Bulletin of the American Physical Society
2008 Annual Meeting of the Division of Nuclear Physics
Volume 53, Number 12
Thursday–Sunday, October 23–26, 2008; Oakland, California
Session MH: Instrumentation II |
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Chair: Mark Stoyer, Lawrence Livermore National Laboratory Room: Jewett Ballroom F |
Sunday, October 26, 2008 10:30AM - 10:42AM |
MH.00001: The HELIOS silicon detector array S.T. Marley A prototype detector array has been constructed for use in the Helical Orbit Spectrometer (HELIOS) at the ATLAS facility at Argonne National Laboratory. HELIOS is a high-resolution spectrometer for use in studying reactions in inverse kinematics on hydrogen or helium targets. HELIOS consists of a large bore, 3T superconducting solenoid oriented with the magnetic and beam axes aligned. The detector array is comprised of four modules each with six 1.2 x 5.6cm position sensitive silicon detectors. On each module, the detectors were affixed with conductive epoxy and wire bonded to custom made multi-layer printed circuit boards. To keep the radial extent of the detectors to a minimum, the modules were assembled on a hollow 1.6 x 1.6 x 68.8 cm aluminum rail centered on the beam axis located upstream from the target. To characterize the timing, position, and energy resolutions, the detectors were evaluated at the Western Michigan University Accelerator Laboratory using elastic proton-proton scattering. The construction, assembly and preliminary testing of the array will be discussed. [Preview Abstract] |
Sunday, October 26, 2008 10:42AM - 10:54AM |
MH.00002: Algorithms for Pulse Shape Analysis Using Silicon Detectors Iain Darby, Sean Liddick, Robert Grzywacz The development of digital pulse processing, wherein the traditional shaping and timing circuitry are replaced by mathematical routines operating on a digitized preamplifier signal, have enabled the implementation of sophisticated pulse shape analysis (PSA) algorithms. This allows substantially more information to be extracted from an experimental pulse than is possible with a traditional analogue system. By applying PSA to Si detectors it is possible to selectively identify experimental pulses arising from specific physical processes. The application of pulse-shape analysis to Silicon strip detectors will be described for the selective identification of pile-up pulses resulting from the sequential $\alpha$-decay of $^{109}$Xe and $^{105}$Te isotopes. A two stage offline PSA algorithm is detailed, which is able to detect pile-up pulses from the sequential alpha decays with time differences between the two individual pulses as low as 100 ns over a wide range of relative amplitudes. The methods to construct idealised pulses and the subsequent extraction of energy and time from experimental measurements will be presented. [Preview Abstract] |
Sunday, October 26, 2008 10:54AM - 11:06AM |
MH.00003: ABSTRACT WITHDRAWN |
Sunday, October 26, 2008 11:06AM - 11:18AM |
MH.00004: Directional \v{C}erenkov Detectors Edwin Norbeck, Yasar Onel, Peter Bruecken, Mitch Miller, Nathan Premo It is sometimes useful to have a particle detector that determines not only the amount of energy deposited in the detector but also the direction from which it came. With a colliding beam machine, such as the LHC, at small angles a detector is exposed both to particles coming from the interaction region and to particles produced by incoming beam particles. A directional detector can identify and enable the elimination of the background from the incoming beam. A charged particle with the velocity of light passing through a medium with an index of refraction n emits (\v{C}erenkov) light at an angle $\theta_c$ with respect to its direction such that $cos\theta_c$ = 1/n. This angle is 45$^\circ$ for n = 1.414. Directional counters can be made by using the directional properties of the \v{C}erenkov light. A photomultiplier tube, by itself, acts as such a detector by responding to \v{C}erenkov light produced in the glass over the photocathode. Various counter configurations have been studied using cosmic- ray muons identified by cosmic-ray telescopes from the NSF-DOE QuarkNet program. These counters are candidates for Forward Shower Counters (FSC) for the CMS experiment at the LHC. [Preview Abstract] |
Sunday, October 26, 2008 11:18AM - 11:30AM |
MH.00005: Characteristics of CMOS Light Detectors at Cryogenic Temperatures James Christian, Erik Johnson, Christopher Stapels, Paul Linsay, Rory Miskimen, Donald Crabb, Frank Augustine Advancing nuclear and high-energy physics often requires experiments conducted in harsh environments, such as a liquid helium bath and a superconducting magnet at several Tesla. These experiments need improved sensors that operate in these conditions. Improvements in detector technology used in extreme environments can improve the data quality and allow new designs for experiments that operate under these conditions. Solid-State Photomultipliers (SSPM), a device built from a monolithic array of photodiodes, can be used in these environments where traditional PMTs may not operate. Measurements of the diode properties at low temperatures down to 5~K are used to determine the potential of CMOS SSPMs in these environments. At temperatures below 60 K, extensive after pulsing is observed, which renders the Geiger photodiodes in the SSPM nonfunctional for biases above breakdown. In proportional mode operation, below the reverse bias breakdown, the photodiodes show a linear response to incident light with a relatively large gain and can be used at temperatures near 5 K. [Preview Abstract] |
Sunday, October 26, 2008 11:30AM - 11:42AM |
MH.00006: Development of a Total Absorption $\gamma$-ray Spectrometer (TAGS) for $\beta$-decay studies at ANL C.J. Chiara, F.G. Kondev, C.J. Lister, M.P. Carpenter, T. Lauritsen, E.A. McCutchan, G. Savard, D. Seweryniak, S. Zhu, M. Smith $\beta$-decay studies of nuclei far from stability are often hindered by the complexity of the daughter's decay scheme. For large decay $Q$-values, the decay strength may be distributed across numerous states de-exciting through many weak $\gamma$ rays. Failure to identify these $\gamma$ rays can result in systematic errors in determination of the $\beta$-decay strength distribution---the ``Pandemonium Effect'' [1]. To circumvent this issue, we are developing a TAGS to be used in conjunction with the CARIBU facility at ANL. The TAGS is a large-volume NaI(Tl) detector with a central well in which the active source is positioned [2], resulting in over 90\% $\gamma$-ray detection efficiency. A Si detector can additionally be placed within the well to allow $\beta$-tagging of the events. The information thus obtained has relevance for better characterization of the total decay heat produced in advanced nuclear reactors and for astrophysics applications. Progress on the development of TAGS at ANL will be presented. [1] J.A.Hardy {\it et al.}, Phys. Lett. {\bf B71}, 307 (1977). [2] R.C.Greenwood {\it et al.}, Nucl. Inst. Meth. {\bf A314}, 514 (1992). [Preview Abstract] |
Sunday, October 26, 2008 11:42AM - 11:54AM |
MH.00007: Compact $\beta$-NMR set-up using tilted-foil polarization C.J. Gross, K.P. Rykaczewski, J.W. Johnson, S.W. Mosko, A.J. Mendez II, D. Shapira, J.F. Liang, R.L. Varner, N. Benczer-Koller, G. Kumbartzki, M. Hass, P.F. Mantica, R. Grzywacz, S.N. Liddick, C.R. Reed, J.C. Batchelder, J.A. Winger We are developing polarized radioactive ion beams for use in $\beta$-NMR measurements. Polarization will be induced via the multi-tilted-foil method developed in the late 70's and 80's. Neutron-rich Cu and Ga radioactive beams will be accelerated to a few MeV and passed through a series of thin carbon foils tilted $\sim$75$^\circ$ with respect to the beam. Subsequent atomic polarization can be transfered to the nucleus through hyperfine coupling. Our goal is to be able to induce enough polarization into the beam (a few percent is sufficient) to enable $\beta$-NMR studies. If successful with HRIBF neutron-rich beams, we would be able to extend magnetic dipole moment measurements of ground states toward the r-process nuclei above $^{78}$Ni. A proof-of-principle experiment of the beam polarization process has been demonstrated by Bendah\'an et al. [Z. Phys. A 331, 343 (1988)]. It is hoped that a small compact system using permanent magnets will permit the use of Ge detectors to select specific isotopes in the beam. [Preview Abstract] |
Sunday, October 26, 2008 11:54AM - 12:06PM |
MH.00008: Diagnostics of Deformation in Thin Diamonds for Coherent Bremsstrahlung Radiators Richard Jones, Matthew Demas, Alisa Engsberg, Guangliang Yang The coherent bremsstrahlung beam line for Hall D at Jefferson Lab requires diamond radiators as thin as possible to reduce the effects of multiple scattering on the photon beam divergence. At thicknesses below 100 microns, stresses on the diamond, both from the way the crystal is mounted and from internal defects, can produce significant warping which degrades the coherent edge and polarization of the beam. The goal for Hall D is to use diamonds of 20 microns thickness. A 20 micron diamond from Element Six was studied using X-ray diffraction at the Cornell CHESS synchrotron facility. The diamond showed a large amount of warping across the entire face of the crystal. Benchtop measurements of surface curvature using a Michelson interferometer are being explored that would provide immediate feedback on crystal flatness and enable rapid studies of different mounting techniques. [Preview Abstract] |
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