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IPPE neutron transmission through vanadium shells

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

2. Purpose and Phenomena Tested
   Neutron leakage spectra between 50 keV and 15 MeV from two vanadium shells
   were measured by the time-of-flight technique using a 14 MeV neutron
   generator. The spheres had radius of 5 and 12 cm and wall thicknesses of
   3.5 and 10.5 cm.
   The experiments were performed in two phases in 1996 and 1997.

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
   310 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 vanadium
   shell. For monitoring the neutron source strength, the alpha 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.

   Two spherical shells of high purity vanadium were available for the experiment.
   They are shown in Figure 2. Their dimensions and masses are given in Table 1.

   The density of every sphere was measured and found to agree with the
   literature value of 6.09 g/cm3. 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 neutron source
   signal 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

   The 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. Their dependence on leakage neutron energy
   in the case of the smaller shell is shown in Figure 4. 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 alpha 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 into 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.[2] 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 results are presented in Table 4 for vanadium shell No. 1 as leakage
   spectrum in terms of neutrons per MeV and per source neutron. For vanadium
   shell No. 2 the measured leakage spectrum is presented in Table 5.

   MCNP-4C input data for Shells 1 and 2 (5 & 12 cm radius) are given in files
   mcnp_r5.inp and mcnp_r12.inp. In the models the spheres and the neutron
   source are described precisely, including anisotropic energy and yield
   distributions of the T(d,n) source.

   For an adequate comparison of measurements and analytical calculation, the
   convolution with the spectrometer response function, describing the energy
   resolution of the spectrometer, is necessary. It is presented in Table 6.

   A correction factor should also be applied before comparing the experimental
   spectra with the Monte Carlo time-independent calculations (see Ref. [2]).
   The function which should be multiplied with the experimental spectrum is
   shown in Figure 5.

   Refs. [1] and [2] discuss 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, B.I. Fursov, M.G. Kobozev, V.A. Talalaiev (Inst.
   of Physics and Power Engineering, Obninsk), U. von Moellendorff (Forschung-
   zentrum Karlsruhe), M. M. Potapenko (Sci. & Res. Ins. of Organic Materials).
   e-mail: simakov@ippe.rssi.ru 
      or   simakov@irs.fzk.de

   Compiler of data for Sinbad:
   P. Ortego
   SEA, Shielding Engineering and Analysis S.L.
   Avda. Atenas 75 Las Rozas, 28230 Madrid, Spain
   Phone: +3491.631.7807
   Fax: +3491.631.8266
   e-mail: p.ortego@retemail.es

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

   The data were contributed by Dr. S.P. Simakov.

8. Availability:

9. References:
   [1] S. P. Simakov et al. "Benchmarking of evaluated nuclear data for
       vanadium by a 14 MeV spherical shell transmission experiment"
       International data Committee, Report INDC(CCP)-417. October 1998.

   [2] S. P. Simakov et al. "Benchmarking of evaluated nuclear data for
       vanadium by a 14 MeV spherical shell transmission experiment"
       Forschungzentrum Karlsruhe, Report FZKA 6096, 1998.

   [3] U. von Moellendorf et al., "A 14-MeV neutron transmission experiment on
       vanadium", 19th Symposium on Fusion Technology, Lisbon, 16-20 Sept. 1996.

10. Data and Format:
    No. Filename       Size(kb) Content
    --  --------       -------- -------
    1  ippe_v-a.htm       11    This information file
    2  ippe_v-e.htm       27    Experiment Description
    3  mcnp_r5.inp        10    MCNP-4C input for V sphere 1 (r=5 cm)
    4  mcnp_r12.inp       10    MCNP-4C input for V sphere 2 (r=12 cm)
    5  ippefig1.jpg       30    Fig. 1: Experimental setup
    6  ippefig2.jpg       26    Fig. 2: 5 and 12 cm radius V spheres
    7  ippefig3.jpg       64    Fig. 3: Angular/energy distribution of '14 MeV' source peak
    8  ippefig4.jpg       55    Fig. 4: Uncertainties of leakage spectra from V shell 1
    9  ippefig5.jpg       44    Fig. 5: Correction for time-of-flight measuring technique
   10  indc-ccp-417.pdf  492    IAEA Report
   11  fzka-6096.pdf     378    Karlsruhe Report

SINBAD Benchmark Generation Date: 01/2003
SINBAD Benchmark Last Update: 01/2003