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RIKEN Neutron Field in the 70-210 MeV Energy Range
1. Name of Experiment:
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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:
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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:
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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:
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None
7. Author/Organizer:
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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:
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Restricted
9. References:
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[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:
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DETAILED FILE DESCRIPTIONS
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Filename Size[bytes] Content
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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
