利用高能单核子敲出反应研究14O核的谱因子

One-nucleon knockout reactions from intermediate- and high-energy radioactive beams have proved to be a powerful tool for studies of the single-particle strucure of rare isotopes far from the valley of beta stability. Recently, study shows that for deeply-bound neutron knockout, a strong reduction in the spectroscopic factor deduced from experimental cross sections by comparison to reaction theory predictions relative to the shell model calculations is found. In some nuclei, e.g. 14O and 32Ar, the spectroscopic factors are only about 25% of that predicted by the shell model theory. Research shows that Eikonal model is not applicable to calculations of the deeply-bound neutron knockout cross sections from intermediate-energy beams of proton-rich rare isotopes; And Eikonal approximation is more reliable at high energies. However,measurements at high energies are still missing. In this proposal, high energy 14O radioactive beams produced by CSR-RIBLL2 will be used to carry out single-nucleon knockout experiments. Cross sections will be measured by using the External Target Facility. Spectroscopic factors will be extracted from the measured cross sections by comparisons with the Eikonal reaction theory. Energy dependence of the reaction mechanisms will be investigated and the reason for the reduction of spectrosopic factors will be quested.

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理想实验手段。近年来，人们在利用中能(<100 AMeV)敲出反应对丰质子核谱因子进行研究时发现，深束缚中子态的谱因子远远小于理论计算值。在有些核中，如14O、32Ar，中子态谱因子的实验值甚至只有理论值的大约0.25倍。有研究认为Eikonal模型在计算中能深束缚核子敲出截面时变得不再适用;只有在高能束流下Eikonal近似才是非常可靠的。然而，到目前为止尚未有高能深束缚核子敲出反应的实验数据。在本基金的支持下，拟利用CSR-RIBLL2提供的高能14O放射性束流进行单核子敲出实验，通过外靶实验装置测量14O单核子敲出截面，结合反应理论计算提取谱因子，进而获得反应机制随束流能量的变化关系，并探索核谱因子衰减的原因。

中高能敲出反应已成为研究不稳定核结构的有力工具。通过测量敲出余核的动量分布及截面，并结合Glauber模型计算，可以得到被敲出核子的轨道角动量及谱因子。近年来的研究发现，在近滴线核中，如14O，深束缚价核子的敲出截面远远小于理论计算值。有研究认为Glauber模型对于描述深束缚核子的敲出过程不再精确。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。.在本基金的支持下，我们利用兰州重离子加速器冷却储存环（CSR）及兰州第二条放射性束流线（RIBLL2）产生了能量为约300 MeV/n的高能放射性束流14O，并利用CSR外靶实验装置对14O在碳靶上的敲出反应进行了研究。实验发现14O np敲出产物12N的产生截面远大于理论估计值，这意味着除了直接敲出机制外12N的产生还可能源于其他未知的反应机制。本工作结果表明敲出反应理论在描述远离稳定线原子核强束缚核子敲出时可能不再适用。强束缚核子被敲出的同时还可能伴随着核心激发及核子发射，从而导致强束缚核子敲出截面减小。这样一来，就可以解释为何强束缚价核子谱因子的实验值小于理论值。