通过高动量转移16O和12C的(p,d)反应寻找原子核中的张量力

The tensor forces play an important role in the pion exchange interactions that provide the most important attraction in nuclear forces. The importance of the tensor forces has been demonstrated to reproduce the properties of nuclear matter as well as to explain the binding energy of deuteron and alpha particles. In contrast, this interaction has not been included explicitly in nuclear models such as mean field models of heavier nuclei. However, recent experiments have revealed a possible important role of the tensor forces in the changes of magic numbers and the orders of single-particle orbitals in neutron-rich nuclei. In theory, recent ab-initio type calculations of light nuclei also show essential importance of the tensor forces for binding nuclei up to mass number 12. Unfortunately, experimental evidences other than deuteron and alpha are indirect and thus we need more direct evidence in heavier nuclei. Present project aims to look for effects of tensor force in 12C and 16O nuclei by deducing the internal momentum distribution at around 2 fm-1 where the effect of the tensor interactions appears as an enhancement of probability. The 2 fm-1 is 400 MeV/c momentum transfer which corresponds to 800 MeV proton beam. By measuring the differential cross sections of (p, d) reaction on 12C and 16O targets at 0 degree using proton beams from 400 MeV to 1.6 GeV at HIRFL/RIBLL2, we would like to see the different behaviors of the cross sections on the internal momentum of the picked up neutron due to the effect of the tensor interactions and search the direct evidence of tensor interaction in high-momentum component in nuclei. 16O (p, d) 15O reaction cross sections at 0 degree are measured for the transition to the normal parity states as well as to the abnormal parity state. The effect of tensor force for the momentum distribution is expected to appear strongly in an abnormal parity transition. Therefore the comparison of the energy dependence of the cross sections of those transitions will provide a clean evidence of the tensor forces. Objective of this experiment is to observe such enhancement of the cross sections in 12C(p, d) 11C and 16O(p, d) 15O reactions and related them to the momentum amplitude at around 2 fm-1.

张量力在介子的交换作用中发挥了重要作用，在核力中提供了重要的吸引作用。其重要性已经在对氘核及α粒子结合能的解释中得到了验证。在这些核中D波的混合是张量力存在的重要证据。但是张量力在涉及重核的模型中都没有被明确地考虑到。然而，最近的实验表明张量力在丰中子核的幻数和单粒子轨道排序变化中可能发挥着重要的作用。在理论方面，最近对轻核进行的ab-initio计算亦显示出张量力在形成质量数至12的核的过程中发挥着不可取代的作用。遗憾的是，实验方面仅有氘核和α粒子中存在张量力的证据，因此，通过实验寻找重核中张量力存在的直接证据是非常有必要的。本项目旨在通过探测2 fm-1处的核子动量分布来研究12C 和 16O中张量力效应。在RIBLL2上测量能量为400-1600MeV的12O(p,d)11C和16O(p,d)15O反应在零度的截面，根据不同末态下截面的能量依赖性来研究高动量成分张量力效应。

张量力也许是人们理解原子核奇特性质的关键因素，本项目通过高动量转移16O和12C的(p,d)反应寻找原子核中的张量力。在本项目支出下，研究了252Cf自发裂变中中子多重度ν和γ-射线多重度Mγ与碎裂质量A*和总动能（TKE）的关联，得到相关表达式Mγ/ν和Mγ (ν)；基于7 Li(p，n)和 7Be 反应中子源测量了56Fe 和 57Fe的千电子伏中子俘获截面和γ-射线谱；在浦项中子装置（PNF）的100 MeV电子直线加速器上利用透射法和飞行时间法测量了209Bi的0.1～100 eV的中子全截面。