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Coplanar-grid detector with single-electrode readout

Description: The coplanar-grid technique provides substantial spectral performance improvement over that of conventional detector designs and electronics when applied to gamma-ray detectors based on compound semiconductors. The technique realizes this improvement by measuring the difference between the induced charge signals from two interdigitated coplanar-grid electrodes. By adjusting the relative gain between the two grid signals prior to subtraction, the difference signal can be made less sensitive to the poor carrier transport properties of the detector material and thus improve the spectral response of the detector. In this paper, the authors discuss a variation of the coplanar-grid method in which the signal from only one grid electrode is read out. The signal response is optimized by changing the relative areas of the two grid electrodes and the bias applied across the detector. In this scheme, only one preamplifier is needed and signal subtraction is not necessary. This eliminates the electronic noise contribution from the additional preamplifier used in the normal coplanar-grid implementation, and conventional single-amplifier detector electronics can be used. Experimental results using CdZnTe detectors are presented.
Date: April 1, 1997
Creator: Amman, M. & Luke, P.N.
Partner: UNT Libraries Government Documents Department

Electron transport uniformity characterization of CdZnTe using alpha particles

Description: Novel electrode configurations, such as coplanar grids, have been successful in mitigating the effects of poor hole transport in CdZnTe gamma-ray detectors. However, poor material uniformity remains a major problem preventing the widespread application of such detectors in gamma-ray spectroscopy. Uniform electron transport is critical for achieving good gamma-ray detection performance in the coplanar-grid configuration. The authors have investigated the use of alpha-particle response as a quick and simple electron transport uniformity screening technique for material selection, and as a method to study other spectral broadening mechanisms in coplanar-grid detectors. The method consists of uniformly illuminating, with an alpha-particle source, the cathode side of the CdZnTe crystal in either a planar or a coplanar-grid detector configuration. In the planar geometry, the variation in the measured pulse heights is dictated in large part by the uniformity of the electron transport. An alpha-particle spectrum that has a single sharp peak with little background indicates uniform electron transport and, consequently, that the CdZnTe crystal should result in a coplanar-grid detector with good gamma-ray detection performance. In the coplanar geometry, the measured pulse-height variation provides information on additional sources of spectral broadening. In this paper the authors present the results of their study to measure the correlation between these simple alpha-particle measurements and the coplanar-grid gamma-ray detector response.
Date: April 1, 1998
Creator: Amman, M.; Lee, J.S. & Luke, P.N.
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

Coplanar-grid CdZnTe detector with three-dimensional position sensitivity

Description: A 3-dimensional position-sensitive coplanar-grid detector design for use with compound semiconductors is described. This detector design maintains the advantage of a coplanar-grid detector in which good energy resolution can be obtained from materials with poor charge transport. Position readout in two dimensions is accomplished using proximity-sensing electrodes adjacent to the electron-collecting grid electrode of the detector. Additionally, depth information is obtained by taking the ratio of the amplitudes of the collecting grid signal and the cathode signal. Experimental results from a prototype CdZnTe detector are presented.
Date: June 1, 1998
Creator: Luke, P.N.; Amman, M.; Lee, J.S. & Yaver, H.
Partner: UNT Libraries Government Documents Department

Electrode design for coplanar-grid detectors

Description: The coplanar-grid charge sensing technique provides a method for improving the spectral response of gamma-ray detectors based on compound semiconductors, which typically have poor charge transport properties. The technique functions by effectively modifying the charge induction characteristics of the detector such that the dependence of detector signal on the depth of radiation interaction is minimized. The effectiveness of this technique however can be compromised by non-uniform charge induction characteristics across the detector. This paper examines such non-uniformity due to fringe effects near the detector edges. Alternate electrode configurations are studied that provide effective compensation for such effects. Results from experimental measurements and computer simulations are presented.
Date: November 1, 1996
Creator: Luke, P.N.; Amman, M.; Prettyman, T.H.; Russo, P.A. & Close, D.A.
Partner: UNT Libraries Government Documents Department

Physics-based generation of gamma-ray response functions for CDZNTE detectors

Description: A physics-based approach to gamma-ray response-function generation is presented in which the response of CdZnTe detectors is modeled from first principles. Computer modeling is used to generate response functions needed for spectrum analysis for general detector configurations (e.g., electrode design, detector materials and geometry, and operating conditions). With computer modeling, requirements for calibration and characterization are significantly reduced. Elements of the physics-based model, including gamma-ray transport, charge drift-diffusion, and circuit response, are presented. Calculated and experimental gamma-ray spectra are compared for a coplanar-grid CdZnTe detector.
Date: September 1, 1997
Creator: Prettyman, T.H.; Mercer, D.J.; Cooper, C.; Russo, P.A.; Rawool-Sullivan, M.; Close, D.A. et al.
Partner: UNT Libraries Government Documents Department

Noise in CdZnTe detectors

Description: Noise in CdZnTe devices with different electrode configurations was investigated. Measurements on devices with guard-ring electrode structures showed that surface leakage current does not produce any significant noise. The parallel white noise component of the devices appeared to be generated by the bulk current alone, even though the surface current was substantially higher. This implies that reducing the surface leakage current of a CdZnTe detector may not necessarily result in a significant improvement in noise performance. The noise generated by the bulk current is also observed to be below full shot noise. This partial suppression of shot noise may be the result of Coulomb interaction between carriers or carrier trapping. Devices with coplanar strip electrodes were observed to produce a 1/f noise term at the preamplifier output. Higher levels of this 1/f noise were observed with decreasing gap widths between electrodes. The level of this 1/f noise appeared to be independent of bias voltage and leakage current but was substantially reduced after certain surface treatments.
Date: October 10, 2000
Creator: Luke, P. N.; Amman, M.; S., Lee J. & Manfredi, P. F.
Partner: UNT Libraries Government Documents Department