超重核与丰中子核的产生研究

The synthesis and studies of superheavy nuclei are very important not only for exploring the existence limit of the charge and mass of atomic nuclei but also for understanding the structure of the universe. Until the end of 2015, a total of 3211 nuclides have been discovered. However, our knowledge on neutron-rich nuclei, especially heavy neutron-rich isotopes is still very scarce. The understanding of the rapid neutron capture nucleosynthesis process (r-process) and thus the origin of the heavy elements strongly relies on the knowledge of their nuclear properties. In recent years, the applicant and the members of this project have carried out some studies on the production of superheavy and neutron-rich nuclei and obtained some interesting results. We predicated the production cross sections for Z=119 and Z=120 isotopes (Phys. Rev. C89, 024615 (2014), Phys. Rev. C90, 014612 (2014)) and proposed several candidate reaction systems and their optimal incident energies for the synthesis of Z=119 and Z=120 elements. We calculated the production cross sections for isotopes along the N=126 neutron shell（Phys. Rev. C93, 014618 (2016), J. Phys. G 42, 085102 (2015)）and we are collaborating with the experimentalists from the Argonne National Laboratory (ANL) on the production of 205Au, 204Pt, 203Ir, 202Os by using the multinucleon transfer reactions in Argonne. By using the projectile fragmentation of 238U in GSI, new heavy neutron-rich isotopes of 236Ac, 224At, 221Po, 222Po, and 213Tl were discovered (Phys. Lett. B691, 234 (2010)). In this project, we plan to carry out both theoretical and experimental investigations in the production of superheavy and neutron-rich nuclei. A series of experiments will be performed using the facilities in China, Europe and USA to produce superheavy and neutron-rich isotopes and study their decay properties. Based on the new experimental results, microscopic and phenomenological models will be developed for the production of superheavy and neutron-rich nuclei with novel reaction mechanisms.

超重核的合成和性质研究不仅对于探索原子核的电荷和质量上限，而且对认识宇宙组成有十分重要的意义。目前实验上已发现3211个核素，但对丰中子核、特别是重丰中子核的研究很缺乏，这些核对核天体物理中核合成的r-过程有重要意义。项目申请人和成员近年来对超重核与丰中子核产生进行了初步研究，取得一些有意义的结果。预言了产生Z=119与120核素的最佳反应系统和入射能量，计算了沿中子幻数N=126同中子素的产生截面；正在和美国ANL合作开展利用多核子转移反应产生N=126丰中子核的实验研究；利用德国GSI的弹核碎裂反应实验产生了多个重丰中子新核素。本项目将从理论和实验两方面进行超重核与丰中子核的产生研究。在实验方面，基于现有国内大科学装置和美国与欧洲的实验装置，开展超重核与丰中子核产生的系列实验研究。在理论方面，发展完善的输运理论模型和唯象模型，通过与实验数据的比较，研究超重核与丰中子核产生的新反应机制。

在国家自然科学基金重点项目资助下，从理论和实验两方面对新核素的产生进行了系统性研究，取得了重要进展。在理论方面，发展了微观输运理论和唯象模型，研究了多核子转移反应中的准弹性碰撞、深部非弹性碰撞和准裂变三种机制；通过分析同位旋平衡过程，总动能-质量分布，角分布以及双微分截面分布，揭示了丰中子新核素的产生机理。预言了丰中子新核素的产生截面，出射角度和出射动能，为国际上开展新核素实验研究提供指导。首次对DNS模型和GRAZING模型进行比较和结合研究，指出总截面应同时包含由GRAZING模型描述的准弹转移截面和由DNS模型描述的深部非弹转移截面。研究了多核子转移反应中的方向效应和准裂变产额的贡献，改进了产生截面的计算方法。研究了N=126附近丰中子核的产生，发现放射性束流更利于产生电荷数比靶核小的丰中子核，预测了丰中子重核的产生截面。计算了热熔合反应产生Z=114新核素的蒸发剩余截面，对于280-283Fl，利用稳定弹核的最大截面在pb量级。对于290-292Fl，需要采用丰中子放射性束流与丰中子的锕系靶核的反应来合成。实验方面，研究了Z～92、N～130核区的新核素合成和重核α衰变谱学。在充气谱仪上成功合成短寿命新核素223Np，224Np，214U。研发了基于构建标准波形、基线修正、平台区拟合的波形算法，可处理时间间隔短至80 ns、幅度低至70 keV的叠加信号。基于该算法，分析了222Np的衰变谱学。