JAEA-Conf 2011-002 - 日本原子力研究開発機構

JAEA-Conf 2011-002
Cowley et al. [18] have measured inclusive (p, 3 He) reactions on Co and Au at different incident energies in the
120 to 200 MeV region. In Figure 3 we present proton-induced 3 He production from Co [18] at 20 o in the
laboratory system, at 120, 160 and 200 MeV incident energies, in comparison with default TALYS calculations
(solid line). We observe that TALYS overestimates the pre-equilibrium production of 3 He. However calculations
with TALYS including only the two-component EM contribution and excluding the Kalbach contribution show a
large underestimation of the experimental data. Calculations applying different values of the Cstrip parameter
suggest an energy dependence for the scaling factor. We observe that for 120 MeV incident-protons, the best fit
of the data in the 30 to 90 MeV emission energy region was obtained for 0.5 ≤ Cstrip ≤ 0.75. For 160 MeV
incident-protons the best fit of the pre-equilibrium emission energy region is obtained for 0.25 < Cstrip ≤ 0.5,
whereas for the 200 MeV incident-protons the best fit is given by Cstrip ≈ 0.25.
The general underestimation of the experimental data for low emission energies in the pre-equilibrium region
may be explained as multiple pre-equilibrium emission. After a light charged particles is emitted in the preequilibrium
phase, the nucleon-target composite system may have enough residual energy to emit a second
particle before reaching statistical equilibrium; this process is defined multiple pre-equilibrium emission. TALYS
includes this mechanism only for the emission single particles (proton, neutron), whereas does not allow a
composite particle to be emitted in the pre-equilibrium phase if another particle has been produced before in the
same phase. We can observe this underestimation also in the production of complex particles from Ni at 175
MeV, as presented in Figure 2. This underestimation become more evident, or in same cases appear, when
calculations are considered with the reduced Cstrip parameter, to better fit the wide pre-equilibrium emission
region. In Figure 4, proton-induced production of 3 He from Au [18] at 20 o in the laboratory system, for incident
energies of 120, 160 and 200 MeV, is compared with default TALYS calculations, TALYS calculations with only
the contribution of the two-component EM to the pre-equilibrium emission and TALYS calculations with varying
values of the Cstrip scaling factor. We observe similar results to the emission of 3 He from Co presented in Figure
3. When TALYS calculations are fitted to the data in the single-emission pre-equilibrium region, we observe an
energy dependence in the value of the Cstrip parameter. Also in the 197 Au(p, 3 He) case, reducing the contribution
of the NT mechanism as described by Kalbach enhances the underestimation of 3 He production for lower
energies in the pre-equilibrium emission region.
We extrapolated a preliminary energy dependence for the scaling factor from the comparison of TALYS
calculations with proton data, to apply a reduction of the NT (and eventually KO, for α particles) contribution to
calculations for quasi-monoenergetic incident neutrons. Our tentative energy dependence for the Cstrip parameter
is given by CStrip = 1.9 – E / 100 MeV, for 90 MeV < E < 180 MeV, while Cstrip = 1 for E < 90 MeV. In Figure
1 we show TALYS calculations with reduced NT contribution (dashed line); these describe the experimental data
in the pre-equilibrium region with better agreement than default calculations (solid line).
Figure 3. Production of 3 He in the interaction of 120, 160 and 200 MeV protons with Co [18]. Experimental data at 20 o in the
laboratory system are compared with default TALYS calculations (solid line) and with TALYS calculations modified
reducing the Kalbach contribution to the pre-equilibrium emission. The NT contribution (Cstrip parameter) has been scaled by
a factor 0.75, 0.50, 0.25 and 0.10. “Cstrip 0.00” line represents TALYS calculations without NT contribution.