Islands of nuclear stability

In this book the superactinide elements begin at Z-114 because this is the first element that was recognized in what is known as the island of stability, also referred to as the Island of Nuclear Stability. The stability of Z-114 is related to its exceptional long half-life of 30 seconds, which provides adequate time for detection and research on it. It also appears that the heavier the element, the shorter its half-life. 

These elements near the predicted islands of nuclear stability around the spherical closed shells at proton numbers 110-114 (or even 126) and 184 neutrons are typically referred to as SHEs. Although arguments have been made (Armbruster and Miinzenberg 1989) that the heavy elements that would not exist except for stabilization by nuclear shells, whether or not they are spherical, should be designated as SHEs, the term has usually been reserved for those elements in the region of the predicted spherical doubly magic nuclei. 

A number of elements beyond element 109 are predicted to lie in an island of nuclear stability around elements 112-118. Two atoms of element 112 were recently produced. It had been predicted that element 112 might not have metallic properties and would not belong in column 12 (IIB). However, the researchers found that its chemical properties are similar to those of mercury, since the atoms seemed to form metallic bonds with a gold surface. Small quantities of elements 113 (Uut) and 115 (Uup) have been produced in nuclear reactions between " " Am and " Ca, apparently forming Uup and three neutrons. The Uup then decayed to form " Uut and an alpha particle. ... 

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. 

When the more than 3600 known nuclides are plotted on the neutron/proton grid in Figure 22.3, they fall in a curved band sometimes called the "band of nuclear stability." Even within the band, only 264 of the nuclides are stable indefinitely. The remainder decay spontaneously, although their rates of decay vary enormously. On either side of the band is a "sea of instability" representing the large number of unstable neutron/proton combinations that have never been seen. Particularly interesting is the "island of stability" predicted to exist for a few superheavy nuclides near 114 protons and 184 neutrons. The first members of this group—287114,288114,289114, and 292116—were prepared in 1999 and do indeed seem to be unusually stable. Isotope 289114, for example, has a half-life of 30.4 seconds. 

Unfortunately, it is expected that the chemistry of these elements will not be able to be studied because the theoretical investigations of nuclear stability predict that these elements will be unstable and have very short hfetimes. Before this was known, a large number of theoretical calculations of the ground-state electronic configurations were made in this region because the proton number Z = 126 was long expected to be the center of the first island of stability. Now this is considered unhkely. Nevertheless, the chemistry of these elements would be very interesting. 

Abstract Shell effects on nuclear stability have created an island of relative stability for nuclides near A = 230-240 and Z = 90-92. Three nuclides, Th, and have half-Uves long enough for significant amounts to have survived since the heavy elements in the Earth s crust were created. When one of these nuclides decays, it starts a journey that ends with an isotope of lead (Z = 82, A 208). The predominant steps in this journey are a and P decays, so that each of the long-lived parents heads a distinct chain. Each chain, as well as a fourth one that is extinct, is described. 

Abstract The Island of Stability of spherical superheavy nuclides exists at the extreme limit of the Chart of the Nuclides, beyond regions of nuclear stability associated with deformed nuclear shapes. In this chapter, the reactions that are used to synthesize these transactinide nuclides are discussed. Particular emphasis is placed on the production of nuclides with decay properties that are conducive to a radiochemical measurement. The cold- and hot-fusion reactions that lead to the formation of evaporation residues are discussed, as are the physical techniques that have been used in production experiments. Recent results from " Ca-induced fusion reactions are included. Speculative methods of producing the more neutron-rich nuclides that populate the approaches to the center of the Island of Stability are also presented. 

A joint Russian and American team of physicists created two new super heavy elements—115 and 113—that provide more support for the island of stability concept. The experiments were conducted between July 14 and August 10 in 2003, but the results of the experiments were not published until February 2004. The experiments were conducted in the Joint Institute of Nuclear Research (JINR) in Dubna, Russia, and also involved the scientists of the Lawrence Berkely National Laboratory located at Berkeley, California. Only four atoms of two isotopes of ununpentium (element 115) were produced, and the results were published in a peer-reviewed scientific journal. Following is the nuclear reaction that produced these four atoms ... 

Investigation of physical and chemical properties of recently synthesized, relatively long-living isotopes of superheavy elements (SHEs) with nuclear charges Z=105 to 116 [1, 2, 3, 4] and their compounds is of fundamental importance. Their measured lifetimes may reach several hours and the nuclei near the top of the island of stability are predicted to exist for many years. The experimental study of the SHE properties is very difficult be-... 

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... 

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],... 

However, the liquid-drop model does not account for the relative stability of certain nuclei called "islands of (relative) nuclear stability" (Z and/or N = 2, 8, 20, 28, 50, 82,126,184). 

Chemists will synthesize millions of new compounds tailored for a wide spectrum of practical uses. Nuclear chemists will be involved in the synthesis of additional chemical elements, hopefully in the region of the superheavy elements predicted to exist in the island of stability. ... 

The scientific interest in the elements since the middle of the twentieth century has been closely linked to the development of physics and the demands of the Cold War arms race. As chemists and physicists looked into the interior of the atom, they learned more about the structure of matter, and that knowledge, in turn, allowed a degree of control over the creation of matter. Nuclear reactors can now produce both useful and deadly materials even as they put a new source of power in to the hands of people around the world. The atom smashers, as the cyclotrons and accelerators were sometimes called, made new elements possible, and scientists continues to explore the elements, looking for the islands of stability among the superheavy elements. 

A nuclide containing numbers of protons and neutrons that place it outside this band of stability will be unstable until it undergoes one or more nuclear reactions that take it into the band of stability. We call these unstable atoms radioactive nuclides, and the changes they undergo to reach stability are called radioactive decay. Note that the band of stability stops at 83 protons. All of the known nuclides with more than 83 protons are radioactive, but scientists have postulated that there should be a small island of stability around the point representing 114 protons and 184 neutrons. The relative stability of the heaviest atoms that have so far been synthesized in the laboratory suggests that this is true. (See Special Topic 2.1 Why Create New Elements.)-... 

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