JAEA-Conf 2011-002 - 日本原子力研究開発機構

JAEA-Conf 2011-002
Figure 2 shows experimental and calculated double-differential (n,xp) cross sections from 20° to
140° in steps of 40°. The experimental data are plotted by closed circles, showing a strong angular
dependence at high emission energies above 20 MeV. The solid curves present the GNASH calculations
with the IHS model. The calculations reproduce generally well the measured spectra except for 20°. The
calculations underestimate the experimental data from 110 MeV to high-energy end at 20°.
In Fig.3, experimental and calculated double-differential (n,xα) cross sections are shown at 20°,
60°, 80° and 120°. The experimental data are plotted by closed circle. The dashed curves denote the
calculations of the GNASH code with the IHS model with ΔR =1.0 fm. These calculations underestimate
the measured spectra above 30MeV at all angles, especially at 20°.
We have paid attention to the ΔR parameter used in the IHS model to improve this
underestimation. According to the recent IHS model analysis [15], ΔR was found to have the energy
dependence. Therefore, the energy-dependence was investigated on the basis of the analyses of Al(p,xα)
data over the wide energy range up to 200 MeV [21-24], because Al is an adjacent nucleus to Si. We have
determined an optimum ΔR value for each experimental data under the condition that ΔR is less than 1.6 fm
corresponding to alpha-particle’s radius. As shown in Fig.4, the deduced ΔR values are nearly 1.1 fm in the
incident energy range below 70 MeV [23,24] close to the original values, 1.0 fm, whereas they are more
than 1.4 fm in the incident energy range above 120 MeV [21,22]. Finally the energy-dependence of the ΔR
parameter was obtained by fitting each ΔR value with the Woods-Saxon function as shown by the solid
curve in Fig.4. The energy-dependent ΔR starts to increase gradually from nearly 70 MeV and approaches
to 1.6 fm in the energy range of more than 160 MeV. The calculations with the energy–dependent ΔR
parameter are shown by the solid curves in Fig.3, reproducing the measured data better than the original
calculations with ΔR=1.0 fm. This suggests that the use of the energy-dependent ΔR parameter is necessary
in the IHS model calculations for incident energies above 70 MeV.
Fig. 2 Comparison between measured (n,xp) spectra from 20° to 140° in steps of 40° and calculation results
of GNASH code with IHS model.