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Performance of a portable, Digital-Signal-Processing MCA with Safeguards Germanium Detectors

Bingham, R. D., Keyser, R. M., Twomey, T. R. ORTEC, PerkinElmer Instruments, Inc 801 South Illinois Avenue Oak Ridge, TN 37831

Abstract

The use of digital signal processing (DSP) has become the standard for high-performance laboratory instruments for measurements in the field of nuclear spectroscopy. In all applications it offers greater stability, improved resolution and greater throughput at high count rates compared to analog or traditional designs. All of these improve the quality of the spectrum and the analysis results. Safeguards applications, especially the isotopic-ratio calculation, depend on the high resolution and stability of the MCA and detector for accurate results. Recently, advances in low-power DSP modules have made it possible to incorporate DSP in useable, portable instruments. A portable multichannel analyzer system consisting of a HPGe detector, with integral bias supply, and a MCA has been developed. This system includes all the benefits of digital processing in a complete instrument for spectroscopy. In addition, the unit includes a local display and keypad, to eliminate or significantly reduce the need for a PC in many field applications. When used with the associated "intelligent" HPGe detector system, the instrument monitors 18 operating parameters of the system, including detector temperature, to derive the overall system state of health. In addition, the unit provides authentication of the entire system and the collected data. The system has been tested using both liquid-nitrogen and electrically cooled detectors. The peak position and resolution have been measured using the commonly available mixed nuclide sources. Performance data for peak resolution and position vs countrate, peak resolution and position vs time, using Safeguards-quality HPGe detectors will be presented.

Introduction

Since their introduction, DSP-based Gamma-ray spectrometers have become the “industry standard” and are now widely used both “standalone” and within larger measurement systems. It has rapidly become clear that the DSP technology had no performance disadvantages relating to spectroscopy; indeed, in every case, they have shown to offer improved resolution, throughput and stability, both over long time periods and wide temperature changes. The wide choice of operating parameters coupled with a high degree of setup automation available, in some cases, means that the instrument performance is easily “tuned” to make the optimum use of this performance in a specific application situation. Not surprisingly, a wide variety of systems have been developed incorporating these digital spectrometers, in counting laboratories, remote monitoring, industrial on-line applications and non-destructive assay applications. DSP systems are proving capable of meeting the most demanding of applications.1

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