JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構

Systematic Measurement of Neutron and
Gamma-ray Yields on Thick Targets Bombarded with
18 MeV Protons
M. Hagiwara a) , T. Sanami a) , Y. Iwamoto b) , N. Matsuda b) , Y. Sakamoto b) , Y. Nakane c) ,
H. Nakashima c) , K. Masumoto a) , Y. Uwamino d) and H. Kaneko e)
a) Radiation Science Center, KEK, b) Division of Environment and Radiation Sciences, NSED, JAEA,
c) Safety Division, J-PARC, JAEA, d) Nishina Center for Accelerator-Based Science, RIKEN,
e) Department of Advanced Radiation Technology, TARRI, JAEA
Nuclear data on proton-induced neutron and -ray
production in the energy range from 10 to 20 MeV is
important to execute the shield design and to estimate
activation of low-energy accelerator facilities for medical use
such as production of radiopharmaceuticals in positron
emission tomography (PET) and a neutron source of an
accelerator-based boron neutron capture therapy (BNCT).
A number of cyclotrons are installed in medical facilities to
produce positron emission radioisotopes such as 18 F through
the 18 O(p,n) 18 F reaction for label tracers used in PET.
The 9 Be(p, n) reaction is one of possible neutron sources used
in an accelerator-based BNCT. These nuclear reactions
simultaneously produce neutrons and -rays, and neutrons
severely activate the accelerator components and the
cyclotron room. The energy and angular distribution of
neutrons should be estimated for radiation safety as well as
clearance of the facility decommission.
However, the experimental data on the energy and
angular distribution for neutron and -ray production are
very scarce especially for proton energies from 10 to
20 MeV. Currently, shielding of the neutrons and -rays as
well as activation of accelerator components and the room
wall are calculated by using calculation codes such as
PHITS 1) and MCNPX 2) . The accuracy of the codes for
such a low energy region should be checked by experimental
data, because most of physical models implemented in the
codes were developed to describe reactions of high-energy
particles. In this report, we describe the measurement of
neutron and -ray energy spectra from various targets ( 9 Be,
Neutron flux (n·MeV -1 ·sr -1 ·C -1 )
4-33
10 1
10 2
10 3
10 4
10 5
10 6
10 7
10 8
10 9
10 10
15 deg.x10 -1
30 deg. x10 -2
60 deg. x10 -3
90 deg. x10 -4
120 deg. x10 -5
150 deg. x10 -6
0 deg.
Beryllium, p18 MeV
Present
ENDF/B-VII
Bertini+Dresner
10
0 3 6 9 12 15 18
0
Energy (MeV)
Fig. 1 Energy spectra of neutrons from thick beryllium
target induced by 18 MeV proton bombardment.
JAEA-Review 2010-065
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nat C, 27 Al, nat Cu and 181 Ta) induced by protons, and
comparisons between the experimental data and calculation
results.
The experiments were carried out with 18 MeV proton
beams delivered to the HB-1 beam line at the AVF cyclotron
of TIARA. The targets are installed in a vacuum chamber.
The NE213 organic liquid scintillators (5.08 cm in diameter
and 5.08 cm in length) were placed in directions of 0, 15, 30,
45, 60, 90, 120 and 150 o at a distance of 2.0 - 4.0 m from the
target to measure the light outputs by neutrons and -rays,
and the time-of-flight (TOF). The events of neutrons and
-rays were separated by using a pulse shape discrimination
technique and these energy spectra were analyzed by the
TOF method and the unfolding method with FERDOU
code 2) , respectively. Figure 1 and 2 show the typical
neutron energy spectra with comparison between measured
and calculation results using MCNPX with ENDF/B-VII
data library and implemented physical models (Bertini +
Dresner model) for beryllium, and using PHITS with LA150
data library for aluminum. The calculation results generally
well reproduce the measured energy spectra.
We will continue systematic measurements of neutron
and -ray spectra from accelerator components induced by
lower energy proton bombardment to check the accuracy of
evaluated data libraries and calculation codes.
References
1) H. Iwase et al., J. Nucl. Sci. Tech. 39 (2002) 1142.
2) M. B. Chadwick et al., Nucl. Sci. Eng. 131 (1999) 293.
3) K. Shin et al., Nucl. Tech. 53 (1981) 78.
Neutron flux (n·MeV -1 ·sr -1 ·C -1 )
10 2
10 3
10 4
10 5
10 6
10 7
10 8
15 deg.x10 -1
30 deg. x10 -2
60 deg. x10 -3
90 deg. x10 -4
120 deg. x10 -5
150 deg. x10 -6
0deg.
10 1
Aluminum, p18 MeV
Present
LA150
10
0 3 6 9 12 15
0
Energy (MeV)
Fig. 2 Energy spectra of neutrons from the aluminum
target induced by 18 MeV proton bombardment.