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Manganese Sphere (OKTAVIAN)

1. Name of Experiment:
Leakage Neutron and Gamma Spectra from 60 cm diameter Manganese Sphere
Pile With 14 MeV Neutrons (July 1987)

2. Purpose and Phenomena Tested:
The neutron and gamma leakage spectra from the outer surface
of the sphere pile with 14 MeV neutrons normalized per source neutron
was measured ([1], [2]). 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 [1] 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. The neutron source spectrum is given in Table 1.
More information about the source neutrons emission is given in [3] and [4].

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. A better representation
of the collimator system is available in [4].

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.
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 manganese metal
powder. The vessel was made of soft stell (JIS SS-41). Inner diameter
and wall thickness of the vessel are 60 cm and 0.5 cm respectively.
A reentrant hole for a beam duct is equipped, the diameter of which
is 5.1 cm up to the centre of the vessel. The details of the pile
geometry are available in Figure 2.

Manganese metal powder was at least 99.95% pure, with density of
4.37 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 [5].

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.

5. Description of Results and Analysis:
The measured neutron leakage spectrum from a 60 cm diameter Manganese
pile is given in Table 3.
The numerical data for the experimental gamma-ray leakage spectra,
measured from teh 60 cm diameter Manganese, pile is given in Table 4<.

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).


Two MCNP5(X) models are provided:
- Mn2dn.i is a simple routine model with neutron source. The neutron source
is defined according to the OKTAVIAN anisotropy specifications.
At any angle corresponds the neutron yielding and energy (discrete values).
 According to methods discussed in [4], the neutron source energy spectrum
in Table 1 may be converted into time domain to perform the resolution
broadening of the time-of-flight spectrum calculated with routine model 2dmn.i.
Then, the folded spectrum may be converted from time into energy domain and
compared with experimental neutron leakage spectrum (Table 3).
This model can easily be modified to calculate the gamma leakage spectrum
with neutron source.  
- Mn3dn.i is a detailed 3–dimensional model including the full experimental
(concerning geometry and material composition) information for neutron spectra
calculations. The source term in the model corresponds to the OKTAVIAN discrete
neutron source specifications. The resolution broadening has to be applied afterwards [4].

6. Quality assessment:
The OKTAVIAN MANGANESE experiment 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
– the neutron realistic effects, in particular those concerning the
background subtraction method
– the gamma source measurements

For detailed evaluation in similar experiments see [4].

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. Milocco
Institut Jožef Stefan, Jamova 39, Ljubljana, Slovenia
e-mail: Alberto.Milocco@ijs.si

Quality assessment:
A. Milocco
Institut Jožef Stefan, Jamova 39, Ljubljana, Slovenia
e-mail: Alberto.Milocco@ijs.si

Reviewer of compiled data:
I. Kodeli
OECD/NEA, 12 bd des Iles, 92130 Issy les Moulineaux, France
e-mail: ivo.kodeli@oecd.org

8. Availability:

9. References:

[1] Sub Working Group of Fusion Reactor Physics Subcommittee:
Collection of Experimental Data for Fusion Neutronics Benchmark,
JAERI-M-94-014, Feb. 1994.
[2] 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.
[3] A. Takahashi, J. Yamamoto, K. Oshima, et al: "Measurement of Double
Differential Neutron Emission Cross Sections for Fusion Reactor Candidate Elements",
Journal of Nuclear Science and Technology, Vol.21, No.8, 577-598 (1984).
[4] A. Milocco, Quality Assessment of the OKTAVIAN Benchmark Experiments,
IJS-DP-10214, April 2009.
[5] Takahashi A., et el.: OKTAVIAN Report, C-83-02 (1983).
[6] I. Kodeli, Recent Progress in the SINBAD Project, EFFDOC-866,
EFF Meeting, Issy-les-Moulinaux (April 2003).

10. Data and Format:

Filename Size[bytes] Content
---------------- ----------- -------------
1 okw-abs.htm 13,563 This information file
2 okmn-exp.htm 17,860 Description of experiment
3 Figure 1 13,827 Experimental arrangement of the OKTAVIAN Facility
4 Figure 2 16,199 Type I vessel
5 Mn2dn.i 4,934 Routine (~2D) MCNP5(X) input with neutron source
6 Mn3dn.i 6,811 Detailed 3D MCNP5(X) input for neutron spectrum analysis
7 j94-014.pdf 22,068,530 Reference
8 j98-024.pdf 10,339,840 Reference
9 Oktavian.pdf 2,934,763 Document describing quality assessment of OKTAVIAN experiments

File okmn-exp.htm contains the following tables:

Table 1: Neutron source spectrum for the Manganese experiment
Table 2: Gamma-ray energy spectrum at the source
Table 3: Measured neutron leakage spectrum from a Mn sphere of 60 cm diameter
Table 4: Measured gamma-ray leakage spectrum from a Mn sphere of 60 cm diameter

Figures are included in GIF format.

SINBAD Benchmark Generation Date: 07/2011
SINBAD Benchmark Last Update: 07/2011