Bulletin of the American Physical Society
2015 Fall Meeting of the APS Division of Nuclear Physics
Volume 60, Number 13
Wednesday–Saturday, October 28–31, 2015; Santa Fe, New Mexico
Session HF: Instrumentation I |
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Chair: Kelly Chipps, Oak Ridge National Laboratory Room: Lamy |
Friday, October 30, 2015 8:30AM - 8:42AM |
HF.00001: Simulation of detector signals in $n+^{3}$He$\rightarrow p+t$ Christopher Coppola The parity violating proton directional asymmetry from the capture of polarized neutrons on $^{3}$He is being measured with a pulsed neutron beam at the Spallation Neutron Source at Oak Ridge National Laboratory. The target is an ion chamber with $^{3}$He at approximately half an atmosphere. Signal wires at different locations in the chamber have different sensitivities to the physics asymmetry, which are determined by the geometry and configuration of the experiment. These geometry factors must be determined by simulation. In addition, a simulation can estimate the statistical precision of the experiment, optimize configuration variables, and assist with error analysis. To achieve the most accurate simulation of the detector signals, a custom simulation was written in C++ using weighted variables and taking advantage of parallel execution. The inputs used to construct the simulation came from measurements of the neutron phase space, ENDF cross sections, and PSTAR ionization data. A cell model was used to combine this physics to produce an accurate simulation of the experimental data. This simulation can be used to calculate accurate and tunable geometry factors, and to produce desired quanities for use in optimization and analysis. [Preview Abstract] |
Friday, October 30, 2015 8:42AM - 8:54AM |
HF.00002: A combined target and detector to measure parity violation in neutron capture on $^3$He for the n3He Experiment Mark McCrea The n3He Experiment aims to measure the parity violating asymmetry in the direction of proton emission relative to the initial neutron polarization direction in the reaction $\vec{n}+^3He\rightarrow T+p+765keV$ to a high precision. The experiment is currently running at the Spallation Neutron Source. Due to the large neutron capture cross section on $^3$He a multiwire ionization chamber operated in current mode is used as both target and detector. The target is filled with $^3$He gas at 0.5 atm pressure and has a length of 33.8 cm. The frame stack consists of 16 signal wire planes and 17 HV planes with 144 signal wires. I will discuss the design, construction and assembly of the detector. Multiple simulations are performed to understand the response of the detector to the neutron beam. I will discuss calculations using Garfield++ to simulate the electron avalanches and ion mobility in the wire chamber fields. [Preview Abstract] |
Friday, October 30, 2015 8:54AM - 9:06AM |
HF.00003: High Efficiency Spin Flipper for the n3He Experiment Christopher Hayes The n$^3$He experiment, constructed on the Fundamental Neutron Physics Beamline (FnPB) at the Spallation Neutron Source, is designed to measure the parity violating (PV) proton asymmetry $A_p$ in the capture reaction \begin{equation}\label{I01} n + ^3\!\mathrm{He} \,\longrightarrow \, ^3 \mathrm{H} + p + 765\, \mathrm{keV} \end{equation} The asymmetry has an estimated value $A_p \sim -1\times10^{-7}$ and is directly related to the weak isospin conserved couplings $h_\rho^{0}$ and $\omega_\rho^{0}$ which are of fundamental interest in the verification of the meson exchange model of low energy NN intereactions. Data production for the n$^3$He experiment began in February 2015 and is scheduled to continue thru December 2015 -- reaching a statistical sensitivity $\delta A_p\sim 10^{-8}$ or better. I will discuss the spin flipper which is designed using the theory of double cosine-theta coils, and capable of flipping neutron spins with an efficiency approaching its maximum value $\epsilon_{sf} = 1$. I will also discuss the theory of Spin Magnetic Resonance (SMR) and how it is employed by the spin flipper to flip 60 Hz pulses of cold neutrons over a range of wavelengths. [Preview Abstract] |
Friday, October 30, 2015 9:06AM - 9:18AM |
HF.00004: Enhanced trigger for the NIFFTE fissionTPC in presence of high-rate alpha backgrounds Jeremy Bundgaard Nuclear physics and nuclear energy communities call for new, high precision measurements to improve existing fission models and design next generation reactors. The Neutron Induced Fission Fragment Tracking experiment (NIFFTE) has developed the fission Time Projection Chamber (fissionTPC) to measure neutron induced fission with unrivaled precision. The fissionTPC is annually deployed to the Weapons Neutron Research facility at Los Alamos Neutron Science Center where it operates with a neutron beam passing axially through the drift volume, irradiating heavy actinide targets to induce fission. The fissionTPC was developed at the Lawrence Livermore National Laboratory's TPC lab, where it measures spontaneous fission from radioactive sources to characterize detector response, improve performance, and evolve the design. To measure $^{244}$Cm, we've developed a fission trigger to reduce the data rate from alpha tracks while maintaining a high fission detection efficiency. In beam, alphas from $^{239}$Pu are a large background when detecting fission fragments; implementing the fission trigger will greatly reduce this background. The implementation of the cathode fission trigger in the fissionTPC will be presented along with a detailed study of its efficiency. [Preview Abstract] |
Friday, October 30, 2015 9:18AM - 9:30AM |
HF.00005: New fission-fragment detector for experiments at DANCE G. Rusev, A.R. Roman, J.K. Daum, R.K. Springs, E.M. Bond, M. Jandel, B. Baramsai, T.A. Bredeweg, A. Couture, A. Favalli, K.D. Ianakiev, M.L. Iliev, S. Mosby, J.L. Ullmann, C.L. Walker A fission-fragment detector based on thin scintillating films has been built to serve as a veto/trigger detector in neutron-induced fission measurements at DANCE. The fissile material is surrounded by scintillating films providing a $4\pi$ detection of the fission fragments. The scintillation events caused by the fission fragment interactions in the films are registered with silicon photomultipliers. Design of the detector and test measurements are described. [Preview Abstract] |
Friday, October 30, 2015 9:30AM - 9:42AM |
HF.00006: Improving UV-glass PMTs with a p-Terphenyl Wavelength Shifter Sylvester Joosten, Zein-Eddine Meziani, Ed Kaczanowicz, Melanie Rehfuss, Burcu Duran, Michael Paolone UV-glass PMTs are often the limiting factor in a Cherenkov detector, due to their poor quantum efficiency (QE) below 300nm due to the UV-glass transparency. The application of a p-Terphenyl wavelength shifter to the face of these PMTs dramatically improves the QE for short wavelengths, rivaling that of a much more expensive quartz PMT. This is especially interesting in the context of multi-anode (MA) PMTs, which are supremely suited for application in future open-environment Cherenkov detectors at very high luminosities due to their small size, lower sensitivity to magnetic fields, and high potential for advanced background rejection. This will become critical at Jefferson Lab entering the 12 GeV era, as well as for a future electron-ion collider. We will discuss the process of coating the PMTs through vacuum evaporation, and the performance testing taking place at Temple University for these multi-anode PMTs, as well as the results obtained with the more traditional 5-inch PMTs that were coated for the low-threshold Cherenkov counter (LTCC) of the CLAS12 spectrometer at Jefferson Lab. [Preview Abstract] |
Friday, October 30, 2015 9:42AM - 9:54AM |
HF.00007: Dimuon Tracking and Triggering at SeaQuest Michael Daugherity The Fermilab E906/SeaQuest experiment measures 120 GeV protons from the Main Injector incident on fixed Hydrogen and Deuterium liquid targets and W, C, and Fe solid targets. Dimuons produced in these interactions from the Drell-Yan process and charmonia states are extremely sensitive probes of nuclear structure, particularly the light quark sea. Therefore the primary goal of SeaQuest is to measure muon pairs to study antiquarks in the nucleon. The spectrometer is optimized to select and analyze dimuons through a 25-m path with two dipole magnets, four detector stations, and multiple layers of hadron shielding. Each of the first three detector stations are instrumented with 6 planes of wire chambers and 2 planes of scintillators, while the fourth station uses scintillators and proportional tubes. SeaQuest has two primary methods for tracking reconstruction using sagitta ratios and Hough Transforms to identify muon tracks. The dimuon trigger is based on scintillator hodoscopes perpendicular to the bend plane at each of the four stations. This talk will report on performance of the tracking and trigger systems in the recent run and plans for future improvements. [Preview Abstract] |
Friday, October 30, 2015 9:54AM - 10:06AM |
HF.00008: Population distribution following atomic charge exchange of 29.85\,keV Ni$^{+}$ on a sodium vapor A.J. Miller, K. Minamisono, B. Isherwood, H.B. Asberry, P.F. Mantica, D.M. Rossi, C.A. Ryder, R. Strum Collinear laser spectroscopy (CLS) is a well-developed technique for measuring hyperfine spectra of ions or atoms. While laser-excitation from the ground state of a singly ionized species may be possible for some elements, the electronic-structure of the corresponding neutral species provides an extended selection of transition frequencies for CLS studies. Atomic charge-exchange reaction is one method to produce atomic beams. The final electronic state population distribution subsequent to charge exchange of a 29.85\,keV Ni$^{+}$ beam impinging on sodium vapor was investigated for four emission lines in Ni\,I using CLS. These measurements were performed at the BEam COoling and LAser spectroscopy (BECOLA) facility at NSCL/MSU. The results were compared to simulations, which considered the calculated charge-exchange cross section and redistribution of the population through rapid spontaneous decay. Fair agreement was obtained between simulation and experiment. The details of cross section calculation and simulation, and extension to other charge-exchange systems will be discussed. [Preview Abstract] |
Friday, October 30, 2015 10:06AM - 10:18AM |
HF.00009: Energy of atomic shakeoff electrons from positron decay of 37K John Behr, Benjamin Fenker, Alexandre Gorelov, Melissa Anholm, Spencer Behling, Michael Mehlman, Dan Melconian, Danny Ashery, Gerald Gwinner We have measured the low-energy atomic shakeoff electron spectrum from the $\beta^+$ decay of $^{37}$K. We collect atomic electrons emitted from laser-cooled $^{37}$K using a nearly uniform electric field at low magnetic field into a position-sensitive microchannel plate. A coincidence with energetic $\beta^+$s removes background. The differential position information translates to a differential electron energy spectrum. The energy spectrum from 1-100 eV is reproduced well by an analytic calculation for hydrogenic wavefunctions [Levinger PR 90 11 (1953)] using potassium quantum defects. Less than one percent of the electrons have energies higher than the 25 eV threshold for double DNA strand breaks, so relative biological effectiveness would not be altered by including these electrons. The average energy carried off by these electrons (a few eV) is smaller than expected from simple Thomas-Fermi estimates (65eV) [Serber and Snyder PR 87 152 (1952)] [Preview Abstract] |
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