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High energy neutron (up to 800 MeV) measurements in iron (HIMAC/NIRS)

 1. Name of Experiment:
    Measurements of high energy neutrons (up to 800 MeV) penetrated through iron
    shields (HIMAC/NIRS) (2002).

 2. Purpose and Phenomena Tested:
    The neutron energy spectra penetrated through iron shields were measured
    using the Self-TOF detector and a NE213 organic scintillator at HIMAC 
    (Heavy-Ion Medical Accelerator) of NIRS (National Institute of Radiological
    Sciences), Japan [1]. Neutrons were generated by bombarding 400 MeV/nucleon
    C-12 ion on a thick copper target. The neutron spectra were measured in the
    energy range from 20 MeV to 800 MeV. The neutron fluence and fluence
    attenuation length were obtained from the experimental results and the 
 3. Description of the Source and Experimental Configuration:
    The shielding experiment was performed at HIMAC PH-2 beam line. Figure 1a
    and Figure 1b show the experimental arrangements using the Self-TOF detector
    and NE213 detector, respectively. The neutrons are produced by bombarding 
    copper target with 400 MeV/nucleon C-12 ions beams on thick (stopping 
    length). The target size was 10 cm x 10 cm and 5 cm thick. A transmission-
    type ionization chamber was placed behind the end window of a beam line 
    as a beam monitor. An NE102A plastic scintillator(100mm x100mm and 3mm 
    thick) placed just in front of the shields, was also used as a relative
    monitor. The Self-TOF detector was placed 509 cm downstream of the target
    front face on the beam axis. An iron collimator of 60 cm x 60 cm and 40 cm
    thickness with a hole of 10 cm x 10 cm was set in front of the Self-TOF
    detector to decrease the accidental signals which were induced by the
    incidence of fragment charged particles on the stop counters, and also
    to inject neutrons almost normally into the detector. A veto counter
    (150 mm x 150 mm and 5 mm thick NE102A plastic scintillator), was placed
    in front of the radiator to remove fragment charged particles from neutrons.

    The Self-TOF detector was fixed at the same position, in opposition of the
    NE213 detector which was placed in contact with the shielding surface, 
    (Measuring point (A)) and distant from the shielding surface (Measuring
    point (B)), 503 cm downstream of the copper target on the beam axis. The 
    measuring point (B) is selected for comparison with the Self-TOF results.

    The assembly of iron shields is 100 cm x 100 cm in size and 10 cm thickness
    was put onto the steel platform to fix the center of the shield on the
    beam axis. The thickness of the shield assembly was changed to be 20,
    40, 60, 80 and 100 cm. The mass density of iron shield is 7.8 g/cm3.

 4. Measurement System and Uncertainties:
    The Self-TOF detector consists of radiator detectors, a start counter and
    a stop counter of nine segments. The schematic drawing of the detector is
    given in Figure 2. The radiator is a stack of 20 thin plastic scintillator
    (NE102A) of 10 cm x 10 cm with 0.6 cm thickness. Each plastic scintillator
    is viewed by a 0.95 cm-diameter photo-multiplier (Hamamatsu R1635) through
    a light guide. The start counter is a plastic scintillator (NE102A) of 10
    cm x 10 cm x 0.5 cm viewed by two 5.08 cm-diameter photo-multipliers 
    (Hamamatsu R2083) from both sides through light guides. The stop counter
    is designed to cover an area 20 cm x 20 cm x 2 cm each of which is viewed
    by a 12.7 cm-diameter photo-multiplier (Hamamatsu R1259) through a light
    guide. The distance between the start and stop counters is adjustable, and
    is chosen to be 1.2 m for a usual measurement.

    An in-coming neutron produces charged particles in twenty radiators, and
    then the charged particles emitted in the forward direction reach any one
    of nine stop counters through the start counter. The energy of the charged
    particle is determined by using the TOF method between the start and stop
    counters. In this detector, we selected only proton events H(n,p) and 
    C(n,p) reactions to obtain the detector response function. The neutron
    energy spectrum can be obtained from the measured proton energy spectrum
    using an unfolding method with the response function which has already
    been measured for neutrons in the energy range of 60 to 800 MeV [2].
    Although the Self-TOF detector can measure neutron above 30 MeV in 
    principle, the detection efficiency is very low for neutrons below 100 MeV
    because low energy charged particles produced in a radiator stop in the 
    following radiators and never reached the start and stop counters.

    The NE213 scintillator (12.7 cm diam. by 12.7 cm thick) was coupled with
    the R4144 photo-multiplier connected to E1458 base (Hamamatsu Photonics.
    Co. Ltd.), which is designed to expand the dynamic range of output pulses
    for high-energy neutron measurements [3]. The thin NE102A plastic
    scintillator (15 cm by 15 cm square and 0.5 cm thick), coupled with the
    H1949 photo-multiplier and base (Hamamatsu Photonics. Co. Ltd.), were
    placed in front of the NE213 scintillator as  veto counter to 
    discriminate charged particles from non-charged particles, neutrons and
    photons. The response matrix has already been measured in the energy
    range up to 800 MeV experimentally at the HIMAC [4].   

 5. Description of Results and Analysis:
    The neutron energy spectra measured by the Self-TOF detector are shown 
    in Table 1 and Figure 3. The source neutron spectrum measured at 0 degree 
    on the beam axis by Kurisawa et al. [5] and the calculated results with
    the MCNPX 2.1.5 Monte-Carlo code [6] combined with the LA150 cross-section
    library [7] are also shown in figure 3. The spectra have a broad peak
    around 200 to 300 MeV with the iron thickness up to 80 cm. The softening
    of the neutron spectra can scarcely be observed with the increasing of
    the shielding thickness. For the calculated spectra the broad peak and
    the softening of the spectra are also observed but those are harder 
    than the measured results for all cases.

    For the NE213 detector, neutron energy spectra measured for both detector
    positions (A) and (B) are shown in Table 2 and Table 3, respectively. In 
    Figure 4 and in Figure 5 the measured and the calculated with the MCNPX 
    2.1.5 code, energy spectra are reported for both detector positions. At
    position (A) in contact with the rear surface of the shield, calculations
    overestimate the measurements with increasing the iron thickness in the
    energy range below 100 MeV. The calculations are fairly in good agreement
    with the measurements in the energy range between 100 and 400 MeV, 
    especially in good agreement in the whole energy range of 20 to 800 MeV 
    for 20 and 40 cm thick iron shields. At the position (B) continuous
    neutron energy spectra could be obtained, however, large error bars can
    be seen at 40 cm and 60 cm thicknesses in the energy range between 20 to
    150 MeV. 

    Since the measured position (B) of the NE213 detector is almost the same
    position where the Self-TOF was set, the neutron energy spectra measured
    by these two detectors are compared in Figure 6. The NE213 spectra cannot 
    reproduce the peak due to the large errors and are also much higher in
    the energy region below 200 MeV for 100 thick iron than the Self-TOF 
    spectra, because the non-collimated NE213 detector detects a lot of
    neutron components scattered from the shield and the room floor.

    In order to obtain the neutron fluence attenuation length, the 
    contribution of the room scattered neutrons must be subtracted from 
    the NE213 results. This components were estimated by MCNPX calculations,
    Figure 7 shows the calculated energy spectra in both cases (with and
    without room floor) at two iron thicknesses of 20 cm and 100 cm. The 
    correction factors are tabulated in Table 4. The attenuation of 
    neutron fluence could be obtained by integrating the neutron flux over
    the energy range. Figure 8 and Table 5 show the attenuation profiles
    of neutron fluence integrated from 100 to 600 MeV for Self-TOF and 
    MCNPX results, from 20 to 800 MeV for NE213 and MCNPX results. The
    neutron fluence attenuation lengths of two different energy ranges
    are summarized in Table 6.

    The calculated neutron fluence are in good agreement with the
    experiment for the Self-TOF and NE213(A) but largely overestimated
    in the calculation for the NE231 (B) results. For the attenuation
    length there is a very good agreement within 5% between experiment
    and calculation. 

 6. Special Features:

 7. Author/Organizer
    Experiment and analysis:
    M. Sasaki, N. Nakao, T. Nunomiya, T. Nakamura*, A. Fukumura
    and M. Takada 
    *Department of Quantum Science and Energy Engineering, Tokohu 
     University Aoba 01, Aramaki, Aoba-ku, Sendai 980-8579, Japan
     Phone : +81 (22) 217-7805
     Fax : +81 (22) 217-7809  
    Compiler of data for Sinbad:
    S. Kitsos
    OECD/NEA, 12 bd des Iles, 92130 Issy les Moulineaux, France
    Reviewer of compiled data:
    I. Kodeli
    OECD/NEA, 12 bd des Iles, 92130 Issy les Moulineaux, France
 8. Availability:

 9. References:
    [1] M. Sasaki, N. Nakao, T. Nonomiya, T. Nakamura, A. Fukumura and 
        M. Takada , "Measurements of high energy neutrons penetrated 
        through iron shields using the self-TOF detector and an NE213
        organic liquid scintillator", Nuclear Instruments and Methods B
        196 113-124(2002)
    [2] M. Sasaki, N. Nakao,T. Nunomiya, T. Nakamura, T. Shibata,
        A. Fukumura, "Response Function Measurements of the Self-TOF
        Neutron Detector for Neutrons up to 800 MeV" J. Nucl.Sci.
        Technol., Vol 38, No.1, 8(2001).
    [3] N. Nakao,T. Nakamura, M. Baba, Y. Uwamino, N. Nakanishi, 
        H. Nakashima and S. Tanaka, Nucl.Instrum. and Methods, A362, 
    [4] M. Sasaki, N. Nakao,T. Nunomiya, T. Nakamura, T. Shibata, 
        A. Fukumura, "Measurements of the response functions of the
        NE213 organic liquid scintillator to neutrons up to 800 MeV" 
        Nucl.Instrum. and Methods, A480, 188(2002).
    [5] T. Kurosawa, N. Nakao,T. Nakamura, Y. Uwamino,T. Shibata, 
        A. Fukumura and K. Murakami, "Measurements of Secondary Neutrons
        Produced from Thick Targets Bombarded by High-Energy Helium and
        Carbon Ions" Nucl. Sci. Eng. 132, 30(1999).
    [6] H.G. Hughes, et al. "MCNPX for Neutron-Proton Transport",
        Proceedings of the Inter. Conf. on Mathematics and Computation,
        Reactor Physics & Environmental Analysis in Nuclear applications,
        American Nucl. Society, Madrid spain,(September 1999).
    [7] M.B. Chadwick, L.J. Cox, P.G. Young and A.S. Meigooni, 
        Nucl. Sci. Eng. 123, 17(1996)

10. Data and Format:

         Filename        Size[bytes]  Content
    -------------------- ----------- -------------
    1  himac_fe-abs.htm  16.500  This information file
    2  himac_fe-exp.htm  16.576  Description of the experiment
    3  fe-f1a.gif        13.853  Fig. 1a: Experimental arrangement at HIMAC of the self-TOF detector
    4  fe-f1b.gif         8.780  Fig. 1b: Experimental arrangement at HIMAC of the NE213 detector
    5  fe-f2.gif         11.628  Fig. 2: Schematic drawing of the Self-TOF detector
    6  fe-f3.gif         13.685  Fig. 3: Comparison of self-TOF measured and MCNPX calculated spectra
    7  fe-f4.gif         14.892  Fig. 4: Comparison of NE213 (A) measured and MCNPX calculated spectra
    8  fe-f5.gif         15.377  Fig. 5: Comparison of NE213 (B) measured and MCNPX calculated spectra  
    9  fe-f6.gif         10.522  Fig. 6: Comparison of measured spectra obtained by self-TOF and NE213
                                         (B) detectors
   10  fe-f7.gif          9.120  Fig. 7: Neutron energy spectra with and without the simulation of room floor
   11  fe-f8.gif         15.489  Fig. 8: Attenuation profiles of neutron fluences for each detector
   12  fe-f9a.gif         5.162  Fig. 9a: Calculational geometry of the MCNPX code - Self-TOF detector
   13  fe-f9b.gif         8.513  Fig. 9b: Calculational geometry of the MCNPX code - NE213 detector
   14  mcnp-ne08.i        9.666  Input data for MCNPX calculations for NE213 detector without concrete
                                 floor (behind 80cm-thick iron shield)
   15  mcnp-ne08f.i       9.841  Input data for MCNPX calculations for NE213 detector with concrete
                                 floor (behind 80cm-thick iron shield)
   16  mcnp-stof04.i      4.799  Input data for MCNPX calculations for Self-TOF detector (behind
                                 40cm-thick iron shield)
   17  iron-NE213.xls    29.696  Neutron spectra by NE213 tables using Microsoft Excel(tm) format
   18  iron-sTOF.xls     18.944  Neutron spectra by self-TOF tables using Microsoft Excel(tm) format 
   19  nim-b.pdf        339.737  Reference 
    File himac_fe-exp.htm contains the following tables:

      Table 1:    Neutron energy spectra measured by self-TOF detector 
      Table 2:    Neutron energy spectra measured by NE213 (A) detector   
      Table 3:    Neutron energy spectra measured by NE213 (B) detector
      Table 4:    Correction coefficients for subtraction of the scattered neutron components 
      Table 5:    Comparison of neutron fluences between experimental and calculated results 
      Table 6:    Attenuation lengths of the neutron fluence for each detector

    Figures are included in GIF format.

SINBAD Benchmark Generation Date: 5/2005
SINBAD Benchmark Last Update: 5/2005