Nuclear Chemists

Another branch of physical chemistry is nuclear chemistry. Nuclear chemists work with radioactive materials, which may occur naturally or be produced artificially in nuclear reactors. Nuclear chemists study the properties of these substances and investigate ways in which radioactive materials may be useful in a wide range of appUcations, including medicine and agriculture among other fields. 

For the past three-quarters of a century, nuclear chemists have synthesized a total of 28 elements that do not occur in nature but occupy positions in the periodic table after the element uranium. As of 2012, a total of 118 elements are known. Nuclear chemists continue to work at extending the periodic table to even heavier elements. 

Almost one-quarter of the chemical elements do not occur on Earth naturally. They have been synthesized in laboratories. 

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American nuclear chemist Glenn Seaborg s team of experimenters isolates plutonium, which proves to be a better fuel for nuclear reactors than uranium because of its greater energy yield. 

Although much of the preceding discussion involved the synthesis of new molecules by organic and inorganic chemists, there is another area of chemistry in which such creation is important—the synthesis of new atoms. The periodic table lists elements that have been discovered and isolated from nature, but a few have been created by human activity. Collision of atomic particles with the nuclei of existing atoms is the normal source of radioactive isotopes and of some of the very heavy elements at the bottom of the periodic table. Indeed nuclear chemists and physicists have created some of the most important elements that are used for nuclear energy and nuclear weapons, plutonium in particular. 

E.g., Shah ca. 1929, Noyes and Noyes 1932, and Fisk 1936. Interestingly, in more recent years, the title has been resurrected by Glenn T. Seaborg (1994), the Nobel laureate nuclear chemist who discovered plutonium and other transuranium elements, worked on the Manhattan Project, and served on John F. Kennedy s Atomic Energy Commission. 

The nuclear chemists at the Lawrence Berkeley Laboratory worked with extremely small samples of lawrencium with short half-lives, which made it difficult to determine the new elements chemical and physical properties. Most of its isotopes spontaneously fission as they give off alpha particles (helium nuclei). Lawrencium s melting point is about 1,627°C, but its boiling point and density are unknown. 

ORIGIN OF NAME Named after and in honor of the nuclear chemist Glenn T. Seaborg. ISOTOPES There a total of 16 Isotopes of unnilhexium (seaborgium) with half-lives ranging from 2.9 milliseconds to 22 seconds. All are artificially produced and radioactive, and they decay by spontaneous fission (SF) or alpha decay. 

This chapter is an overview of what magnetic nuclear relaxation can bring to our knowledge of the actinide ions and their use in the nuclear industry. Most results are quite recent and the field is wide open. The author hopes this chapter will attract the attention of NMR specialists who should not be distraught by the experimental difficulties that always accompany the handling of radioactive materials. On the other hand, nuclear chemists and physicists will hopefully discover that NMRD is an interesting supplement to their favorite spectroscopic techniques. 

Chemists and physicists have collaborated since the middle of the twentieth century to make new elements substances never before seen on Earth. They are expanding the Periodic Table, step by painful step, into uncharted realms where it becomes increasingly hard to predict which elements might form and how they might behave. This is the field of nuclear chemistry. Instead of shuffling elements into new combinations - molecules and compounds - as most chemists do, nuclear chemists are coercing subatomic particles (protons and neutrons) to combine in new liaisons within atomic nuclei. 

But for chemists, the hydrogen bomb tests had a happier fallout too. Scientists at the Mike test collected coral from a nearby atoll contaminated with radioactive debris, and sent it to Berkeley for analysis. There the nuclear chemists found two new elements, with atomic numbers 99 and 100. They were named after two of the century s most creative physicists einsteinium and fermium. 

As a branch of chemistry, the activities of nuclear chemists frequentiy span several traditional areas of chemistry such as organic, analytical, inorganic, and physical chemistry. Nuclear chemistry has ties to all branches of chemistry. For example, nuclear chemists are frequently involved with the synthesis and preparation of radiolabeled molecules for use in research or medicine. Nuclear analytical techniques are an important part of the arsenal of the modem analytical chemist. The study of the actinide and transactinide elements has involved the joint efforts of nuclear and inorganic chemists in extending knowledge of the periodic table. Certainly, the physical concepts and reasoning at the heart of modem nuclear chemistry are familiar to physical chemists. In this book we will touch on many of these interdisciplinary topics and attempt to bring in familiar chemical concepts. 

A frequently asked question is What are the differences between nuclear physics and nuclear chemistry Clearly, the two endeavors overlap to a large extent, and in recognition of this overlap, they are collectively referred to by the catchall phrase nuclear science. But we believe that there are fundamental, important distinctions between these two fields. Besides the continuing close ties to traditional chemistry cited above, nuclear chemists tend to study nuclear problems in different ways than nuclear physicists. Much of nuclear physics is focused on detailed studies of the fundamental interactions operating between subatomic particles and the basic symmetries governing their behavior. Nuclear chemists, by contrast, have tended to focus on studies of more complex phenomena where statistical behavior is important. Nuclear chemists are more likely to be involved in applications of nuclear phenomena than nuclear physicists, although there is clearly a considerable overlap in their efforts. Some problems, such as the study of the nuclear fuel cycle in reactors or the migration of nuclides in the environment, are so inherently chemical that they involve chemists almost exclusively. 

One term that is frequently associated with nuclear chemistry is that of radiochemistry. The term radiochemistry refers to the chemical manipulation of radioactivity and associated phenomena. All radiochemists are, by definition, nuclear chemists, but not all nuclear chemists are radiochemists. Many nuclear chemists use purely nonchemical, that is, physical techniques, to study nuclear phenomena, and thus their work is not radiochemistry. 

Recently, a good deal of attention has been given to the solar neutrino problem and its solution. The 2002 Nobel Prize in physics was awarded to Ray Davis and Masatoshi Koshita for their pioneering work on this problem. Of special interest is the important role of nuclear and radiochemistry in this work as Davis is a nuclear chemist. The definition and solution of this problem is thought to be one of the major scientific advances of recent years. 

The chemical elements are the building blocks of nature. All substances are combinations of these elements. There are (as of 2005) 113 known chemical elements with the heaviest naturally occurring element being uranium (Z = 92). The 22 heaviest chemical elements, the transuranium elements, are manmade. The story of their synthesis, their properties, their impact on chemistry and physics, and their importance to society is fascinating. This story is of particular importance to nuclear chemistry because most of our knowledge of these elements and their properties comes from the work of nuclear chemists, and such work continues to be a major area of nuclear chemical research. One of us (GTS) has been intimately involved in the discovery and characterization of these transuranium elements. 

Before illustrating this procedure for several cases of interest to nuclear chemists, we can point out another important property of the Schrodinger equation. If the potential energy V is independent of time, we can separate the space and time variables in the Schrodinger equation by setting... 

Continuing our survey of some simple applications of wave mechanics to problems of interest to the nuclear chemist, let us consider the problem of a particle confined to a one-dimensional box (Fig. E.2). This potential is flat across the bottom of the box and then rises at the walls. This can be expressed as ... 

Another important quantum mechanical problem of interest to nuclear chemists is the penetration of a one-dimensional potential barrier by a beam of particles. The results of solving this problem (and more complicated variations of the problem) will be used in our study of nuclear a decay and nuclear reactions. The situation is shown in Figure E.5. A beam of particles originating at — oo is incident on a barrier of thickness L and height V0 that extends from x = 0 to x = L. Each particle has a total energy E. (Classically, we would expect if E < V0, the particles would bounce off the barrier, whereas if E > V0, the particles would pass by the barrier... 

The same tensions are at play in the Noddacks insistence on isolating naturally existing elements, as opposed to obtaining them by means of nuclear fusion. According to Van Tiggelen, this made them into chemists, possibly geochemists, but not radiochemists - perhaps nuclear chemists would be more appropriate. The... 

We have seen that four nuclides, each having an integral number of a quartets, comprise about 70 percent of the earth s crust. These four obviously have even numbers both of protons and neutrons. Moreover, of the 274 stable nuclides known, 162 likewise have even numbers both of protons and neutrons. Only four (H2, Li6, B10, and N14) have odd numbers both of protons and neutrons, whereas the remaining hundred or so stable nuclides are odd-even nuclei, about half of them having even numbers of neutrons, the other half having even numbers of protons. The differences in the relative abundances of the various classes of nuclides are very striking, and their explanations are a favorite topic for conjecture among nuclear chemists. Many such explanations involve the concept of closed nuclear shells (or a quartets ) with the assumption that complete shells (and possibly half-filled shells also) are especially stable. (See, for example, Exercise 8.)... 

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. ... 

As it turns out this guy is an ex-nuclear chemist so we start rapping about chems. I pointed out to him that about half of all the chems listed in the Merck Index give photography as a principal use so why in the hell aren t they here in his store He said that with the refinement of premade solutions no one has need of basic chemicals. Surely some purists still require the stuff, 1 say. But he said he never heard of such a thing. Before 1 left I asked him if he could special order any chems from the Eastman-Kodak fine chemicals division but he said he couldn t. 

I was first made aware of organometallic compounds through reading Modern Aspects of Inorganic Chemistry (1935) by two academics, H. J, Emeleus and J. S. Anderson at Imperial College, London, where I was a student. However, names such as Zeise s compound , Reihlen s butadiene iron tricarbonyl and Hein s polyphenylchromium compounds , none of whose structures were known, remained latent in my memory through over seven years as a nuclear chemist. 

Although I was appointed an Assistant Professor at Harvard University because I was a nuclear chemist , I took the advice of my predecessor at Imperial College, Prof. H. V. A. Briscoe, that I had better return to inorganic chemistry - otherwise no job in England ... 

Nuclear chemists obviously will continue trying to produce still more synthetic elements with atomic numbers greater than 102. 

Chemical studies of these elements must be performed with isotopes having not only a fleeting existence but producible only in atom quantities. In Table 1 we list the most frequently made isotopes, their half lives, and the atoms that have been synthesized for each data point. Except for 255] the nuclides listed can be created only by nuclear reactions between accelerated charged particles and transplutonium target nuclei. For this reason and the short lifetimes of the isotopes, all chemical studies are carried out at large heavy-ion accelerators. Such research calls upon nuclear physics for the methods of element synthesis and detection while the research goals are aimed toward atomic and chemical properties. Therefore, this field of research most easily falls into the domain of the nuclear chemist. 

Nuclear chemists consIcJer (3 ctecay to be a more general process that Includes three decay modes negatron emission (which the text calls S decay ), positron emission, and electron capture. 

In Germany in 1938, Otto Hahn and Fritz Strassmann, skeptical of claims by Enrico Fermi and Irene Johot-Curie that bombardment of uranium by neutrons produced new so-called transuranic elements (elements beyond uranium), repeated these experiments and chemically isolated a radioactive isotope of barium. Unable to interpret these findings, Hahn asked Lise Meitner, a physicist and former colleague, to propose an explanation for his observations. Meitner and her nephew, Otto Frisch, showed that it was possible for the uranium nucleus to be spfit into two smaller nuclei by the neutrons, a process that they termed fission. The discovery of nuclear fission eventually led to the development of nuclear weapons and, after World War II, the advent of nuclear power to generate electricity. Nuclear chemists were involved in the chemical purification of plutonium obtained from uranium targets that had been irradiated in reactors. They also developed chemical separation techniques to isolate radioactive isotopes for industrial and medical uses from the fission products wastes associated with plutonium production for weapons. Today, many of these same chemical separation techniques are being used by nuclear chemists to clean up radioactive wastes resulting from the fifty-year production of nuclear weapons and to treat wastes derived from the production of nuclear power. 

During the last 25 years, a large number of radioactive species has been discovered. One of the prime objectives of nuclear chemists has been to assign the atomic number and the mass number to the nuclides which are responsible for observed activities. In general, the atomic number is found by chemical analysis, whereas the mass assignment is most unambiguously obtained by methods involving mass spectrometric techniques. 

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