[back to index] [experiment]


ISIS Deep-Penetration of Neutrons through Concrete and Iron Shields

 1. Name of Experiment:
    ISIS Benchmark Experiment on Deep-Penetration Neutrons through Concrete and
    Iron Shields (1998)
 2. Purpose and Phenomena Tested:
    The purpose of this experiment was to measure the deep-penetration neutrons
    through a thick bulk shield at an intense spallation neutron source facility,
    ISIS, of the Rutherford Appleton Laboratory (RAL), United Kingdom [1], [2].

 3. Description of the Source and Experimental Configuration:
    The source is a thick tantalum target (total length of 296.5 mm) impinged
    by 800 MeV - 200 A protons, producing neutrons. This target, placed at the
    center of the target station, is shielded with approximately 3-m-thick steel
    and 1-m-thick ordinary concrete in the upward direction, through which the
    neutrons are transmitted (Fig.1 and Fig.2). On top of the shield of the
    target station (Fig.3), the neutron flux attenuations through concrete and
    iron shields, which were additionally placed up to 1.2-m and 0.6-m thicknesses
    respectively (Fig.4), were measured using activation detectors of graphite,
    bismuth, aluminum and a multi-moderator spectrometer using indium-oxide
    activation detector. The attenuation lengths for concrete and iron of
    high-energy neutrons above 20 MeV at 90 degrees to the proton beam axis were
    obtained from the 12C(n, 2n)11C reaction rates. The neutron energy spectra
    in the energy range from thermal to 400 MeV behind concrete and iron were also
    obtained by an unfolding analysis using the reaction rates of 12C(n, 2n)11C,
    27Al(n, a)24Na, 209Bi(n, xn)210-xBi (x=4~10), and 115In(n, g)116mIn.

 4. Measurement System and Uncertainties:
    Two types of graphite activation detectors were used: one was a disk type of
    8-cm diameter  3-cm thickness; the other was the Marinelli type (Fig.5),
    for measuring the spatial neutron flux distribution on the shield top without
    an additional shield and behind additional concrete and iron shields of
    various thicknesses. This detector uses the 12C(n, 2n)11C reaction : the half
    life of 11C is about 20 min., which makes a good rapidly activated
    neutron flux monitor for an energy above 20 MeV.

    Bismuth detectors (8-cm diameter  1.1-cm thickness), were used to obtain the
    high-energy neutron spectrum by using 209Bi(n, xn)210-xBi (x=4~12) reactions.
    Their threshold energies regularly increase from 22 MeV of 209Bi(n, 4n) to 70
    MeV of 209Bi(n, 10n) with an interval of 8 MeV corresponding to the binding
    energy per nucleon. The half lives of 200Bi to 206Bi are between 36.4 min. and
    15.31 days.
    The aluminum detector was of the Marinelli type with the same size as the
    graphite detector (see Fig.5). The threshold energy of the 27Al(n,a)24Na
    reaction is 3.25 MeV and the half life of 24Na is 15.02 hr. The cross-section
    data shown in Fig.6 are from the ENDF/B-VI high-energy library
    calculated by Fukahori using the ALICE code [3]. 
    As for the Indium-oxide loaded multi-moderator activation detector, In2O3
    powder (2.875 g) was filled in a spherical cavity of 0.735-cm radius in a
    cylindrical acryl, and it was placed in a spherical polyethylene moderator
    (Bonner sphere) [4]. Five kinds of detectors were used, which used four kinds
    of moderators and no moderator(bare). Fig.7 shows a cross-sectional view of
    these detectors. Using the reaction rates of the detectors, the neutron energy
    spectrum can be available through an unfolding technique.
    A neutron dose meter (Rem Ion Monitor, Harwell, U.K.) and a gamma-ray dose
    meter (RO2, Eberline, Inc., U.S.A) were used in a current mode for measuring
    the neutron and gamma-ray dose-equivalent rates, respectively. This
    REM-counter was a conventional BF3 ion-chamber covered with a polyethylene
    moderator of cylindrical shape, which had low sensitivity to neutrons of
    energies higher than 20 MeV.
    The specifications of each detector can be found in the Table 1. The response
    functions and cross sections of the activation detectors are tabulated in
    Table 2. The initial guess spectra that were used for the unfolding are
    tabulated in Table 3.

    The errors of the results (reaction rates) of the experiment can be estimated
    by the equation :
                delta(R) = squareroot(delta(Qh)2 + delta(c)2 + delta(p)2)

    - delta(Qh) is the error of the beam current which was estimated to be about 1%,
    - delta(c) is the statistical error of the photo peak area
    - delta(p) is the error of the peak efficiency of HPGe detector estimated by
      the EGS4 Monte Carlo code, which is within a few %.
    delta(R) is then dominated by delta(c), which varies from 2 to 50% depending on
    the total peak counts
 5. Description of Results and Analysis:
    The neutron energy spectra were obtained on the floor without an additional
    shield, behind a 60-cm-thick additional concrete shield and a 30-cm-thick
    additional iron shield.
    The obtained neutron spectrum on the shield top floor has two components: a
    hadron cascade peak of around 100 MeV in the energy range above 10 MeV and
    a broad peak including evaporation and slowing down neutrons around 500 keV
    below 10 MeV. The neutron spectrum through an additional 60-cm-thick concrete
    shield placed on the shield top shows an evaporation peak around 1 MeV and a
    rather flattened lethargy spectrum down to thermal energy, especially in the
    low-energy component below 100 keV. This reflects the slowing-down effect due
    to the elastic collisions of light elements, like hydrogen in the concrete.
    This spectrum has a typical 1/E slowing-down spectrum after the concrete.

    The neutron spectrum through a 30-cm thick iron shield also has a typical
    spectrum after the iron, where high-energy neutron components above a few MeV
    are slowed down to less than 1 MeV by inelastic collisions with iron; also, a
    broad peak over the region from 10 eV to 500 keV is remarkable due to the low
    inelastic cross section of iron in this energy region and the increasing
    neutron capture cross section below 10 keV.

    The neutron attenuation length for concrete at 90 degrees to the 800-MeV proton
    beam axis obtained in this study is compared with other experimental and
    calculated results (Fig.8 and Table 4): the present value of 125.4 g/cm2 is
    just between the values of 120 g/cm2 for 25-GeV proton by Stevenson et al. [5]
    and 143 g/cm2 for 12-GeV proton by Ban et al. [6] For the attenuation length of
    iron, the present value of 161.1 g/cm2 is slightly larger than that of 148 g/cm2
    obtained by Jeffrey et al.using a 800-MeV proton accelerator at Los Alamos
    National Laboratory [7]. Stevenson and Ban have also given values of
    147(+/-)10 g/cm2 for 25-GeV protons and 188(+/-)12 g/cm2 for 12-GeV protons,
    respectively : the present value is just between them.

    The calculations of the benchmark using the MARS Monte Carlo code are described 
    in [18] and [19].

 6. Special Features:

 7. Author/Organizer
    Experiment and analysis:
    T. Nunomiya, N. Nakao*, P. Wright, T. Nakamura, E. Kim, T. Kurosawa,
    S. Taniguchi, M. Sasaki, H. Iwase, T. Shibata, Y. Uwamino, S. Ito,
    and David R. Perry 
    *High Energy Accelerator Research Organization (KEK),
     Oho 1-1, Tsukuba, Ibaraki, 305-0801, Japan
     Phone: +81-298-79-6004

    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]  T. Nunomiya, N. Nakao, P. Wright, T. Nakamura, E. Kim, T. Kurosawa,
         S. Taniguchi, M. Sasaki, H. Iwase, T. Shibata, Y. Uwamino, S. Ito, and 
         D. R. Perry, "Experimental Data of Deep-Penetration Neutrons through a
         Concrete and Iron Shield at the ISIS Spallation Neutron Source Facility 
         using an 800-MeV Proton Beam", KEK Report 2001-24 (Feb. 2002). 

    [2]  T. Nunomiya, N. Nakao, P. Wright, T. Nakamura, E. Kim, T. Kurosawa, S.
         Taniguchi, M. Sasaki, H. Iwase, Y. Uwamino, T. Shibata, S. Ito and D. R. Perry,
         "Measurement of deep penetration of neutrons produced by 800-MeV proton beam
         through concrete and iron at ISIS", Nucl. Instr. Meth. B 179 (2001) pp89-102 

    [3]  M. Blann, Code ALICE/89, Private Communication (1989).

    [4]  Y. Uwamino, T. Nakamura, A. Hara, "Nucl. Instr. Meth." A239 (1985) 299.

    [5]  G. R. Stevenson, K. L. Liu and R. H. Thomas, "Health Phys." 43 (1982) 13.

    [6]  S. Ban, H. Hirayama, K. Kondo, S. Miura, K. Hozumi, M. Taino, A. Yamamoto,
         H. Hirabayashi and K. Katoh, "Nucl. Instr. Meth." 174 (1980) 271.

    [7]  J. S. Bull, J. B. Donahue and R. L. Burman, "Proceeding of the fourth workshop
         on simulating accelerator radiation environments", Knoxville, Tennessee,
         (September 1998) 201.

    [8]  A. Carne, G. H. Eaton, F. Atchison, T. A. Broome, D. J. Clarke, B. R.
         Diplock, B. H. Poulten and K. H. Roberts, "SNS Target Station Safety
         Assessment (Support Document to SNS Target Station Hazard Survey
         SNS/ENV/N1/83 Rev.1)". SNSPC/P6/82,(1983).

    [9]  M. Kinno and S. Yokosuka, Fujita, Co., Japan, Private Communication (1999).

    [10] E. Kim, T. Nakamura and A. Konno, "Nucl. Sci. Eng." 129 (1998) 209.

    [11] Y. Uno, Y. Uwamino, T. S. Soewarsono and T. Nakamura, "Nucl. Sci. Eng."
         122 (1996) 247.

    [12] "Evaluated Nuclear Data File", ENDF/B-VI, National Neutron Cross Section
         Center, Brookhaven National Laboratory (1990).

    [13] T. Fukahori, Proceeding of the 1990 Symposium on Nuclear Data, Tokai,
         Japan, JAERI-M 91-032 (1991) 106.

    [14] H. G. Hughes, et. al., "MCNPX for Neutron-Proton Transport", Proceedings
         of the International Conference on Mathematics and Computation, Reactor
         Physics & Environmental Analysis in Nuclear Applications, American
         Nuclear Society, Madrid Spain, (September 1999).

    [15] M. B. Chadwick, L. J. Cox, P. G. Young and A. S. Meigooni, "Nucl. Sci.
         Eng." 123 (1996) 17.

    [16] International Commission on Radiological Protection, ICRP
         Publication 51, (1987).

    [17] S. Ban, H. Hirayama and K. Katoh, "Nucl. Instr. Meth." 184 (1981) 409

    [18] T. Nunomiya, N. Nakao, H. Iwase and T. Nakamura, "Deep-Penetration
         Calculation for the ISIS Target Station Shielding Using the MARS Monte 
         Carlo Code", KEK Report 2002-12 (Mar. 2003). 

    [19] N. Nakao, T. Nunomiya, H. Iwase and T. Nakamura, "MARS14 deep-Penetration
         calculation for the ISIS Target Station Shielding", Nucl. Instr. and Meth.
         A 530 (2004) pp379-390.

10. Data and Format:

	 Filename    Size[bytes]       Content
    --------------- ------------- -----------------
   1 isis-abs.htm         23.030  This information file 
   2 isis-exp.htm         62.993  Description of Experiment 
   3 isis-fig1.gif        20.352  Fig. 1: Cross-sectional view of the neutron spallation
                                  target station with an 800-MeV proton beam at ISIS. (preview)
   4 isis-fig1.tif        36.370  Fig. 1: high quality tif 
   5 isis-fig2.gif        91.461  Fig. 2: Sketches of tantalum target and target assembly 
                                  with reflectors and moderators(preview) 
   6 isis-fig2.tif       318.710  Fig. 2: high quality tif 
   7 isis-fig3.gif        39.033  Fig. 3: Cross-sectional view of the shielding plug
                                  above the target vessel.(preview)
   8 isis-fig3.tif        72.946  Fig. 3: high quality tif
   9 isis-fig4.gif        46.041  Fig. 4: Horizontal and vertical cross-sectional views
                                  of iron igloo and additional shield. The five detector 
                                  positions of "center", "up", "down", "left" and "right" 
                                  are shown as white circles in the upper figure. (preview)
  10 isis-fig4.tif        59.842  Fig. 4: high quality tif
  11 isis-fig5.gif        14.817  Fig. 5: Cross-sectional view of the disk and Marinelli-
                                  type graphite activation detectors.(preview)
  12 isis-fig5.tif        18.844  Fig. 5: high quality tif
  13 isis-fig6.gif         4.118  Fig. 6: Cross section data of the 27Al(n,a)24Na 
                                  reaction from ENDF/B-VI calculated by Fukahori using the ALICE code. (preview)
  14 isis-fig6.tif        28.756  Fig. 6: high quality tif
  15 isis-fig7.gif        43.845  Fig. 7: Cross-sectional view of indium-oxide 
                                  multimoderator activation detectors.(preview)
  16 isis-fig7.tif        18.178  Fig. 7: high quality tif
  17 isis-fig8.gif         6.504  Fig. 8: Comparison of various data on the neutron
                                  attenuation length for concrete as a function of
                                  the incident proton energy.(preview)
  18 isis-fig8.tif        17.210  Fig. 8: high quality tif
  19 isis-fig9.gif       176.698  Fig. 9: Experimental setup with a 120-cm-thick 
                                  additional concrete shield and surrounding iron igloo
                                  at the top center of the target station.(preview)
  20 isis-fig9.tif     1.063.832  Fig. 9: high quality tif
  21 isis-fig10.gif      163.214  Fig. 10: Experimental setup with a 60-cm-thick
                                  additional concrete shield using activation detectors 
                                  and a Bonner sphere.(preview)
  22 isis-fig10.tif    1.063.832  Fig. 10: high quality tif
  23 isis-fig11.gif      168.146  Fig. 11: Experimental setup with a 10-cm-thick
                                  additional concrete shield using activation detectors. (preview) 
  24 isis-fig11.tif    1.063.832  Fig. 11: high quality tif
  25 isis-fig12.gif        3.422  Fig. 12: Measured cross section data of the 12C(n, 2n) reaction (preview)
  26 isis-fig12.tif       21.582  Fig. 12: high quality tif
  27 isis-fig13.gif        8.810  Fig. 13: Measured and calculated cross section data of 
                                  the 209Bi(n, xn) (x=4~10) reaction.(preview) 
  28 isis-fig13.tif       67.454  Fig. 13: high quality tif
  29 isis-fig14.gif        9.142  Fig. 14: Response functions of indium-loaded multi-
                                  moderator detectors and a comparison with the measured data.(preview)
  30 isis-fig14.tif       61.312  Fig. 14: high quality tif
  31 isis-fig15.gif       53.639  Fig. 15: Proton beam-current history measured at the
                                  RIKEN and graph plotted at the accelerator control room (preview)
  32 isis-fig15.tif      173.302  Fig. 15: high quality tif
  33 isis-fig16.gif       59.941  Fig. 16: Spatial distribution of the 12C(n, 2n)11C
                                  reaction rate with the thickness of an additional
                                  concrete shield.(preview)
  34 isis-fig16.tif       44.110  Fig. 16: high quality tif
  35 isis-fig17.gif       52.220  Fig. 17: Spatial distribution of the 12C(n, 2n)11C
                                  reaction rate with the thickness of an additional iron shield.(preview)
  36 isis-fig17.tif       46.010  Fig. 17: high quality tif
  37 isis-fig18.gif       49.968  Fig. 18: Attenuation profiles of the 12C(n, 2n)11C
                                  reaction rates as a function of the distance from
                                  the shield top at the "center", "up", "down", "left"
                                  and "right" positions.(preview) 
  38 isis-fig18.tif      102.708  Fig. 18: high quality tif
  39 isis-fig19.gif       36.252  Fig. 19: Attenuation profiles of the 209Bi(n, xn)210-xBi
                                  (x=4~10) reactions at the "center" position for an
                                  additional concrete shield and iron shield. (preview)
  40 isis-fig19.tif       67.408  Fig. 19: high quality tif
  41 isis-fig20.gif       29.527  Fig. 20: Attenuation profiles of the neutron and
                                  gamma-ray dose equivalents at the "center" position
                                  compared with the 12C(n, 2n) reaction rate for an
                                  additional concrete shield and iron shield.(preview)
  42 isis-fig20.tif       81.682  Fig. 20: high quality tif
  43 isis-fig21.gif       16.950  Fig. 21: Neutron energy spectra on the shield top
                                  floor, 60-cm-thick additional concrete shield and
                                  30-cm-thick additional iron shield.(preview) 
  44 isis-fig21.tif       27.018  Fig. 21: high quality tif
  45 isis_nse.pdf      1.949.212  Reference  
  46 KEKrep2002-12.pdf 1.513.153  Reference

  File isis-exp.htm contains the following tables:

Table 1:     Physical properties of the activation detectors used in this
Table 2:     Bonner sphere response functions used in the SAND2 unfolding which
             were calculated using MCNPX2.1.5 with LA150 library
Table 3:     Initial guess spectra used in SAND2 unfolding calculated by Nakao
             et al. using the ANISN code
Table 4:     Comparison of the experimental attenuation lengths of high-energy
             neutrons at 90 degrees to the proton beam axis
Table 5:     Atomic compositions and averaged densities of the target system
             and the surrounding materials
Table 6:     Shielding material information
Table 7:     Reaction rate of graphite activation detector - Reaction rate as a
             function of the detector position
Table 8:     Reaction rate of graphite activation detector - Reaction rate as a
             function of the additionnal shield thickness
Table 9:     Attenuation lengths of high-energy neutrons for concrete and iron at
             five positions on the additional shield in g/cm2
Table 10:    Reaction rate of Bi activation detector
Table 11:    Reaction rate of Al activation detector
Table 12:    Reaction rate of Indium-loaded multi-moderator detectors (Bonner sphere)
Table 13:    Dose equivalent rate measured by using rem counter
Table 14:    Neutron energy spectra on the shield top floor, on the 60-cm-thick
             additional concrete and on the 30-cm-thick additional iron shield
Table 15:    Physical quantities to be calculated
Table 16:    ICRP Publ. 51 [16] neutron to dose conversion factor

  Figures are included in GIF and TIF formats.

SINBAD Benchmark Generation Date: 6/2005
SINBAD Benchmark Last Update: 3/2006