Bulletin of the American Physical Society
2011 Fall Meeting of the APS Division of Nuclear Physics
Volume 56, Number 12
Wednesday–Saturday, October 26–29, 2011; East Lansing, Michigan
Session HD: Instrumentation V |
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Chair: Douglas Higinbotham, Thomas Jefferson National Accelerator Facility Room: Heritage |
Friday, October 28, 2011 10:30AM - 10:42AM |
HD.00001: Astrobox - a novel detector for nuclear astrophysics studies with low-energy protons B.T. Roeder, E. Simmons, M. McCleskey, A. Spiridon, L. Trache, R.E. Tribble, E. Pollacco, G. Pascovici In many radiative proton capture reactions on sd-shell nuclei or heavier, resonances dominate. One way these resonances can be studied is by measuring very-low energy protons from $\beta$-delayed proton decays. In the past, we produced and separated chosen exotic nuclei with MARS, implanted them in thin silicon strip detectors and observed the $\beta$-delayed protons while pulsing the beam. With this technique, we measured protons with low background for E$_{p}$ = 400-1500 keV. However, to measure lower-energy protons, careful subtraction of a substantial background from the positrons was needed. To reduce this background, we have developed Astrobox, a gas detector using micromegas electron amplifiers. In the first in-beam test of this gas detector at Texas A\&M University, it was found to be more transparent to positrons than the thin silicon detectors, and we were able to measure low-energy protons down to 200 keV with no positron background. The design of Astrobox and the results of the first test measurement of the device, which observed low-energy protons from the $\beta$-delayed proton decay of $^{23}$Al with very-low positron background for the first time, will be presented. [Preview Abstract] |
Friday, October 28, 2011 10:42AM - 10:54AM |
HD.00002: Fast Timing Measurements Using CeBr$_3$ Scintillators N. D'Olympia, S. Lakshmi, P. Chowdhury, E. Jackson, J. Glodo, U. Shirwadkar, K. Shah Continued research in advancing scintillation detector technology for both basic and applied nuclear science has recently focused on novel alkali halides. One candidate, CeBr$_3$, is capable of achieving $\approx$120 ps timing resolution, and has also been found to have an energy resolution on the order of 3-5\%. In this work, the utility of CeBr$_3$ detectors for research in basic nuclear physics has been investigated through fast-timing measurements of nanosecond and sub-nanosecond isomer half-lives. A $t_{1/2}$=1.4 ns 2$^{+}$ state in $^{152}$Sm was populated in the decay of a $^{152}$Eu $\gamma$-calibration source, and a $t_{1/2}$=537 ps 9/2$^{-}$ state in $^{177}$Hf in the decay of $^{177}$Lu, produced through thermal neutron activation of a natural Lu foil in the UMass Lowell Research Reactor. Half-lives were measured using a multi-parameter data acquisition setup to obtain energy gated time spectra. Results of these measurements with CeBr$_3$ detectors will be discussed in the context of next generation nuclear science research. [Preview Abstract] |
Friday, October 28, 2011 10:54AM - 11:06AM |
HD.00003: Resistive Plate Chamber Rate Capability Studies Daniel Jumper Bakelite RPCs have been used in first level muon trigger applications ~in the CMS and ATLAS experiments at LHC and in the PHENIX experiment~at RHIC. ~In hadron colliders RPCs have to withstand high levels of background ~rates. Using a novel method to test rate capability with a radioactive source, we have studied the possibility to further increase the rate capability~of bakelite RPCs by changing the resistivity of the bakelite surface coating. [Preview Abstract] |
Friday, October 28, 2011 11:06AM - 11:18AM |
HD.00004: Nuclear Spectroscopy using Novel, Position-Sensitive Detectors S. Lakshmi, P. Chowdhury, E.G. Jackson, S. Hota, C.J. Lister, S. Gros, M. McClish, R. Farrel, K. Shah Novel, position-sensitive particle and gamma detectors were tested for applications in nuclear physics experiments. An efficient compact setup was used to measure angular correlation between the alpha particle decay of $^{224}$Ra to an excited state in $^{220}$Rn, and the subsequent gamma decay to the ground state in $^{220}$Rn. A 1'' X 1'' position-sensitive avalanche photo-diode (PSAPD) was used for detecting the alpha particles and a planar germanium double-sided strip detector (GeDSSD) for detecting the gamma rays. Significant solid angle coverage is achieved in a single, fixed geometry, due to the excellent position resolutions of the PSAPD (400 microns) and the GeDSSD (5 mm) by positioning the detectors close to the source. Distortion correction algorithms for the PSAPD, pixel efficiencies, method of angle reconstruction and the measured angular correlation have been improved iteratively. Latest results will be presented. [Preview Abstract] |
Friday, October 28, 2011 11:18AM - 11:30AM |
HD.00005: Gamma Ray Interactions in Planar Germanium Strip Detectors E.G. Jackson, S. Lakshmi, P. Chowdhury, A.Y. Deo, C.J. Guess, S. Hota, C.J. Lister The position resolution of the interaction point of a gamma ray within the volume of a planar germanium crystal is under investigation. A 16x16 planar double-sided strip detector of high-purity germanium, measuring 92x92x20mm, with 16 horizontal strips on one face and 16 vertical strips on the other, is used. Comparing the strongest strip signal from each side of the detector allows for a X-Y pixelation of the gamma ray interaction in the crystal. Energy and efficiency calibrations are performed with standard $^{152}$Eu and $^{133}$Ba sources placed at fixed distances from the detector face. The measured efficiency of each pixel is compared to calculated geometric efficiencies. Next steps involve the analysis of two-pixel events which pick out Compton scatters within the planar crystal. Results and status report will be presented. [Preview Abstract] |
Friday, October 28, 2011 11:30AM - 11:42AM |
HD.00006: Depth of Gamma Ray Interaction in a Planar Ge Double-sided Strip Detector via Digital Signal Processing T. Harrington, J. Thomas, S. Lakshmi, P. Chowdhury, C.J. Lister Using a 1 GHz Lecroy Digital Oscilloscope to digitize waveforms, C$++$ programs and analysis software were developed for various digital signal processing (DSP) applications. In this research, we have focused on the DSP applications using a 16x16 planar high purity germanium double-sided strip detector, which measures 92x92x20mm. Using a $^{137}$Cs source, electron and hole current signals were collected for photopeak events using one strip from both the front and back of the detector. The time resolution was measured by performing a custom constant fraction discrimination (CFD) routine on the waveforms and histogramming the time differences. The optimum time resolution was investigated by adjusting the CFD parameters. By analyzing the time differences between the electron and hole current signals, the possibility of determining the depth of a gamma ray's interaction point within the germanium detector was examined. The method used to determine time resolution, the optimization of the constant fraction discrimination parameters, and analysis techniques will be presented. [Preview Abstract] |
Friday, October 28, 2011 11:42AM - 11:54AM |
HD.00007: Upgrading the PHENIX Muon Trigger using Resistive Plate Chambers to Enhance Proton Spin Measurements Rusty Towell Determining the contributions of the sea quarks and other partons to the spin structure of the proton is important to our understanding of QCD. Collisions of longitudinally polarized protons at high energies provide a measurement of the flavor dependent contributions. In particular, the production of W-bosons at forward rapidity is sensitive to the flavor dependent spin contributions. The PHENIX detector at RHIC is well designed to make this measurement but required an upgrade to the forward trigger. The new PHENIX Muon Trigger will help select W-bosons events that can be detected through the appearance of a high-energy muon in one of the two existing muon spectrometers. The trigger upgrade is based on new front-end electronics for the muon tracking chambers and the addition of two stations of Resistive Plate Chambers in both muon arms. The stations of RPCs closest to the interaction point have recently been assembled and installed. The design and performance of these chambers will be reviewed along with the measurements possible in the next polarized proton run. [Preview Abstract] |
Friday, October 28, 2011 11:54AM - 12:06PM |
HD.00008: Improved Timing Resolution using digital pulse shape processing Nicole Larson, Sean Liddick, Andreas Stolz, Scott Suchyta At fragmentation facilities radioactive isotopes are identified using a combination of energy loss and time-of-flight measurements. At the NSCL, the time-of-flight is measured between a~scintillator placed at the intermediate dispersive image of the A1900 fragment separator and a detector immediately preceding the experimental station. To increase the rates of radioactive isotopes delivered to the experimental station the momentum acceptance of the A1900 is increased. Maintaining satisfactory particle identification with larger momentum acceptance requires correcting the time-of-flight of the radioactive isotope based on their position at the intermediate dispersive image. The correction is currently derived from standard analog circuits using timing filter amplifiers, constant fraction discriminators, and TAC modules. Digital pulse-shape processing may offer the possibility to reduce the timing uncertainty in the position determination thus improving the sensitivity of the particle identification. Preliminary results will be presented. [Preview Abstract] |
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