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给我们提供了有关核-核碰撞相互作用势的重要信息。特别是，势垒高度是选择聚变反应中导致合成超重元素的轰击能量的关键参数。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。为了提取铅/铋基冷聚变中的势垒分布，我们测量了^&lt；48&gt；Ti，^&lt；54&gt；Cr，^&lt；56&gt；Fe，^&lt；&gt；Ni和^&lt；70&gt；锌弹丸在^&lt；208&gt；铅靶上后角准弹性散射的激发函数。这些实验是在日本原子能机构(JAEA)的串列助推器设施中进行的。势垒分布由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得到。结果表明，势垒分布的质心偏离了几个预测的势垒高度，并向低能侧移动。考虑到弹丸的四极振动和靶的八极振动的两个声子激发的耦合效应，势垒分布的形状被很好地再现了。这项研究结果在库仑势垒反应机制和核结构的国际会议(Fusion06)和日本和美国物理学会核物理分会联席会议(HAW05)上公布，最近发表在《物理评论通讯》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.