为什么113 115元素不能人工合成出来 高手来

原子核的性质呈现某种周期性的变化，当原子核内的质子数或中子数为2,8,20,28,50,82,126（126仅对中子数而言）时原子核特变稳定，上述数字称为幻数。幻数核的比结合能大，因而比较稳定，幻数核的丰度比邻近的核也要大得多。

不过科学技术发展飞速。参阅/上的报道：

科学家首次合成第117号元素 将填补已发现的第116号和118号元素之间缺失的“一环”

俄美科学家成功合成了一种拥有117个质子的新元素，它可能就是科学家一直寻找的第117号元素(ununseptium)，这将填补目前已被发现的第116号和118号元素之间缺失的“一环”。相关研究论文将在近期出版的《物理评论快报》（Physical Review Letters）上刊发。

以俄罗斯杜布纳联合核研究所尤里·奥加涅相为学术带头人的国际科研小组，使用该研究所的粒子回旋加速器，用由20个质子和28个中子组成的钙48原子，轰击含有97个质子和152个中子的锫249原子，生成了6个拥有117个质子的新原子，其中的5个原子有176个中子，另一个原子有177个中子。

杜布纳联合核研究所于2000年和2006年分别合成了第116号和迄今为止最重的第118号元素。第117号新元素成功合成后，从第112号至118号元素7种相邻新元素的产生都出自同门，这不能不说是人类科技史上一大奇观。

该项科研成果也支持了理论界长期以来的假设：新合成的元素会越来越重，它们最终会变得更加稳定，其寿命也比迄今为止的人造元素更长，这将证实“稳定岛”的存在。第117号新元素的相关实验证实了这一观点。奥加涅相小组对新元素进行放射性衰变分析后认为：“为预测超重元素‘稳定岛’的存在提供了实验证据。”

20世纪60年代，科学家提出了“稳定岛”理论。该理论认为，在质子数为114、中子数为184的区域附近存在一些衰变相对稳定的元素，这就是超重元素稳定岛。在这个“稳定岛”内的超重元素是相当稳定的，它们的半衰期甚至可能达到1015年。但到目前为止所生成的超重元素及其同位素的寿命都很短，大多在秒和毫秒的量级。

据悉，该研究的各项工作分别在俄罗斯杜布纳联合核研究所、美国加州劳伦斯利弗莫尔国家实验室、美国橡树岭国家实验室、范德堡大学、内华达大学完成。

1869年问世的门捷列夫元素周期表是宇宙的基本规律之一，也为人类认识自然提供了一把刻度精准的尺子。紧握这把尺子，核物理学家于上世纪60年代提出了“稳定岛”理论。迄今为止，人类能够合成重元素，但却始终没有登上“稳定岛”。而“岛”上的无限风光正是科学的无限魅力，她将刷新人类物理学、化学、天体演化乃至宇宙观的所有基本“页面”。成功地合成117号元素，也许能够成为通往“稳定岛”的一座航标。

from 科学网

New York Times:

A team of Russian and American scientists has discovered a new element that has long stood as a missing link among the heaviest bits of atomic matter ever produced. The element, still nameless, appears to point the way toward a brew of still more massive elements with chemical properties no one can predict.

Get Science News From The New York Times ? The team produced six atoms of the element by smashing together isotopes of calcium and a radioactive element called berkelium in a particle accelerator about 75 miles north of Moscow on the Volga River, according to a paper that has been accepted for publication at the journal Physical Review Letters.

Data collected by the team seem to support what theorists have long suspected: that as newly created elements become heavier and heavier they will eventually become much more stable and longer-lived than the fleeting bits of artificially produced matter seen so far.

If the trend continues toward a theorized “island of stability” at higher masses, said Dawn A. Shaughnessy, a chemist at Lawrence Livermore National Laboratory in California who is on the team, the work could generate an array of strange new materials with as yet unimagined scientific and practical uses.

By scientific custom, if the latest discovery is confirmed elsewhere, the element will receive an official name and take its place in the periodic table of the elements, the checkerboard that begins with hydrogen, helium and lithium and hangs on the walls of science classrooms and research labs the world over.

“For a chemist, it’s so fundamentally cool” to fill a square in that table, said Dr. Shaughnessy, who was much less forthcoming about what the element might eventually be called. A name based on a laboratory or someone involved in the find is considered one of the highest honors in science. Berkelium, for example, was first synthesized at the University of California, Berkeley.

“We’ve never discussed names because it’s sort of like bad karma,” she said. “It’s like talking about a no-hitter during the no-hitter. We’ve never spoken of it aloud.”

Other researchers were equally circumspect, even when invited to suggest a whimsical temporary moniker for the element. “Naming elements is a serious question, in fact,” said Yuri Oganessian, a nuclear physicist at the Joint Institute for Nuclear Research in Dubna, Russia, and the lead author on the paper. “This takes years.”

Various aspects of the work were done at the particle accelerator in Dubna; the Livermore lab; Oak Ridge National Laboratory and Vanderbilt University in Tennessee; the University of Nevada, Las Vegas; and the Research Institute of Atomic Reactors in Dimitrovgrad, Russia.

For the moment, the discovery will be known as ununseptium, a very unwhimsical Latinate placeholder that refers to the element’s atomic number, 117.

“I think they have an excellent convincing case for the first observation of element 117; most everything has fallen into line very well,” said Walter D. Loveland, a professor of chemistry at Oregon State University who was not involved in the work.

Elements are assigned an atomic number according to the number of protons — comparatively heavy particles with a positive electric charge — in their nuclei. Hydrogen has one proton, helium has two, and uranium has 92, the most in any atom known to occur naturally. Various numbers of charge-free neutrons add to the nuclear mass of atoms but do not affect the atomic number.

As researchers have artificially created heavier and heavier elements, those elements have had briefer and briefer lifetimes — the time it takes for unstable elements to decay by processes like spontaneous fission of the nucleus. Then, as the elements got still heavier, the lifetimes started climbing again, said Joseph Hamilton, a physicist at Vanderbilt who is on the team.

The reason may be that the elements are approaching a theorized “island of stability” at still higher masses, where the lifetimes could go from fractions of a second to days or even years, Dr. Hamilton said.

In recent years, scientists have created several new elements at the Dubna accelerator, called a cyclotron, by smacking calcium into targets containing heavier radioactive elements that are rich in neutrons — a technique developed by Dr. Oganessian.

Because calcium contains 20 protons, simple math indicates scientists would have to fire the calcium at something with 97 protons — berkelium — to produce ununseptium, element 117.

Berkelium is mighty hard to come by, but a research nuclear reactor at Oak Ridge produced about 20 milligrams of highly purified berkelium and sent it to Russia, where the substance was bombarded for five months late last year and early this year.

An analysis of decay products from the accelerator indicated that the team had produced a scant six atoms of ununseptium. But that was enough to title the paper, “Synthesis of a new element with atomic number Z=117.”

That is about the closest thing to “Eureka!” that the dry conventions of scientific publication will allow. The new atoms and their decay products displayed the trend toward longer lifetimes seen in past discoveries of such heavy elements. The largest atomic number so far created is 118, also at the Dubna accelerator.

Five of the six new atoms contained 176 neutrons to go with their 117 protons, while one atom contained 177 neutrons, said Jim Roberto, a physicist at Oak Ridge on the project.

Atomic nuclei can be thought of as concentric shells of protons and neutrons. The most stable nuclei occur when the outermost shells are filled. Some theories predict this will happen with 184 neutrons and either 120 or 126 protons: the presumed center of the island of stability.

What happens beyond that point is anyone’s guess, said Kenton Moody, a radiochemist on the team at Livermore. “The question we’re trying to answer is, ‘Does the periodic table come to an end, and if so, where does it end?’ ” Dr. Moody said.

By JAMES GLANZ