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Final Report: Planetary Instrument Definition and Design Program (PIDDP) Support Project

Description: The results of Sandia National Laboratories' participation in the NASA Planetary Definition and Design Program are summarized. Areas reported include the characterization of large area cadmium zinc telluride spectrometers and the application of simulation techniques to the prediction of device performance. Also investigated was the response of mercuric iodide devices in the region from 1 to 100 KeV. A literature study to determine the status or radiation damage measurements in room temperature semiconductor devices is also reported.
Date: March 1, 1999
Creator: Franks, L. A. & James, R. B.
Partner: UNT Libraries Government Documents Department

Testing of Kaonetics Devices at BNL

Description: The goal of these measurements was to evaluate whether there is evidence of emission of X-rays, gamma-rays, and neutrons by devices developed by Kaonetics Technologies, Inc. during their operation.
Date: June 1, 2011
Creator: Bolotnikov, A.; Smith, G. & and James, R.B.
Partner: UNT Libraries Government Documents Department

Lead iodide X-ray and gamma-ray spectrometers for room and high temperature operation

Description: In this study, we report on the results of the investigation of lead iodide material properties. The effectiveness of zone refining purification methods on the material purity is determined by ICP-MS and ICP-OES and correlated to the electrical and physical material properties. We show that this zone refining method is very efficient in removing impurities from lead iodide and we also determine the segregation coefficient for some of these impurities. Triple axis x- ray diffraction (TAD) analysis has been used to determine the crystalline perfection of the lead iodide after applying various cutting, etching, and fabrication methods. The soft lead iodide crystal was found to be damaged when cleaved by a razor blade, but by using a diamond wheel saw, followed by etching, the crystallinity of the material was improved, as observed by TAD. Low temperature photoluminescence also indicates an improvement in the material properties of the purified lead iodide. Electrical properties of lead iodide such as carrier mobility, were calculated based on carrier- phonon scattering. The results for the electrical properties were in good agreement with the experimental data.
Date: February 1, 1997
Creator: Hermon, H.; James, R.B. & Cross, E.
Partner: UNT Libraries Government Documents Department

Mercuric iodide sensor technology

Description: This report describes the improvement in the performance and the manufacturing yield of mercuric iodide detectors achieved by identifying the dominant impurities, carrier traps, and processing steps limiting device performance. Theoretical studies of electron and hole transport in this material set fundamental limits on detector performance and provided a standard against which to compare experimental results. Spectroscopy techniques including low temperature photoluminescence and thermally stimulated current spectroscopy were applied to characterize the deep level traps in this material. Traps and defects that can be introduced into the detector during growth, from the contact, and during the various steps in detector fabrication were identified. Trap energy levels and their relative abundances were determined. Variations in material quality and detector performance at the micron scale were investigated to understand the distribution in electric field in large volume detectors suitable for gamma-ray spectroscopy. Surface aging and contact degradation was studied extensively by techniques including atomic force microscopy, transmission electron microscopy, and variable angle spectroscopic ellipsometry. Preferred handling and processing procedures for maximizing detector performance and yield were established. The manufacturing yield of high resolution gamma-ray detectors was improved from a few percent to more than 30%.
Date: September 1, 1996
Creator: James, R.B.; Anderson, R.J. & Schlesinger, T.E.
Partner: UNT Libraries Government Documents Department

Cadmium zinc telluride charged particle nuclear detectors

Description: This report describes the improvements in understanding of transport phenomena in cadmium zinc telluride radiation sensors achieved through studies of alpha particle response and spatially resolved photoconductivity mapping. Alpha particle response waveforms and photocurrent profiles both indicate non-uniformities in the electric field which may have detrimental effects on detector performance. Identifying and eliminating the sources of these nonuniformities will ultimately lead to improved detector performance.
Date: February 1, 1997
Creator: Toney, J.E.; James, R.B. & Antolak, A.
Partner: UNT Libraries Government Documents Department

Material properties of large-volume cadmium zinc telluride crystals and their relationship to nuclear detector performance

Description: The material showing the greatest promise today for production of large-volume gamma-ray spectrometers operable at room temperature is cadmium zinc telluride (CZT). Unfortunately, because of deficiencies in the quality of the present material, high-resolution CZT spectrometers have thus far been limited to relatively small dimensions, which makes them inefficient at detecting high photon energies and ineffective for weak radiation signals except in near proximity. To exploit CZT fully, it will be necessary to make substantial improvements in the material quality. Improving the material involves advances in the purity, crystallinity, and control of the electrical compensation mechanism. Sandia National Laboratories, California, in close collaboration with US industry and academia, has initiated efforts to develop a detailed understanding of the underlying material problems limiting the performance of large volume gamma-ray spectrometers and to overcome them through appropriate corrections therein. A variety of analytical and numerical techniques are employed to quantify impurities, compositional and stoichiometric variations, crystallinity, strain, bulk and surface defect states, carrier mobilities and lifetimes, electric field distributions, and contact chemistry. Data from these measurements are correlated with spatial maps of the gamma-ray and alpha particle spectroscopic response to determine improvements in the material purification, crystal growth, detector fabrication, and surface passivation procedures. The results of several analytical techniques will be discussed. The intended accomplishment of this work is to develop a low-cost, high-efficiency CZT spectrometer with an active volume of 5 cm{sup 3} and energy resolution of 1--2% (at 662 keV), which would give the US a new field capability for screening radioactive substances.
Date: September 1, 1997
Creator: James, R.B.; Lund, J. & Yoon, H.
Partner: UNT Libraries Government Documents Department

Structural and chemical analysis of grain boundaries and tellurium precipitates in commercial Cd{sub 1{minus}x}Zn{sub x}Te

Description: The structure and chemistry of grain boundaries in commercial Cd{sub 1{minus}x}Zn{sub x}Te, prepared by the high-pressure Bridgman technique, have been analyzed using transmission electron microscopy, scanning electron microscopy, infrared-light microscopy and visible-light microscopy. These analyses show that the grain boundaries inside the Cd{sub 1{minus}x}Zn{sub x}Te materials are decorated with tellurium precipitates. Analysis of a tellurium precipitate at a grain boundary by transmission electron microscopy and selected-area electron diffraction found the precipitate to consist of a single, saucer-shaped grain. Electron diffraction from the precipitate was consistent with the trigonal phase of tellurium (space group P3{sub 1}21), which is the equilibrium phase at room temperature and atmospheric pressure. This precipitate was found to be aligned with one of the adjacent CZT grains such that the tellurium (0{bar 1}11) planes were nearly parallel to the CZT (111) planes. High-resolution transmission electron microscopy of the Te/Cd{sub 1{minus}x}Zn{sub x}Te interface showed no tertiary phase at the interface. The structures of the grain boundaries and the Te/Cd{sub 1{minus}x}Zn{sub x}Te interface are discussed and related to their possible implications on Cd{sub 1{minus}x}Zn{sub x}Te gamma-ray detector performance.
Date: June 1, 1998
Creator: Heffelfinger, J.R.; Medlin, D.L. & James, R.B.
Partner: UNT Libraries Government Documents Department

Analysis of grain boundaries, twin boundaries, and Te precipitates in CdZnTe grown by high-pressure Bridgeman method

Description: Grain boundaries and twin boundaries in commercial Cd{sub 1{minus}x}Zn{sub x}Te, which is prepared by a high pressure Bridgeman technique, have been investigated with transmission electron microscopy, scanning electron microscopy, infrared light microscopy and visible light microscopy. Boundaries inside these materials were found to be decorated with Te precipitates. The shape and local density of the precipitates were found to depend on the particular boundary. For precipitates that decorate grain boundaries, their microstructure was found to consist of a single, saucer shaped grain of hexagonal Te (space group P3{sub 1}21). Analysis of a Te precipitate precipitates by selected area diffraction revealed the Te to be aligned with the surrounding Cd{sub 1{minus}x}Zn{sub x}Te grains. This alignment was found to match the (111) Cd{sub 1{minus}x}Z{sub x}Te planes with the (1{bar 1}01) planes of hexagonal Te. Crystallographic alignments between the Cd{sub 1{minus}x}Zn{sub x}Te grains were also observed for a high angle grain boundary. The structure of the grain boundaries and the Te/Cd{sub 1{minus}x}Zn{sub x}Te interface are discussed.
Date: March 1, 1998
Creator: Heffelfinger, J.R.; Medlin, D.L. & James, R.B.
Partner: UNT Libraries Government Documents Department

Status of radiation damage measurements in room temperature semiconductor radiation detectors

Description: The literature of radiation damage measurements on cadmium zinc telluride (CZT), cadmium telluride (CT), and mercuric iodide (HgI{sub 2}) is reviewed for the purpose of determining their applicability to space applications. CZT strip detectors exposed to intermediate energy (1.3 MeV) proton fluences exhibit increased interstrip leakage after 10{sup 10} p/cm{sup 2} and significant bulk leakage after 10{sup 12} p/cm{sup 2}. CZT exposed to 200 MeV protons shows a two-fold loss in energy resolution after a fluence of 5 {times} 10{sup 9} p/cm{sup 2} in thick (3 mm) planar devices but little effect in 2 mm devices. No energy resolution effects were noted from moderated fission spectrum neutrons after fluences up to 10{sup 10} n/cm{sup 2}, although activation was evident. CT detectors show resolution losses after fluences of 3 {times} 10{sup 9} p/cm{sup 2} at 33 MeV for chlorine-doped detectors. Indium doped material may be more resistant. Neutron exposures (8 MeV) caused resolution losses after fluences of 2 {times} 10{sup 10} n/cm{sup 2}. Mercuric iodide has been studied with intermediate energy protons (10 to 33 MeV) at fluences up to 10{sup 12} p/cm{sup 2} and with 1.5 GeV protons at fluences up to 1.2 {times} 10{sup 8} p/cm{sup 2}. Neutron exposures at 8 MeV have been reported at fluences up to 10{sup 15} n/cm{sup 2}. No radiation damage was found under these irradiation conditions.
Date: April 1, 1998
Creator: Franks, L.A. & James, R.B.
Partner: UNT Libraries Government Documents Department


Description: High-pressure Bridgman (HPVB) and vertical zone melting (HPVZM) growth processes have been applied for the manufacturing of Cd{sub 1-x}Zn{sub x}Te (x = 0.04-0.2), CdSe and ZnSe crystal tapes with sizes up to 120 x 120 x 12 mm. The influences of the technological parameters describing the growth processes on the crystal quality and some selected material properties are discussed. The dependence of the inclusion (bubbles) content on the deviation from melt stoichiometry is determined. A method for growing plates with low content of inclusions is described. High-resistivity crystal tapes of undoped CdZnTe (10{sup 10} Ohm x cm), CdSe (10{sup 11} Ohm x cm) and ZnSe (>10{sup 11} Ohm x cm) were prepared. The possibility of tape growth on oriented seeds is shown for the example of CdSe. The primary differences between HPVB and HPVZM results are described. The main HPVZM advantage for II-VI compound crystal growth is the possibility of obtaining crystals with more stoichiometric composition or with a controlled deviation from stoichiometry. Hence, HPVZM is preferable for growing high-resistivity II-VI crystals with low inclusion content and possibly with better transport properties. Keywords for this report are: Crystal growth, shaped crystal growth, ZnSe, CdSe, CdZnTe, CZT, HPVB, Bridgman, HPVZM, zone melting, radiation detectors.
Date: July 7, 2002
Partner: UNT Libraries Government Documents Department


Description: CdZnTe (CZT) has been traditionally used as substrate for HgCdTe (MCT) epitaxy. The constraint of good lattice matching plays a fundamental role in the use of this substrate. In, fact, despite the difficulties in growing large area of affordable high-quality substrates, CZT wafers remain the best choice for high yield infrared devices. Nevertheless, material quality of the substrate and epilayer play a limiting role in IR focal plane array (FPA) detector technology. Furthermore, data suggest that the quality of the epilayer is affected by imperfections in the CZT substrate. In addition the pixel size for the current generation of FPAs (less than 20 {micro}m) suggests a need for detailed microscale characterization and an understanding of the substrates and epilayers on at least the spatial scale of the pixel dimensions. In an effort to understand the correlation between material quality and device performances, we have begun to study CZT substrates to investigate bulk and surface properties. The National Synchrotron Light Source (NSLS, BNL) permits a wide variety of material investigations that take advantage of the highly collimated photon radiation emitted from the X-ray and VUV-IR rings. Synchrotron radiation offers the capability to combine good resolution and shorter exposure times than conventional X-ray sources, which allow the ability for high-resolution mapping of relatively large areas in an acceptable amount of time. Transmission X-ray diffraction techniques, such as white beam topography and rocking curves, have already been used for bulk investigation [l] as well as IR transmission microspectroscopy. Surface studies on CZT substrates were performed using X-ray diffraction. By correlating results from the different material and device investigations, we offer a more complete characterization of bulk and surface crystalline quality and their effects on device performance. Information on the location of grain boundaries and precipitates, evaluation of impurity content, and stoichiometry variations will ...
Date: August 18, 2005
Partner: UNT Libraries Government Documents Department


Description: CdZnTe (CZT) is a very promising material for nuclear-radiation detectors. CZT detectors operate at ambient temperatures and offer high detection efficiency and excellent energy resolution, placing them ahead of high-purity Ge for those applications where cryogenic cooling is problematic. The progress achieved in CZT detectors over the past decade is founded on the developments of robust detector designs and readout electronics, both of which helped to overcome the effects of carrier trapping. Because the holes have low mobility, only electrons can be used to generate signals in thick CZT detectors, so one must account for the variation of the output signal versus the locations of the interaction points. To obtain high spectral resolution, the detector's design should provide a means to eliminate this dependence throughout the entire volume of the device. In reality, the sensitive volume of any ionization detector invariably has two regions. In the first, adjacent to the collecting electrode, the amplitude of the output signal rapidly increases almost to its maximum as the interaction point is located farther from the anode; in the rest of the volume, the output signal remains nearly constant. Thus, the quality of CZT detector designs can be characterized based on the magnitude of the signals variations in the drift region and the ratio between the volumes of the driR and induction regions. The former determines the ''geometrical'' width of the photopeak i.e., the line width that affects the total energy resolution and is attributed to the device's geometry when all other factors are neglected. The latter determines the photopeak efficiency and the area under the continuum in the pulse-height spectra. In this work, we describe our findings from systematizing different designs of CZT detectors and evaluating their performance based on these two criteria.
Date: August 26, 2007
Partner: UNT Libraries Government Documents Department

Polarization Studies of CdZnTe Detectors Using Synchrotron X-Ray Radiation.

Description: New results on the effects of small-scale defects on the charge-carrier transport in single-crystal CdZnTe (CZT) material were produced. We conducted detailed studies of the role of Te inclusions in CZT by employing a highly collimated synchrotron x-ray radiation source available at Brookhaven's National Synchrotron Light Source (NSLS). We were able to induce polarization effects by irradiating specific areas with the detector. These measurements allowed the first quantitative comparison between areas that are free of Te inclusions and those with a relatively high concentration of inclusions. The results of these polaration studies will be reported.
Date: July 1, 2007
Creator: Camarda, G. S.; Bolotnikov, A. E.; Cui, Y.; Hossain, A. & James, R. B.
Partner: UNT Libraries Government Documents Department

Distribution of zinc, resistivity, and photosensitivity in a Vertical Bridgman grown Cd1-xZnxTe ingot.

Description: We present the results of a comprehensive study of distribution of zinc, resistivity, and photosensitivity in a Cd{sub 1-x}Zn{sub x}Te ingot grown by the Vertical Bridgman method. We used several complementary methods, viz., glow discharge mass spectroscopy, photoluminescence-, resistivity-, and photosensitivity-mapping, along with photo-induced current transient spectroscopy to characterize the material. We identified electronic levels in the band-gap responsible for compensation, recombination, and photosensitivity.
Date: May 1, 2008
Creator: Babentsov, V.; Franc, J.; Fauler, A.; Fiederle, M. & James, R. B.
Partner: UNT Libraries Government Documents Department

CZT Virtual Frisch-grid Detector: Principles and Applications

Description: Cadmium Zinc Telluride (CdZnTe or CZT) is a very attractive material for using as room-temperature semiconductor detectors, because it has a wide bandgap and a high atomic number. However, due to the material's poor hole mobility, several special techniques were developed to ensure its suitability for radiation detection. Among them, the virtual Frisch-grid CZT detector is an attractive option, having a simple configuration, yet delivering an outstanding spectral performance. The goal of our group in Brookhaven National Laboratory (BNL) is to improve the performance of Frisch-ring CZT detectors; most recently, that effort focused on the non-contacting Frisch-ring detector, allowing us to build an inexpensive, large-volume detector array with high energy-resolution and a large effective area. In this paper, the principles of virtual Frisch-grid detectors are described, especially BNL's innovative improvements. The potential applications of virtual Frisch-grid detectors are discussed, and as an example, a hand-held gamma-ray spectrometer using a CZT virtual Frischgrid detector array is introduced, which is a self-contained device with a radiation detector, readout circuit, communication circuit, and high-voltage supply. It has good energy resolution of 1.4% (FWHM of 662-keV peak) with a total detection volume of {approx}20 cm{sup 3}. Such a portable inexpensive device can be used widely in nonproliferation applications, non-destructive detection, radiation imaging, and for homeland security. Extended systems based on the same technology have potential applications in industrial- and nuclear-medical-imaging.
Date: March 24, 2009
Creator: Cui,Y.; Bolotnikov, A.; Camarda, G.; Hossain, A. & James, R. B.
Partner: UNT Libraries Government Documents Department

DOE Coal Gasification Multi-Test Facility: fossil fuel processing technical/professional services

Description: A conceptual design, including process descriptions, heat and material balances, process flow diagrams, utility requirements, schedule, capital and operating cost estimate, and alternative design considerations, is presented for the DOE Coal Gasification Multi-Test Facility (GMTF). The GMTF, an engineering scale facility, is to provide a complete plant into which different types of gasifiers and conversion/synthesis equipment can be readily integrated for testing in an operational environment at relatively low cost. The design allows for operation of several gasifiers simultaneously at a total coal throughput of 2500 tons/day; individual gasifiers operate at up to 1200 tons/day and 600 psig using air or oxygen. Ten different test gasifiers can be in place at the facility, but only three can be operated at one time. The GMTF can produce a spectrum of saleable products, including low Btu, synthesis and pipeline gases, hydrogen (for fuel cells or hydrogasification), methanol, gasoline, diesel and fuel oils, organic chemicals, and electrical power (potentially). In 1979 dollars, the base facility requires a $288 million capital investment for common-use units, $193 million for four gasification units and four synthesis units, and $305 million for six years of operation. Critical reviews of detailed vendor designs are appended for a methanol synthesis unit, three entrained flow gasifiers, a fluidized bed gasifier, and a hydrogasifier/slag-bath gasifier.
Date: July 13, 1979
Creator: Hefferan, J.K.; Lee, G.Y.; Boesch, L.P.; James, R.B.; Rode, R.R. & Walters, A.B.
Partner: UNT Libraries Government Documents Department

Defects and impurities in mercuric iodine processing

Description: In the fabrication of mercuric iodide HgI{sub 2} room temperature radiation detectors, as in any semiconductor process, the quality of the final device is very sensitive to the impurities and defects present. Each process step can change the effects of existing defects, reduce the number of defects, or introduce new defects. In HgI{sub 2} detectors these defects act as trapping and recombination centers, thereby degrading immediate performance and leading to unstable devices. In this work we characterized some of the defects believed to strongly affect detector operation. Specifically, we studied impurities that are known to be present in typical HgI{sub 2} materials. Leakage current measurements were used to study the introduction and characteristics of these impurities, as such experiments reveal the mobile nature of these defects. In particular, we found that copper, which acts as a hole trap, introduces a positively charged center that diffuses and drifts readily in typical device environments. These measurements suggest that Cu, and related impurities like silver, may be one of the leading causes of HgI{sub 2} detector failures.
Date: March 1, 1996
Creator: van Scyoc, J.M.; James, R.B.; Schlesinger, T.E. & Gilbert, T.S.
Partner: UNT Libraries Government Documents Department

Analysis of Cd{sub 1{minus}x}Zn{sub x}Te microstructure

Description: The microstructure and chemical inhomogeneities of commercially available Cd{sub 1{minus}x}Zn{sub x}Te (CZT) have been evaluated using electron microscopy and microanalytical techniques. Since imperfections, such as inclusions, cracks and extended crystallographic defects are known to affect the performance of CZT gamma-ray spectrometers, understanding the nature and origins of such imperfections is vital to the improvement of device performance. CZT that is grown using a high-pressure Bridgeman method has a polycrystalline microstructure that contains numerous grain boundaries, twins and inclusions. In this study, scanning electron microscopy and X-ray energy-dispersive spectroscopy were used to analyze inclusions and cracks inside CZT material. Such analysis found regions of material rich in C, O, Si, Zn and Te. Transmission electron microscopy revealed small subgrains and thin platelets of a second phase material located inside the large-grain CZT matrix. Details of these microstructural features and their possible origins are discussed.
Date: August 1, 1997
Creator: Heffelfinger, J. R.; Medlin, D. L.; Yoon, H. & James, R. B.
Partner: UNT Libraries Government Documents Department

Miniature gamma-ray camera for tumor localization

Description: The overall goal of this LDRD project was to develop technology for a miniature gamma-ray camera for use in nuclear medicine. The camera will meet a need of the medical community for an improved means to image radio-pharmaceuticals in the body. In addition, this technology-with only slight modifications-should prove useful in applications requiring the monitoring and verification of special nuclear materials (SNMs). Utilization of the good energy resolution of mercuric iodide and cadmium zinc telluride detectors provides a means for rejecting scattered gamma-rays and improving the isotopic selectivity in gamma-ray images. The first year of this project involved fabrication and testing of a monolithic mercuric iodide and cadmium zinc telluride detector arrays and appropriate collimators/apertures. The second year of the program involved integration of the front-end detector module, pulse processing electronics, computer, software, and display.
Date: August 1, 1997
Creator: Lund, J.C.; Olsen, R.W.; James, R.B. & Cross, E.
Partner: UNT Libraries Government Documents Department