Cadmium-Zinc-Telluride Fabrication and Material Improvements, A Few Steps Closer to HPGe Performance (#3794)
S. Taherion1, E. Chen1, P. Lu1, J. Kumar1, P. Wang1, P. Kharzaei1, Z. He2, Y. Zhu2, M. Streicher2, B. Williams2, J. Xia2
1 Redlen, Saanichton, BC, Canada
We review methods and processes involved in performance improvements of 15mm thick CdZnTe (CZT) detectors. In particular, we address the role of fabrication and material uniformity, prescreening, and attachment. We describe optical and electrical methods employed in prescreening of the materials and report the effect of surface and metal contact properties on the performance. The effects of wall, anode, and cathode surface quality, and in particular the effects on the performance uniformity of all pixels are explained. We briefly address the importance of material quality and annealing, and show the results from different annealing conditions. We revisit the surface residual damage removal by chemical methods after current lapping and polishing processes by slurry. Finally, we report noticeable performance improvements achieved by direct attachment of the detector to the digital ASIC.
Keywords: Cadmium-Zinc-Telluride, Room Temperature gamma and X-ray detector
Process Monitoring with High-Resolution CZT (#1383)
C. G. Wahl1, W. Kaye1, F. Zhang1, Y. A. Boucher1, J. M. Jaworski1, K. Moran1, T. Matthews1, D. Tefft1, H. Yang1, W. Wang1, B. Kitchen1, M. Ulrich1, T. Slatina1, S. Brown1, Z. He1
1 H3D, Inc., Ann Arbor, Michigan, United States of America
During nuclear power plant operation and maintenance, knowing the quantity and presence of radioisotopes in sub-system piping is critical for providing a comprehensive understanding of plant operation and for reducing worker dose. A new instrument, Polaris-S, has been designed to monitor key piping segments in real time for changes in radiological conditions and for the appearance of new isotopes. Polaris-S is based on large-volume pixelated CZT detectors with better than 1.1% FWHM energy resolution at 662 keV. The features needed to make this system suitable for such measurements will be discussed, including being able to operate in a wide range of dose rates and wirelessly transmit data. Representative results in nuclear-power measurements will be discussed, showing the instrument’s capabilities and limitations. Further, spectral and temporal analysis methods required to make best use of these data will be presented.
Keywords: CZT, high-resolution spectrometer, process monitor
PRISM – A CZT-Based Portable Radiation Imaging Spectroscopy and Mapping System (#2135)
P. J. Barton1, M. Turqueti1, A. Haefner1, R. Barnowski1, D. Hellfeld2, V. Negut1, L. Mihailescu1, K. Vetter1
1 Lawrence Berkeley National Laboratory (LBNL), Berkeley, California, United States of America
Previous free-moving hand-held broad-energy gamma ray imagers, specifically the High Efficiency Multimode Imager (HEMI), have demonstrated the benefits of an active mask, combining coded mask and Compton imaging. The 4-pi nonuniformity of the two-plane HEMI system had been overcome with a partially populated spherical arrangement of detector modules, providing omnidirectional responses for both imaging modalities. Free-moving imaging is achieved with the continuous situational awareness provided by a light detection and ranging (LIDAR) unit, visual camera, and an inertial measurement unit (IMU). A custom low-power discrete 384 channel data acquisition (DAQ) system was built around continuous digitization of the peak-held shaped signals from the application specific integrated circuit (ASIC) attached to each of the (up to 192) 1 cm3 coplanar grid CdZnTe crystals. A low-power high pin count field programmable gate array (FPGA) board acquires and sends digitized values via local ethernet to a compact single board computer for 3D gamma ray image reconstruction and integration with 3D scene data from the on-board contextual sensors. The assembled hand-portable system represents a truly unique Portable Radiation Imaging Spectroscopy and Mapping (PRISM) detection platform.
Keywords: CZT, coded aperture, Compton imaging, Gamma Ray Imaging
Compact High-resolution Silicon-CZT Beta-gamma Detection System for Nuclear Weapon Test Monitoring (#1713)
A. M. Alhawsawi1, A. T. Farsoni1, E. M. Becker2, L. Ranjbar1, M. Mannino1
1 Oregon State University, School of Nuclear Science and Engineering, Corvallis, Oregon, United States of America
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) bans all nuclear explosion tests for military or civilian purposes. The International Monitoring System (IMS) was established to verify compliance with the treaty. It consists of several monitoring stations that detect: seismic activities, hydrocoustic activities, infrasound waves, and radionuclide particles and noble gases. Radioxenon detection provides the most robust evidence of a nuclear weapon test. There are four Radioxenon isotopes of interest: 131mXe (t1/2 = 11.93 days), 133mXe (t1/2 = 2.19 days), 133Xe (t1/2 = 5.25 days) and 135Xe (t1/2 = 0.38 days). All for Radioxenons emit beta and gamma radiation in coincidence or conversion electrons and x-rays in coincidence during their decay process.
The radiation detection group at Oregon State University developed a new radioxenon detection system based on Si and CZT detectors. The system is made of the “PIPSBox” silicon gas cell recently developed by Canberra to detect beta and conversion electrons, and two coplanar CZT detectors to detect x-rays and gamma rays. The PIPSBox silicon gas cell offers many advantages such as: (1) increasing the frequency of air sampling at IMS stations because memory effect does not affect the PIPSBox gas cell like it does with plastic gas cells currently used at IMS stations, (2) reducing the Minimum Detectable Concentration (MDC) for Radioxenons due to better energy resolution of silicon, and minimal background interference from previous measurements. The detection system was simulated using MCNP6 and was characterized by 131mXe to determine optimum operating voltages, proper gain, and the length of the coincidence window.
Pulse waveforms of the silicon and CZT detectors were analyzed using an 8-channel, 125 MHz digital signal processor with a 14-bit resolution. A coincidence firmware was implemented in the on-board FPGA to identify specific coincidences events between silicon and CZT detectors.
Keywords: PIPSBox, Copalanr CZT, Digital Pulse Processing, Beta-Gamma Coincidence, Radioxenon
Development and Performance of Advanced Room Temperature Solid State Drift Detectors and Electronics in Synchrotron Radiation, X-ray Astronomy and Astrophysics (#2466)
A. G. Vacchi1, 2
1 Udine University, Dep of Mathematics, Computer Science and Physics, Udine, Italy
On the solid ground of the realization of a tracking system within the frames of the ALICE-LHC experiment based on very large area silicon drift detectors, a coherent effort has been carried ahead to adapt the whole technological frame to the field of high spectroscopy resolution low energy X-ray detection systems. The scientific drive that sets the specifications for this effort, which is involving a large collaboration, comes from the extreme needs of synchrotron light beam lines and X-ray astrophysics ground breaking projects. The encouraging results, that will be presented, have motivated a large community in using the versatility and performances of this detection system in different directions.
Keywords: Solid state advanced drift detector systems; Large Area High resolution low energy X-ray detectors
Large Area Si Pixel Sensor Processing on 8" High Resistive Wafers and Applying the Monolithic Pixel Sensor for Inspection of Art (#2053)
J. Kalliopuska1, J. Uher2, K. Lavanti1, J. Jakubek3, J. Salmi1, M. Jakubek3, S. Vähänen1, E. Trojanova3
1 Advacam Oy, Semiconductors, Espoo, Finland
The Si pixel sensor manufacturing has been commonly done on 4”-6” (100-150 mm) high resistivity wafers for the past 10-20 years. The main advantage in transferring the production to 8” (200 mm) wafers is the doubled process area compared to 6” wafers. This enables either manufacturing of large-area sensors up to 15x15 cm2 or doubling the number of produced sensors per wafer. The processing of these large area sensors on 8” wafer can considerably increase their manufacturing yield and reduce the cost of the sensor.
During past two years Advacam has been prototyping processing of fine pitch p-on-n pixel sensors on 8" Float Zone (FZ) and Magnetic Czochralski (MCZ) wafers. Recently, both the FZ and MCZ silicon have become available in 8" wafers with higher resistivity than 5000 Ohm-cm and lifetimes of few milliseconds. The 8” wafers received from the suppliers were Single Side Polished (SSP) with thickness of 725 μm. At the beginning of the processing the wafers were thinned and polished down to thicknesses of 300, 380, 500 and 675 μm. The successfully manufactured large area monolithic 1x5 pixel sensors with 55 μm pitch were flip chip bonded to Timepix readout ASICs. This 1x5 pixels sensor single row module was mounted into WidePIX 1x5 camera and tested in an art inspection application.
Comparison of the Si processing on 6” and 8” wafers will be given in terms of the overall yield, electrical characteristics and X-ray imaging properties. The electrical characterization comprises Current-Voltage (IV) and Capacitance-Voltage (CV) measurements across the wafers. The X-ray imaging properties comprise uniformity of the sensor materials in terms of resistivity and full charge collection efficiency; charge sharing between the pixels and between the Timepix ASICs at their boundaries; and overall stability of the cameras.
Keywords: Silicon, 200 mm, processing, pixel, sensor, detector, inspection, non-destructive testing, NDT, art, restoration, Magnetic Czochralski, Float Zone