Barrier Distributions in Heavy-Ion Fusion Reactions for Super-heavy Elements Synthesis

重离子反应中的库仑势垒分布为我们提供了有关核-核碰撞相互作用势的重要信息。特别是在合成超重元素的聚变反应中，势垒高度是选择轰击能量的一个关键参数。到目前为止，已经提出了几种核-核势，并预测了不同的势垒高度。为了提取Pb/Bi基冷聚变中的势垒分布，我们测量了^<48>Ti，^<54>Cr，^<56>Fe，^<64>Ni和^<70>Zn弹丸在^<208>Pb靶上后向准弹性散射的激发函数。实验在日本原子能机构（JAEA）的串联助推器设施进行。势垒分布来自于测量的准弹性散射截面相对于卢瑟福散射截面的一阶导数。结果发现，势皇分布的质心显示出偏离几个预测的势垒高度向低能侧。在库仑势垒下，考虑了四极振动和八极振动两种声子激发的耦合效应，计算结果较好地再现了势垒分布的形状，并在国际反应机理与核结构会议上发表（Fusion 06）和日本和美国物理学会核物理部门的联合会议（HAW 05），最近发表在《物理评论快报》上。

Coulomb barrier distribution in heavy-ion reaction gives us important information about the interaction potential for nucleus-nucleus collisions. Especially, the barrier height is a key quantity for choosing the bombarding energy in fusion reactions leading to the synthesis of super-heavy elements. Up to now, several nucleus-nucleus potentials have been proposed and different barrier heights are predicted. Therefore, it is necessary to experimentally obtain the barrier distributions in such massive systems.In order to extract the barrier distribution in Pb/Bi-based cold fusion, we have measured excitation functions for quasi-elastic scattering of ^<48>Ti, ^<54>Cr, ^<56>Fe, ^<64>Ni, and ^<70>Zn projectiles on ^<208>Pb target at backward angles. The experiments were carried out at the tandem-booster facility of Japan Atomic Energy Agency (JAEA). The barrier distributions were derived from the first derivative of measured quasi-elastic scattering cross sections relative to the Rutherford scattering cross section. It was found that the centroids of the barrier distributions show a deviation from several predicted barrier heights toward the low energy side. The shape of the barrier distributions is well reproduced by the results of a coupled-channel calculation taking account of the coupling effects of two phonon excitations of the quadrupole vibration for the projectiles and of the octupole vibration for the targets.The research results were announced in international conferences on reaction mechanism and nuclear structure at the Coulomb barrier (Fusion06) and Joint meeting of nuclear physics divisions of Japan and American Physics Societies (HAW05), and have recently published in Physical Review Letter.