Miniaturization in x ray and gamma ray spectroscopy

The paper presents advances in two new sensor technologies and a miniaturized associated electronics technology which, when combined, can allow for very significant miniaturization and for the reduction of weight and power consumption in x-ray and gamma-ray spectroscopy systems: (1) Mercuric iodide (HgI2) x-ray technology, which allows for the first time the construction of truly portable, high-energy resolution, non-cryogenic x-ray fluorescence (XRF) elemental analyzer systems, with parameters approaching those of laboratory quality cryogenic instruments; (2) the silicon avalanche photodiode (APD), which is a solid-state light sensitive device with internal amplification, capable of uniquely replacing the vacuum photomultiplier tube in scintillation gamma-ray spectrometer applications, and offering substantial improvements in size, ruggedness, low power operation and energy resolution; and (3) miniaturized (hybridized) low noise, low power amplification and processing electronics, which take full advantage of the favorable properties of these new sensors and allow for the design and fabrication of advanced, highly miniaturized x-ray and gamma-ray spectroscopy systems. The paper also presents experimental results and examples of spectrometric systems currently under construction. The directions for future developments are discussed

Performance and durability of HgI_2 X-ray detectors for space missions

Considerable progress has been achieved in HgI_2 detector fabrication technology and amplification electronics. An energy resolution of 198 eV (full width at half maximum) has been obtained for the Mn K_α line of 5.9 keV in a practical X-ray probe without the use of cryogenic cooling. Detectors prepared with Parylene-C encapsulation have demonstrated perfect reliability in two-year tests under high vacuum and temperature and bias cycling. Other HgI_2 detectors have been used to demonstrate proton-radiation-damage resistance to levels of 10^(12) protons/cm^2 at 10.7 MeV. It is concluded that HgI_2 detectors are suitable for the ordinary requirements of energy dispersive detectors in X-ray spectroscopy systems

Advances in the development of encapsulants for mercuric iodide X-ray detectors

Advances in the development of protective impermeable encapsulants with high transparency to ultra-low-energy X-rays for use on HgI_2 X-ray detectors are reported. Various X-ray fluorescence spectra from coated detectors are presented. The X-ray absorption in the encapsulants has been analyzed using characteristic radiation from various elements. Results suggest that low-energy cutoffs for the detectors are not determined solely by the encapsulating coatings presently employed but are also influenced by the front electrode and surface effects, which can affect the local electric field or the surface recombination velocity. An energy resolution of 182 eV (FWHM) has been achieved for Ni L lines at 850 eV. Improved detector sensitivity to X-ray energies under 700 eV is demonstrated

Low Energy X-Ray Spectra Measured with a Mercuric Iodide Energy Dispersive Spectrometer in a Scanning Electron Microscope

A mercuric iodide energy dispersive x-ray spectrometer, with Peltier cooling provided for the detector and input field effect transistor, has been developed and tested in a scanning electron microscope. X-ray spectra were obtained with the 15 keV electron beam. An energy resolution of 225 eV (FWHM) for Mn-Kα at 5.9 keV and 195 eV (FWHM) for Mg-K line at 1.25 keV has been measured. Overall system noise level was 175 eV (FWHM). The detector system characterization with a carbon target demonstrated good energy sensitivity at low energies and lack of significant spectral artifacts at higher energies

Large area silicon drift detectors for x-rays -- New results

Large area silicon drift detectors, consisting of 8 mm and 12 mm diameter hexagons, were fabricated on 0.35 mm thick high resistivity n-type silicon. An external FET and a low-noise charge sensitive preamplifier were used for testing the prototype detectors. The detector performance was measured in the range 75 to 25 C using Peltier cooling, and from 0.125 to 6 {micro}s amplifier shaping time. Measured energy resolutions were 159 eV FWHM and 263 eV FWHM for the 0.5 cm{sup 2} and 1 cm{sup 2} detectors, respectively (at 5.9 keV, {minus}75 C, 6 {micro}s shaping time). The uniformity of the detector response over the entire active area (measured using 560 nm light) was < 0.5%

APPROACHING CRYOGENIC GE PERFORMANCE WITH PELTIER COOLED CDTE

A new class of hand-held, portable spectrometers based on large area (lcm2) CdTe detectors of thickness up to 3mm has been demonstrated to produce energy resolution of between 0.3 and 0.5% FWHM at 662 keV. The system uses a charge loss correction circuit for improved efficiency, and detector temperature stabilization to ensure consistent operation of the detector during field measurements over a wide range of ambient temperature. The system can operate continuously for up to 8hrs on rechargeable batteries. The signal output from the charge loss corrector is compatible with most analog and digital spectroscopy amplifiers and multi channel analyzers. Using a detector measuring 11.2 by 9.1 by 2.13 mm3, we have recently been able to obtain the first wide-range plutonium gamma-ray isotopic analysis with other than a cryogenically cooled germanium spectrometer. The CdTe spectrometer is capable of measuring small plutonium reference samples in about one hour, covering the range from low to high burnup. The isotopic analysis software used to obtain these results was FRAM, Version 4 from LANL. The new spectrometer is expected to be useful for low-grade assay, as well as for some in-situ plutonium gamma-ray isotopics in lieu of cryogenically cooled Ge

The use of a mercuric iodide detector for X-ray fluorescence analysis in archaeometry

For about two decades, energy dispersive X-ray fluorescence (EDXRF) has been employed in Rome for the analysis of works of art. A short history of the applications of EDXRF to paintings and alloys is presented. Finally, the usefulness of mercuric iodide room-temperature semiconductor detectors in this field is shown

Applications of non-cryogenic portable EDXRF systems in archaeometry

In this paper the most relevant developments in the realisation of portable Energy-Dispersive X-ray Fluorescence (EDXRF) equipments are discussed. In particular, the latest advances in non-cryogenic (Peltier cooled) X-ray detectors and miniaturised X-ray generators are shown. The energy resolution of the new detection systems is adequate to resolve the characteristic X-ray emission lines of contiguous elements. This small size and low power make the system ideal for portable instrumentation and have stimulated the development of small- and low-power X-ray generators which can be used for the excitation of fluorescence radiation in a broad energy range (5-40 keV). Finally, the use of EDXRF related to archaeometric research (pigments in ancient paintings and major elements in the metal alloys) is emphasised. Recent results obtained with new HgI2 and silicon PIN detector systems combined with miniaturised highly stable air-cooled X-ray generators are described

Applications of non-cryogenic portable EDXRF systems in archaeometry

In this paper the most relevant developments in the realisation of portable Energy-Dispersive X-ray Fluorescence (EDXRF) equipments are discussed. In particular, the latest advances in non-cryogenic (Peltier cooled) X-ray detectors and miniaturised X-ray generators are shown. The energy resolution of the new detection systems is adequate to resolve the characteristic X-ray emission lines of contiguous elements. This small size and low power make the system ideal for portable instrumentation and have stimulated the development of small- and low-power X-ray generators which can be used for the excitation of fluorescence radiation in a broad energy range (5-40 keV). Finally, the use of EDXRF related to archaeometric research (pigments in ancient paintings and major elements in the metal alloys) is emphasised. Recent results obtained with new HgI2 and silicon PIN detector systems combined with miniaturised highly stable air-cooled X-ray generators are described