keV Full-width At Half-maximum Research Articles

Characterization of a Pixelated Cadmium Telluride Detector System Using a Polychromatic X-Ray Source and Gold Nanoparticle-Loaded Phantoms for Benchtop X-Ray Fluorescence Imaging.

Pixelated semi-conductor detectors providing high energy resolution enable parallel acquisition of x-ray fluorescence (XRF) signals, potentially leading to performance enhancement of benchtop XRF imaging or computed tomography (XFCT) systems utilizing ordinary polychromatic x-ray sources. However, little is currently known about the characteristics of such detectors under typical operating conditions of benchtop XRF imaging/XFCT. In this work, a commercially available pixelated cadmium telluride (CdTe) detector system, HEXITEC (High Energy X-ray Imaging Technology), was characterized to address this issue. Specifically, HEXITEC was deployed into our benchtop cone-beam XFCT system, and used to detect gold Kα XRF photons from gold nanoparticle (GNP)-loaded phantoms. To facilitate the detection of XRF photons, various parallel-hole stainless steel collimators were fabricated and coupled with HEXITEC. A pixel-by-pixel spectrum merging algorithm was introduced to obtain well-defined XRF + scatter spectra with parallel-hole collimators. The effect of charge sharing addition (CSA) and discrimination (CSD) algorithms was also investigated for pixel-level CS correction. Finally, the detector energy resolution, in terms of the full-width at half-maximum (FWHM) values at two gold Kα XRF peaks (~68 keV), was also determined. Under the current experimental conditions, CSD provided the best energy resolution of HEXITEC (~1.05 keV FWHM), compared with CSA and no CS correction. This FWHM value was larger (by up to ~0.35 keV) than those reported previously for HEXITEC (at ~60 keV Am-241 peak) and single-crystal CdTe detectors (at two gold Kα XRF peaks). This investigation highlighted characteristics of HEXITEC as well as the necessity for application-specific detector characterization.

New architecture for the analog front-end of Medipix4

The Medipix4 chip is the latest member of the family of Medipix pixel detector readout chips aimed at high rate spectroscopic X-ray imaging. Unlike its predecessors, it will be possible to tile the chip on all 4 sides permitting seamless large area coverage. This paper focuses on the development of the new Medipix4 front-end architecture capable of event-by-event data processing allowing accurate photon energy reconstruction, with charge sharing correction at an increased rate compared to Medipix3. The architecture is particularly well adapted for readout of pixelated high-Z detector materials allowing accurate energy binning of incoming hits at a fine pixel pitch. The new front-end architecture has a linear response up to 150 keV (CdTe), a count-rate capability up to 5.1×108 photons.mm−2s−1 for 10% dead time loss at 10 keV (CdTe) , and an energy resolution aiming for 2.2 keV FWHM (Full Width Half Maximum) at 60 keV (CdTe). The layout accommodates sensors with either 70μm or 140μm pitch of contacts.

Evaluation of a photon counting Medipix3RX cadmium zinc telluride spectral x-ray detector.

We assess the performance of a cadmium zinc telluride (CZT)-based Medipix3RX energy-resolving and photon-counting x-ray detector as a candidate for spectral microcomputed tomography (micro-CT) imaging. It features an array of , pixels, each with four simultaneous threshold counters that utilize real-time charge summing. Each pixel's response is assessed by imaging with a range of incident x-ray intensities and detector integration times. Energy-related assessments are made by exposing the detector to the emission from an I-125 radioisotope brachytherapy seed. Long-term stability is assessed by repeating identical exposures over the course of 1h. The high yield of properly functioning pixels (98.8%), long-term stability (linear regression of whole-chip response over 1h of acquisitions: ; standard deviation: 3.7 counts), and energy resolution [2.5keV full-width half-maximum (FWHM) (single pixel), 3.7keV FWHM (across the full image)] make this device suitable for spectral micro-CT.

Characteristic Performance Evaluation of a New SAGe Well Detector for Small and Large Sample Geometries

Environmental scientific research requires a detector that has sensitivity low enough to reveal the radiological content for the presence of potential contaminants in the sample at a reasonable counting time. CANBERRA developed a germanium detector geometry called Small Anode Germanium (SAGe) Well detector. The SAGe Well detector is a new type of low capacitance device manufactured using small anode technology capable of advancing many environmental scientific research applications. The performance of this detector has been evaluated for a range of sample sizes and geometries counted inside the well, and on the end cap of the detector. The detector has energy resolution performance similar to semi-planar detectors, and offers significant improvement over the existing coaxial and Well detectors. Energy resolution performance of 750 eV Full Width at Half Maximum (FWHM) at 122 keV <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\gamma$</tex></formula> -ray energy and resolution of 2.0–2.3 keV FWHM at 1332 keV <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\gamma$</tex></formula> -ray energy are guaranteed for detector volumes up to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$425 ~\hbox{cm}^{3}$</tex> </formula> . The SAGe Well detector offers an optional 28 mm well diameter with the same energy resolution performance as the standard 16 mm well. Such outstanding performance will benefit environmental applications in revealing the detailed radionuclide content of samples, particularly at low energy. The detector is compatible with electric coolers without any sacrifice in performance and supports the CANBERRA Mathematical efficiency calibration method (In situ Object Calibration Software or ISOCS, and Laboratory SOurceless Calibration Software or LabSOCS). In addition, the SAGe Well detector supports true coincidence summing available in the ISOCS/LabSOCS framework. The improved resolution performance of this new device greatly enhances its detection sensitivity for a range of sample sizes and geometries counted inside the well. This results in lower minimum detectable concentrations (MDC) compared to Traditional Well detectors. The SAGe Well detectors are compatible with Marinelli beakers and compete very well with semi-planar and coaxial detectors for large samples in many applications.

$Q$ Spectroscopy With Superconducting Sensor Microcalorimeters

The total reaction energy (Q) of individual nuclear decays was measured using microcalorimeters with transition-edge-sensor (TES) thermometers. For alpha-decaying actinides (e.g., U-235, Pu-239, Np-237, Am-241), Q is in the 4-6 MeV range. Nearly all of this energy goes into the relatively light alpha particle, and approximately 100 keV is left over for the much heavier, recoiling daughter atom. Alpha-particle energy spectroscopy with TES-microcalorimeters has shown the ability to simultaneously resolve peaks that overlap in conventional alpha spectroscopy, with resolution now less than 1 keV full-width-at-half-maximum (FWHM) at 5.3 MeV. For total reaction energy spectroscopy, we use the same TES design as our alpha detectors, but embed a small radioactive sample (of about 1 Bq) directly inside an absorber designed to capture all the emitted particles (alpha, recoil nucleus, electrons, X-rays) with near 100% efficiency. We have measured Q-spectra of alpha-decaying isotopes with spectral resolution of 2-3 keV FWHM. For some actinide analytical problems, the Q -spectrum is simpler than the alpha-spectrum: fewer peaks, further apart, and easier to quantify. We will discuss sensor design, methods for embedding radionuclides, and spectral data.

Recording X-ray spectra with an audio digitizer

X-ray spectra were recorded with a notebook computer and analyzed by software on the computer, without a pulse height analyzer (PHA) or a digital signal processor (DSP). An audio (microphone or line) input on a personal computer has a built-in analogue-to-digital converter (ADC) for digital audio recording. The output signal of the X-ray detector is recorded through the audio input of the computer and then analyzed by software on the computer. On the basis of this method, X-rays from a radium source were measured with a cadmium telluride detector. K X-rays of bismuth were detected. Full width at half maximum (FWHM) was 5.6 keV at Kα of bismuth (77.1 keV), enough to separate Kβ (87.3 keV) from Kα of bismuth. The present method achieved almost equal energy resolution as that of the regular method (5.3 keV FWHM at 77.1 keV). Copyright © 2010 John Wiley & Sons, Ltd.

Measurement of ion cascade energies through resolution degradation of alpha particle microcalorimeters

Atomic cascades caused by ions impinging on bulk materials have remained of interest to the scientific community since their discovery by Goldstein in 1902. While considerable effort has been spent describing and, more recently, simulating these cascades, tools that can study individual events are lacking and several aspects of cascade behavior remain poorly known. These aspects include the material energies that determine cascade magnitude and the variation between cascades produced by monoenergetic ions. We have recently developed an alpha particle detector with a thermodynamic resolution near 100 eV full-width-at-half-maximum (FWHM) and an achieved resolution of 1.06 keV FWHM for 5.3 MeV particles. The detector relies on the absorption of particles by a bulk material and a thermal change in a superconducting thermometer. The achieved resolution of this detector provides the highest resolving power of any energy dispersive technique and a factor of 8 improvement over semiconductor detectors. The exquisite resolution can be directly applied to improved measurements of fundamental nuclear decays and nuclear forensics. In addition, we propose that the discrepancy between the thermodynamic and achieved resolution is due to fluctuations in lattice damage caused by ion-induced cascades in the absorber. Hence, this new detector is capable of measuring the kinetic energy converted to lattice damage in individual atomic cascades. This capability allows new measurements of cascade dynamics; for example, we find that the ubiquitous modeling program, SRIM, significantly underestimates the lattice damage caused in bulk tin by 5.3 MeV alpha particles.

Silicon carbide X-ray detectors for planetary exploration

Planetary exploration places high demands on instrumentation and presents some of the harshest operating environments and constraints known, including extreme thermal conditions, high-radiation tolerance and the need for low mass and power. We present data on a novel X-ray detector, the Semi-Transparent SiC Schottky Diode (STSSD), which shows promising energy resolution (1.3 keV Full-Width Half-Maximum at 5.9 keV) at room temperature and good radiation tolerance to proton irradiation (with a dose of ∼10 13 cm −2, energy ∼50 MeV) with some degradation in resolution to 2.5 keV. Future development of SiC detectors will lead, in principle, to X-ray imaging spectroscopic arrays capable of meeting the stringent demands of future planetary exploration missions. We outline the detector requirements necessary for use in the environment likely to be encountered in a mission to the Jovian system, which has the harshest radiation environment of all the planetary magnetospheres.

Isotopic analysis of plutonium using a combination of alpha and internal conversion electron spectroscopy

A combination alpha and conversion electron spectrometer was developed to quantify 239Pu/240Pu and 238Pu/241Am isotopic ratios of plated sources. The spectrometer was constructed with a commercially available low noise passivated ion-implanted planar silicon (PIPS) detector that was cooled to 77 K with liquid nitrogen. The combination spectrometer was used to quantify alpha-particles, conversion electrons, gamma-rays and X-rays associated with the decay of various plutonium isotopes and 241Am. Two amplifiers operated in parallel with different gains allowed for simultaneous acquisition of the lower energy region (21-60 keV) for internal conversion electrons, gamma-rays and X-rays, and the higher energy region (5050 keV-5550 keV) for alpha-particles. Energy resolutions of 2.2 keV FWHM (full-width at half maximum) for the 38.7 keV M conversion electrons and 11.2 keV for the 5499.2 keV alpha-particles from 238Pu were measured. The energy resolution combined with a spectral deconvolution method was sufficient to be able to quantify the radioactivity using the alpha-spectra as well as the electron spectra; however, quantification of the radioactivity using the internal conversion electron spectra was more problematic because of the presence of X-rays, gamma-rays, Compton scatter electrons and the number of electron peaks present. Deconvolution of the alpha-spectra yielded 239Pu and 240Pu activities (as % of total Pu activity), which differed from expected values by -3.0% to 5.4%. Deconvolution of an internal conversion electron spectrum of a high 239Pu and low 241Am activity sample yielded 239Pu and 240Pu activities, which differed by -17.1 and -35.5% relative to the alpha-measurements, respectively. Determination of the Pu activity using the electron spectra was more problematic in samples where the 241Am activity dominated. Determination of 238Pu and 241Am activity by the electron spectroscopy data was also obtained and compared with the alpha-spectroscopy results. Theoretical investigation of the removal of 241Am or use of a 400 eV electron spectrometer indicated that the internal conversion electron spectra could be used to determine the 238Pu, 239Pu, 240Pu/241Am (when present) activity with and without spectral deconvolution, respectively.

Synchrotron characterization of deep depletion epitaxial GaAs detectors

We report the results of a series of synchrotron characterizations of two epitaxial GaAs detectors of active areas 2.22 mm2 and thicknesses 40 and 400 μm. In spite of an order of magnitude difference in depletion depths, the detectors were found to have comparable performances at ∼−40 °C, with energy resolutions of ∼1 keV full width at half maximum (FWHM) at 7 keV rising to ∼2 keV FWHM at 200 keV and noise floors in the range of 1–1.5 keV. At the lower energies, the energy resolution was dominated by leakage current and electromagnetic pickup. At the highest energies, however, the measured resolutions appear to approach the expected Fano limit; e.g., ∼950 eV at 200 keV. Both detectors were remarkably linear, with average rms nonlinearities of 0.2% over the energy range of 10–60 keV. By raster scanning the active areas with 20×20 μm2 monoenergetic photon beams, it was found that the nonuniformity in the spatial response of both detectors was less than 1% and independent of energy. The material used to fabricate the detector is extremely pure. For example, low temperature photoluminescence measurements indicate that the density of the As antisite defect (EL2) is of the order of 1012 cm−3, which is ∼2–3 orders of magnitude lower than that generally reported. This indirect measurement of material purity is confirmed by Monte Carlo simulations of the detector x-ray response, which show that in order to reproduce the observed energy-loss spectra, electron and hole trapping cross-section/density products must be ≪1 cm−1.

Schottky junctions on semi-insulating LEC gallium arsenide for X- and /spl gamma/-ray spectrometers operated at and below room temperature

This work deals with the study of a Schottky junction used as an X- and /spl gamma/-ray detector in a spectrometer operated in the temperature range from -30/spl deg/C to +22/spl deg/C. The device (7 mm/sup 2/ active area and 100 /spl mu/m thickness), fabricated on liquid encapsulated Czochralski (LEG) semi-insulating Gallium Arsenide, is designed with a noninjecting ohmic contact which allows biasing voltages up to 550 V. At room temperature (22/spl deg/C) the energy resolution is found to be relatively poor (15.5-keV full-width at half-maximum (FWHM) at 59.5 keV) due to the large junction reverse current, whose density (7-37 nA/mm/sup 2/ at V/sub bias/=100-500 V) is within the typical values for Schottky junctions on SI LEC GaAs. By cooling of the detector to -30/spl deg/C, the noise of the reverse current is drastically lowered, thus achieving electronic noise levels around 160-180 rms electrons (1.6-1.8 keV FWHM), At 500-V bias, the /sup 241/Am spectrum has been resolved down to an energy of 4 keV with charge collection efficiency of cce=97% and a resolution of about 2-keV FWHM for the Np L lines and 2.4-keV FWHM for the 59.5-keV /spl gamma/ photons. The linearity of the detector has been measured to be better than /spl plusmn/0.6% within the explored energy range (14-59 keV). From the experimental spectra, it has been analyzed how either the electronic noise or the trapping of the signal charge contribute to the energy resolution of the spectrometer. The result is that despite the high measured cce. The trapping gives a contribution higher than 1.5 keV FWHM for the 59.5-keV spectral line. A comparison between the experimental results and Monte Carlo simulations, based on the Hecht model of charge trapping in detectors, is shown to give a satisfactory justification of the observed phenomena. A total mean drift length of carriers has been experimentally derived, finding an exponential dependence upon the bias voltage applied to the detector.

Nuclear structure of 159Tb, 161Tb and 163Tb studied with the (t, α) reaction

The 160Dy(t, α) 159Tb, 162Dy(t, α) 161Tb, and 164Dy(t, α) 163Tb reactions have been studied using a 17 MeV triton beam from the McMaster University Tandem Accelerator. The α-spectra were analyzed with a magnetic spectrograph and the resolution obtained in the best spectra was 16–19 keV FWHM (full-width half maximum). Transferred l-values were determined by comparing the measured angular distributions with distorted-wave Born-approximation predictions. The results were interpreted in terms of the Nilsson model with pairing and Coriolis-mixing effects included. Prior to these experiments the only information available on excited states of 163Tb was from an unpublished (d, 3He) experiment. Now several rotational bands based on single-proton Nilsson states have been assigned. The 3 2 +[411] , 1 2 +[411] , 5 2 −[532] , 7 2 −[532] , 5 2 +[413], 1 2 +[420] and 3 2 −[541] bands have been observed.

Development of liquid xenon detectors for gamma ray astronomy

The application of liquid xenon in high-resolution detectors for gamma-ray astronomy is being investigated. Initial results from a pulse-shape analysis of ionization signals in a liquid-xenon gridded chamber indicate that it is possible to achieve the necessary liquid purity for the transport of free electrons with simple techniques. The energy resolution has been measured as a function of applied electric field, using electrons and gamma =rays from a /sup 207/Bi source. At a field of 12 kV/cm the noise-subtracted energy resolution of the dominant 569-keV gamma -ray line is 34 keV FWHM (full width at half maximum). This value is mostly determined by recombination of electron-ion pairs on delta-electron tracks. >

One-neutron transfer reactions toSm150

The ($d, t$) reaction on $^{151}\mathrm{Sm}$ has been investigated at a deuteron energy of 17 MeV; the ($d, p$) reaction on the isotope $^{149}\mathrm{Sm}$ at a deuteron energy of 12.5 MeV. For the stripping reaction angular distributions were taken in 2.5\ifmmode^\circ\else\textdegree\fi{} steps in the range of $7.5\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}{\ensuremath{\theta}}_{\mathrm{lab}}\ensuremath{\le}35\ifmmode^\circ\else\textdegree\fi{}$ and in 5\ifmmode^\circ\else\textdegree\fi{} steps for $35\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}\ensuremath{\theta}\ensuremath{\le}60\ifmmode^\circ\else\textdegree\fi{}$. The experimental energy resolution is 10-12 keV full width at half-maximum (FWHM). For the pickup reaction angular distributions were taken in 2.5\ifmmode^\circ\else\textdegree\fi{} steps in the range of $7.5\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}{\ensuremath{\theta}}_{\mathrm{lab}}\ensuremath{\le}30\ifmmode^\circ\else\textdegree\fi{}$ and in 5\ifmmode^\circ\else\textdegree\fi{} steps up to ${\ensuremath{\theta}}_{\mathrm{lab}}=45\ifmmode^\circ\else\textdegree\fi{}$. The experimental energy resolution is 6-8 keV FWHM. Spectroscopic factors and $l$ transfers were extracted by distorted-wave Born approximation analysis. The spectroscopic information is compared to one-nucleon transfer results of the lower mass Sm isotopes.

Delay Line Readouts for High Purity Germanium Medical Imaging Cameras

High purity germanium offers excellent potential for use in nuclear medical imaging cameras. A position and energy readout technique using two inexpensive delay lines has been developed for these cameras. Results obtained with a 1-cm2 , 4 mm deep, 5×5 strip high purity germanium detector are 2.1 mm full width spatial resolution, a measured single strip resolution of 0.65 mm full width half maximum (FWHM), a 25 element uncollimated energy resolution of 2.95 keV FWHM, and 2.65 keV FWHM for a single central element at 140 keV.

The design and application of lithium drift silicon diodes as nuclear radiation detectors

A range of lithium-drifted silicon radiation detectors is described. Areas up to 8 cm2 and thicknesses up to 0.6 cm have been achieved. At - 20°C, a resolution of 8 kev full width half maximum was obtained on 661 kev beta particles using a 1 cm2 detector 0.1 cm thick. The performance of the detectors is discussed in relation to other device parameters.