SINBAD ABSTRACT NEA-1552/37
High energy neutron (up to 800 MeV) measurements in iron (HIMAC/NIRS)
1. Name of Experiment:
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Measurements of high energy neutrons (up to 800 MeV) penetrated through iron
shields (HIMAC/NIRS) (2002).
2. Purpose and Phenomena Tested:
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The neutron energy spectra penetrated through iron shields were measured
using the Self-TOF detector and a NE213 organic scintillator 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 and 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
and Figure 1b show the experimental arrangements using the Self-TOF detector
and NE213 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 509 cm downstream of 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)), 503 cm downstream of the copper target on the beam axis. The
measuring point (B) is selected for comparison with the Self-TOF results.
The assembly of iron shields is 100 cm x 100 cm in size and 10 cm thickness
was put onto the steel platform to fix the center of the shield on the
beam axis. The thickness of the shield assembly was changed to be 20,
40, 60, 80 and 100 cm. The mass density of iron shield is 7.8 g/cm3.
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 scintillator
(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 10
cm x 10 cm x 0.5 cm viewed by two 5.08 cm-diameter photo-multipliers
(Hamamatsu R2083) from both sides through light guides. The stop counter
is designed to cover an area 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, we selected only proton events H(n,p) and
C(n,p) reactions 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 function which has 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 100 MeV
because low energy charged particles produced in a radiator stop in the
following radiators and never reached 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 has already been measured in the energy
range up to 800 MeV experimentally at the HIMAC [4].
5. Description of Results and Analysis:
------------------------------------
The neutron energy spectra measured by the Self-TOF detector are shown
in Table 1 and Figure 3. The source neutron spectrum measured at 0 degree
on the beam axis by Kurisawa et al. [5] and the calculated results with
the MCNPX 2.1.5 Monte-Carlo code [6] combined with the LA150 cross-section
library [7] are also shown in figure 3. The spectra have a broad peak
around 200 to 300 MeV with the iron thickness up to 80 cm. The softening
of the neutron spectra can scarcely be observed with the increasing of
the shielding thickness. For the calculated spectra the broad peak and
the softening of the spectra are also observed but those are harder
than the measured results for all cases.
For the NE213 detector, neutron energy spectra measured for both detector
positions (A) and (B) are shown in Table 2 and Table 3, respectively. In
Figure 4 and in Figure 5 the measured and the calculated with the MCNPX
2.1.5 code, energy spectra are reported for both detector positions. At
position (A) in contact with the rear surface of the shield, calculations
overestimate the measurements with increasing the iron thickness in the
energy range below 100 MeV. The calculations are fairly in good agreement
with the measurements in the energy range between 100 and 400 MeV,
especially in good agreement in the whole energy range of 20 to 800 MeV
for 20 and 40 cm thick iron shields. At the position (B) continuous
neutron energy spectra could be obtained, however, large error bars can
be seen at 40 cm and 60 cm thicknesses in the energy range between 20 to
150 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 in Figure 6. The NE213 spectra cannot
reproduce the peak due to the large errors and are also much higher in
the energy region below 200 MeV for 100 thick iron 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.
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 both cases (with and
without room floor) at two iron thicknesses of 20 cm and 100 cm. The
correction factors are tabulated in Table 4. The attenuation of
neutron fluence could be obtained by integrating the neutron flux over
the energy range. Figure 8 and Table 5 show the attenuation profiles
of neutron fluence integrated from 100 to 600 MeV for Self-TOF and
MCNPX results, from 20 to 800 MeV for NE213 and MCNPX results. The
neutron fluence attenuation lengths of two different energy ranges
are summarized in Table 6.
The calculated neutron fluence are in good agreement with the
experiment for the Self-TOF and NE213(A) but largely overestimated
in the calculation for the NE231 (B) results. For the attenuation
length there is a very good agreement within 5% between experiment
and calculation.
6. Special Features:
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None
7. Author/Organizer
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Experiment and analysis:
M. Sasaki, N. Nakao, T. Nunomiya, T. Nakamura*, A. Fukumura
and M. Takada
*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, N. Nakao, T. Nonomiya, T. Nakamura, A. Fukumura and
M. Takada , "Measurements of high energy neutrons penetrated
through iron shields using the self-TOF detector and an NE213
organic liquid scintillator", Nuclear Instruments and Methods B
196 113-124(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] 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 Helium and
Carbon Ions" Nucl. Sci. Eng. 132, 30(1999).
[6] 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,(September 1999).
[7] 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
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1 himac_fe-abs.htm 16.500 This information file
2 himac_fe-exp.htm 16.576 Description of the experiment
3 fe-f1a.gif 13.853 Fig. 1a: Experimental arrangement at HIMAC of the self-TOF detector
4 fe-f1b.gif 8.780 Fig. 1b: Experimental arrangement at HIMAC of the NE213 detector
5 fe-f2.gif 11.628 Fig. 2: Schematic drawing of the Self-TOF detector
6 fe-f3.gif 13.685 Fig. 3: Comparison of self-TOF measured and MCNPX calculated spectra
7 fe-f4.gif 14.892 Fig. 4: Comparison of NE213 (A) measured and MCNPX calculated spectra
8 fe-f5.gif 15.377 Fig. 5: Comparison of NE213 (B) measured and MCNPX calculated spectra
9 fe-f6.gif 10.522 Fig. 6: Comparison of measured spectra obtained by self-TOF and NE213
(B) detectors
10 fe-f7.gif 9.120 Fig. 7: Neutron energy spectra with and without the simulation of room floor
11 fe-f8.gif 15.489 Fig. 8: Attenuation profiles of neutron fluences for each detector
12 fe-f9a.gif 5.162 Fig. 9a: Calculational geometry of the MCNPX code - Self-TOF detector
13 fe-f9b.gif 8.513 Fig. 9b: Calculational geometry of the MCNPX code - NE213 detector
14 mcnp-ne08.i 9.666 Input data for MCNPX calculations for NE213 detector without concrete
floor (behind 80cm-thick iron shield)
15 mcnp-ne08f.i 9.841 Input data for MCNPX calculations for NE213 detector with concrete
floor (behind 80cm-thick iron shield)
16 mcnp-stof04.i 4.799 Input data for MCNPX calculations for Self-TOF detector (behind
40cm-thick iron shield)
17 iron-NE213.xls 29.696 Neutron spectra by NE213 tables using Microsoft Excel(tm) format
18 iron-sTOF.xls 18.944 Neutron spectra by self-TOF tables using Microsoft Excel(tm) format
19 nim-b.pdf 339.737 Reference
File himac_fe-exp.htm contains the following tables:
Table 1: Neutron energy spectra measured by self-TOF detector
Table 2: Neutron energy spectra measured by NE213 (A) detector
Table 3: Neutron energy spectra measured by NE213 (B) detector
Table 4: Correction coefficients for subtraction of the scattered neutron components
Table 5: Comparison of neutron fluences between experimental and calculated results
Table 6: 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
