Bulletin of the American Physical Society
Joint Fall 2009 Meeting of the Texas Sections of the APS, AAPT, and SPS
Volume 54, Number 13
Thursday–Saturday, October 22–24, 2009; San Marcos, Texas
Session G4: Nuclear Physics |
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Chair: Victor Michalk, Texas State University Room: LBJ Student Center 3-13.1 |
Saturday, October 24, 2009 10:00AM - 10:12AM |
G4.00001: Improving the Accuracy of Neutron Multiplicity Counting Scott Stewart Neutron Multiplicity Counting is an assay method used in non-destructive analysis of plutonium for safeguards applications. It is widely used in nuclear material accountancy by international (IAEA) and national inspectors. The method uses the measurement of the correlations in a pulse train to extract information on the spontaneous fission rate in the presence of neutrons from ($\alpha $,n) reactions and induced fission. There is currently interest in improving the accuracy of the technique in order to reduce the number of samples that need to be analyzed chemically. Therefore the achievable accuracy of the technique is being studied in detail. The accuracy of a neutron multiplicity measurement can be affected by a number of variables. Monte Carlo neutron transport simulations with MCNP have been done to understand how the density, isotopic composition, chemical composition and moisture in the material affect the count rate. These calculated count rates have been analyzed with the ``point model'' in order to determine the effect on the deduced plutonium mass. In practice, dead time in the electronics affects the count rate. Uncorrelated neutron sources have been measured in order to determine optimum settings for dead time compensation. [Preview Abstract] |
Saturday, October 24, 2009 10:12AM - 10:24AM |
G4.00002: Simulations for the NIFFTE Time Projection Chamber Remington Thornton The Neutron Induced Fission Fragment Tracking Experiment (NIFFTE) collaboration's Time Projection Chamber (TPC) is designed to make high precision fission cross-section measurements. These measurements have long-term applications for future generations of nuclear power plant designs. An important component of this project is accurate simulation of the active volume including the physical features of the tracks and the electronics. Tracks are generated using the Geometry And Tracking (Geant4) simulation code, while the detector response simulation is custom written. After reading in tracks, from the Geant4 simulations, the detector response simulation transforms the data using a series of modules with behavior characterized by the TPC design. Asynchronous trigger, 3-D charge diffusion, capacitive charge sharing, digitization, random trigger cells, and noise from the electronics have been modeled. The detector response simulation was designed and written so that it can be reused in future TPC projects. This talk will focus on how these detector response modules are produced and used. [Preview Abstract] |
Saturday, October 24, 2009 10:24AM - 10:36AM |
G4.00003: Track Reconstruction Techniques for the NIFFTE Time Projection Chamber Sarvagya Sharma The Time Projection Chamber (TPC), being constructed by the NIFFTE (Neutron Induced Fission Fragment Tracking Experiment) collaboration will be used for high-precision fission cross-section measurements. These measurements will aid in the design of future generation nuclear power plants. The track reconstruction effort has employed various machine-based image processing algorithms. One of the methods investigated, the Hough Transform is a brute force attempt at finding tracks that isolates features in the TPC space by populating histograms. The dimensions of these histograms represent the unknown track parameters. The second, Binary Space Partitioning (BSP), recursively divides the TPC volume until all tracks are segregated. To determine track fit parameters, an iterative Kalman Filter has been implemented that accounts for multiple scattering and kinks in the track. The final tracks obtained from the reconstruction routines are traced back to the origin for vertex reconstruction. Comparing simulated and reconstructed tracks have shown the validity of these track reconstruction methods. This talk shall illustrate these techniques intended for track finding and fitting. [Preview Abstract] |
Saturday, October 24, 2009 10:36AM - 10:48AM |
G4.00004: Charmonium Production in Heavy-Ion Collisions - Revisited Xingbo Zhao, Ralf Rapp We revisit the traditional picture of charmonium suppression as a signature of the Quark-Gluon Plasma (QGP) formation in heavy-ion ($A$-$A$) collisions. Our quantitative calculations are based on a kinetic rate-equation approach which includes both suppression and regeneration mechanisms in a thermal fireball. Initial conditions are obtained from experimental data in $p$-$p$ and $p$-$nucleus$ collisions. Specifically, we study transverse momentum ($p_t$) and longitudinal momentum (rapidity $y$) spectra of charmonia in $A$-$A$ collisions. These are believed to provide a valuable discrimination power of suppression and regeneration mechanisms, and thus reveal properties of charmonia in the QGP. We present the numerical results and compare to experimental data at SPS and RHIC energies and give predictions at LHC energy. [Preview Abstract] |
Saturday, October 24, 2009 10:48AM - 11:00AM |
G4.00005: Gamma-Jet Measurements in Au+Au Collisions with the Solenoidal Tracker At RHIC (STAR) Martin Codrington One of the most intriguing results from RHIC experiments thus far, is the observed suppression of hadrons at high transverse momentum; which is attributed to final state medium-induced energy loss of hard scattered partons. To quantify the energy loss, and the response of the medium to the deposited energy and momentum; a probe is needed that has negligible interaction with the medium itself, and thereby can provide a calibration of the momentum scale of the underlying process. One such probe is a prompt photon (i.e. produced from the initial hard-scattering process). Studying correlations of a prompt photon with a jet ($\gamma $+Jet), should allow one to study the attenuation and modification of a jet with well-defined energy quantitatively. And thus promises to provide a wealth of information about the energy-loss process. There is, however, a large background of photons from the decay of neutral mesons (mainly the $\pi ^{0})$. Ideally, a large fraction of these decay photons are rejected before a correlation study is undertaken. In the STAR experiment, this can be done using the transverse shower profile measured in the Shower Maximum Detector (SMD) of the Barrel Electromagnetic Calorimeter (BEMC). The latest results of this analysis will be presented. [Preview Abstract] |
Saturday, October 24, 2009 11:00AM - 11:12AM |
G4.00006: A Sensitivity Analysis of Dose Calibrator Linearity Assessment Mario Bencomo, Marvin Friedman A total of eight variations of least squares fitting, both unweighted and (log-transformation and instrument errors) weighted, were applied to data arising from (simulated) exponential radioactive decay measurements in an ionization chamber dose calibrator during its linearity-of-response assessment. The fitting techniques were subjected to a sensitivity analysis, prompted by the instrument's decreased precision at low levels of radioactivity, which consisted of modifying a selected low-activity data point prior to fitting. The increased robustness of the weighted techniques was demonstrated by the sensitivity analysis. A relatively large (10\%) change in a low activity (imprecise) measurement value had only minimal effect in the best-fit curve parameters with the weighted techniques, but significantly changed the parameters with the unweighted techniques. These analyses shed new light on the inadequacies of the accepted methodology when transformation bias and measurement-dependent variation of instrument precision are taken into account. [Preview Abstract] |
Saturday, October 24, 2009 11:12AM - 11:24AM |
G4.00007: A New Skyrme Type Energy Density Functional Carson Fuls The quest for a modern energy density functional (EDF) with enhanced predictive power for properties of nuclei is one of the major problems in modern nuclear theory. We have recently constructed a new EDF starting with the Skyrme type EDF and taking into account effects of ground state correlations. We have used an extensive set of data on properties of nuclei in our fit to determine the parameters of the EDF. The set includes binding energy, charge rms radii, spin-orbit splitting of single-particle orbits, rms radii for valence neutrons and centroid energies for the isoscalar giant monopole resonance (ISGMR) for many different nuclei ranging from very light $^{16}$O to very heavy $^{208}$Pb. We have used the simulated annealing method in addition to an advanced least square method to search the hyper-surface of the Skyrme parameter space for the global minima. The new interaction named KDEX better predicts the rms radii of $^{16}$O and $^{208}$Pb which has been a problem in most previous interactions. Work on implementing, extension, and modification of the form of the EDF is on-going. [Preview Abstract] |
Saturday, October 24, 2009 11:24AM - 11:36AM |
G4.00008: Discrete Character of Meson Masses M.A.K. Lodhi, Norman Redington Regge plots have played an important role in the study of mesons for nearly half a century. The success of quark model reduced interest in this approach, but predicting the existence and shape of Regge trajectories remains as a test of success of a phenomenological meson model. Approximately linear Regge trajectories have been shown to arise from one of the earliest string models of the meson, and their existence is still regarded as an evidence for a meson as a pair of quarks. Regge expressed mesons of a family as trajectories in the mass squared-angular momentum plane as a multiple set of curves. These lines are analogous to the hydrogen atom energy level-angular momentum relationship. Further investigation shows that these sets of multiple lines can be reduced to a single line representing an entire meson family. In this work, the entire set of multiple lines representing the light meson family is replaced by a single line, which arises naturally when the squared mass of each meson depends linearly on the squared mass of the pion. This relation is analogous to the Rydberg formula for the hydrogen spectrum, with the electron mass replaced by the pion mass. [Preview Abstract] |
Saturday, October 24, 2009 11:36AM - 11:48AM |
G4.00009: Accelerator-driven thorium-cycle fission power Akhdiyor Sattarov A flux-coupled stack of superconducting isochronous cyclotrons could be used to drive thorium-cycle fission power. The 800 MeV proton beams produce fast neutrons through spallation, then the fast neutrons transmute the thorium into uranium and drive fission. The thorium reactor would provide GW electric power, eat its own long-lived waste, run for 7 years between core accesses, operate below criticality, and be stable against melt-down. Reserves of thorium are sufficient to provide the world's energy needs for a thousand years. [Preview Abstract] |
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