The discovery of the heaviest elements
The discovery of the heaviest elements
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DOI：
10.1103/revmodphys.72.733
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发表时间：
2000-07
影响因子：
44.1
通讯作者：
S. Hofmann;G. Münzenberg
中科院分区：
文献类型：
--
作者：
S. Hofmann;G. Münzenberg
核壳模型预测，下一个超过208 Pb的双魔壳闭合是在Z= 114和126之间的质子数和中子数N= 184。实验研究的突出目标是探索球形超重元素（SHE）的这一区域。这篇文章描述了在达姆施塔特的GSI鉴定107至112号元素的实验方法。用铅和铋靶测量了冷聚变反应单中子蒸发通道的激发函数。最大横截面的测量在束能量远低于融合势垒估计在一个维度。这些研究表明，核子转移是引发聚变的一个重要过程。最近的努力，在JINR，杜布纳，调查的热熔融反应的生产SHE的使用锕系元素的目标。第一个结果是合成了元素112和114的富中子同位素。然而，最令人惊讶的结果是1999年在伯克利LBNL取得的。在对86 Kr + 208 Pb→ 294 118* 反应的研究中，测量了三条衰变链，并将其归属于超重核293 118。衰变数据显示，对于最重的元素，主要的衰变模式是α发射，而不是裂变。结果进行了讨论的理论模型的框架。本文还对实验装置的进一步发展和新技术的应用提出了计划。在更高的灵敏度，探索该地区的球形SHE的现在似乎是可行的，超过30年后的预测。
The nuclear shell model predicts that the next doubly magic shell closure beyond 208 Pb is at a proton number between Z= 114 and 126 and at a neutron number N= 184. The outstanding aim of experimental investigations is the exploration of this region of spherical superheavy elements (SHE’s). This article describes the experimental methods that led to the identification of elements 107 to 112 at GSI, Darmstadt. Excitation functions were measured for the one-neutron evaporation channel of cold-fusion reactions using lead and bismuth targets. The maximum cross section was measured at beam energies well below a fusion barrier estimated in one dimension. These studies indicate that the transfer of nucleons is an important process for the initiation of fusion. The recent efforts at JINR, Dubna, to investigate the hot-fusion reaction for the production of SHE’s using actinide targets are also presented. First results were obtained on the synthesis of neutron-rich isotopes of elements 112 and 114. However, the most surprising result was achieved in 1999 at LBNL, Berkeley. In a study of the reaction 86 K r+ 208 Pb→ 294 118*, three decay chains were measured and assigned to the superheavy nucleus 293 118. The decay data reveal that, for the heaviest elements, the dominant decay mode is alpha emission, not fission. The results are discussed in the framework of theoretical models. This article also presents plans for the further development of the experimental setup and the application of new techniques. At a higher sensitivity, the exploration of the region of spherical SHE’s now seems to be feasible, more than 30 years after its prediction.