SINBAD ABSTRACT NEA-1553/75
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 losses. 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: L(E)=4*pi*N(E)/(eps(E)*dOmega*Nn) where: 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: ---------------- None 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: ------------ Unrestricted 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: --------------- DETAILED FILE DESCRIPTIONS -------------------------- 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