[back to index] [experiment]


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

 1. Name of Experiment:
    Measurements of high energy neutrons (up to 800 MeV) penetrated through 
    concrete shields (HIMAC/NIRS) (2001).

 2. Purpose and Phenomena Tested:
    The neutron energy spectra penetrated through concrete shields were measured
    using the Self-TOF detector, an NE213 organic liquid scintillator and the Bi
    and C activation detectors 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 attenuation length were obtained from the experimental
    results and the calculation.
 3. Description of the Source and Experimental Configuration:
    The shielding experiment was performed at HIMAC PH-2 beam line. Figure 1a,
    Figure 1b and Figure 1c show the experimental arrangements using the
    Self-TOF detector, NE213 detector and the (Bi and C) activation 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 506 cm downstream from 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)), 500 cm downstream of the copper target on the beam axis. The 
    measuring point (B) is selected for comparison with the Self-TOF results.
    Five pairs of Bi and C activation detectors were insert between each 
    concrete shield of 50 cm thickness (50, 100, 150 and 200 cm thickness)
    and behind the most downstream shield of 250 cm thickness on the beam 
    line, simultaneously. After 10 hours irradiation, the measurements of the
    gamma-rays from the activation detectors were carried out with two
    high-purity Germanium (HPGe) detectors (GC-1818 and GC-2020, Canberra
    Industries, Inc.).

    The assembly of concrete shields is 100 cm x 100 cm in size was put onto
    the steel platform to fix the center of the shield on the beam axis. The
    Self-TOF detector and the NE213 detector were used to measure neutron energy 
    spectra penetrating through shields up to 200 cm thickness, Bi and C 
    activation detectors were used to measure them up to 250 cm thickness.
 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 scintillators
    (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
    10cm x 10cm x 0.5cm viewed by two 5.08 cm-diameter photo-multiplier
    (Hamamatsu R2083) from both sides through each light guide. The stop counter
    is designed to cover an area of 60 cm x 60 cm and is segmented into nine 
    plastic scintillators (NE102A) of 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, only proton events H(n,p) and C(n,p) reactions
    have been selected 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 functions which have 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 
    130 MeV because low energy charged particles produced in a radiator stop
    in the following radiators and never reach 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 have already been measured in the energy range up to
    800 MeV experimentally at the HIMAC [4]. 

    The Bismuth detector, 8 cm-diam. x 1.1 cm-thickness, was used through the
    209Bi(n,4n)206Bi to 209Bi(n,10n)200Bi reactions. The cross section data
    have already been measured by Kim et al.[5] in the energy range of 20 to 
    150 MeV and the measured data are in good agreement with ENDF/V-VI high-
    energy library data [6] calculated by Fukahori [7]. Their threshold energies
    monotonously increase from 22 MeV of 209Bi(n,4n) to 70 MeV of 209Bi(n,10n)
    with the interval of 8 MeV corresponding to binding energy per nucleon. 
    The half lives of Bi-200 to Bi-206 are between 36.4 min. and 15.31 days. 
    The physical properties of 209Bi(n,xn) reaction are shown in Table 1.

    The 12C(n,2n)11C reaction has the threshold energy of about 20 MeV and the 
    reaction cross section has recently been measured up to 150 MeV also by
    Kim and al.[5] and [8], which has almost constant value of about 20 mb 
    above 20 MeV. The half life of C-11 is about 20 min., which is shortly-
    activated good neutrons flux monitor of energy above 20 MeV. The detector
    size is 8 cm-diam. x 1 cm-thickness.

 5. Description of Results and Analysis:
    The neutron energy spectra measured by the Self-TOF detector are shown 
    in Table 2 and Figure 3 compared with the results of the LAHET 2.7 Monte
    Carlo code calculation [9]. The source neutron spectrum measured at
    0 degree on the beam axis by Kurosawa et al. [10] is also shown in
    Figure 3. The spectra have a broad peak around 200 to 300 MeV and the
    shapes of the spectra do not change so much with the concrete thickness.
    The softening of the neutron spectra can scarcely be observed with the 
    increasing of the shielding thickness. For the calculated spectra, the
    LAHET results tend to overestimate with increasing the thickness, 
    especially for neutrons above 300 MeV. At 200 cm thickness, the
    discrepancy between measurements and calculation is growing up to
    factor 7 in the energy range of 300 MeV to 400 MeV.

    The neutron energy spectra measured by NE213 for both detector positions
    (A) and (B) are shown in Table 3 and Table 4, respectively. They are 
    respectively compared in Figure 4 and in Figure 5 with the results of
    MCNPX calculation [11] combined with the LA150 cross section library [12],
    and also with the source neutron spectrum [10]. MCNPX results underestimate
    the measurements in the energy range below 100 MeV and above 400 MeV, and
    overestimate that in the in the energy range between 150 and 400 MeV. With
    increasing the concrete thickness, the calculated spectra show a good
    agreement with the experimental results up to 150 cm, but large 
    underestimation can be seen at 200 cm thickness in the energy range
    below 100 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. The NE213 spectra cannot reproduce
    the peak due to the large errors and are also much higher in the energy
    region below about 100 MeV  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.
    Concerning Activation detectors, neutron energy spectra are shown in
    Table 5 and in Figure 6. The calculated results with the MCNPX are also
    shown on the  same figure. The measured spectra give large overestimation
    of 300% at 50 cm depth of 250 cm shielding thickness compared with the
    MCNPX results. This large discrepancy becomes smaller with the shield
    thickness and at 250 cm depth the MCNPX calculation gives very good
    agreement with the experimental results.
    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 the two cases (with and without room floor) 
    at two concrete thicknesses of 100 cm and 200 cm. The correction factors
    are tabulated in Table 6. The attenuation of neutron fluence could be
    obtained by integrating the neutron flux over the energy range. Figure 8
    shows the attenuation profiles of neutron fluence integrated from 100 to
    600 MeV for Self-TOF and LAHET results, from 20 to 800 MeV for NE213  and
    Bi and C activation detectors and MCNPX results. The neutron fluence
    attenuation lengths of two different energy ranges are summarized in
    Table 7. The calculated neutron fluence are in good agreement with the
    experiment for the Self-TOF and NE213(A) but the experimental results
    become smaller than the calculated results with increasing the shielding
    thickness. For the attenuation length, calculated results indicate a 
    little larger values than the measured ones up to 27% for all measurements.

 6. Special Features:

 7. Author/Organizer
    Experiment and analysis:
    M. Sasaki, E. Kim, T. Nunomiya, T. Nakamura*, N. Nakao, T. Shibata, 
    Y. Uwamino, S. Ito and A. Fukumura 
    *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, E. Kim, T. Nunomiya, T. Nakamura, N. Nakao, T. Shibata, 
        Y. Uwamino, S. Ito and A. Fukumura, "Measurements of high energy
        neutrons penetrated through concrete shields using the self-TOF,
        NE213 and activation detectors", Nuclear Science and Engineering 
        Vol.141 Number 2 140-153(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] E. Kim, T. Nakamura and A. Konno, "Measurements Neutrons Spallation
        Cross Sections of C-12 and Bi-209 in the 20 to 150 MeV Energy Range",
        Nucl. Sci. Eng. 129, 209(1998).
    [6] "Evauated Nuclear Data File", ENDF/B-VI, National Neutron Cross
        Section Center, Brookhaven National Laboratory (1990).
    [7] T. Fukahori, Proceedings of the 1990 Symposium on Nuclear Data,
        Tokai, Japan, JAERI-M 91-032, 106(1991).
    [8] Y. Uno, Y. Uwamino, T.S. Soewarsono and T. Nakamura, "Measurements
        of the Neutron Activation Cross Sections of C-12, Si-30, Ti-47, 
        Ti-48, Cr-52, Co-59 and Ni-58 between 15 and 40 MeV", Nucl. Sci. 
        Eng. 122, 247(1996). 
    [9] R.E. Prael, H. Lichtenstein, "User Guide to LCS: The LAHET Code
        System", MS B226, LANL(1989).
   [10] 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 Neon Ions",
        Journal of Nucl. Sci. and Tech., 36, 41(1999).
   [11] 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, (1999).
   [12] 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-conc-abs.htm  20.268   This information file
    2  himac-conc-exp.htm  18.865   Description of the experiment
    3  conc-f1a.gif        24.327   Figure 1a: Experimental arrangement at HIMAC of the self-TOF detector
    4  conc-f1b.gif        15.824   Fig. 1b: Experimental arrangement at HIMAC of the NE213 detector
    5  conc-f1c.gif        16.269   Fig. 1c: Experimental arrangement at HIMAC of the Bi and C Activation
    6  conc-f2.gif          9.293   Fig. 2: Schematic drawing of the Self-TOF detector
    7  conc-f3.gif         16.724   Fig. 3: Comparison of self-TOF  measured and LAHET calculated spectra
    8  conc-f4.gif         17.060   Fig. 4: Comparison of NE213 (A) measured and MCNPX calculated spectra
    9  conc-f5.gif         17.073   Fig. 5: Comparison of NE213 (B) measured and MCNPX calculated spectra  
   10  conc-f6.gif         16.367   Fig. 6: Comparison of Bi and C  measured and MCNPX calculated spectra 
   11  conc-f7.gif         12.243   Fig. 7: Neutron energy spectra with and without the simulation of room floor
   12  conc-f8.gif         17.990   Fig. 8: Attenuation profiles of neutron fluences for each detector
   13  conc-f9a.gif         9.715   Fig. 9a: Calculational geometry of the MCNPX code - NE213 detector
   14  conc-f9b.gif         4.297   Fig. 9b: Calculational geometry of the MCNPX code - activation detectors
   15  mcnp-bi.i           11.242   Input data for MCNPX calculations for NE213 detector (behind concrete
                                    shield, Bi activation detector)  
   16  conc-sTOF.xls       18.432   Neutron spectra by self-TOF tables using Microsoft Excel(tm) format 
   17  conc-NE213.xls      32.768   Neutron spectra by NE213 tables using Microsoft Excel(tm) format
   18  conc-bi.xls         27.648   Neutron spectra by Bi and C tables using Microsoft Excel(tm) format 
   19  nse.pdf            409.243   Reference

    Note that the neutron spectra measured by the Self-TOF detector are different in
    the nse.pdf and in the conc-sTOF.xls because of different unfolding codes used.
    (nse.pdf <- FERDO-U, conc-sTOF.xls <- FORIST). The *xls. data should be used.

    File himac-conc-exp.htm contains the following tables:

      Table 1 :    Physical parameters of activation detectors
      Table 2 :    Neutron energy spectra measured by self-TOF detector 
      Table 3 :    Neutron energy spectra measured by NE213 (A) detector   
      Table 4 :    Neutron energy spectra measured by NE213 (B) detector
      Table 5 :    Neutron energy spectra measured by Bi and C Activation detectors
      Table 6 :    Correction coefficients for subtraction of the scattered neutron components
      Table 7 :    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