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IPPE neutron transmission through iron shells

 1. Name of Experiment:
    IPPE neutron transmission benchmark experiment with 14 MeV neutrons through
    iron shells.

 2. Purpose and Phenomena Tested:
    Neutron leakage spectra between 50 keV and 15 MeV from five iron shells
    were measured by the time-of-flight technique using a 14 MeV neutron
    generator. The spheres had radius from 4.5 to 30.0 cm and wall thicknesses
    from 2.5 to 28.0 cm.
    The experiments were performed in period 1989 to 1995.

 3. Description of Source and Experimental Configuration
    A Cockroft-Walton type accelerator, the KG-0.3 pulse neutron generator in
    Obninsk, was used to accelerate deuterons to a maximum kinetic energy of
    280 keV. The layout of the experiment is shown in Figure 1.
    The deuterons were led through a conical aluminum tube of only 0.5 mm wall
    thickness and collimated by a diaphragm with an 8 mm hole to a solid
    Titanium-Tritium target based on a copper radiator 0.8 mm thick and with
    diameter 11 mm. Beam spot diameter was 5 mm.
    The center of the target is located in the geometrical center of the iron
    shell. For monitoring the neutron source strength, the alfa particles
    generated in the deuterium-tritium reaction were detected at 175 deg. through
    a 1 mm diameter collimator by a silicon surface barrier (SSB) detector.
    The ion pulse width is 2.5 ns. The repetition period of the pulse can be set
    arbitrarily to multiples of 200 ns. The mean beam current for 800 ns. period
    is 1 microampere.
    The mean energy and yield of the '14 MeV' neutron source peak are slightly
    angle dependent, as shown in Figure 3.
    Five spherical shells of pure iron were available for the experiment.
    They are shown in Figure 2. Their dimensions are given in Figure 2 and Table 1.
    The weight of every sphere was measured and atom density was calculated.
    The material composition is given in Table 2.

 4. Measurement System and Uncertainties:
    The detector used was a fast scintillator detector located at an angle of 8
    deg. relative to beam trajectory extension and at a flight path of 6.8 m.
    The detector was installed in a lead house behind a concrete wall. A conical
    hole drilled through the wall acted as a collimator (see Figure 1).
    The detector itself consisted of a cylindrical paraterphenyl cristal of 5 cm
    diameter and 5 cm height. It was coupled to a FEU-143 photomultiplier.
    The time-of-flight measurement is made in the usual inverse method, i.e.
    using the detector signal as a start signal and the delayed deuteron pick-up
    pulse as a stop signal. In this way only the useful neutron bursts, i.e.
    those producing a signal in the detector are used, so avoiding dead time
    To experimental spectra were corrected for the background effects. To 
    measure the background neutron spectra, a 1 m long by 18 - 26 cm diameter
    iron shadow bar and a 30 cm long borated polyethylene cylinder were placed
    between the detector and the sphere (Figure 1).
    The estimated uncertainties of the experimental data and their main
    components are listed in Table 3. During the experiment the main spectrometer
    parameters (detector efficiency, absolute normalization factor, etc.) were 
    measured several times, hence the stability of the spectrometer could be 
    estimated by calculating the mean square deviation of individual runs.
    Two radioactive reference sources were used, Cf252 for neutron detector
    calibration and Pu238 for alfa detector calibration, with their specific
    uncertainties. The uncertainties of corrections for Cf-chamber scattering
    and time-of-flight conversion to energy, calculated with MCNP, were estimated
    at about 1-2%.
    In Table 3 the quadratic sum of components 2-5, considered as systematic, is
    calculated and its quadratic summation with the statistical uncertainty gives
    the total uncertainty of the experimental data.

 5. Description of Results and Analysis:
    The measured TOF spectra were corrected for the background effects and
    converted to the energy spectrum. The leakage spectrum, L(E), representing
    the differential fluence of leakage neutrons, integrated over the full
    sphere (4 pi sr) and normalised to 1 source neutron, was then calculated
    from the following expression:


      N(E)   = neutron energy spectrum, converted from measured TOF spectra,
      eps(E) = neutron detection efficiency (see Ref. [1] for details),
      dOmega = detector solid angle (=(pi*r*r)/(L*L), where r is the detector
               radius and L the distance from the sphere to the detector),
        Nn   = number of source neutrons.

     The experimental results are presented in 
    Table 4 for iron shell No. 1 (r= 4.5 cm, wall thickness = 2.5 cm), 
    Table 5 for iron shell No. 2 (r=12.0 cm, wall thickness = 7.5 cm),
    Table 6 for iron shell No. 3 (r=12.0 cm, wall thickness =10.0 cm),
    Table 7 for iron shell No. 4 (r=20.0 cm, wall thickness =18.1 cm),
    Table 8 for iron shell No. 5 (r=30.0 cm, wall thickness =28.0 cm)

    as leakage spectrum in terms of neutrons per MeV and per source neutron.

    MCNP-4C input data for Shells #1 - #5 (4.5 - 30 cm radius) are given in files
    mcnp_fe1.inp, mcnp_fe2.inp, mcnp_fe3.inp, mcnp_fe4.inp and mcnp_fe5.inp.
    In the models the spheres and the neutron source are described pricisely,
    including anisotropic energy and yield distributions of the T(d,n) source.
    For an adequate comparison of measurements and analitical calculation, the
    convolution with the spectrometer response function, describing the energy
    resolution of the spectrometer, is necessary. It is presented in Table 9.
    A correction factor was applied for the experimental spectra to account for 
    the time-of-flight procedure with bulk smaples. This has been done with the 
    Monte Carlo time-independent calculations (see Ref. [1]).
    Refs. [1] and  [4] discusses also the corrections for non-spherical effects,
    which should be taken into account in case of 1-dimensional (spherical)
    calculations using codes like ANISN, ONEDANT, ANTRA-1 etc.

 6. Special Features:

 7. Author/Organizer
    Experiment and Analysis:
    S.P. Simakov, B.V. Devkin, M.G. Kobozev, V.A. Talalaev (Inst. of Physics
    and Power Engineering, Obninsk),
    U. Fischer, U. von Moellendorff (Forschungszentrum Karlsruhe).

    Reviewer of Compiled Data
    I. Kodeli
    OECD/NEA, 12 bd. des Iles,
    92130 Issy les Moulineaux, France

 8. Availability:

 9. References:
   [1] S.P. Simakov, B.V. Devkin, M.G. Kobozev, V.A. Talalaev, U. Fischer,
       U. von Möllendorff, “Validation of evaluated data libraries against an iron
       shell transmission experiment and against the Fe(n,xn) reaction cross section
       with 14 MeV neutron source”, Report EFF-DOC-747, NEA Data Bank, Dec. 2000, Paris
   [2] B.V. Devkin, M.G. Kobozev, S.P. Simakov, V.V. Sinitca, V.A. Talalaev,
       U. Fischer, U. von Möllendorff, E. Wiegner, “Neutron Leakage Spectra from Iron
       Spheres”. In: Fusion Technology 1994, ed. by K. Herschbach et al., vol. 2,
       p. 1357, Elsevier Science, Amsterdam, 1995.
   [3] S.P. Simakov, B.V. Devkin, M.G. Kobozev, A.A. Lychagin, V.A Talalaev,
       A.A. Androsenko, “14 MeV Facility and Research in IPPE”,
       Report INDC(CCP)-351, IAEA, Vienna, 1993; Voprocy Atomnoy Nauki i Tehniki,
       Seriya Yadernye Konstanty, Obninsk, 1997, no. 3-4, p. 93.
   [4] B.V. Devkin, M. G. Kobozev, S.P. Simakov, U. Fischer, F. Kappler, U. von Möllendorff,
       “Evaluation of Corrections for Spherical-Shell Neutron Transmission Experiments
       by the Monte-Carlo Technique”, Report FZKA 5862, Karlsruhe, 1996; Voprocy Atomnoy
       Nauki i Tehniki, Seriya Yadernye Konstanty, Obninsk, 1997, no. 1-2, p. 38.

10. Data and Format:

        Filename   Size[kbytes]   Content
    -------------- ----------- -------------
     1  ippe_fe-a.htm      11    This information file
     2  ippe_fe-e.htm      52    Experiment Description
     3  mcnp_fe1.inp        6    MCNP-4C input for Fe sphere 1 (r= 4.5 cm, wall= 2.5 cm)
     4  mcnp_fe2.inp        6    MCNP-4C input for Fe sphere 2 (r=12.0 cm, wall= 7.5 cm)
     5  mcnp_fe3.inp        6    MCNP-4C input for Fe sphere 3 (r=12.0 cm, wall=10.0 cm)
     6  mcnp_fe4.inp        6    MCNP-4C input for Fe sphere 4 (r=20.0 cm, wall=18.1 cm)
     7  mcnp_fe5.inp        6    MCNP-4C input for Fe sphere 5 (r=30.0 cm, wall=28.0 cm)
     8  ippefig1.jpg       54    Fig. 1: Experimental setup
     9  ippefig2.jpg       78    Fig. 2: Configuration and sizes of five Fe spheres
    10  ippefig3.jpg       78    Fig. 3: Angular/energy distribution of '14 MeV' source peak
    11  EFF-DOC-747.pdf   425    EFF-DOC-747 NEA Data Bank Report

 SINBAD Benchmark Generation Date: 12/2004
 SINBAD Benchmark Last Update: 12/2004