High energy neutron (up to 800 MeV) measurements in concrete shields (HIMAC/NIRS)
1. Name of Experiment:
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Measurements of high energy neutrons (up to 800 MeV) penetrated through
concrete shields (HIMAC/NIRS) (2001).
2. Purpose and Phenomena Tested:
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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:
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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:
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None
7. Author/Organizer
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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:
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Unrestricted
9. References:
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[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,
454(1995).
[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:
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DETAILED FILE DESCRIPTIONS
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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
detectors
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
