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Performance comparison of four compact room-temperature detectors – two cadmium zinc telluride (CZT) semiconductor detectors, a LaCl3(Ce) scintillator, and an NaI(Tl) scintillator

Description: The performance characteristics of four compact, room-temperature detectors – two scintillators and two semiconductor detectors – have been studied. All are commercially-available detectors. The two scintillators were a Æ13mmX13mm lanthanum chloride [LaCl3(Ce)] detector and a Æ25mmX25mm sodium iodide [NaI(Tl)] detector. The two semiconductor detectors were a 10X10X3 mm3 cadmium zinc telluride (CZT) detector with a coplanar gridded anode and a 5X5X5 mm3 CZT detector with an extended cathode. The efficiency, resolution, and peak shape performance of these devices are compared in this work. Since LaCl3(Ce) is a relatively new commercial scintillator material, additional information on the performance of this detector is presented. Specifically, we discuss the impact of naturally-occurring radioactive 138La on the background spectra measured with this scintillator. Additionally, two of the three LaCl3(Ce) crystals that we obtained commercially were internally contaminated with an alpha particle-emitting radionuclide which we have identified as 227Ac+daughters. This contamination had a profound impact on the usefulness of these two detectors.
Date: October 1, 2004
Creator: Hartwell, J. K.
Partner: UNT Libraries Government Documents Department

A new intense neutron generator and high-resolution detector for well logging applications

Description: Advances in both ion source and gamma-ray detector technology at LBNL are being used to develop a new high-sensitivity neutron logging instrument. Up to 37 mA of current per 10-20 {mu}s pulse, 80-95% D{sup +}, has been produced by a 2 inch diameter pulsed multicusp ion source. A D-T neutron flux of 10{sup 9}-10{sup 10} n/s is projected from this data. CdZnTe is being developed as a possible gamma-ray detector because of its potential for good energy resolution and efficiency, and ability to operate at room temperature. 3-D time-dependent Monte Carlo calculations show the utility of this system for locating contaminants, especially chlorine-containing solvents, at remediation sites.
Date: October 1, 1996
Creator: Celata, C.M.; Amman, M. & Donahue, R.
Partner: UNT Libraries Government Documents Department

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


Description: Binary and ternary A(illegible)B(illegible) compounds are conventionally grown from melt. This technique is very complicated and requires complex equipment to provide high pressures and high temperatures to grow stoichiometric compositions. New opportunities for designing materials used in the infrared technique and ionizing radiation detectors are opened by advantages in nanotechnology. In particular difficulties in Cd{sub 1-x}Zn{sub x}Te with various Zn content are traditionally used in infrared optics and as a material for ionizing radiation detectors. Zn concentration in the nanopowders produced by the new vapor deposition technique varies from x=0.02 to x=0.1, including the composition Cd{sub illegible}Zn{sub illegible}Te, which is the most promising as a material for ionizing radiation detectors working at room temperature without cooling.
Date: August 29, 2007
Partner: UNT Libraries Government Documents Department


Description: In the past, various virtual Frisch-grid designs have been proposed for cadmium zinc telluride (CZT) and other compound semiconductor detectors. These include three-terminal, semi-spherical, CAPture, Frisch-ring, capacitive Frisch-grid and pixel devices (along with their modifications). Among them, the Frisch-grid design employing a non-contacting ring extended over the entire side surfaces of parallelepiped-shaped CZT crystals is the most promising. The defect-free parallelepiped-shaped crystals with typical dimensions of 5x5{approx}12 mm3 are easy to produce and can be arranged into large arrays used for imaging and gamma-ray spectroscopy. In this paper, we report on further advances of the virtual Frisch-grid detector design for the parallelepiped-shaped CZT crystals. Both the experimental testing and modeling results are described.
Date: August 21, 2007
Partner: UNT Libraries Government Documents Department

High-energy characterization of two large-volume multi-element CdZnTe detectors

Description: We present results of experiments to characterize two large-volume, multi-element CdZnTe detectors for gamma-ray spectroscopy at high energy. The first detector consisted of four 1.5 cm x 1.5 cm x 0.75 cm coplanar grid detectors. The measurements for the four-element design were performed with various configurations. The second detector consisted of eight 1 cm x 1 cm x 0.5 cm coplanar grid detectors arranged in a 2 x 2 x 2 array. The high-energy gamma-ray sources included {sup 60}Co(1332), {sup 228}Th(2614), {sup 244}Cm/{sup 13}C(6129), and Fe(n,{gamma})(7645). The front-end electronics consisted of eight spectroscopy-grade preamplifiers/shapers/pulse stretchers, built on circuit boards close to the arrays. For the four-element measurements the shapers/pulse stretchers were replaced with commercial amplifiers. An eight-channel data acquisition system with list mode output was used to record gamma-ray events for each detector element in each array. The list mode data were analyzed to produce coincidence and singles spectra and efficiencies for the various sources. The Compton continuum and the escape peaks are suppressed in the coincidence spectra relative to the singles spectra. We compare these spectra and efficiencies at high energy to results at lower energies and to Monte Carlo predictions.
Date: January 1, 2001
Creator: Moss, C. E. (Calvin E.); Browne, M. C. (Michael C.); Ianakiev, K. D. & Prettyman, T. H. (Thomas H.)
Partner: UNT Libraries Government Documents Department

Gamma Ray Detector Using Gallium Arsenide to Develop an Electrode Detector

Description: The emphasis of the DOE-funded detector project at the University of Michigan has been on the improvement of the performance of room-temperature gamma ray spectrometers. We have concentrated on the material known as CZT, a blend of cadmium and zinc tellurides, as the material of primary interest.
Date: March 26, 1999
Creator: Knoll, G.F.
Partner: UNT Libraries Government Documents Department

Advanced semiconductor detector development: Development of a room-temperature, gamma ray detector using gallium arsenide to develop an electrode detector. Progress report, September 30, 1994--September 29, 1995

Description: Devices fabricated from wide bandgap materials that can be operated without cooling suffer from poor energy resolution and are limited to very small volumes; this arises largely from poor hole mobility in compound semiconductors. Three different device configurations are being investigated for possibly overcoming this limitation: buried grid-single carrier devices, trenched single carrier devices, and devices using patterned coplanar electrodes (CdZnTe). In the first, leakage problems were encountered. For the second, a set of specifications has been completed, and electron cyclotron resonance etching will be done at an off-campus facility. For the third, Aurora will supply 3 different CdZnTe detectors. An analytical study was done of the patterned electrode approach.
Date: July 1, 1995
Creator: Knoll, G.F.
Partner: UNT Libraries Government Documents Department

Electronic states in Cd{sub 1{minus}x}Zn{sub x}Te/CdTe strained layer coupled double quantum wells and their photoluminescence

Description: Experimental and theoretical investigation of electronic states in a strained-layer CdTe/CdZnTe coupled double quantum well structure are presented. The optical properties of this lattice-mismatched heterostructure were characterized with photoluminescence (PL), PL excitation and polarization spectroscopies. Influence of electrical field on exciton states in the strained-layer CdTe/CdZnTe coupled double quantum well structure is experimentally studied. The confined electronic states were calculated in the framework of the envelope function approach, taking into account the strain effect induced by the lattice-mismatch. Experimental results are compared with the calculated transition energies.
Date: December 31, 1994
Creator: Li, T.; Lozykowski, H.J. & Reno, J.
Partner: UNT Libraries Government Documents Department

Characterization inconsistencies in CdTe and CZT gamma-ray detectors

Description: In the past few years, significant developments in cadmium telluride (CdTe) and cadmium zinc telluride (CZT) semiconductor materials have taken place with respect to both quality and yield. Many of the more recent developments have occurred in the area of CZT crystal growth. This has resulted in an explosion of interest in the use of these materials in ambient temperature gamma-ray detectors. Most, if not all, of the manufacturers of CdTe and CZT have acquired government funding to continue research in development and applications, indicating the importance of these improvements in material quality. We have examined many detectors, along with the accompanying manufacturer`s data, and it has become apparent that a clear standard does not exist by which each manufacturer characterizes the performance of their material. Result is a wide variety of performance claims that have no basis for comparison and normally cannot be readily reproduced. This paper first supports our observations and then proposes a standard that all manufacturers and users of these materials may use for characterization.
Date: October 1, 1994
Creator: Lavietes, A.D. & McQuaid, J.H.
Partner: UNT Libraries Government Documents Department

Cadmium zinc telluride spectral modeling

Description: Cadmium Zinc Telluride (CZT) detectors are the highest resolution room-temperature gamma ray detectors available for isotopic analysis. As with germanium detectors, accurate isotopic analysis using the spectra requires peak deconvolution. The CZT peak shapes are asymmetric, with a long low energy tail. The asymmetry is a result of the physics of the electron/hole transport in the semiconductor. An accurate model of the physics of the electron/hole transport through an electric field will allow the parameterization of the peak shapes as a function of energy. In turn this leads to the ability to perform accurate spectral deconvolution and therefore accurate isotopic analysis. The model and the peak-shape parameterization as a function of energy will be presented.
Date: April 1, 1998
Creator: Dardenne, Y. X., LLNL
Partner: UNT Libraries Government Documents Department

Effect of electron transport properties on unipolar CdZnTe radiation detectors: LUND, SpectrumPlus, and Coplanar Grid

Description: Device simulations of (1) the laterally-contacted-unipolar-nuclear detector (LUND), (2) the SpectrumPlus, (3) and the coplanar grid made of Cd{sub 0.9}Zn{sub 0.1}Te (CZT) were performed for {sup 137}Cs irradiation by 662.15 keV gamma-rays. Realistic and controlled simulations of the gamma-ray interactions with the CZT material were done using the MCNP4B2 Monte Carlo program, and the detector responses were simulated using the Sandia three-dimensional multielectrode simulation program (SandTMSP). The simulations were done for the best and the worst expected carrier nobilities and lifetimes of currently commercially available CZT materials for radiation detector applications. For the simulated unipolar devices, the active device volumes were relatively large and the energy resolutions were fairly good, but these performance characteristics were found to be very sensitive to the materials properties. The internal electric fields, the weighting potentials, and the charge induced efficiency maps were calculated to give insights into the operation of these devices.
Date: January 7, 2000
Creator: James, Ralph B.
Partner: UNT Libraries Government Documents Department

Spatial Mapping of Cadmium Zinc Telluride Materials Properties and Electrical Response to Improve Device yield and Performance

Description: Cadmium zinc telluride has experienced tremendous growth in its application to various radiation sensing problems over the last five years. However, there are still issues with yield, particularly of the large volume devices needed for imaging and sensitivity-critical applications. Inhomogeneities of various types and on various length scales currently prevent the fabrication of large devices of high spectral performance. This paper discusses the development of a set of characterization tools for quantifying these inhomogeneities, in order to develop improvement strategies to achieve the desired cadmium zinc telluride crystals for detector fabrication.
Date: January 26, 1998
Creator: Scyoc, J. M. Van; Brunet, B. A.; Yoon, H.; Gilbert, T. S.; Hilton, N. R.; Lund, J. C. et al.
Partner: UNT Libraries Government Documents Department

Performance of CdZnTe detectors passivated with energetic oxygen atoms

Description: Noise caused by surface-leakage current can degrade the performance of CdZnTe spectrometers, particularly devices with closely spaced contacts such as coplanar grid detectors. In order to reduce surface leakage, the authors are treating CdZnTe detector surfaces with energetic, neutral oxygen atoms. Energetic oxygen atoms react with the surface to form a resistive oxide layer. Because the reaction is effective at room temperature, deleterious heating of the substrate is avoided. In most cases, leakage current and noise are shown to decrease significantly after treatment. The effect of the treatment on the performance of coplanar grid detectors is presented.
Date: December 1, 1998
Creator: Prettyman, T.H.; Hoffbauer, M.A. & Rennie, J.
Partner: UNT Libraries Government Documents Department

Silicon and zinc telluride nanoparticles synthesized by pulsed laser ablation: Size distributions and nanoscale structure

Description: Size distributions of Si and ZnTe nanoparticles produced by low energy density ArF (193 nm) pulsed laser ablation into ambient gases were measured as a function of the gas pressure and target-substrate separation, D{sub ts}, using atomic force microscopy (AFM) and high resolution scanning electron microscopy (HRSEM). For low energy density (Ed = 1.04 J/cm{sup 2}) ablation of Si into He at pressures of 0.5, 1.5, 4 and 10 torr, large nanoparticles were most numerous at D{sub ts} = 10 mm, with smaller nanoparticles found at 20 mm and 40 mm. For each D{sub ts} value a maximum of the mean nanoparticle diameter occurred for a He pressure near 6 torr, in contrast to other recent measurements in which the size of Si nanoparticles increased monotonically with the He pressure. High resolution Z-contrast transmission electron microscopy (HRZTEM) and electron energy loss spectroscopy (EELS) revealed that ZnTe nanoparticles formed by ablation into nitrogen at E{sub d} = 0.74 J/cm{sup 2} consisted of a crystalline ZnTe core surrounded by an amorphous ZnO shell. Growth defects and surface steps were clearly visible in the ZnTe crystalline core. The dependences of the mean diameter of ZnTe nanocrystals on nitrogen pressure and D{sub ts}, were qualitatively similar to those found for Si in He.
Date: August 1, 1997
Creator: Lowndes, D.H.; Rouleau, C.M. & Duscher, G.
Partner: UNT Libraries Government Documents Department

Fine-scale spatial response of CdZnTe radiation detectors

Description: Several studies have suggested that the uniformity of Cadmium Zinc Telluride (CZT) detectors play an important role in their performance when operated as gamma-ray spectrometers. However the detailed gamma response of simple planar detectors as a function of position over the device area is largely unknown. To address this issue the authors have built a system capable of measuring the detector response with a resolution of {approximately}250 {micro}m. The system consists of a highly collimated ({approximately}200 {micro}m) photon source (<150 kev) scanned over the detector using a computer controlled two-axis translation stage. Fifteen samples configured as planar detectors were examined with the new apparatus. The material grade of the detectors examined varied from counter to select discriminator. Two classes of spatial response variation were observed and are presented here. Infrared (IR) transmission images were also acquired for each sample and correlation between features in the pulse height spectrum and crystalline defects were observed.
Date: November 7, 1998
Creator: Brunett, B. A.; Scyoc, J. M. Van; Hilton, N. R.; Lund, J. C.; James, R. B. & Schlesinger, T. E.
Partner: UNT Libraries Government Documents Department

Compensation and trapping in CdZnTe radiation detectors studied by thermoelectric emission spectroscopy, thermally stimulated conductivity, and current-voltage measurements

Description: In today's commercially available counter-select-grade CdZnTe crystals for radiation detector applications, the thermal ionization energies of the traps and their types, whether electron or hole traps, were measured. The measurements were successfully done using thermoelectric emission spectroscopy (TEES) and thermally stimulated conductivity (TSC). For reliability, the electrical contacts to the sample were found to be very important and, instead of Au Schottky contacts, In Ohmic contacts had to be used. For the filling of the traps, photoexcitation was done at zero bias, at 20K and at wavelengths which gave the maximum bulk photoexcitation for the sample. Between the temperature range from 20 to 400 K, the TSC current was found to be on the order of {approximately} 10,000 times or even larger than the TEES current, in agreement with theory, but only TEES could resolve the trap type and was sensitive to the deep traps. Large concentration of hole traps at 0.1 and 0.6 eV were observed and smaller contraction of electron traps at 0.4 eV was seen. These deep traps cause compensation in the material and also cause trapping that degrades the radiation detection measurement.
Date: January 7, 2000
Creator: James, Ralph B.
Partner: UNT Libraries Government Documents Department

Purification, Growth, Fabrication and Characterization of Wide Bandgap Materials for Gamma-Ray Detectors

Description: The objective of this project was to improve the performance and the fabrication of cadmium zinc telluride room temperature gamma ray detetors This paper outlines the necessity for controlled surface preparation and deposition of ohmic contacts.
Date: April 30, 1999
Creator: Arnold Burger, Ph.D.
Partner: UNT Libraries Government Documents Department

Preliminary uranium enrichment analysis results using cadmium zinc telluride detectors

Description: Lawrence Livermore National Laboratory (LLNL) and EG&G ORTEC have jointly developed a portable ambient-temperature detection system that can be used in a number of application scenarios. The detection system uses a planar cadmium zinc telluride (CZT) detector with custom-designed detector support electronics developed at LLNL and is based on the recently released MicroNOMAD multichannel analyzer (MCA) produced by ORTEC. Spectral analysis is performed using software developed at LLNL that was originally designed for use with high-purity germanium (HPGe) detector systems. In one application, the CZT detection system determines uranium enrichments ranging from less than 3% to over 75% to within accuracies of 20%. The analysis was performed using sample sizes of 200 g or larger and acquisition times of 30 min. The authors have demonstrated the capabilities of this system by analyzing the spectra gathered by the CZT detection system from uranium sources of several enrichments. These experiments demonstrate that current CZT detectors can, in some cases, approach performance criteria that were previously the exclusive domain of larger HPGe detector systems.
Date: September 8, 1995
Creator: Lavietes, A.D.; McQuaid, J.H. & Paulus, T.J.
Partner: UNT Libraries Government Documents Department

High-efficiency, thin-film cadmium telluride photovoltaic cells. Annual subcontract report, 20 January 1994--19 January 1995

Description: This report describes work performed to develop and optimize the process of radio frequency (RF) sputtering for the fabrication of thin-film solar cells on glass. The emphasis is on CdTe-related materials including CdTe, CdS, ZnTe, and ternary alloy semiconductors. Pulsed laser physical vapor deposition (LPVD) was used for exploratory work on these materials, especially where alloying or doping are involved, and for the deposition of cadmium chloride layers. For the sputtering work, a two-gun sputtering chamber was implemented, with optical access for monitoring temperature and growth rate. We studied the optical and electrical properties of the plasmas produced by two different kinds of planar magnetron sputter guns with different magnetic field configurations and strengths. Using LPVD, we studied alloy semiconductors such as CdZnTe and heavily doped semiconductors such as ZnTe:Cu for possible incorporation into graded band gap CdTe-based photovoltaic devices.
Date: August 1, 1995
Creator: Compaan, A.D.; Bohn, R.G. & Rajakarunanayake, Y.
Partner: UNT Libraries Government Documents Department