Bulletin of the American Physical Society
2006 Division of Nuclear Physics Annual Meeting
Wednesday–Saturday, October 25–28, 2006; Nashville, Tennessee
Session DH: Instrumentation I |
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Sponsoring Units: DNP Chair: Will Johns, Vanderbilt University Room: Gaylord Opryland Cheekwood F |
Friday, October 27, 2006 2:00PM - 2:12PM |
DH.00001: Absolute Polarization Measurements At RHIC In The Coulomb Nuclear Interference Region Oleg Eyser, Igor Alekseev, Alessandro Bravar, Gerry Bunce, Satish Dhawan, Ronald Gill, Willy Haeberli, Haixin Huang, Yousef Makdisi, Itaru Nakagawa, Alexander Nass, Hiromi Okada, Edward Stephenson, Dima Svirida, Thomas Wise, Jeff Wood, Anatoli Zelenski The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) is the world's first polarized proton collider which currently delivers center of mass energies of 200 GeV. For polarimetry, proton-Carbon and proton-proton scattering is used in the Coulomb Nuclear Interference (CNI) region at low momentum transfer -t. While two proton-Carbon polarimeters provide fast polarization measurements with small statistical errors at several times during an accelerator store, a polarized Hydrogen Jet device is needed for absolute normalizaton over multiple stores. The jet polarization is constantly monitored in a Breit-Rabi unit. In 2005 the Jet polarimeter has been used with both RHIC beams and can, therefore, be combined with both Carbon polarimeters. Systematic errors have been studied in detail and results were compared to the previous run in 2004 when the Jet polarimeter had an extended acceptance for only one beam. Results of the analyzing power at 100 GeV have been published and other energies up to the RHIC goal of 250 GeV are under investigation. [Preview Abstract] |
Friday, October 27, 2006 2:12PM - 2:24PM |
DH.00002: Development of a beam profile diagnostics device for the VENUS ECR ion source beam line Cary Pint, Daniela Leitner, Damon Todd This work describes the design and development of the instrumentation for a beam profile diagnostics unit for the low energy beam transport line of the superconducting Electron Cyclotron Resonance (ECR) ion source VENUS (Versatile ECR ion source for Nuclear Science). VENUS is currently being commissioned at LBNL and serves as the prototype ECR injector source for next generation heavy ion accelerators. In order to enhance simulations of beam transport from extraction in VENUS, a measurement device (called a harp) consisting of a grid of thin conducting wires is placed into the beam line, directly downstream from extraction, to measure the beam profile. Utilizing the diagnostics unit developed and described in this work, the first measurements of the beam profile for a simple helium beam are presented. By changing the Glaser current to focus the ion beam onto the harp, the helium beam profiles illustrate that the extracted beam has the same symmetry as the plasma surface from which they are extracted, and not the uniform circular symmetry that is assumed in most simulation models. These results give quantitative insight into the enhancement of initial conditions needed for using simulations to give a physically accurate description of beam transport from extraction of an ECR source. [Preview Abstract] |
Friday, October 27, 2006 2:24PM - 2:36PM |
DH.00003: Ion signals with R134a and R134 in a parallel plate proportional counter Edwin Norbeck, J.E. Olson, Y. Onel The electrical signals from a PPAC (parallel plate avalanche counter) are identical for R134a (1,1,1,2-tetrafluoroethane) and R134 (1,1,2,2-tetrafluoroethane) except for the ion part, which, for R134a, is slower and smaller, but with the same area. The two compounds are identical except for the location of one fluorine atom. With three fluorine atoms on one end, the more common R134a has a large electric dipole moment, about the same as water; while R134 is symmetric, with no dipole moment. The attraction of the polar R134a molecules interferes with the motion of the ions, which results in a longer ion collection time. The counter is two circular plates of 1.0 cm$^2$ area separated by 0.5 mm operating at 700 torr and 2120 V. The ion signal is constant for a time t$_0$ and then goes linearly to zero at time t$_1$. The values of t$_0$ and t$_1$ are 1.3 $\mu$s and 1.8 $\mu$s for R134a, but only 0.8 $\mu$s and 1.3 $\mu$s for R134. These are not precise times because the signals are very small and the values depend on the location of the primary ion formation (from a $^{137}$Cs $\gamma$ source). During the constant part of the signal the ions are moving between the plates. The signal goes toward zero as the ions are collected at the cathode. For both gasses the large signal from electrons is fast with a full width at half maximum of only 1.0 ns. [Preview Abstract] |
Friday, October 27, 2006 2:36PM - 2:48PM |
DH.00004: Validation of the GEANT4 code for simulations of a plastic $\beta$-detector and its application to efficiency calibration V.V. Golovko, V.E. Iacob, J.C. Hardy Precise $\beta^+ $-branching-ratio measurements are required to determine \textit{ft}-values as a part of our program to test the Standard Model via unitarity of the Cabibbo-Kobayashi-Moskava matrix. For the measurements to be useful in this test, their precision must be close to 0.1{\%}~[1]. In a branching-ratio measurement, we collect a radioactive species in mylar tape, and then move the tape to a counting station, where the sample is positioned between a scintillator used to detect $\beta $-particles, and a HPGe detector for $\gamma $-rays. The signals from both detectors are recorded for all events in which there is a $\beta -\gamma $ coincidence. Although we obtain the $\beta $ branching ratio from the absolute intensity of the coincidence $\gamma $ rays, the relative efficiency of the $\beta $-detector as a function of $\beta $ energy is crucial to our achieving a precise result since different $\gamma $-ray peaks correspond to $\beta $-transitions with different end-point energies. We have studied our $\beta $-detector response function using Monte Carlo calculations performed by GEANT4 code. Since there are always question about the validity of any particular simulation code, the simulated results were compared to measured $\beta $-spectra from various standard $\beta $-sources, as well as with Monte Carlo simulated $\beta $-response functions obtained with the EGS-code~[2]. [1] J.~C. Hardy and I.~S. Towner. \textit{PRC}, 71(5):055501, 2005. [2] V.~E. Iacob, J.~C. Hardy, and N.~Nica. \textit{BAPS 49}, no 6, p~J9 111, 2004. [Preview Abstract] |
Friday, October 27, 2006 2:48PM - 3:00PM |
DH.00005: Implementation of a beta NQR system at the NSCL for ground state quadrupole moment measurements R.R. Weerasiri, P.F. Mantica, K. Minamisono, J. Pereira, J. Pinter, J. Stoker The nuclear electric quadrupole moment is one of the most important basic properties of the nucleus, which provides a direct measure of the nuclear charge distribution. A beta ray detected nuclear magnetic resonance $(\beta$-NMR) technique in the presence of an electric-field gradient is capable of measuring ground state quadrupole moments (\textit{Q}) of beta unstable nuclei $(\beta$-NQR). For such measurements, a $\beta$- NQR system is being constructed based on the present $\beta$-NMR system at the NSCL. Due to the quadrupole interaction, several different radio frequencies (\textit{rf}) are required to saturate NMR transitions, which are produced by function generators. Several LCR resonance circuits are used to provide \textit{rf} field for the NMR and they have to be switched one after the other within very short time period because of the shorter lifetime of the nucleus of interest. Poorly known \textit {Q} (${}^{37}$K) will be measured to test the system and unknown \textit{Q} (${}^{35}$K) will be measured later. The neutron rich \textit{sd} shell and the \textit{pf} shell are of interest as well. [Preview Abstract] |
Friday, October 27, 2006 3:00PM - 3:12PM |
DH.00006: The Radio Frequency Fragment Separator for Rare Isotope Beams at the NSCL Joshua Stoker, Vladimir Andreev, Daniel Bazin, Ana Becerril, Marc Doleans, Dimitry Gorelov, Patrick Glennon, Terry Grimm, Don Lawton, Paul Mantica, Felix Marti, Jack Ottarson, Hendrik Schatz, John Vincent, Jim Wagner, Xiaoyu Wu, Al Zeller Secondary beams at the National Superconducting Cyclotron Laboratory (NSCL) are separated through a combined application of magnetic rigidity and energy loss filtering. Design and construction of a Radio Frequency Fragment Separator (RFFS) for further beam purification is underway. The RFFS will apply a time-varying electromagnetic field to induce transverse beam separation. This method relies on velocity differences of the beam species to selectivey apply separation to unwanted fragments. The technical design of the RFFS and the expected purification of exotic beams are shown in detail[1]. \\ \noindent [1] Gorelev, D. \emph{et al.}, ``RF Kicker System for Secondary Beams at the NSCL'' Proc of Part Accel Conf 2005, Knoxville, TN [Preview Abstract] |
Friday, October 27, 2006 3:12PM - 3:24PM |
DH.00007: ABSTRACT WITHDRAWN |
Friday, October 27, 2006 3:24PM - 3:36PM |
DH.00008: Polarization sensitivity measurements in SeGA detectors David Miller, Krzysztof Starosta, Przemek Adrich, Aaron Chester, Constantin Vaman, Dirk Weisshaar For isotopes far from stability, the nuclear shell structure is modified influencing the location of intruder states within major shells. Parity is a key observable in nuclear spectroscopy to identify the intruder states for example in the ``island of inversion'' around $^{32}$Mg where the $f_{7/2}$ neutron orbital is expected to play a key role. Linear polarization measurements of $\gamma$-rays are a probe to access the parities of energy levels. Utilizing the segmentation of detectors in the Segmented Germanium Array (SeGA) at the NSCL and analyzing the hitpatterns thereof allows the detectors to be used as Compton polarimeters. The linear polarization sensitivity of SeGA has been measured using $\alpha$-$\gamma$ correlations from a $^{249}$Cf source. Existing analog electronics for data acquisition worked in parallel to the first phase of a new digital data acquisition system being implemented at the NSCL. The results and future improvements that could have substantial impact to the detector sensitivity are discussed. [Preview Abstract] |
Friday, October 27, 2006 3:36PM - 3:48PM |
DH.00009: Alpha-Gamma Coincidence Spectroscopy using a Si PSAPD and Ge DSSD combination C.M. Wilson, P. Chowdhury, R. Gramer, S.K. Tandel, N.J. Hammond, C.J. Lister, S.M. Fischer, E.F. Moore, K.M. Teh, M. McClish, K.S. Shah, R. Farrell A 14mm x 14mm position-sensitive silicon avalanche photodiode [1] was tested for use as a charged particle detector, using alpha particles from 249Cf and 228Th sources. To determine the position of interaction event-by-event, an algorithm was developed to correct for the ``pin-cushion'' distortion characteristic of four-corner charge-fractionation devices. The detector was then tested in alpha-gamma coincidence spectroscopy, in conjunction with a double-sided germanium strip detector made up of 16 vertical and 16 horizontal 5mm wide contact strips on opposite sides [2]. The goal was to achieve high solid-angle geometry in a single set-up, with the position-sensing capabilities of both detectors yielding angular correlation information between the coincident radiation. Limitations and improvements in using such detectors will be discussed in light of the experience gained with these initial measurements. [1] K.S. Shah, et al, IEEE Trans. Nucl. Sci. 49(4),1687(2002). [2]G.D. Jones et al., Proc. Conf. \textit{Nuclei at the Limits}, Argonne, AIP Conf. Proc. \textbf{764}, 348 (2005). [Preview Abstract] |
Friday, October 27, 2006 3:48PM - 4:00PM |
DH.00010: Multiplexed Analog Shaped Electronics (MASE): A new approach to the readout of segmented silicon arrays Romualdo de Souza, Carl Metelko, Sylvie Hudan, Andrew Alexander, John Poehlman A new approach in the signal processing and readout of highly segmented silicon detector arrays is described. The realization of this approach is Multiplexed Shaped Analog Electronics (MASE), an electronic system that allows the effective readout of highly segmented detector arrays when the occupancy in a single event is low. MASE combines the features of good energy resolution with time resolution adequate for random rejection. It employs the tight integration of analog signal conditioning together with digital signal manipulation in discrete component surface mount technology. External digitization of a sparsified analog stream makes MASE cost effective and scalable. It can be used as easily to read out 4096 channels as it can to read out a single silicon detector. Both the design and the performance characteristics of MASE are presented. [Preview Abstract] |
Friday, October 27, 2006 4:00PM - 4:12PM |
DH.00011: Energy Spectrums from Unshaped Signals Eliza Osenbaugh-Stewart Digital signal processing was used to produce an energy spectrum from the raw output of a preamplifier. It is our hope to use the signals generated from the preamplifier for pulse shape discrimination. Therefore we needed to generate a energy spectrum without relaying on the shaping done by an amplifier. The voltage pulse produced by a germanium detector was recorded with a flash ADC. The data was then filtered twice, first using a low-pass recursive filter to get rid of high frequency noise and again to remove lower frequency problems. The resulting pulse was integrated to determine the energy. This was tested with various spectrums and produces expected results with a small decrease in energy resolution as compared to shaped data. At this time optimal filtering is being studied as a possible way to increase energy resolution. [Preview Abstract] |
Friday, October 27, 2006 4:12PM - 4:24PM |
DH.00012: Shielding Design for the CARIBU Project Eugene Moore, Samuel Baker, Richard Pardo, Guy Savard The CAlifornium Radioactive Ion Breeder Upgrade (CARIBU) [1] will serve as a source of radioactive ions to be accelerated by the ATLAS accelerator [2]. CARIBU will consist of an open, 1 Ci Cf-252 source electroplated on a Ta backing. Fission fragments emitted from the source will be captured in a He gas cell with DC and RF fields that will direct the radioactive ions toward the exit nozzle. The ions will be mass analyzed and transported to a charge breeding ECR source and injected into ATLAS. The radiation fields produced by an unshielded 1 Ci Cf-252 source exceed 4 rem/hr (neutron), and 250 mR/hr (gamma) at 1 meter. In order to allow unlimited access to the CARIBU source area, we are designing a shielding system to reduce the radiation fields to $\sim $1 mrem/hr at 30 cm from accessible surfaces. The MCNPX code [3] is being used to model the neutron and gamma radiation shielding. The results of the simulations and some comparisons with measurements will be presented. REFERENCES [1] www.phy.anl.gov/atlas/caribu.html [2] www.phy.anl.gov/atlas/index.html [3] mcnpx.lanl.gov/. [Preview Abstract] |
Friday, October 27, 2006 4:24PM - 4:36PM |
DH.00013: CASSPERR - an Improved Resonant Nuclear Reaction Analysis Detector Arthur Pallone, J. Derek Demaree Although it is a powerful tool, nuclear reaction analysis is not yet widely practiced at ion beam facilities because data is acquired sequentially, i.e. collecting data at incremental energies (depths). Data collection can be improved by increasing the efficiency of detection or reducing the noise. The most commonly used method to reduce the noise is to passively shield the detector from the background (typically cosmic rays or naturally-occurring radioactive elements). The volume of shielding required to decrease the noise from these interfering backgrounds occupies too much space for implementation at most ion beam facilities. Active shielding via coincidence rejection requires that a cosmic ray interact with both the detector and the coincidence shield. The low probability for both interactions to occur limits the effectiveness of this coincidence rejection technique. Sum coincidence spectrometry is a common technique used in nuclear decay studies and in neutron activation analysis. Singru suggested that this technique be applied to (p, $\gamma \quad \gamma )$ reactions. The development, testing, and some potential materials research applications of the CAScade SPEctrometer for Resonant Reactions (CASSPERR) based on this technique are presented. [Preview Abstract] |
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