Ralph James - Opening Remarks
RTSd Opening Remarks
Homogeneity and detector characteristics of melt grown CdZnTe implementing accelerated crucible rotation (#3701)
S. K. Swain1, J. J. McCoy1, L. Matei2, A. Burger2, K. Lynn1
1 Washington State University, Center for Materials Research, Pullman, Washington, United States of America
Inhomogeneity in the distribution of solutes is known to adversely influence the performance and cost of large area/volume cadmium zinc telluride (CZT) based devices, due to the variation in electro-optical and structural properties. Modified vertical Bridgman technique is well suited for faster growth of detector grade crystals. However, axial segregation of Zn is a classical problem. Additionally, due to the relativey higher growth temperatures, unintentional impurities are believed to be present and negatively affect the transport characteristics. In the present paper, we have demonstrated that by implementing accelerated crucible rotation technique, it is possible to grow large grain detector grade CZT crystals below the congruent melting point from a highly off-stoichiometric melt at growth rates comparable or faster than typically growth rates employed in melt growth. Growths under varying conditions of stoichiometry and rotation patterns were performed and compared. Excellent axial homogeniety in the Zn distribution has been reproducibly obtained by employing crucible rotation profile that is asymmetric with respect to acceleration and deceleration. Performance of radiation detector fabricated from these crystals will be discussed.
Keywords: CdZnTe detectors, Zn distribution
Three-Dimensional Position-Sensitive CdZnTe Gamma-Neutron Detectors (#3642)
Z. He1, Y. Zhu1, M. Streicher1, S. Brown1, B. Williams1, J. Xia1, J. Chu1, D. Goodman1, D. Shy1
1 University of Michigan, Nuclear Engineering and Radiological Sciences, Ann Arbor, Michigan, United States of America
Advancements on 3-dimensional (3-D) position-sensitive CdZnTe detectors at University of Michigan during the past year are summarized. These include collaboration with Redlen Technologies to investigate the effects of crystal annealing, electrode fabrication and attachment processes. CdZnTe crystals have been direct-attached to ASIC carrier boards and the energy resolution for single-pixel events has been improved from 0.4 – 0.5% FWHM to 0.3 – 0.4% FWHM due to the reduction on electronic noise. The first Orion digital 3-D CdZnTe detector system having an array of 3x3 CdZnTe crystals, each has dimensions of 2x2x1.5 cm^3, has shown an energy resolution better than 0.60% FWHM at 662 keV for all events. Thermal neutron imaging has been demonstrated using a Cf-252 source moderated by high-density polyethylene and time-encoded coded aperture imaging technique. Fast neutron detection has been demonstrated due to very low energy threshold between 4 – 5 keV with a 3-MeV dynamic range. The time-encoded coded aperture has enabled high-resolution gamma-ray imaging without artifacts in the reconstructed images due to gaps between CdZnTe detectors. Three-dimensional gamma-ray images have been overlaid with images obtained from other sensors for source localization. These developments have shown unique capabilities of 3-D CdZnTe detectors for gamma-ray, thermal and fast neutron detection and characterization.
Keywords: CdZnTRe, gamma-ray spectrometer, neutron detector, gamma-ray imager, thermal neutron imager
Nuvision: a Portable Multimode Gamma Camera based on HiSPECT Imaging Module (#2037)
G. Montémont1, P. Bohuslav2, J. Dubosq4, B. Feret4, O. Monnet1, O. Oehling3, L. Skala2, S. Stanchina1, L. Verger1, G. Werthmann3
1 CEA LETI, Grenoble, France
We have recently developed Nuvision, a portable gamma camera based on CZT detectors. It uses the HiSPECT imaging module architecture featuring IDeFX-HD ASICs and 3D subpixel positioning architecture. This device weights 3 kilograms, is waterproof (IP65) and is fully autonomous: it embeds an hybrid ARM processor/FPGA system on a chip and is powered by a battery allowing 7 hour operation. It can be interfaced to a computer or tablet by wired or wireless local area network.
The detector is a 40x40x6 mm thick CZT with 2.5 mm anode pitch allowing a overall resolution of 2.5 % at 122 keV and 1.5 % at 662 keV.The system uses coded aperture mask imaging to provide high sensitivity and high resolution in a limited frontal field of view (45 degrees). It also uses Compton imaging to coarsely localize out of field radiation. Thus, we take profit of the complementarity of both imaging methods.
It has been tested on various isotopes from Am-241 to Co-60 and it can perform spectrometric imaging with automated isotope recognition, visualizing multi-isotope image easily. System sensitivity is sufficient to localize a 50 nSv/h Co-57 source in natural background in less than 1 second and a 50 nSv/h Cs-137 source in less than 1 minute. Additionally, processing speed allows to perform real time imaging and to observe mobile sources.
We describe CZT detector spectral and imaging performance, the FPGA based 3D positioning and the list-mode image reconstruction technique used.
Keywords: CZT detectors, gamma imaging, coded aperture, compton imaging, gamma spectrometry