Bulletin of the American Physical Society
APS April Meeting 2013
Volume 58, Number 4
Saturday–Tuesday, April 13–16, 2013; Denver, Colorado
Session Q3: Invited Session: Origin of the Elements |
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Sponsoring Units: DNP DAP Chair: Virginia Trimble, University of California, Irvine Room: Plaza E |
Monday, April 15, 2013 10:45AM - 11:21AM |
Q3.00001: Moseley Centennial Lecture: The Works of Henry Moseley, 1887-1915 Invited Speaker: Eric Scerri In 1913 Henry Moseley, an unknown young English physicist published an article in the Philosophical Magazine under the title of ``The High Frequency Spectra of the Elements.'' The 10-page article was to have far reaching implications in both chemistry and physics and helped to resolve a major conundrum in the periodic table of the elements. The talk will briefly examine the life and work of Moseley who died tragically while fighting in the trenches of World War I in 1915. The build-up to the discovery of atomic number took several different avenues including contributions from Rutherford and Barkla. However the more direct motivation for Moseley's work, as he readily acknowledged, were the articles of an unknown Dutch econometrician Anton Van den Broek who attempted to improve on Mendeleev's periodic table. Moseley began as a student of Rutherford at Manchester and took a keen interest in the development of research using X-rays following the work of Roentgen, von Laue and Bragg. Although Rutherford was at first reluctant to enter this new field he soon yielded to young Moseley's request and sent him to Leeds for brief training with Bragg. On returning to Manchester, Moseley devised an ingenious apparatus in which a set of metal samples could be rotated so as to become the target for a beam of electrons in order to measure the frequencies of the emitted K X-rays. The first set of such experiments used nine successive elements in the periodic table, from titanium to zinc. Moseley's now immense fame rests with the results of this study as well as a subsequent one which extended the study into a further 30 elements, in addition to the use that his method was put to by himself as well as subsequent chemists and physicists. [Preview Abstract] |
Monday, April 15, 2013 11:21AM - 11:57AM |
Q3.00002: Hans A. Bethe Prize Talk: Nuclear and Neutrino Astrophysics: The Weak Interaction and the Origin of the Elements Invited Speaker: George Fuller The weak interaction has the unique ability to transmute neutrons into protons and {\it vice versa}. As a result, it plays a crucial role in the cosmos: enabling stars to shine for eons; refrigerating the cores of massive stars and setting them up for instability, leading to collapse and supernova explosions; and ultimately facilitating the assembly of nuclei in stars and in the early universe. In many cases the weakly interacting agents in these processes are the ghost-like neutrinos. Though much about these particles remains mysterious, spectacular recent advances in cosmological and laboratory probes have revealed a great deal about neutrino properties, {\it e.g.,} mass-squared differences and flavor mixing parameters. I will describe recent efforts to understand what these newly-revealed properties mean for how neutrinos transform their flavors in core collapse supernovae and, in turn, what flavor transformation might mean for the expected supernova neutrino burst signature and for the synthesis of the heaviest elements. I will also discuss how primordial nucleosynthesis considerations coupled with anticipated laboratory neutrino oscillation experiments and high-precision cosmic microwave background and large scale structure observations are setting up a nearly over-determined situation, one which can provide a probe of new beyond-standard -model neutrino physics. [Preview Abstract] |
Monday, April 15, 2013 11:57AM - 12:33PM |
Q3.00003: The Quest for New Elements Invited Speaker: Jacklyn Gates In 1966 Myers and Swiatecki predicted a new closed shell, centered at an element with Z$=$126 and A$=$310. In this region, now referred to as the ``Island of Stability,'' shell-effects were predicted to stabilize elements with Z$\approx $114-126 against fission, leading to predicted half-lives of years or longer and the predicted existence of so-called ``superheavy'' nuclei. By comparison, the heaviest known element at that time was rutherfordium (Rf), with Z$=$104 and a half-life of about one minute. Some of the theoretical calculations even predicted half-lives longer than the age of the universe, suggesting that these superheavy elements may even exist in nature. Later predictions suggested that nuclides in the Island of Stability might be produced at rates more characteristic of element with Z$\le $100. Initial experiments were unsuccessful in discovering superheavy nuclei in nature or at particle accelerators, leading to a concerted effort by experimentalists and theoreticians to i) improve the theoretical predictions ii) develop techniques to improve the sensitivity of experiments and iii) to progressively extend the known elements towards this region. Over the next five decades, fourteen new elements with Z$\ge $105 and more than a hundred isotopes were discovered. Experimental sensitivies were increased by six orders of magnitude. Within the last decade, six new elements and more than fifty new isotopes with Z$\ge $112 have been discovered. These most recent discoveries have begun to approach the edges of the Island of Stability. The nuclei exhibit longer lifetimes and higher production rates than those found in some of the lighter elements. This presentation will discuss the advances that have led us to the shores of the Island of Stability and where the field goes from here. [Preview Abstract] |
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