Bulletin of the American Physical Society
2011 Annual Meeting of the Four Corners Section of the APS
Volume 56, Number 11
Friday–Saturday, October 21–22, 2011; Tuscon, Arizona
Session E7: Nuclear Physics Theory and Experiment |
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Chair: Erich Varnes, University of Arizona Room: UA Student Union Tubac |
Friday, October 21, 2011 3:25PM - 3:37PM |
E7.00001: Post Helium-3 Neutron Detection at BYU John E. Ellsworth, J. Bart Czirr, Lawrence B. Rees, Nathan Hogan, Adam Wallace, Stephen Black, Steven Gardiner, Brian James, Suraj Bastola, Nirdosh Chapagain, Andrew Hoffman Development of spectrometers for studying low flux neutrons mixed in a field of gamma and cosmic rays has continued at BYU since 1982. As $^{3}$He, the archetypal neutron detector medium, becomes scarcer, BYU and associates have been pursuing technologies that may serve as acceptable detectors, even for low energy fission neutrons. Presented will be 1) some technologies: typical $^{3}$He safeguard monitoring equipment, capture gating techniques, multi-pulse discrimination, and hybrid developments; 2) some tools: low room-return lab, LANL LANSCE time of flight, and fission spectroscopy; 3) and some lessons learned: PMT timing disparity, plastic non- linearity, and pulse fragmentation. [Preview Abstract] |
Friday, October 21, 2011 3:37PM - 3:49PM |
E7.00002: Z$_{2}$ lattice Gauge Theory Derar Altarawneh, Michael Engelhardt We have studied Z2 lattice Gauge theory, in which the lattice links are associated with values $\pm $1, using the standard plaquette action. We employed two methods. Firstly we used Metropolis Monte Carlo simulations both in 1+1 space-time and 3+1 space-time dimensions. We calculated averages of Wilson loops as a function of the coupling constant c. Secondly, we only considered 1+1 space-time dimensions and used analytical methods. We used the local gauge transformations and the center transformations to reduce the number of degrees of freedom. Each local transformation enables us to fix one link in the lattice, which means reducing the degrees of freedom by one. Our system consisted of (nxn) lattice points, so applying the local gauge transformations at (n$^{2 }$-1) points allows us to fix (n$^{2 }$-1) links and reduce the degrees of freedom by (n$^{2 }$-1) units. Also using periodic boundary conditions and center transformations, the number of degrees of freedom is reduced by two more units. After reducing the link degrees of freedom, they can be mapped to plaquette variables, in terms of which the system becomes solvable analytically. At the end we verified agreement between the simulation method and the analytical method in our results for the average action. [Preview Abstract] |
Friday, October 21, 2011 3:49PM - 4:01PM |
E7.00003: Study of the fission spectrum of less than 1 MeV neutrons using a Lithium-glass detector Suraj Bastola, Lawrence Rees, Czirr Bart The fission spectrum of neutrons with kinetic energies less than 1 MeV is of considerable practical importance for the design of nuclear reactors. However, it is not as precisely known as that for higher energy neutrons. One of the major problems scientists have previously encountered is room return neutrons. These are neutrons that reflect from the walls, ceiling or floor of the lab. Another problem is finding a way to measure accurately the neutron time of flight. This is the time neutrons take to travel from a fission event to the detector. Time of flight is used to measure the neutron energy. To avoid the room return, I am going to perform an experiment about 45 feet above the ground in the BYU Indoor Practice Facility, so that neutrons from the source will not scatter from nearby surfaces and return to the detector. To find the time of flight to a greater accuracy, I have been using a Time to Amplitude Converter (TAC). A TAC has a capacitor that charges linearly as the voltage builds up. With a 12-bit digitizer system, we can measure the time to 0.1 nanoseconds, whereas the same digitizer can only measure time in steps of 4 nanoseconds. So, we will get a more accurate measurement of time of flight with the TAC. [Preview Abstract] |
Friday, October 21, 2011 4:01PM - 4:13PM |
E7.00004: Error estimates in importance truncated nuclear structure calculations Michael Kruse, Bruce Barrett The importance truncation procedure, used in both quantum chemistry and now in nuclear structure calculations, has led to the possibility of doing large scale many-body calculations, without the need to use all the millions (possibly billions) of basis states present. Once the calculations are done in a truncated basis, an extrapolation on the energy is made, in order to recover the full model space calculation. However, these extrapolations have recently come into question as to their reliability. In this talk I will show some truncated nuclear structure calculations, which I then compare to the exact calculations. I will also discuss the many-body implications of working in this particular truncated model space, specifically, the question of size-extensivity. [Preview Abstract] |
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