J. Pantazis’s research while affiliated with Emmanuel College - Massachusetts and other places

This paper presents the peak-to-background ratio improvement, which can be achieved in PIXE and XRF applications by the use of thin crystal detectors. This improvement becomes apparent in the presence of an intense γ-ray source, which can be produced either after proton irradiation of a sample (PIXE), or after the deexcitation of the radionuclide in Radioisotope induced XRF analysis (RIXRF). In order to study theoretically the energy response of a silicon crystal in the X-ray energy region with respect to its thickness and the energy of the incident yradiation, a Monte-Carlo simulation was performed. Experimentally, two detectors having crystal thickness of 300 urn and 3 mm respectively were employed in specific analytical applications of PIXE, PIXE induced XRF and RIXRF techniques. The peak-to-background ratios obtained for various characteristic X-rays were compared between the two detectors. The performance of the two detectors was also compared in monochromatic XRF analysis of samples with low average atomic number matrix content.

Most energy-dispersive X-ray fluorescence (EDXRF) instruments use Si diodes as X-ray detectors. These provide very high energy resolution, but their sensitivity falls off at energies of 10–20 keV. They are well suited for measuring the K lines of elements with Z < 40, but for heavier elements, one must use K lines at low efficiency or use L or M lines that often overlap other lines. Either is a challenge for accurate quantitative analysis. CdTe detectors offer much higher efficiency at high energy but poorer energy resolution compared with Si diodes. In many important EDXRF measurements, both high and low Z elements are present. In this paper, we will compare the precision and accuracy of systems using the following: (1) a high resolution Si detector, (2) a high efficiency CdTe detector, and (3) a composite system using both detectors. We will show that CdTe detectors generally offer better analytical results than even a high resolution silicon drift detectors for K lines greater than 20 or 25 keV, whereas the high resolution Si detectors are much better at lower energies. We will also show the advantages of a combined system, using both detectors. Although a combined system would be more expensive, the increased accuracy, precision, and throughput will often outweigh the small increase in cost and complexity. The systems will be compared for representative applications that include both high and low Z elements. Copyright

Thermoelectrically cooled X-ray detectors are widely used in both portable and laboratory X-ray spectrometers. The most common detectors are fully depleted 500 µm devices behind a Be window to provide a vacuum tight enclosure. These provide good resolution and efficiency for characteristic X-rays from 2 keV to about 20 keV but a larger energy range is desirable. In many applications, one needs to measure elements with K lines below 2 keV and above 20 keV with good efficiency. Recent research at Amptek, Inc. has focused on enhancing both the upper and lower ends of this energy range. First, to improve efficiency at high energies, SDDs have been fabricated on 1 mm wafers. Second, to improve efficiency at low energies, windows made of 50 nm Si3N4 on a Si grid have been developed. Third, to improve resolution at low energies, electronic noise has been reduced by using a modified trapezoidal pulse shape with lower /f noise index. The performance of systems utilizing these enhancements will be presented.

A portable Gamma-Ray Spectroscopy system has been designed and tested for identification of nuclear materials in the field. A P-I-N CdZnTe detector was developed to minimize the leakage current and to improve energy resolution. The detector has a sensitive volume of 200 mm3 and has been constructed with novel heterojunction contacts. Thermoelectric cooling is used to reduce leakage currents in the detector element and the input thermal noise to the FET. Risetime discrimination is used to offset the negative effects of incomplete charge collection. The detector probe is connected to a single unit comprised of detector electronics, an MCA and a portable computer, all operated from battery power. Results from testing with laboratory radioisotopic sources are presented.

Portable/hand-held X-ray fluorescence (XRF) instruments now achieve performance comparable to laboratory-sized, expensive, liquid nitrogen cooled systems. The availability of these systems has expanded XRF applications out of the laboratory to in situ analysis including that for lead in paint, alloy identification, process control, restriction of hazardous substances/waste from electrical and electronic equipment (RoHS/WEEE) compliance, and art and archaeology. The development of small, low-power, high-performance, and cost-effective X-ray detectors was a critical part of this transformation. This paper will look back at the development and technical achievements of the Amptek X-ray detector as well the future direction of portable XRF. Copyright © 2009 John Wiley & Sons, Ltd.

The accuracy and precision of energy dispersive X-ray fluorescence (EDXRF) improve with improved detector energy resolution. However, there are always trade-offs between the highest energy resolution and the highest count rates, there are practical difficulties in achieving the very best energy resolution, and there are many system level issues beyond energy resolution alone. Energy resolution is commonly used to differentiate systems but the benefits of improved energy resolution, in accuracy and precision of the analytical results, are not always clear. In the results reported here, EDXRF analysis has been carried out on a set of reference materials as a function of energy resolution. Several different detectors were used, including Si-PIN diodes, silicon drift diodes (SDD), and CdTe detectors. Their operating parameters were adjusted to give a range of energy resolutions. At 5.9 keV, the resolution ranged from 139 eV to 325 eV for SDD and Si- PIN devices, and to 450 eV for CdTe. The source was a 40 kVp W anode X-ray tube used in a backscatter geometry and the spectra were analyzed using the XRF-FP software.

Compact, high performance X-ray and gamma-ray spectroscopy systems are required for many applications, both in the field and in the laboratory. The X-123 provides this by combining Amptek's thermoelectrically cooled X-ray and gamma-ray detectors and Amptek's digital signal processing technology with a compact, high efficiency power supply in a small package. The detectors include Si-PIN devices for low energy X-rays, CdTe diodes for higher energy X-rays, and stacked CdTe diodes for low to medium energy gamma-rays. The digital signal processor provides better resolution, better throughput, better stability, and much better configurability than the prior analog solution. The X-123 includes detector, preamp, shaping amplifier, multichannel analyzer, and power supplies in a package measuring 10 cm times 7 cm times 2.5 cm, with a mass of 180 g and a total power consumption of 1.2W. This paper presents the design of the X-123, a comparison of its performance to analog solutions, and its use in applications.