不稳定核中深束缚价核子敲出机制研究

Knockout reactions at intermediate and high energies have proven to be a powerful tool for probing the single-particle structure of rare isotopes. The spectroscopic factors and orbital angular momenta of the removed nucleons can be deduced by comparison of the experimental cross sections and longitudinal-momentum distributions to those calculated in the Glauber reaction theory. Recently, study shows that for strongly bound valence nucleon knockout, the experimental cross sections are much smaller than reaction theory predictions. Research shows that the Glauber model might be not valid for the cases of knockout of strongly bound valence nucleons. The intranuclear cascade (INC) calculations suggest that nucleon evaporation from the one-nucleon removal residues plays a major role in the reduction of strongly bound nucleon removal cross sections. However, the mechanisms in the knockout of strongly bound nucleons are still not well understood. In this proposal, the proton-rich 14O beams produced by RIBLL2 will be used to bombard reaction targets. The reaction residues as well as the evaporated protons will be measured by using the External Target Facility, and the excitation energy spectrum of unbound states in 13O could then be reconstructed. The strongly bound nucleon knockout mechanism will be investigated by comparison of the experimental results to the model predictions.

中高能敲出反应已成为研究非稳定核结构的有力工具。通过测量核子敲出余核的动量分布及产生截面，并结合Glauber模型计算，可以获知被敲出核子的轨道角动量及谱因子。近年来研究发现，在近滴线核中，如14O，32Ar和36Ca，深束缚价核子的敲出截面远小于理论计算值。有研究认为Glauber模型对于描述深束缚核子的敲出不再精确。核内级联（INC）模型研究显示，深束缚核子被敲出时还可能伴随着核芯激发及核子蒸发等非直接过程，从而导致了深束缚核子敲出截面小于Glauber模型估计值。然而，人们对深束缚核子敲出机制尚未有统一的理解。基于此，本项目计划利用RIBLL2产生的丰质子14O束流轰击反应靶，通过CSR外靶装置对重碎片（12N、11C）和具有类弹速度的前冲质子进行符合测量，以重建14O单中子敲出产物13O的非束缚激发态，通过对比实验结果和相关模型计算结果，深入研究深束缚价核子敲出反应机制。

基于中高能放射性束的单核子敲出反应是探索远离β稳定线稀有核素单粒子结构的重要实验手段。近年来，人们在利用中能(<100AMeV)敲出反应对不稳定核深束缚价核子谱因子进行研究时发现，谱因子的实验提取值远远小于理论计算值。在有些核中，如14O、16C、32Ar，深束缚价核子态谱因子的实验值甚至只有理论值的大约0.25倍。在利用CSR外靶装置对14O敲出反应研究的基础之上，本工作测量了240AMeV能量下16C深束缚价质子敲出截面，结合已有的中低能区16C质子敲出截面数据，首次对深束缚价核子敲出反应提取的谱因子的束流能量依赖性进行了研究。结果显示，基于敲出反应和eikonal反应理论模型得到的谱因子并未显示出明显的能量依赖性，即：在~80和~250AMeV的能量区域，敲出反应得到的核谱因子具有很好的一致性。