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RIKEN Neutron Field in the 70-210 MeV Energy Range

 1. Name of Experiment:
    RIKEN Development of a Quasi-monoenergetic Neutron Field from the 
    Li-7(p,n)Be-7 Reaction in the 70-210 MeV Energy Range.   

 2. Purpose and Phenomena Tested:
    A quasi-monoenergetic neutron field was developed using the Li-7(p,n)Be-7
    reaction in the energy range from 70 to 210 MeV in the ring cyclotron
    facility at RIKEN [1]. Neutrons were generated from a 10-mm-thick Li-7
    target injected by protons accelerated to 70, 80, 90, 100, 110, 120, 135,
    150 and 210 MeV.

 3. Description of Source and Experimental Configuration:
    A quasi-monoenergeric neutron field was developed at the E4 experimental
    room of the RIKEN ring cyclotron facility illustrated in Fig. 1.
    This room has a big charged-particle spectrometer, named SMART (Swinger
    and Magnetic Analyzer with a Rotator and a Twister), for nuclear-physics
    research; a part of it is used as a neutron beam line. Ions are
    accelerated in two steps with an AVF-cyclotron and a ring-cyclotron,
    and are transported to E4-room. The beam swinger permits to bombard the
    accelerated particles onto a target in a scattering chamber at any
    angle up to 110. 

    Quasi-monoenergetic neutrons were produced from a 10-mm-thick Li-7 metal
    target (99.98 atm% enriched, 0.54 g/cm3) injected by 70, 80, 90, 100,
    110, 120, 135, 150, 210 MeV protons. Proton beam was focused on the
    center of the Li target within ~2-mm-diameter. The beam intensity used
    is up to 100 nA in order to suppress the activities induced in other
    experimental instruments. 

    The protons that penetrated the Li-7 target were focused by the PQ1
    and PQ2 quadruple-magnets, and were bent towards the beam dump by a
    PD1-dipole-magnet as shown in Fig. 1. A beam dump of lead is set in the
    beam duct through the PD1, and the whole PD1 is insulated so as to be
    used as a Faraday cup. Fig. 2 shows a side view of the neutron beam
    line along with the experimental arrangement.

    The neutrons produced at 0 from the target pass through a 3-cm-thick
    acrylic vacuum window and a 120-cm-thick iron collimator having
    22-cm-wide x 22-cm-high hole, and reach the neutron measurement area.
    Concrete and iron shields are additionally equipped in order to shield
    the spurious neutrons produced at the PD1 beam dump.

    The neutron energy spectra were measured with an NE213 organic liquid
    scintillator using the time-of-flight (TOF) method. The absolute peak
    neutron yields were obtained by measurement of 0.478 MeV gamma-rays
    from Be-7 nuclei produced in the Li-7 target.

 4. Measurement System:
    The neutron energy spectra were measured by the time-of-flight (TOF)
    method using a 12.7-cm-diameter x 12.7-cm-long NE213 organic liquid
    scintillator. The neutron detector was placed both 12 and 20 m away
    from the Li-7 target in order to obtain a good time resolution of the
    TOF measurement for the high-energy neutrons. The detector efficiency
    shown in Fig. 3 was determined by a calculation code from [2].

    The peak neutron fluences were measured by two relative neutron fluence
    monitors in the position of 8.37 and 12.0 m from the Li-7 target along
    the neutron beam line. An NE213 organic liquid scintillator (5.08-cm-
    diameter x 5.08-cm-long) near to the PD1 magnet (Monitor 1) and an
    NE102A plastic scintillator (2-cm-wide x 2-cm-high x 0.5-cm-thick) at
    the collimator exit (Monitor 2), were also equipped as shown in Fig. 2
    because of an uncertainty in the amount of proton charges through the
    beam dump in a low-current experimental run. The counts of these
    neutron fluence monitors were calibrated to the absolute monoenergetic
    peak neutron fluence on the beam line after an estimation of the number
    of Be-7 nuclei produced in the Li-7 target. The number of residual Be-7
    nuclei equals the number of peak neutrons released in the 4p direction
    [3]. In order to determine the number of residual Be-7 nuclei in the
    target, 0.478 MeV gamma-ray emitted from the decay of Be-7 with a
    half-life of 53.3 day was measured with a high-purity Ge detector.
    The efficiency of the Ge-detector was determined with 3% accuracy.
    Correction factors for neutron attenuation through the acrylic window 
    and air and also neutron scattering at the collimator were evaluated
    by Monte Carlo calculation.

 5. Description of Results and Analysis:
    The peak neutron fluences at the two measuring positions of 8.37 and
    12 m from the target issued from the evaluation of the target activity
    are listed in Table 1. In this table are also listed the correction
    factors applied for the neutron attenuation through the acrylic window 
    and air and also neutron scattering at the collimator. The peak neutron
    fluences were also estimated by integrating over the peak region of the
    neutron-energy spectra resulted by the NE213 scintillator measurements.
    The fluences obtained by these two methods are listed and compared in
    the Table 2. The neutron-energy spectra measured with the TOF method
    are shown in Figure 4. The characteristics of these spectra are given
    in Table 4 and the numerical data in Tables 5, 6, and 7.

    Error Assessment:

    The absolute peak neutron fluence was obtained within 7.5% accuracy
    with the target activity measurements and within 15.6% with the
    integrated spectra over the peak region obtained by the NE213
    scintillator measurements. The detailed errors are tabulated in
    Table 3.

 6. Special Features:

 7. Author/Organizer:
    Noriaki Nakao, Tokushi Shibata:
    High Energy Accelerator Research Organization (KEK), Tanashi Branch
    Tanashi, Tokyo 188-8501, Japan
    Phone: +81-424-69-2245 (for N.N)
    FAX: +81-424-69-2145 (for N.N)
    e-mail: Noriaki.Nakao@kek.jp

    Yoshitomo Uwamino, Noriyoshi Nakanishi:
    The Institute of Physical and Chemical Research (RIKEN)
    Wako, Saitama 351-0198, Japan

    Takashi Nakamura, Masashi Takada, Eunju Kim, Tadahiro Kurosawa:
    Cyclotron and Radioisotope Center (CYRIC), Tohoku University,
    Sendai, Miyagi 980-8578, Japan
    Compiler of data for Sinbad:
    S. Kitsos
    OECD/NEA, 12 bd des Iles, 92130 Issy les Moulineaux, France
    E-mail: stavros.kitsos@free.fr

    Reviewer of compiled data:
    I. Kodeli
    OECD/NEA, 12 bd des Iles, 92130 Issy les Moulineaux, France
    e-mail: ivo.kodeli@oecd.org

 8. Availability:

 9. References:
    [1] Nakao N., et al.: "Development of a quasi-monoenergetic neutron
        field using Li-7(p,n)Be-7 reaction in the 70-210 MeV energy range
        at RIKEN", Nucl. Instr. and Meth., A420 pp218-231 (1999). 
    [2] Cecil R.A., Anderson B.D., Madey R.: Nucl. Instr. and Meth. 161,
        439 (1979).
    [3] Schery S.D., et al.: Nucl. Instr. and Meth. 147, 399 (1977).
    [3] Nakao N. homepage: http://idsun1.kek.jp/nakao/research/nyield/nyield.htm

10. Data and Format:

      Filename   Size[bytes]   Content
    ------------ ----------- -------------
  1 riken-a.htm      10,297 This information file
  2 riken-e.htm      34,255 Description of experiment
  3 riken-f1.jpg    267.420 Fig. 1: Experimental arrangement of RIKEN ring cyclotron
  4 riken-f2.jpg    215.503 Fig. 2: Cross-sectional view of the neutron-beam course
  5 riken-f3.gif      7.079 Fig. 3: Neutron detection efficiencies of a NE213 scintillator
  6 riken-f4.jpg     94.256 Fig. 4: Neutron energy spectra measured by TOF method
  7 riken-r1.pdf  1,404,897 Reference

    File riken-e.htm contains the following tables:

      Table 1:  Peak neutron fluence estimated by the target activity
      Table 2:  Peak neutron fluence measured by the NE213 scintillator
      Table 3:  Caracteristics of the neutron energy spectra 
      Table 4:  Neutron energy spectra from 70, 80 and 90 MeV protons
      Table 5:  Neutron energy spectra from 100, 110 and 120 MeV protons
      Table 6:  Neutron energy spectra from 135, 150 and 210 MeV protons

   Figures are included in GIF and JPG formats.

SINBAD Benchmark Generation Date: 05/2003
SINBAD Benchmark Last Update: 05/2003