Bulletin of the American Physical Society
2012 Fall Meeting of the APS Division of Nuclear Physics
Volume 57, Number 9
Wednesday–Saturday, October 24–27, 2012; Newport Beach, California
Session CC: Instrumentation I: JLab/Fission |
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Chair: Mark Jones, Thomas Jefferson National Accelerator Facility Room: Plaza III |
Thursday, October 25, 2012 8:30AM - 8:42AM |
CC.00001: ABSTRACT WITHDRAWN |
Thursday, October 25, 2012 8:42AM - 8:54AM |
CC.00002: ABSTRACT WITHDRAWN |
Thursday, October 25, 2012 8:54AM - 9:06AM |
CC.00003: Thin Diamond Radiator Fabrication for the GlueX Experiment Brendan Pratt The GlueX experiment at Jefferson Lab requires 20 m diamond radiators for photon beam production via coherent bremsstrahlung with mosaic spread on the order of 20 r rms. With current diamond thinning techniques, one can produce 20 m diamonds of sufficient area, but these diamonds have been shown to have rocking curve widths orders of magnitude worse than this figure. The UConn nuclear physics group has developed the capability to mill monocrystalline diamond to arbitrary thickness profiles using laser ablation with a high-power pulsed UV laser. Surface profiles and rocking curve measurements are presented which demonstrate that this process results in diamond radiators which meet the GlueX criteria for thickness, flatness, and crystal mosaic spread. [Preview Abstract] |
Thursday, October 25, 2012 9:06AM - 9:18AM |
CC.00004: Collimation and tagging instrumentation for the GlueX Photon Beamline Richard Jones A new high energy polarized photon source is being constructed for the GlueX experiment at Jefferson Lab. Linear polarization is obtained using coherent bremsstrahlung from an oriented diamond radiator. By collimating the photon beam to a fraction of the characteristic bremsstrahlung angle $m_e/E_0$, linear polarization of 40\% is obtained at a photon energy of 9~GeV, for an incident electron beam of 12~GeV. Active stabilization of the photon beam spot on the collimator face is required in order to establish and maintain the alignment of the beam on the collimator axis with the required degree of accuracy. A photon beam centroid monitor has been developed for this purpose, based on the design of an electron beam halo detector that was invented for use at SLAC 30 years ago. Beam tests of this device in Hall B at 6 GeV show that it has the required bandwidth and sensitivity to be used in an active feedback loop in the electron beam steering controls. Such a feedback circuit is capable of locking the Hall D photon beam on the Hall D collimator with the required accuracy for GlueX at frequencies up to 1~kHz, over a wide range in beam current. [Preview Abstract] |
Thursday, October 25, 2012 9:18AM - 9:30AM |
CC.00005: Atomic Hydrogen Polarimetry for Precision Electroweak Experiments Wouter Deconinck In parity-violating electron scattering experiments the measurement of the electron beam polarization using Compton or M\o{}ller polarimetry is frequently the dominant experimental systematic uncertainty (\textit{e.g.} HAPPEx-III, PV-DIS, PREx, and $Q_{Weak}$ at Jefferson Lab, and PVA4 at the University of Mainz). Future experiments, in particular the SoLID and MOLLER experiments at Jefferson Lab and the P2 experiment at the University of Mainz, will require electron beam polarimetry with a precision better than 0.5\%. Improving M\o{}ller polarimetry with polarized iron foil targets to this level is challenging due to heating-induced target depolarization and the Levchuk effect. A new M\o{}ller polarimeter with polarized atomic hydrogen at 0.3\,K trapped inside an internal target in a strong solenoidal magnetic field is being developed at the University of Mainz in collaboration with several US groups. This technique is not affected by the Levchuk effect and will allow for non-invasive, continuous polarization measurements. The depolarizing effect due to the ionization into single electrons and H$^-$ or H$_2^+$ ions will be mitigated through a system of electrodes. I will present the atomic hydrogen polarimeter, and discuss in-beam tests at the University of Mainz. [Preview Abstract] |
Thursday, October 25, 2012 9:30AM - 9:42AM |
CC.00006: SPIDER: a path to 1 amu resolution of neutron-induced fission fragments C.W. Arnold, F. Tovesson, K. Meierbachtol, A.B. Laptev, T.A. Bredeweg, M. Jandel, R.O. Nelson, M.C. White A time-of-flight fission fragment detector capable of determining the velocity and total energy of various nuclear species to high precision has been designed for beam experiments at LANL and tested with a $^{252}$Cf source. A system of thin carbon foils, electron reflectors, microchannel plates, and delay-line anodes are presently being optimized to measure the path length and velocity of fission fragments to high precision. Future incorporation of an ionization chamber will complete one leg of the SPIDER detector and pave the way for 1 amu resolution measurements of neutron-induced fission fragments. The present capabilities of SPIDER will be discussed. [Preview Abstract] |
Thursday, October 25, 2012 9:42AM - 9:54AM |
CC.00007: Measuring the Alpha Decay to Spontaneous Fission Branching Ratio of Cf-252 with the NIFFTE TPC Lucas Snyder The NIFFTE collaboration has developed a fission Time Projection Chamber (TPC) designed to measure the neutron induced fission cross section to a higher accuracy than has been measured previously. The fission TPC has completed a key development phase by measuring the alpha/SF branching ratio of Cf-252. The branching ratio was used as a benchmark in working toward confirming the ability of the fission TPC to track and identify alpha particles and fission fragments. The results of the branching ratio and particle identification measurements will be presented. [Preview Abstract] |
Thursday, October 25, 2012 9:54AM - 10:06AM |
CC.00008: Progress and Expectations for the NIFFTE Fission TPC Brandon Seilhan The Neutron Induced Fission Fragment Tracking Experiment (NIFFTE) aims to improve current neutron-induced fission cross-section measurements through the use of a purpose-built Time Projection Chamber (TPC). Recent improvements to the fission TPC, including a sixfold increase in instrumented area and the capability to determine neutron time-of-flight, improve the ability of the fission TPC to precisely measure fission cross-sections. The current status, ongoing development, and plans for future measurements will be presented. [Preview Abstract] |
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