JAEA-Conf 2011-002 - 日本原子力研究開発機構

JAEA-Conf 2011-002
hint at the origin of possible flaws as they try to isolate different physics processes.
The second, thick target is more meaningful as they allow for a comparison of the degree of agreement of
double-differential production yields at a different target depth. These data provide an integral check of
accumulated effects, including scattering, and absorption of the particles traversing the target material. In the
following only thick target simulations for secondary neutron production are considered.
PHITS is the multi-purpose 3-D Monte Carlo transport code system for all particles and heavy ions with all
energies up to 200 GeV. 1) Below 10 MeV/nucleon, only the ionization process for the nucleus transport is taken
into account, but above 10 MeV/nucleon the nucleusnucleus collisions up to 100 GeV/nucleon is described by
the simulation model JQMD (JAERI Quantum Molecular Dynamics).
For the ionization process of the charged particles and nuclei, the SPAR code is used for the average stopping
power, the first order of Moliere model for the angle straggling, and the Gaussian, Landau, and Vavilov theories
for the energy straggling around the average energy loss according to the charge density and velocity. In addition
to the SPAR code, the ATIMA package, developed at GSI, has been implemented as an alternative code for the
ionization process. The total nucleusnucleus reaction cross-section, as an alternative to the Shen formula, NASA
systematics developed by Tripathi was also adopted. 2) In this study, the PHITS code of version 215 was used.
FLUKA is a general purpose tool for calculations of particle transport and interactions with matter, covering
an extended range of applications spanning from proton and electron accelerator shielding to target design,
calorimetry, activation, dosimetry, detector design, Accelerator Driven Systems, cosmic rays, neutrino physics,
radiotherapy etc. 3) FLUKA implements both DPMJET and RQMD as event generators to simulate nucleus-nucleus
interactions.
De-excitation and evaporation of the excited residual nuclei is performed by calling the FLUKA evaporation
module. At medium/high energy (above a few GeV/n) the DPMJET model is used. DPMJET is a Monte Carlo
model for sampling hadron-hadron, hadron-nucleus and nucleus-nucleus collisions at accelerator and cosmic ray
energies (Elab from 5-10 GeV/n up to 1011 GeV/n) based on the two components Dual Parton Model in
connection with the Glauber formalism. The DPMJET model is not valid for energies below a few GeV/nucleon.
For this reason, RQMD model is used to enable FLUKA to treat ion interactions from 100 MeV/n up to 5
GeV/n. The RQMD is a relativistic model based on “Quantum Molecular Dynamics” (QMD). This is an approach
where individual nucleons evolve according to an effective Hamiltonian, involving two– and three–body
interaction terms. 4) In this study, the FLUKA code of version 2006 was used.
In this study, the reactions of carbon ion beam with 400 MeV/n on graphite target was considered. Therefore,
two kinds of calculations, FLUKA using RQMD model and PHITS using JQMD, were performed to compare
with the measurement. The secondary neutron fluxes were calculated at the angles of 0 0 , 30 0 , 60 0 and 90 0 .The
measurement data from experiments in HIMAC facility in Japan were used in benchmarking. 5) The calculation
model was constructed considering the experiment condition in HIMAC.
Double differential neutron yield in the angular range of 0 0 -90 0 with respect to the carbon ion beam was
calculated using PHITS and FLUKA codes. The results of benchmark calculations were presented in the Figure 1
to Figure 4 compared with the experiments.
In the forward direction, in the angle of 0 0 , the PHITS and FLUKA had been in a good agreement with
experiments in the energy range under 100 MeV and over 300 MeV. PHITS had underestimated about 40 % of
maximum near the neutron energy of 200 ~ 300 MeV. The FLUKA code has overestimated about 20 % of
maximum at the same region. In the angle of 30 0 and 60 0 , PHITS showed the underestimations in the whole
energy range. FLUKA showed the underestimations in the high energy region and over estimations in the low
energy region. But the both of two codes shows differences under the 20 % maximum for a few energy bins. At
the angle of 90 0 , both of the two codes were in good agreement with the measurements
The main difference between two codes was the shape of the neutron spectra in the angle of 30 0 and 60 0 . In the
lateral shielding design, this difference affects the dose rate for the very thick shield material. The ratio of the high
energy neutrons to the low energy neutrons affects the reduction rate of the dose rate after passing the thick shield.