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
 technique.

 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%
 copper.

 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
 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 (lcs)

 Example of Experiment Analysis:
 The sample input for the MCNP-4B code in ref.[5] explicitly defines
 the hole for the target beam duct, but the leakage current tally
 encloses the entire sphere surface. Therefore, part of the tally
 surface "sees" the source directly, which is incorrect. A new input
 was prepared without the hole for the target beam duct. The energy
 bins of the tally were also refined to provide more detail on the
 shape of the leakage spectrum for better comparison with the measurement.
 The new MCNP input (file mcnp4b.inp) combines the neutron spectrum and
 the gamma spectrum measurements, which are given separately in [5].
 The secondary gamma-ray transport must be calculated separately using
 the input (mcnp4b_g.inp [7]).

 Two calculations were performed: one with pure ENDF/B-VI Rev.1
 data from the original MCNP library and the second in which the
 data for aluminium and iron were taken from EFF-3 (=FENDL-2).
 The results for the neutron spectrum measurement are compared in
 Figure 3 for energies below 1 MeV and in Figure 4 for the high
 energy part of the 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.


6. Special Features:
 ----------------
 None

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:
 A. Trkov
 Institute Jozef Stefan, Jamova 39, 1000 Ljubljana, Slovenia
 E-mail: Andrej.Trkov@ijs.si

 Reviewer of compiled data:
 I. Kodeli
 Institute Jozef Stefan, Jamova 39, 1000 Ljubljana, Slovenia
 E-mail: Ivan.Kodeli@ijs.si

 F. Maekawa
 JAERI, Tokai-mura, Naka-gun, Ibaraki-ken, 319-1195 JAPAN
 E-mail: fujio@fnshp.tokai.jaeri.go.jp


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] 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,
 "http://ripcnt01.iaea.org/nds/databases/fendl/fen-bench.htm".
 [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).

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

 FILE bytes Description NAME
 ---- ------ ---------------------------------------------- ------------
 1 13.236 This information file okal-abs htm
 2 16.040 Description of Experiment okal-exp htm
 3 7.158 3-D model for MCNP-4B calculations (n,gamma) mcnp4b inp
 4 1.896 3-D model for MCNP-4B gamma-ray calculations mcnp4b_g inp
 5 13.827 Fig. 1: Aluminium sphere geometry okal-f1 gif
 6 6.734 Fig. 2: Experimental setup okal-f2 gif
 7 60.582 Fig. 1: Al sphere geometry (high quality TIF) okal-f1 tif
 8 35.788 Fig. 2: Experimental setup (high quality TIF) okal-f2 tif
 9 11.481 Fig. 3: Neutron Leakage Spectra (low energy) okal-f3 gif
 10 10.351 Fig. 4: Neutron Leakage Spectra (high energy) okal-f4 gif
 11 11.794 Fig. 5: Neutron Leakage Spectra (full range) okal-f5 gif
 12 15.080 Fig. 6: Gamma Leakage Spectra (low energy) okal-f6 gif
 13 15.440 Fig. 7: Gamma Leakage Spectra (high energy) okal-f7 gif
 14 15.469.391 Reference j94-014 pdf
 15 7.518.191 Reference j98-024 pdf
 16 352.607 Reference o-c83-01 pdf

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

 Tab. 1: A table with the source neutron spectrum from the sample
 MCNP input in ref.[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).