fujio Maekawa, Masayuki Wada, Chihiro Ichihara, Yo Makita,
 Akito Takahashi, Yukio Oyama:
 Compilation of Benchmark Results for Fusion Related Nuclear Data,
 JAERI-Data/Code 98-024, Nov. 1998.
 [8] Sumita K., et el.: OKTAVIAN Report, C-83-01 (1983).
 [9] A. Milocco, Quality Assessment of the OKTAVIAN Benchmark Experiments,
 IJS-DP-10214, April 2009
 [10] A. Milocco, A. Trkov, MCNPX/MCNP5 Routine for Simulating D–T Neutron
 Source in Ti-T Targets, IJS-DP-9988, July 2008
 [11] 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:

 FILE   bytes Description                                            NAME
 ---- ------ ----------------------------------------------          ------------
  1    15,606 This information file                                  okal-abs htm
  2    16.147 Description of Experiment                              okal-exp htm
  3 2,934,763 Document describing quality assessment of OKTAVIAN
              experiments                                            Oktavian.pdf
  4     4,640 Routine (~2D) MCNP5(X) input with neutron source       AL2dns.i
  5     3,456 Routine (~2D) MCNP5(X) input with gamma source         AL2dgs.i
  6     6,388 Detailed 3D MCNP5(X) input for neutron spectrum calc.  AL3dn.i
  7     6,471 Detailed 3D MCNP5(X) input with DT source -gamma calc. AL3dg.i
  8    51,672 patch for MCNP5 to calculate D-T neutron source        DT_MCNP5.TXT
  9    29,688 source.F for MCNPX to calculate D-T neutron source     source.F
 10    12,709 srcdx.F for MCNPX to calculate D-T neutron source      srcdx.F
 11   493,108 Document describing D–T source routine for MCNPX/MCNP5 D-T.pdf
 12     7.158 1D MCNP-4B input model for (n,gamma) (OBSOLETE)        mcnp4b.inp
 13     1.896 1D MCNP-4B input for gamma calculations (OBSOLETE)     mcnp4b_g.inp
 14    13.827 Fig. 1: Aluminium sphere geometry                      okal-f1.gif
 15     6.734 Fig. 2: Experimental setup                             okal-f2.gif
 16    60.582 Fig. 1: Al sphere geometry (high quality TIF)          okal-f1.tif
 17    35.788 Fig. 2: Experimental setup (high quality TIF)          okal-f2.tif
 18    11.481 Fig. 3: Neutron Leakage Spectra (low energy) -1D model okal-f3.gif
 19    10.351 Fig. 4: Neutron Leakage Spectra (high energy)-1D model okal-f4.gif
 20    11.794 Fig. 5: Neutron Leakage Spectra (full range) -1D model okal-f5.gif
 21    15.080 Fig. 6: Gamma Leakage Spectra (low energy) -1D model   okal-f6.gif
 22    15.440 Fig. 7: Gamma Leakage Spectra (high energy) -1D model  okal-f7.gif
 23 15.469.391 Reference 5                                           j94-014.pdf
 24 7.518.191 Reference 7                                            j98-024.pdf
 25   556,871 Reference 8                                            o-c83-01.pdf
 26   585,384 Reference 11                                           ane-10.pdf

   The file okal-exp.htm contains the following tables:

   Tab. 1: Table with the source neutron spectrum from the sample MCNP input in [5].
   Tab. 2: Equivalent source neutron spectrum from Table 4.4 in ref.[5].
   Tab. 3: Measured leakage neutron current spectrum from ref.[5].
   Tab. 4: Measured leakage gamma spectrum from ref.[5].

   Figures are included in TIFF format using LZW compression and GIF format (preview).

SINBAD Benchmark Generation Date: 9/2000
SINBAD Benchmark Last Update: 2/2010