An Island of Stability

Since the radioactive half-lives of the known transuranium elements and their resistance to spontaneous fission decrease with increase in atomic number, the outlook for the synthesis of further elements might appear increasingly bleak. However, theoretical calculations of nuclear stabilities, based on the concept of closed nucleon shells (p. 13) suggest the existence of an island of stability around Z= 114 and N= 184. Attention has therefore been directed towards the synthesis of element 114 (a congenor of Pb in Group 14 and adjacent superheavy elements, by bombardment of heavy nuclides with a wide range of heavy ions, but so far without success. 

One isotope of element 114, with 184 neutrons, is predicted to be another doubly magic nucleus, and is therefore expected to sit right in the middle of an island of stability in the space of superheavy nuclei (Fig. 13). Nuclear scientists suspect that it may have a half-life of as much as several years. Element 114 has thus become a kind of Holy Grail for element-makers. If it turns out to be stable, this would show that these researchers are not necessarily doomed to search for increasingly fleeting glimpses of ever heavier and less stable new elements. There might be undiscovered elements out there that you can (in principle, at least) hold in your hand. 

The isotope of element 114 with 184 neutrons is predicted to be especially stable, since it has magic numbers of both protons and neutrons in its nuclei. This element may sit atop an island of stability in the sea of possible combinations of subatomic nuclear particles. Other islands, here picked out in contours whose height denotes the degree of stability, occur for lighter elements such as some isotopes of lead and tin... 

It can be seen that elements in and near the island of stability based on element 114 can be predicted to have chemical properties as follows element 114 should be a homologue of lead, that is, should be eka-lead and element 112 should be eka-mercury, element 110 should be eka-platinum, etc. If there is an island of stability at element 126, this element and its neighbors should have chemical properties like those of the actinide and lanthanide elements. 

We now know these predictions were wrong, in part. While we believe there are a group of superheavy nuclei whose half-lives are relatively long compared to lower Z elements, we do not believe they form an island of stability. Rather, we picture them as a continuation of the peninsula of known nuclei (Fig. 15.1 lb). We also believe that their half-lives are short compared to geologic time scales. Therefore, they do not exist in nature. The most stable of the superheavy nuclei, those with Z = 112, N 184, are predicted to decay by a-particle emission with half-lives of 20 days. 

The Flerov Laboratory of Nuclear Reactions (FLNR) in Dubna, Russia, has recently announced the observation of relatively long-lived isotopes of elements 108, 110, 112, 114, and 116 [63-66] confirming the over 30 years old theoretical prediction of an island of stability of spherical superheavy elements. Due to the half-lives of the observed isotopes in the range of seconds to minutes, chemical investigations of these heaviest elements in the Periodic Table appear now to be feasible. The chemistry of these elements should be extremely interesting due to the predicted dramatic influence of relativistic effects [67], In addition, the chemical identification of the newly discovered superheavy elements is highly desirable as the observed decay chains [63-66] cannot be linked to known nuclides which has been heavily criticized [68,69],... 

Naeye, Robert. An Island of Stability. Discover (August 1994) 15. 

Most superheavy elements exist for only a tiny fraction of a second. Thirty seconds is a very long life span for a superheavy element. This long life span of element 114 points to what scientists have long suspected that an island of stability would be found beginning with element 114. Based on how long element 114 lasted, their predictions may have been correct. However, scientists still must try to confirm that element 114 was in fact created. The results of a single experiment are never considered valid unless the experiments are repeated and produce the same results. 

The hunt for new elements continues. To date, many elements between 93 and 118 have been synthesized artificially nuclear reactions. The heaviest elements are very unstable and cannot be of any practical use, but scientists predicted that an island of stability exists at around element 114 (one atom of this element was reported in January 1999, and it does seem to be more stable than other similarly heavy elements). Attempts have already been made to predict the properties of, as yet, undiscovered elements using Periodic trends. 

Quantum calculations suggested that the nuclei of elements with even numbers of protons and neutrons are stable and particularly so when certain magic numbers are met (see chapter 9). An island of stability was predicted in the vicinity of the element having Z = 114 and N = 184. Such elements are of interest both Ifom the standpoint of nuclear physics and chemistry. The chemistries of individual atoms with nuclear half-lives under 10 seconds, sometimes as brief as 1 second, can be studied immediately following their creation, atom-by-atom, in accelerators using online chemical techniques. 

In a review published in 2006, GSI nuclear chemist Matthias Schadel noted that until the early 1980s scientists expected an island of stability centered at Z = 114 and N = 184 which was surrounded by a sea of instability. He declared that current studies... 

All atomic mass numbers from 1 to 238 are found naturally on earth except for masses 5 and 8. About 285 relatively stable and 67 naturally radioactive isotopes occur on earth totahng 352. In addition, the neutron, technetium, promethium, and the transuranic elements Oying beyond uranium) have now been produced artificially. In lune 1999, scientists at the Lawrence Berkeley National Laboratory reported that they had found evidence of an isotope of Element 118 and its immediate decay products of Elements 116,114, and 112. This sequence of events tended to reinforce the theory that was predicted since the 1970s that an island of stability existed for nuclei with approximately 114 protons and 184 neutrons. This island refers to nuclei in which the decay lasts for a period of time instead of a decay that occurs instantaneously. However, on luly 27,2001, researchers at LBNL reported that their laboratory and the facilities at the GSI Laboratory in Germany and at J anese laboratories failed to confirm the results of their earlier experiments where the fusion of a krypton atom with a lead target resulted in Element 118, with chains of decay leading to Elements 116, 114, and 112, and on down to Element 106. Therefore, the discovery was reported to be spurious. However, with the announcement it was said that different... 

The Karlsruhe Chart of the Nuclides has this same basic structure but with the addition of all known radioactive nuclides. The heaviest stable element is bismuth (Z = S3, N = 126). The figure also shows the location of some high Z unstable nuclides - the major thorium (Z = 90) and uranium (Z = 92) nuclides. Theory has predicted that there could be stable nuclides, as yet unknown, called superheavy nuclides on an island of stability at about Z = 114, A = 184, well above the current known range. 

The microscopic stabilization of a Z = 114 nucleus results in a spherical nucleus that is more strongly bound than predicted by the macroscopic model. This effect produces a barrier to deformations leading to fission where there would otherwise be none [10, 12, 13, 23, 25-27]. At the time of these model calculations, the Periodic Table ended at the extreme limit of the actinides (Z = 103), with some experimental evidence for observation of the first transactinide elements. The overall trend with increasing atomic number was shorter half-lives and decreasing resistance to decay by spontaneous fission. The shell-model calculations indicated that well beyond the limits of the known elements the trends might reverse, allowing an extension of the Periodic Table [9]. This led to the concept of an Island of Stability . The term superheavy elements was coined to describe the nuclides occupying the Island. 

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