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 DC: Instrumentation II: Low Energy, Gamma |
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Chair: Jolie Cizewski, Rutgers University Room: Plaza III |
Thursday, October 25, 2012 10:30AM - 10:42AM |
DC.00001: Detection system for the St. George recoil mass separator S. Kalkal, J. Hinnefeld, L. Morales, D. Robertson, E. Stech, G.P.A. Berg, J. Gorres, M. Couder, M. Wiescher The St. George recoil mass separator is designed for the study of low energy ($\alpha $,$\gamma )$ reactions of astrophysical interest in inverse kinematics. The energy range of recoils will be 0.07 to 0.9 MeV/nucleon. A detection system is being developed for separating the recoils from the residual scattered beam at the focal plane. The detection system will consist of two position sensitive microchannel plate (MCPs) timing detectors separated by 50cm followed by a single sided silicon strip detector. Simulations were performed using the codes SIMION and GEANT4. Different designs for guiding the secondary electrons emitted from a thin carbon foil to the MCP were studied in the simulations. Good timing and position resolution and minimization of transmission loss due to grids were key factors in selecting the final design. Time of flight will be recorded between the two MCPs. The delay line technique will be used for extracting the position information from the MCPs. The energy of the recoils will be recorded by the Si detector. A dedicated vacuum chamber and the modular design of the detection system will facilitate future improvements and customization for particular experiments. [Preview Abstract] |
Thursday, October 25, 2012 10:42AM - 10:54AM |
DC.00002: Exotic and Stable Nuclear Beam Neutron Spectroscopy without Time-of-Flight: A DSP-Based Deuterated Scintillator Array Michael Febbraro, Frederick Becchetti, Ramon Torres-Isea, Alan Howard, Amy Roberts, Jim Kolata Due to the limited beam intensity and other factors associated with exotic, short-lived secondary radioactive nuclear beams (RNB), we have developed a multi-element deuterated liquid scintillator array for the study of reactions involving neutrons. The system is well suited for RNB experiments involving neutrons such as the study of (p,n), (d,n), and (3He, n) reactions with neutron energy above 5 MeV and well separated states of interest. Because time-of-flight (ToF) is not necessary [1], the detectors can be located in close proximity to the reaction chamber allowing for good angular coverage and absolute detector efficiency compared to traditional ToF systems. The use of Digital Pulse Shape Discrimination (DPSD) for neutron spectroscopy experiments without ToF has been demonstrated and preliminary results from stable and exotic beam testing conducted at the UM-UND Twin-Sol LE-RNB facility lat UND will be reported. In addition, preliminary results from the new hydrogen-plastic scintillator Eljen-399 capable of neutron/gamma discrimination will also be discussed. This work is supported by NSF grant PHY 0969456. \\[4pt] [1] ``Evaluation of Large Deuterated Scintillators for Fast Neutron Detection ....,'' M. Ojaruega, et al., Nucl. Instrum. Methods A652 (2011) 397-399. [Preview Abstract] |
Thursday, October 25, 2012 10:54AM - 11:06AM |
DC.00003: Designing the Coupling of Gammasphere and ORRUBA C.M. Shand, S.D. Pain, A. Ratkiewicz, J.A. Cizewski, D.W. Bardayan, M.P. Carpenter, S. Hardy, C.J. Lister, W.A. Peters, D. Seweryniak, S. Zhu In studies of the structure of single-particle states, the ability to detect charged particles and $\gamma$ rays in coincidence provides significantly more insight than detecting either alone. The $\gamma$-ray spectrum carries structure information which would otherwise be lost when only particles are detected. In addition to light-ion transfer reactions, other nuclear reactions that benefit from coincident detection of particles and $\gamma$ rays include inelastic scattering, transfer with heavy-ions, and surrogates for neutron-induced reactions. The coupling of Gammasphere and ORRUBA is well suited to the coincident detection of charged particles and $\gamma$ rays. With up to 110 Compton-suppressed HPGe detectors, Gammasphere provides high detection efficiency and energy resolution for $\gamma$ rays. The position-sensitive silicon strip detector array ORRUBA provides large solid angle coverage and good angular resolution for charged particles. The substantial internal geometry of Gammasphere allows the barrel of ORRUBA to fit within it. The current status, including design work, of coupling the two detector arrays will be discussed. This work is supported in part by the U.S. D.O.E. and N.S.F. [Preview Abstract] |
Thursday, October 25, 2012 11:06AM - 11:18AM |
DC.00004: Evaluating a new segmented germanium detector contact technology E.G. Jackson, C.J. Lister, P. Chowdhury, E. Hull, R. Pehl New technologies for making gamma ray detectors position sensitive have many applications in space science, medical imaging, homeland security, and in nuclear structure research. One promising approach uses high-purity germanium wafers with the planar surfaces segmented into orthogonal strip patterns forming a Double-Sided Strip Detector (DSSD). The combination of data from adjoining strips, or pixels, is physics-rich for Compton image formation and polarization studies. However, sensitivity to charge loss and various kinds of cross-talk [1] have limited the usefulness of first generation devices. We are investigating new contact technologies, developed by PhDs Co [2], based on amorphous-germanium and yttrium contacts RF sputter deposited to a thickness of $\sim $ 1000 {\AA}. New techniques allow both physical and photolithographic segmentation of the contacts with inter-strip gap widths of 0.25 mm. These modifications should improve all aspects of charge collection. The new detector technology employs the same material and fabrication technique for both the n- and p- contacts, thus removing artificial asymmetry in the data. Results from tests of cross-talk, charge collection, and scattering asymmetry will be presented and compared with older technologies. This mechanically cooled counter, NP-7, seems to represent a breakthrough.\\[4pt] [1] S. Gros \textit{et al.}, Nucl. Inst. Meth. A 602, 467 (2009).\\[0pt] [2] E. Hull \textit{et al} Nucl Inst Meth A 626, 39 (2011) [Preview Abstract] |
Thursday, October 25, 2012 11:18AM - 11:30AM |
DC.00005: A New Gas Ionization Chamber For HELIOS Jianping Lai The HELIcal Orbit Spectrometer (HELIOS) has become an important tool in studying reactions using radioactive ion beams, and its special design has successfully alleviated problems that arise from studying reactions in inverse kinematics, such as kinematic compression. Here we introduce a new gas ionization chamber, which will significantly improve heavy recoil detection in HELIOS. On one hand, it will help eliminate background by detecting the heavy secondary recoils in coincidence with the light reaction products detected in the silicon detector array; on the other hand, our chamber can tolerate count rates of at least 100 kHz. As a result, a high detection efficiency will be achieved. This design, which functions well with beam rates above $10^5$ pps, and obtains a $\delta$$Z/Z$ resolution better than 2\%, will be presented. In addition, we will also show the first test results from this detector, which illustrate the detector's performance. In the future, this detector will be used for radioactive ion beam experiments of interest for nuclear structure and nuclear astrophysics, such as those important for X-ray burst nucleosynthesis. [Preview Abstract] |
Thursday, October 25, 2012 11:30AM - 11:42AM |
DC.00006: Compton suppression and event triggering in a commercial data acquisition system Samuel Tabor, D.D. Caussyn, Vandana Tripathi, J. VonMoss, S.N. Liddick A number of groups are starting to use flash digitizer systems to directly convert the preamplifier signals of high-resolution Ge detectors to a stream of digital data. Some digitizers are also equipped with software constant fraction discriminator algorithms capable of operating on the resulting digital data stream to provide timing information. Because of the dropping cost per channel of these systems, it should now be possible to also connect outputs of the Bismuth Germanate (BGO) scintillators used for Compton suppression to other digitizer inputs so that BGO logic signals can also be available in the same system. This provides the possibility to perform all the Compton suppression and multiplicity trigger logic within the digital system, thus eliminating the need for separate timing filter amplifiers (TFA), constant fraction discriminators (CFD), logic units, and lots of cables. This talk will describe the performance of such a system based on Pixie16 modules from XIA LLC with custom field programmable gate array (FPGA) programming for an array of Compton suppressed single Ge crystal and 4-crystal ``Clover'' detector array along with optional particle detectors. Initial tests of the system have produced results comparable with the current traditional system of individual electronics and peak sensing analog to digital converters. The advantages of the all digital system will be discussed. [Preview Abstract] |
Thursday, October 25, 2012 11:42AM - 11:54AM |
DC.00007: Test results of CHICO2 C.Y. Wu, D. Cline, A.B. Hayes, E. Kwan, A. Chyzh, I.Y. Lee CHICO is a highly segmented 4$\pi $ position-sensitive parallel-plate avalanche counter and has been used very successfully for many experiments as an auxiliary detector for Gammapshere. With the advent of the gamma-ray energy tracking array such as GRETINA, the development of a new generation of auxiliary detectors with a mating position resolution is absolutely needed. The upgrade of CHICO to CHICO2 with the matching position resolution for GRETINA is one of the coordinated efforts to accomplish this goal and is nearly complete. The test will be performed in the summer of 2012 with the new hardware and software. The new hardware includes the pixelated cathode board coupled with the delay-line readout for the position measurement and the 5-channel fast amplifier for processing both anode and cathode signals. The pulse height in addition to the time for the anode will be recorded for each event. The firmware for the new VME-based data acquisition system has been developed in anticipation of CHICO2 as an auxiliary detector for GRETINA and Gammasphere. The description of both hardware and software together with the test results will be presented. This work is supported by DOE, DE-AC52-07NA27344 (LLNL) and DE-AC02-05CH11231 (LBNL) as well as the NSF for U. of Rochester. [Preview Abstract] |
Thursday, October 25, 2012 11:54AM - 12:06PM |
DC.00008: The Ion Surfing Transport Method for Beam Thermalization Devices Amanda Gehring, Maxime Brodeur, Georg Bollen, David Morrissey, Stefan Schwarz Projectile fragments can be thermalized in buffer gas to supply rare ions to low energy experiments. We present here studies of ``ion surfing'' [1], a new method for transporting ions through gas-filled devices that use a RF gradient to repel the ions from the walls. Instead of relying on a fixed potential gradient to guide the thermal ions through the length of the cell, the ions are transported by a traveling wave superimposed on the RF field. The travelling wave is formed by an oscillating sinusoidal field applied to repeating sets of four electrodes. The field on each subsequent electrode is offset by 90 degrees in phase. Transport efficiency and velocity measurements were performed for rubidium and potassium ions over a wide range of conditions. With the optimal parameters currently attainable, $>$90{\%} efficient transport over 10 cm at 80 mbar was observed for Rb and K ions with max velocities of 75 m/s and 50 m/s, respectively. The measurements were conducted in preparation for the cyclotron gas cell at the National Cyclotron Laboratory at Michigan State University. We will present the results of the latest measurements and comparisons to detailed simulations. \\[4pt] [1] G. Bollen, Int. J. Mass Spect. \textbf{299} (2011) 131 [Preview Abstract] |
Thursday, October 25, 2012 12:06PM - 12:18PM |
DC.00009: Training Neural Networks to See Beyond Missing Information M.E. Howard, L.J. Schradin, J.A. Cizewski While the human eye may easily see a distorted image and imagine the original image, a rigorous mathematical treatment of the reconstruction may turn out to be a programming nightmare. We present a case study of nuclear physics data for which a significant population of events from a microchannel plate (MCP) detector are missing information for one of four MCP corners. Using events with good data for all four MCP corners to train a neural network, events with only three good corners are treated on equal footing in the analysis of position measurements, recovering much needed statistics. As this neural network is available within the framework of standard physics analysis packages such as ROOT and PAW, implementation is quite straightforward. We conclude with a discussion of the obvious advantages and limitations of this method as compared with an analytic approach. Work supported in part by the National Science Foundation and the Department of Energy. [Preview Abstract] |
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