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Nuclear Science, IEEE Transactions on

Issue 4  Part 2 • Date Aug 1997

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Displaying Results 1 - 10 of 10
  • High-speed parallel implementation of a modified PBR algorithm on DSP-based EH topology

    Page(s): 1658 - 1672
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    Algebraic Reconstruction Technique (ART) is an age-old method used for solving the problem of three-dimensional (3-D) reconstruction from projections in electron microscopy and radiology. In medical applications, direct 3-D reconstruction is at the forefront of investigation. The simultaneous iterative reconstruction technique (SIRT) is an ART-type algorithm with the potential of generating in a few iterations tomographic images of a quality comparable to that of convolution backprojection (CBP) methods. Pixel-based reconstruction (PBR) is similar to SIRT reconstruction, and it has been shown that PBR algorithms give better quality pictures compared to those produced by SIRT algorithms. In this work, we propose a few modifications to the PBR algorithms. The modified algorithms are shown to give better quality pictures compared to PBR algorithms. The PBR algorithm and the modified PBR algorithms are highly compute intensive, Not many attempts have been made to reconstruct objects in the true 3-D sense because of the high computational overhead. In this study, we have developed parallel two-dimensional (2-D) and 3-D reconstruction algorithms based on modified PBR. We attempt to solve the two problems encountered by the PBR and modified PBR algorithms, i.e., the long computational time and the large memory requirements, by parallelizing the algorithm on a multiprocessor system. We investigate the possible task and data partitioning schemes by exploiting the potential parallelism in the PBR algorithm subject to minimizing the memory requirement. We have implemented an extended hypercube (EH) architecture for the high-speed execution of the 3-D reconstruction algorithm using the commercially available fast floating point digital signal processor (DSP) chips as the processing elements (PEs) and dual-port random access memories (DPR) as channels between the PEs. We discuss and compare the performances of the PBR algorithm on an IBM 6000 RISC workstation, on a Silicon Graphics Indigo 2 workstation, and on an EH system. The results show that an EH(3,1) using DSP chips as PEs executes the modified PBR algorithm about 100 times faster than an LBM 6000 RISC workstation. We have executed the algorithms on a 4-node IBM SP2 parallel computer. The results show that execution time of the algorithm on an EH(3,1) is better than that of a 4-node IBM SP2 system. The speed-up of an EH(3,1) system with eight PEs and one network controller is approximately 7.85 View full abstract»

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  • A compact high-current circular microtron

    Page(s): 1673 - 1676
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (108 KB)  

    A compact high-current circular microtron has been developed. This microtron is operated with the Russian second type of acceleration to reduce its size and has an electron gun outside the accelerating cavity to increase the beam current. The uniform magnetic field is about 0.19 T, and the energy gain per orbit is about 0.9 MeV. The beam current at a microwave power of 2.2 MW is 200 mA at 4 MeV and 80 mA at 9.5 MeV View full abstract»

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  • Performance of an aerogel threshold particle identification detector readout by hybrid photon detectors

    Page(s): 1621 - 1629
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (188 KB)  

    This paper describes an aerogel threshold particle identification detector developed for use in BABAR, the experiment to be run at the asymmetric e+e- B-factory PEP-II under construction at the Stanford Linear Accelerator Center (SLAC). Results of extensive tests performed at the CERN PS indicate that this detector is capable of separating pions from below-threshold particles in a wide momentum range. The detector is read by a new version of a hybrid photon detector (HPD). The HPD has been chosen because of its excellent behavior in high magnetic fields, where it can be successfully exploited to preserve the required particle identification (PID) performance View full abstract»

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  • Numerical analysis of electron orbits in a compact high-current circular microtron

    Page(s): 1677 - 1683
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    The performance of a compact high-current circular microtron is investigated by means of computer simulation. The microtron investigated here is operated with the Russian second type of acceleration and has an electron gun, composed of a cathode and an anode, located outside the accelerating cavity. The simulation results enable us to see the possibility of stable acceleration, to estimate the capture coefficient, and to predict the initial conditions necessary for stable acceleration View full abstract»

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  • On-line PET monitoring of radiotherapy beams: image reconstruction and Monte Carlo simulations of detector geometries

    Page(s): 1646 - 1657
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    The image reconstruction algorithm and design considerations for an annihilation gamma-ray coincidence detection camera are presented. The imaging system is designed to provide fast, on-line monitoring of the positron-emitting activity created by narrow gamma-ray, proton, or heavy-ion radiotherapy beams in tissue for determining total dose, performing range verification for charged particles, and for determining the oxygen content as a function of depth. A model of the detection system was developed and implemented using Monte Carlo techniques. Simulations based on this model are compared with experimental results from a prototype system and are used to study the detection efficiency and imaging characteristics of the system, while parameters such as scintillation crystal spacing, length, and separation are varied. In addition the effects of intercrystal shielding, extended activity distributions, and attenuation on detection efficiency and image reconstruction are presented. Simulation results suggest that the detection geometry which optimizes the sensitivity and spatial resolution utilizes tightly packed, narrow, uncoupled scintillation crystals with no intercrystal shielding. The one-dimensional reconstruction algorithm requires that the angular acceptance be minimized to reduce blurring for extended activity distributions. It is also shown that the depth-of-interaction blurring effect present in annular Positron Emission Tomography imaging systems may be removed through the calibration procedure and the one-dimensional image reconstruction algorithm used for this system View full abstract»

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  • Evaluation of polymer-coated CsI:Tl as an alpha/beta pulse shape discriminating flow cell

    Page(s): 1630 - 1634
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    A pulse shape discriminating flow-cell radiation detection system constructed with polymer-coated CsI:Tl was evaluated for simultaneous gross alpha/gross beta quantification. The CsI:Tl scintillator was crushed and sieved to 63-90-μm particle size and encapsulated with Parylene C to slow its dissolution rate. Averaged over the first hour of use, the pulse shape discrimination figure of merit was 1.4, and the detection efficiencies (±1σ) were 64.9±5.7%, 52.5±4.5%, and 4.5±0.2% for 233U, 90Sr/90Y, and 14C, respectively. The typical background count rates in the alpha and beta pulse shape window were 0.004 and 0.17 cps, respectively. The resultant minimum detectable activities (±1σ) for a 30-s count time were calculated to be 0.19±0.01 Bq, 0.9±0.1 Bq, and 11.4±0.6 Bq for 233U, 90Sr/90Y, and 14C, respectively. Although the 3-μm-thick encapsulation slowed CsI:Tl dissolution, the detection efficiency declined by a factor of two after 4.8 h, while the pulse shape resolution degraded slightly. With an appropriate coating, CsI:Tl is a good candidate for a heterogeneous pulse shape discriminating flow-cell View full abstract»

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  • High-power test of thermionic RF-gun at the Pohang Accelerator Laboratory

    Page(s): 1639 - 1645
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (148 KB)  

    A one-cell RF-gun with a dispenser cathode was fabricated for high-brightness applications at the Pohang Accelerator Laboratory. The gun was designed to withstand heavy beam loading and breakdown for long-pulse operation. After some RF-conditioning, the gun could be powered up to a nominal RF-power of 3.5 MW during 6 μs. The gun produced an electron beam with an average current of 300 mA and energy up to 1 MeV, normally operated with a 6-μs macropulse and 12-Hz repetition rate. The beam loading and the energy spectra were measured to confirm the gun's performance. The beam emittance was measured and compared with simulation results. The breakdown problem due to the field-emitted electrons and the backward electrons in the gun is discussed View full abstract»

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  • The gamma-ray burst monitor for the Russian Mars 1996 mission

    Page(s): 1692 - 1701
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (172 KB)  

    We describe an innovative detector designed primarily for the study of cosmic gamma-ray bursts aboard interplanetary spacecraft. The experiment is a fully functional, low cost, low mass, low-power instrument, which, when combined with other similar instruments, has the capability of localizing bursts to arcminute precision. The burst monitor is based on a photomultiplier tube and a plastic/CsI(Tl) phoswich detector and records photons in the 20-150-keV energy range with time resolutions up to several milliseconds. In addition, it records photon energy spectra. Events in the plastic scintillator are distinguished by a pulse shape discrimination circuit and are used to count electrons and protons. In a planetary orbiter or fly-by mission, this capability can be used to detect the presence of a magnetosphere. We describe in detail a version of this instrument which was built for the Russian Mars 1996 mission View full abstract»

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  • Experiences with the application of LAN emulation in a data acquisition system

    Page(s): 1635 - 1638
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (56 KB)  

    We applied for the first time the ATM technology and the LAN Emulation protocol in an existing data acquisition system. The distributed data acquisition system, based on standard host computers connected via TCP/IP over ethernet to processors in VME crates was upgraded using ethernet to ATM bridges and ATM switches. The maximum data rates in the new situation are a factor of five higher than in the previous architecture because the VME processors have individual bottleneck-free network connections to the host computer. This system scales with the available ATM network bandwidth and host computer CPU power View full abstract»

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  • Photocurrent mapping as a probe of transport properties and electric field distributions in cadmium zinc telluride detectors

    Page(s): 1684 - 1691
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    We have performed two-dimensional cross-sectional photocurrent mapping of Cd0.9Zn0.1Te detectors grown by the high-pressure Bridgman method as a means of probing the electric field distribution. We have analyzed the results using a model based on the drift-diffusion equation. In the case of a uniform electric field and excitation far from the electrodes, the result is virtually identical in form to the Hecht relation. We adapt the Hecht relation to analyze photocurrent data and generalize it to the case of a nonuniform electric field. The spatial distribution of photocurrent for the material that we have examined suggests a nonuniformity in either the electric field or the electron mobility-lifetime product. These observations may help to explain the slope changes observed in detector response pulses View full abstract»

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IEEE Transactions on Nuclear Science focuses on all aspects of the theory and applications of nuclear science and engineering, including instrumentation for the detection and measurement of ionizing radiation; particle accelerators and their controls; nuclear medicine and its application; effects of radiation on materials, components, and systems; reactor instrumentation and controls; and measurement of radiation in space.

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