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arXiv 1202.2660nucl-exnucl-th
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在30.4和40.0 MeV处中子与208 Pb的散射和核子光学势的同位旋依赖性

Neutron scattering from 208Pb at 30.4 and 40.0 MeV and isospin dependence of the nucleon optical potential

R. P. DeVito, Dao T. Khoa, Sam M. Austin, U. E. P. Berg, Bui Minh Loc

摘要:

分析涉及远离稳定核的数据时,常常需要中子散射的光学势(OP)。由于中子数据很少,而质子散射数据更丰富,因此估计中子和质子光学势的差异是有用的。这一信息包含在核子OP的同位旋依赖性中,本文试图为核子-~(208)Pb系统提供这一信息。本文的目的是获得精确的n+208 Pb散射数据,并利用它和现有的p+208 Pb和208 Pb(p,n)208$Bi*_{IAS}数据,获得30-60 MeV能量范围内核子OP的同位旋依赖性的精确估计。在30.4和40.0 MeV下测量了n+208 Pb散射的截面,典型的相对(归一化)精度为2-4%(3%)。使用密歇根州立大学的光束摆动器飞行时间系统覆盖了15至130度的角度范围。这些数据进行了分析,一致的光学模型研究的中子数据和弹性p+208 Pb散射在45 MeV和54 MeV。这些结果与45 MeV的208 Pb(p,n)反应的耦合道分析相结合,激发了208 Bi中的0^+同量异位素类似态。新的数据和分析给出了30.4MeV的核子-208 Pb OP的同位旋杂质的精确估计,它是由质子OP的库仑修正引起的。CH 89全球系统学对真实质子OP的修正只有百分之几,而对虚势的修正在核表面超过20%。基于对40 MeV的p+208 Pb弹性测量数据的分析,预测了能量在54 MeV附近的p+208 Pb OP的库仑修正也具有类似的强度和形状。

英文摘要:

Analysis of data involving nuclei far from stability often requires optical potential (OP) for neutron scattering. Since neutron data is seldom available, while proton scattering data is more abundant, it is useful to have estimates of the difference of the neutron and proton optical potentials. This information is contained in the isospin dependence of the nucleon OP. Here we attempt to provide it for the nucleon-208Pb system. The goal of this paper is to obtain accurate n+208Pb scattering data, and use it, together with existing p+208Pb and 208Pb(p,n)208$Bi*_{IAS} data, to obtain an accurate estimate of the isospin dependence of the nucleon OP at energies in the 30-60 MeV range. Cross sections for n+208Pb scattering were measured at 30.4 and 40.0 MeV, with a typical relative (normalization) accuracy of 2-4% (3%). An angular range of 15 to 130 degrees was covered using the beam-swinger time of flight system at Michigan State University. These data were analyzed by a consistent optical model study of the neutron data and of elastic p+208Pb scattering at 45 MeV and 54 MeV. These results were combined with a coupled-channel analysis of the 208Pb(p,n) reaction at 45 MeV, exciting the 0^+ isobaric analog state in 208Bi. The new data and analysis give an accurate estimate the isospin impurity of the nucleon-208Pb OP at 30.4 MeV, caused by the Coulomb correction to the proton OP. The corrections to the real proton OP given by the CH89 global systematics was found to be only few percent, while for the imaginary potential it was over 20% at the nuclear surface. Based on the analysis of the measured elastic p+208Pb data at 40 MeV, a Coulomb correction of similar strength and shape was also predicted for the p+208Pb OP at energy around 54 MeV.

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