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CERF shielding experiment at CERN (2004)

 1. Name of Experiment:
    Measurement of Neutron Energy Spectra behind Shielding of a 120 GeV/c
    Hadron Beam Facility, CERF (2004)

 2. Purpose and Phenomena Tested:
    High energy neutron spectra between 12 MeV and 380 MeV were measured using a
    120 GeV/c hadron beam on a cylindrical copper target, at the CERF (CERN-EU High
    Energy Reference Field) facility at CERN.
    Measurements were performed at various longitudinal locations behind lateral
    shields of concrete or iron, using an NE213 organic liquid scintillator.
    The corresponding MARS15 Monte Carlo simulations were also performed, and the
    results were compared to the experimental energy spectra.

 3. Description of Source and Experimental Configuration:
    Fig. 1 shows the beam line of the CERF facility with 80 or 160 cm thick
    concrete for side shields and 80 cm thick concrete and 40 cm thick iron for
    roof shield. A copper target (50 cm thick, 7 cm diameter) can be placed at
    two different locations, A or B, as shown in Fig. 1. The beam line is inclined
    horizontally at approximately 2.1 degrees. The experimental arrangement is
    presented in the subdirectory \Exp-arrangement\.
    A positively charged hadron beam consisting of a mixture of protons (34.8 %),
    pions (60.7 %) and kaons (4.5 %) with momentum of 120 GeV/c impacted on the
    target. The number of incident beam particles was measured relatively by a PIC
    (precision ionization chamber) beam monitor which is calibrated to absolute
    number of beam particles.
    Densities of shielding materials and composition of the concrete shield are
    given in Tables 1 and 2, respectively.

 4. Measurement System:
    Neutron measurements were carried out using an NE213 organic liquid scintillator
    (12.7 cm diameter by 12.7 cm long), at different positions behind the shield,
    as shown in Fig. 1. The measurement locations covered an angular range with
    respect to the beam axis between 13 and 133 degrees. The detector locations and
    their angles from the beam incidence points of target location A and B are given
    in Table 3.
    Two NE102A plastic scintillators (veto counters) of 5 mm thickness were used to
    reject charged particle events. A larger veto (30 cm × 30 cm) was located
    upstream of the NE213 detector mainly to reject muon background, and a smaller
    veto counter (15 cm × 15 cm) was in front of the NE213 to reject charged
    particles from the shielding wall or roof.
    The electronic measurement circuit: the output signal from the NE213 detector
    was divided into two by a signal divider and fed to a CFD1 and an ADC. After
    the CFD1 selected pulses from the NE213 above threshold, charged particle
    events (especially muons) from upstream detected by the large veto counter
    (L-veto) were rejected by Veto1 in a coincidence module (Coin1).
    The next one (Coin2) rejected the events that occured during the computer busy.
    The signals to ADCs from the NE213 were total or slow components which were
    generated by gating in the total or the slow (decay) region of the signal pulse.
    The signal from the small veto counter (Sveto) was fed to the ADC to get the
    total component of charged particle events from the shield. The Lveto signal
    was fed to the ADC without VETO1 only in the beginning of the experiment to
    determine the discrimination level of charged particles.

 5. Description of Results and Analysis:

    Neutron events were selected by eliminating ray events from the 2-dimensional
    view of the total and slow components of the NE213 signals, and also by
    discriminating charged particle events detected by the S-veto.
    Neutron energy spectra were obtained by the unfolding method using the FORIST
    code. The complete FORIST data are to be found in the subdirectory \CERFforist\.
    The response matrix for 12 to 380 MeV neutrons for the unfolding was made from
    the response functions for this neutron spectrometer which have been
    experimentally investigated in the neutron energy range up to 390 MeV in
    separate experiments.
    The uncertainty of the response function is 15%.

    The experiment was simulated by the authors using the Monte-Carlo MARS15 code.
    The complete MARS15 input data used in this analysis are included in the
    subdirectory \MARS-input\.
    The transport calculations are presented in details in Ref. [3].

    The numerical data of the neutron dose are given in Table 4.
    Fig. 2 shows measured neutron energy spectra behind 80 and 160 cm thick
    concrete, and 40 cm thick iron both for target locations A and B obtained by the
    unfolding method. A broad peak of cascade can be seen around 80 MeV in all energy
    spectra. Since the maximum neutron energy of the response matrix is 380 MeV, the
    experimental data above that energy could not be obtained. Bumps in the fluxes
    around the maximum energy can be seen in the spectra at forward angles since
    neutrons in the energies of higher than 380 MeV, of which fluxes are not
    negligible, contributed to the results of maximum energy group in the unfolding

    MARS15 calculation results are also shown in Fig. 2. Although slight
    discrepancies between the experiment and the calculation can be seen at forward
    angles such as the A3, B4 and B5 locations after 80 cm thick concrete, the
    calculated spectra generally agreed very well with the experimental spectra
    within the experimental errors.

    The data constitute a useful benchmark to verify the accuracy of radiation
    transport codes.

 6. Special Features:

 7. Author/Organizer:
    Experiment and analysis:
    Noriaki Nakao
  (Former Institution)
    High energy Accelerator Research Organization (KEK)
    Oho 1-1, Tsukuba, Ibaraki 306-0801, Japan
  (Present address)
    Accelerator Physics / Accelerator Division,
    Fermi National Accelerator Laboratory,
    MS220, P.O.Box 500,  Batavia, IL 60510-0500, USA
    Phone:1-630-840-3315    Fax:1-630-840-6039
    Compiler of data for Sinbad:
    B. Maidou
    URANUS, 78 470 St Rémy les Chevreuse, France
    Screened by:
    I. Kodeli
    OECD/NEA, 12 bd des Iles, 92130 Issy les Moulineaux, France

 8. Availability:

 9. References:
    [1] N. Nakao, S. Taniguchi, S.H. Rokni, S. Roesler, M. Brugger, M. Hagiwara,
        H. Vincke, H. Khater and A.A. Prinz, "Measurement of Neutron Energy Spectra
        behind Shielding of a 120 GeV/c Hadron Beam Facility, CERF", SLAC 
        RADIATION PHYSICS NOTE, RP-06-06 (2006) 

    [2] N. Nakao, S. Taniguchi, S.H. Rokni, S. Roesler, M. Brugger, M. Hagiwara,
        H. Vincke, H. Khater and A.A. Prinz, "Measurement of Neutron Energy
        Spectra behind Shielding of a 120 GeV/c Hadron Beam Facility", Proc.
        of International Conference on Accelerator Application (AccApp05),
        Venice, Italy, Aug.29-Sep.1 (2005);also SLAC-PUB-11569(2005) 

    [3] N. Nakao, "MARS15 Monte Carlo Simulation for CERF Shielding
        Experiment", SLAC RADIATION PHYSICS NOTE, RP-06-07, March 30, 2006.

    [4] N. Nakao, S. Taniguchi. S. Roesler, M. Brugger, M. Hagiwara, H. Vincke,
        H. Khater, A.A. Prinz, S.H. Rokni and K. Kosako, "Measurement and
        calculation of high-energy neutron spectra behind shielding at the
        CERF 120 GeV/c hadron beam facility", Nucl. Instrum. Methods Phys. Res.,
        B 266, 1 (2008) 93-106.

    CERF Web site by N. Nakao: http://www.slac.stanford.edu/~nakao/CERF/

10. Data and Format:

    Filename          Size[bytes] Content
    ----------------- ----------- ----------------
  1 cerf-a.htm             10,657 This information file
  2 cerf-e.htm             22,787 Tables with numerical data
  3 cerf-geo.jpg          167,901 Fig. 1: Experimental Geometry
  4 Exp-arrangement       262,314 Experimental arrangement
  5 CERFforist          1,609,762 Files for unfolding analysis
  6 MARS-input            312,811 MARS15 Monte Carlo Simulation Files
  7 cerf-spec.jpg         144,838 Fig. 2: Measured spectra
  8 RP-06-06.pdf        4,130,624 Ref. [1]
  9 slac-pub-11569.pdf    193,265 Ref. [2]
 10 RP-06-07.pdf        1,499,421 Ref. [3]

    File cerf-e.htm contains the following table:

     Table 1: Material densities.
     Table 2: Composition of concrete.
     Table 3: Detector locations and angles.
     Table 4: Measured neutron spectra.

    Figures are included in the JPG and PDF formats.

SINBAD Benchmark Generation Date: 10/2008
SINBAD Benchmark Last Update: 10/2008