摘要
近库仑势垒(近垒)能区重离子熔合反应涉及耦合道效应和人工合成超重元素,一直是核物理学的研究热点。在所有耦合道中,核子转移是最复杂的一种,相关的实验结论也不一致。为进一步研究核子转移效应,选择丰中子弹核^(18)O参与的核反应体系,其通常有大的正Q值双中子转移道,同时质子削裂道由于其丰中子和负反应Q值特性而被抑制,因此中子转移效应预期更显著。为此,选择^(16,18)O+^(52)Cr体系进行研究,其中^(18)O+^(52)Cr有大的正Q值双中子转移道,^(16)O+^(52)Cr被选作参考体系。实验在中国原子能科学研究院北京HI-13串列加速器的静电偏转板装置上完成的,基于耦合道程序CCFULL对实验数据进行了分析。结果表明,在垒下能区^(18)O+^(52)Cr体系仅表现出微弱的与正Q值双中子转移相联系的垒下熔合截面增强,且在多个^(18)O诱发熔合反应的体系中均表现出这个特征,具有一定的系统性规律。
Near-Coulomb-barrier(near-barrier)fusion of heavy-ions is a complicated reaction process which is related to the quantum tunneling and coupled-channels effect as well as the synthesization of super-heavy elements.It has been a hot topic since the discovery of sub-barrier fusion enhancement phenomenon in 1978.The proposed concept of fusion barrier distribution has stimulated many highprecision experiments and pushed the understanding of the coupled channels involved in the nearbarrier heavy-ion fusion process.The relevant effects of low-lying inelastic excitations have been highlighted based on this idea.Among the coupled channels involved in the heavy-ion fusion process,coupling to nucleon transfers is a complicated problem.Up to now,the experimental conclusions for the transfer effects are still controversial and the theories still can’t deal with this coupling self-consistently.For studying this mechanism experimentally,the neutron-rich ^(18)O-induced fusion with medium-mass target is an ideal choice,since this type of system usually has a big positive Q-value two-neutron(2n)transfer channel and simultaneously has no positive Q-value proton stripping channels,wherein both the two factors may contribute to the sub-barrier fusion enhancement.For this,the^(16,18)O+^(52)Cr systems were selected,wherein ^(18)O+^(52)Cr was measured for studying the effect of positive Q-value 2n stripping channel while 16O+^(52)Cr for a reference.The experiment has been performed by using the electrostatic deflector at near-barrier energy region at the R60° nuclear reaction terminal of the Beijing HI-13 Tandem Accelerator at the China Institute of Atomic Energy.The fusion evaporation residues at forward small angles were separated from the scattered beam-like particles,and then identified based on the time-of-flight and energy signals of the particles,that is the TOF-E method.The experimental data were analyzed by using the coupled-channels code CCFULL.The measured fusion excitation function of ^(16)O+^(52)Cr can be well reproduced by the CCFULL calculations.While,for ^(18)O+^(52)Cr,the calculated results including both the 2^(+)_(1) vibrational state of ^(18)O and 2_(1)^(+) vibrational state of ^(52)Cr somewhat underestimate the sub-barrier experimental result.Combing with the available experimental results of ^(18)O+^(118)Sn,^(74)Ge,a systematic conclusion of no remarkable sub-barrier fusion enhancement for the systems with positive Q-value 2n-stripping channel can be tentatively obtained.This finding offers a challenge for the prevailing argument that the sub-barrier fusion of heavy-ions is greatly enhanced due to strong coupling to the positive Q-value neutron transfer channels.The present result offers a critical restriction for the current theoretical models,and whilst the experimental studies for more systems are needed to extend this systematics.
作者
段海锐
贾会明
林承键
温培威
杨磊
马南茹
杨峰
骆天鹏
张焕乔
DUAN Hairui;JIA Huiming;LIN Chengjian;WEN Peiwei;YANG Lei;MA Nanru;YANG Feng;LUO Tianpeng;ZHANG Huanqiao(China Institute of Atomic Energy,Beijing 102413,China;School of Physics and Technology,Guangxi Key Laboratory of Nuclear Physics and Technology,Guangxi Normal University,Guilin 541004,China)
出处
《原子能科学技术》
北大核心
2025年第12期2602-2607,共6页
Atomic Energy Science and Technology
基金
国家重点研发计划(2023YFA1606402)
国家自然科学基金(12275360,U2167204,12175314,12235020)
稳定支持基础科研计划。
关键词
垒下熔合增强
正Q值中子转移效应
耦合道
sub-barrier fusion enhancement
positive Q-value neutron transfer effect
coupled-channels
