Drift Detector Research Articles

Optimal Signal Shaping in Solid State Detector Spectrometers

The performance of the most widely used shapers in solid state detector spectrometers is investigated in respect to noise suppression and count rate ability. Three shaper types have been experimentally checked with two detector types – X-ray Silicon Drift Detector and HPGe gamma detector. The results show small difference in noise line width and negligible difference in obtainable energy resolution while the high count rate performance depends noticeably on shaper type selected. This allows for simultaneous optimization of noise and count rate performance.

Design and fabrication of quasi-double-sided silicon drift detector for x-ray detection

Silicon drift detectors (SDDs) with excellent energy resolution are widely used in the field of x-ray detection. Normally, the higher energy resolution of a SDD is mainly due to the lower capacitance compared with other silicon radiation detectors. It is worth noting that the energy resolution is also related to imperfect charge collection and ballistic deficit, which are susceptible to the device drift voltage. However, the maximum drift voltage is limited to twice the depletion voltage because of the reach-through effect in a classical SDD. In order to address this issue, a novel quasi-double-sided silicon drift detector (QD-SDD) was designed and fabricated by the thin film deposition technology. The so-called QD-SDD consists of a symmetrical drift ring structure on both the front and bottom sides. According to the simulation results, QD-SDD can be biased at a larger drift voltage, and thus building a larger drift electrical field than the classical single-sided SDD. Furthermore, the fabricated QD-SDD sensors were characterized using a 55-Fe radioactive source. The energy resolution at the 5.9 keV Mn Kα line can be improved from 210 eV to 170 eV by increasing the bias voltage on the outermost drift ring on both sides from −80 V to −130 V.

Dual imaging modality of fluorescence and transmission X-rays for gold nanoparticle-injected living mice.

X-ray fluorescence (XRF) imaging for metal nanoparticles (MNPs) is a promising molecular imaging modality that can determine dynamic biodistributions of MNPs. However, it has the limitation that it only provides functional information. In this study, we aim to show the feasibility of acquiring functional and anatomic information on the same platform by demonstrating a dual imaging modality of pinhole XRF and computed tomography (CT) for gold nanoparticle (GNP)-injected living mice. By installing a transmission CT detector in an existing pinhole XRF imaging system using a two-dimensional (2D) cadmium zinc telluride (CZT) gamma camera, XRF and CT images were acquired on the same platform. Due to the optimal X-ray spectra for XRF and CT image acquisition being different, XRF and CT imaging were performed by 140 and 50kV X-rays, respectively. An amount of 40mg GNPs (1.9nm in diameter) suspended in 0.20ml of phosphate-buffered saline were injected into the three BALB/c mice via a tail vein. Then, the kidney and tumor slices of mice were scanned at specific time points within 60min to acquire time-lapse in vivo biodistributions of GNPs. XRF images were directly acquired without image reconstruction using a pinhole collimator and a 2D CZT gamma camera. Subsequently, CT images were acquired by performing CT scans. In order to confirm the validity of the functional information provided by the XRF image, the CT image was fused with the XRF image. After the XRF and CT scan, the mice were euthanized, and major organs (kidneys, tumor, liver, and spleen) were extracted. The ex vivo GNP concentrations of the extracted organs were measured by inductively coupled plasma mass spectrometry (ICP-MS) and L-shell XRF detection system using a silicon drift detector, then compared with the in vivo GNP concentrations measured by the pinhole XRF imaging system. Time-lapse XRF images were directly acquired without rotation and translation of imaging objects within an acquisition time of 2min per slice. Due to the short image acquisition time, the time-lapse in vivo biodistribution of GNPs was acquired in the organs of the mice. CT images were fused with the XRF images and successfully confirmed the validity of the XRF images. The difference in ex vivo GNP concentrations measured by the L-shell XRF detection system and ICP-MS was 0.0005-0.02% by the weight of gold (wt%). Notably, the in vivo and ex vivo GNP concentrations in the kidneys of three mice were comparable with a difference of 0.01-0.08wt%. A dual imaging modality of pinhole XRF and CT imaging system and L-shell XRF detection system were successfully developed. The developed systems are a promising modality for in vivo imaging and ex vivo quantification for preclinical studies using MNPs. In addition, we discussed further improvements for the routine preclinical applications of the systems.

Reconstruction of 3D topographic landscape in soft X-ray fluorescence microscopy through an inverse X-ray-tracing approach based on multiple detectors

The study of X-ray fluorescence (XRF) emission spectra is a powerful technique used in applications that range from biology to cultural heritage. Key objectives of this technique include identification and quantification of elemental traces composing the analyzed sample. However, precise derivation of elemental concentration is often hampered by self-absorption of the XRF signal emitted by light constituents. This attenuation depends on the amount of sample present between the radiation source and detection system and allows for the exploitation of self-absorption in order to recover a sample topography. In this work, an X-ray-tracing application based on the use of multiple silicon drift detectors, is introduced to inversely reconstruct a 3D sample with correct topographical landscape, from 2D XRF count rates maps obtained from spectroscopy. The reconstruction was tested on the XRF maps of a simulated sample, which is composed of three cells with different size but similar composition. We propose to use the recovered 3D sample topography in order to numerically compute the self-absorption effects on the X-ray fluorescence radiation, thereby showing that a quantitative correction is possible. Lastly, we present a web application which implements the suggested methodology, in order to demonstrate its feasibility and applicability, available at: https://github.com/ElettraSciComp/xrfstir.

An Experimental Analysis of Drift Detection Methods on Multi-Class Imbalanced Data Streams

The performance of machine learning models diminishes while predicting the Remaining Useful Life (RUL) of the equipment or fault prediction due to the issue of concept drift. This issue is aggravated when the problem setting comprises multi-class imbalanced data. The existing drift detection methods are designed to detect certain drifts in specific scenarios. For example, the drift detector designed for binary class data may not produce satisfactory results for applications that generate multi-class data. Similarly, the drift detection method designed for the detection of sudden drift may struggle with detecting incremental drift. Therefore, in this experimental investigation, we seek to investigate the performance of the existing drift detection methods on multi-class imbalanced data streams with different drift types. For this reason, this study simulated the streams with various forms of concept drift and the multi-class imbalance problem to test the existing drift detection methods. The findings of current study will aid in the selection of drift detection methods for use in developing solutions for real-time industrial applications that encounter similar issues. The results revealed that among the compared methods, DDM produced the best average F1 score. The results also indicate that the multi-class imbalance causes the false alarm rate to increase for most of the drift detection methods.

SDDs for high-rate and high-resolution electron spectroscopy

Silicon Drift Detectors (SDDs) are a promising technology for electron spectroscopy, due to their excellent energy resolution and capability to sustain high interaction rate. We present a model based on a Geant4 simulation for the electron response. We then investigate the possibility to use a SDD as a versatile and compact β spectrometer that can be operated with standard technologies.

EXTP Large Area Detector: Qualification procedure of the mass production

A 7.24 × 12.03 cm2 sensor, Silicon Drift Detector (SDD), has been developed for the enhanced X-ray Timing and Polarimetry (eXTP) mission of the Chinese Academy of Science, with a large contribution by a European consortium inherited from the ESA-M3 LOFT mission study. In the frame of the project X-ray Observatories (XRO), active in the National Scientific Commission 2 of the INFN, we report the details of the qualification procedure to select from the mass production the 640 sensors that will equip the Large Area Detector (the eXTP instrument dedicated to the X-ray spectroscopy in the range 2-30 keV), with energy resolution below 240 eV FWHM at 6 keV during the entire mission duration of at least 5 years. This stringent requirement dictates the need to thoroughly verify the characteristics of each single sensor before integration in the final layout. We describe the dedicated testing facilities that have been developed. We report on the detector selection criteria and test results obtained in the pre-series production.

High-resolution Compton spectroscopy using x-ray microcalorimeters.

X-ray Compton spectroscopy is one of the few direct probes of the electron momentum distribution of bulk materials in ambient and operando environments. We report high-resolution inelastic x-ray scattering experiments with high momentum and energy transfer performed at a storage-ring-based high-energy x-ray light source facility using an x-ray transition-edge sensor (TES) microcalorimeter detector. The performance was compared with a silicon drift detector (SDD), an energy-resolving semiconductor detector, and Compton profiles were measured for lithium and cobalt oxide powders relevant to lithium-ion battery research. Spectroscopic analysis of the measured Compton profiles demonstrates the high-sensitivity to the low-Z elements and oxidation states. The line shape analysis of the measured Compton profiles in comparison with computed Hartree-Fock profiles is usually limited by the resolution of the semiconductor detector. We have characterized an x-ray TES microcalorimeter detector for high-resolution Compton scattering experiments using a bending magnet source at the Advanced Photon Source with a double crystal monochromator, providing monochromatic photon energies near 27.5keV. The momentum resolution below 0.16 atomic units (a.u.) was measured, yielding an improvement of more than a factor of 7 over a state-of-the-art SDD for the same scattering geometry. Furthermore, the lineshapes of narrow valence and broad core electron profiles of sealed lithium metal were clearly resolved using an x-ray TES compared to smeared and broadened lineshapes observed when using the SDD. High-resolution Compton scattering using the energy-resolving area detector shown here presents new opportunities for spatial imaging of electron momentum distributions for a wide class of materials with applications ranging from electrochemistry to condensed matter physics.

Feasibility of a 109Cd-based portable XRF device for measuring skin iron concentration in anaemic and β−Thalassaemic patients

Iron is an essential element vital for growth and development. The severe effects on the body due to iron deficiency or overload have prompted sustained research into accurate in vivo iron measurement techniques for the past several decades. X-ray fluorescence (XRF) analysis of iron in the body has been investigated in this work because of the non-invasive nature of the technique. A system has been designed using a silicon drift detector to measure the low-energy iron K α x-rays excited in the samples by the silver x-rays from 109Cd of energy 22 keV and 25 keV. The source is contained within a tantalum shielding cap designed to reduce the spectral background. The system was calibrated against 3D printed polylactic acid (PLA) phantoms filled with solutions of iron at various concentrations. The iron x-ray signals were normalized to a nickel x-ray signal which improved the system’s reproducibility. The 3D phantoms and normalisation resulted in a linear calibration line (p < 0.001 and r2 > 0.999). For a real-time measurement of 1800 s, the minimum detectable limit for the system was measured to be 1.35 ± 0.35 ppm which is achieved with a low radiation dose of 1.1 mSv to the skin surface. This low detection limit and low dose mean the system is feasible for application to human measurements in both iron deficiency and overload disease. The system will proceed to post-mortem validation studies prior to in vivo system efficacy testing.

New experimental bremsstrahlung cross-section for light ion beams up to 60 MeV and comparison to theoretical models

Recent works focused on bremsstrahlung radiation as a non-invasive tool for monitoring proton beams used in radiobiology (>20 MeV). In order to study the validity of theoretical models of bremsstrahlung cross sections, bremsstrahlung X-rays between 4 keV and 15 keV coming from a carbon target irradiated by proton beams in the energy range from 15 MeV to 50 MeV were measured by a silicon drift detector. The obtained data vary from 10 mb keV−1 to 1000 mb keV−1 and fit well the literature and with theoretical model calculation. These results strongly support that bremsstrahlung X-rays models can be used to develop promising online tools for proton beam monitoring.

Evaluation of 20 Elements in Soils and Sediments by ED-XRF of Monochromatic Excitation

There is an urgent need for the accurate analysis of heavy metal contamination in the field of ecology and environmental sciences, especially in the case of trace heavy metals, such as cadmium. Using doubly curved crystals (DCC) to achieve the monochromatic X-ray excitation of the sample to be measured and a silicon drift detector (SDD) to collect the fluorescence of the sample elements, combined with an algorithm analysis of the fundamental parameters (FP), the monochromatic energy-dispersive X-ray fluorescence (MED-XRF) system significantly improved the detection limits of the target elements. The detection limits, precision, and accuracy of the MED-XRF acquisition for 20 elements, including cadmium, lead, and arsenic, were evaluated and compared with the Determination of Inorganic Elements in Soil and Sediment Wavelength-Dispersive X-ray Fluorescence Spectrometry report and tested on the actual samples. The test results showed that the detection limit of the inorganic elements in soil and sediment determined by MED-XRF was mostly better than the industry standard, especially the detection limit of Cd, which was 0.04 mg/kg. The accuracy and correctness fully met the requirements for daily laboratory testing and, as a quality control tool, the actual sample testing and laboratory ICP-MS results were consistent. The research conducted in this project constituted a useful attempt to expand and improve the analytical methods for inorganic elements in soil and sediment, showing that MED-XRF is superior to conventional ED-XRF and WD-XRF and is the current new method of analysis for a low content of Cd in soil. MED-XRF offers a very important contribution to research on soil census, conservation, the rational use of agricultural land, and soil restoration and improvement, and provides strong support for field testing.

Calorimeter calibration of the ComPol CubeSat gamma-ray polarimeter

ComPol is a proposed CubeSat mission dedicated to long-term study of gamma-ray polarisation of astrophysical objects. Besides spectral and timing measurements, polarisation analysis can be a powerful tool in constraining current models of the geometry, magnetic field structure and acceleration mechanisms of different astrophysical sources. The ComPol payload is a Compton telescope optimised for polarimetry and consists of a 2 layer stacked detector configuration. The top layer, the scatterer, is a Silicon Drift Detector matrix developed by the Max Planck Institute for Physics and Politecnico di Milano. The second layer is a calorimeter consisting of a CeBr3 scintillator read-out by silicon photo-multipliers developed at CEA Saclay. This paper presents the results of the prototype calorimeter calibration campaign, executed in March 2022 at IJCLab Orsay and simulations of the expected performance of the polarimeter using updated performance figures of the detectors.

The SIDDHARTA-2 calibration method for high precision kaonic atoms x-ray spectroscopy measurements

The SIDDHARTA-2 experiment at the DAΦNE collider aims to perform the first kaonic deuterium x-ray transitions to the fundamental level measurement, with a systematic error at the level of a few eV. To achieve this challenging goal the experimental apparatus is equipped with 384 Silicon Drift Detectors (SDDs) distributed around its cryogenic gaseous target. The SDDs developed by the SIDDHARTA-2 collaboration are suitable for high precision kaonic atoms spectroscopy, thanks to their high energy and time resolutions combined with their radiation hardness. The energy response of each detector must be calibrated and monitored to keep the systematic error, due to processes such as gain fluctuations, at the level of 2–3 eV. This paper presents the SIDDHARTA-2 calibration method which was optimized during the preliminary phase of the experiment in the real background conditions of the DAΦNE collider, which is a fundamental tool to guarantee the high precision spectroscopic performances of the system over long periods of data taking, as that required for the kaonic deuterium measurement.

Novel Spiral Silicon Drift Detector with Equal Cathode Ring Gap and Given Surface Electric Fields.

Since the advent of semiconductor detectors, they have been developed for several generations, and their performance has been continuously improved. In this paper, we propose a new silicon drift detector structure that is different from the traditional spiral SDD structure that has a gap between the cathode ring and the width of cathode ring, increasing gradually with the increase of the radius of the cathode ring. Our new structure of spiral SDD structure has equal cathode ring gap and a given surface electric field, which has many advantages compared with the traditional structure. The novel SDD structure controllably reduces the area of silicon oxide between the spiral rings, which in turn reduces the surface leakage current due to the reduction of total oxide charge in the silicon oxide and electronic states on the silicon/silicon oxide interface. Moreover, it has better controllability to adjust this spiral ring cathode gap to achieve better surface electric field distribution, thus realizing the optimal carrier drift electric field and achieving the optimal detector performance. In order to verify this theory, we have modeled this new structure and simulated its electrical properties using the Sentaurus TCAD tool. We have also analyzed and compared different spiral ring cathode gap structures (from 10 µm to 25 µm for the gap). According to the simulation results of potential, electric field, and electron concentration, we have obtained that a spiral ring cathode gap of 10 µm has the best electrical characteristics, more uniform distribution of potential and surface electric field, and a more smooth and straight electron drift channel.

Evaluation of the performance of modern X-ray fluorescence spectrometry systems for the forensic analysis of glass

Micro X-ray Fluorescence Spectrometry (µXRF) is a well-established technique for the elemental analysis of glass in forensic casework. The standard test method for the forensic analysis of glass using µXRF (ASTM E2926) provides recommendations for the number of replicate measurements that should be collected to characterize a known source and the criteria for the comparison between the known and questioned samples. However, these recommendations were based on interlaboratory data collected using µXRF instrumentation equipped with traditional lithium-doped silicon (SiLi) detectors. This interlaboratory study aimed to evaluate the performance of modern µXRF systems equipped with silicon drift detectors (SDDs) for the forensic comparison of glass. While the SDD-µXRF instruments resulted in improved precision and detection limits (1.4 µg·g−1–1386 µg·g−1) and excellent discrimination (>99 %) of different-source samples, the false exclusion rates for same-source samples were relatively high (>20 %). Two methods were evaluated to reduce the high false exclusion rates: increasing the number of fragments collected for the known source and modifying the recommended comparison criteria. To reduce the false exclusion rate to 5 % or less, a minimum of five known fragments were needed. Alternatively, modifying the recommended comparison criterion reduced the false exclusion rate from 23 % to 2 %, while maintaining low false inclusions (<1%). The findings in this study demonstrate the improved sensitivity and precision observed in glass measurements acquired with µXRF-SDD systems. However, these systems may require adjustments to sampling and the comparison criteria to minimize potential error rates in the forensic comparison of glass fragments.

The Effects of Different Anode Positions on the Electrical Properties of Square-Silicon Drift Detector.

The Silicon Drift Detector (SDD) with square structure is often used in pixel-type SDD arrays to reduce the dead region considerably and to improve the detector performance significantly. Usually, the anode is located in the center of the active region of the SDD with square structure (square-SDD), but the different anode positions in the square-SDD active area are also allowed. In order to explore the effect on device performance when the anode is located at different positions in the square-SDD active region, we designed two different types of square-SDD in this work, where the anode is located either in the center (SDD-1) or at the edge (SDD-2) of its active region. The simulation results of current density and potential distribution show that SDD-1 and SDD-2 have both formed a good electron drift path to make the anode collect electrons. The experimental results of device performance at the temperature range from −60 °C to 60 °C show that the anode current of the two fabricated SDDs both decreased with the decrease of temperature, but their voltage divider characteristics exhibited high stability resistance value and low temperature coefficient, thereby indicating that they could both provide corresponding continuous and uniform electric field at different temperatures. Finally, SDD-1 and SDD-2 have energy resolutions of 248 and 257 eV corresponding to the 5.9 keV photon peak of the Fe-55 radioactive source, respectively. Our experimental results demonstrate that there is no significant impact on the device performance irrespective of the anode positions in the square-SDD devices.

Characterization measurements of the TRISTAN multi-pixel silicon drift detector

Sterile neutrinos are a minimal extension of the standard model of particle physics. A laboratory-based approach to search for this particle is via tritium β-decay, where a sterile neutrino would cause a kink-like spectral distortion. The Karlsruhe Tritium Neutrino (KATRIN) experiment extended by a multi-pixel Silicon Drift Detector system has the potential to reach an unprecedented sensitivity to the keV-scale sterile neutrino in a lab-based experiment. The new detector system combines good spectroscopic performance with a high rate capability. In this work, we report about the characterization of charge-sharing between pixels and the commissioning of a 47-pixel prototype detector in a MAC-E filter.

Use of a Mylar filter to eliminate vacuum ultraviolet pulse pileup in low-energy x-ray measurements.

We describe a method to reduce vacuum ultraviolet (VUV) pulse pileup (PPU) in x-ray pulse-height Silicon Drift Detector (SDD) signals. An Amptek FAST SDD, with C1 (Si3N4) window, measures bremsstrahlung emitted from PFRC-2 plasma to extract the electron temperature (Te) and density (ne). The C1 window has low transmissivity for photons with energy below 200eV though will transmit some VUV and soft x-ray photons, which PFRC-2 plasmas abundantly emit. Multi-VUV-photon PPU contaminates the interpretation of x rays with energy > 100eV, particularly in a low-energy exponential tail. The predicted low transmissivity of ∼1μm thick Mylar [polyethylene terephthalate (PET)] to photons of energy <100 eV led to the selection of Mylar as the candidate filter to reduce VUV PPU. Experiments were conducted on an x-ray tube with a graphite target and on a quasi-Maxwellian tenuous plasma (ne ∼ 109cm-3) with effective temperatures reaching 1500eV. A Mylar filter thickness of 850nm is consistent with the results. The Mylar-filter-equipped SDD was then used on the PFRC-2 plasma, showing a substantial reduction in the low-energy x-ray signal, supporting our hypothesis of the importance of VUV PPU. We describe the modeling and experiments performed to characterize the effect of the Mylar filter on SDD measurements.

Timing Performances of SDD as Photodetector Candidate for Proton Therapy Application

In the proton therapy, charged particles interact with tissue depositing dose in the tumor, providing enhanced tumor coverage compared to conventional radiotherapy. However, proton range uncertainties limit the full exploitation in clinical practice of the localized dose deposition. Range and dose monitoring in real time would be beneficial to deliver safer and more effective treatments. A possible solution is to use the signature of high-energy (2–8 MeV) prompt gamma rays, produced naturally along the beam path by excited nuclei. In this article, we study the timing capability of the silicon drift detector (SDD) as a photodetector candidate to be used for the scintillator readout for high-energy gamma rays detection. The peculiar drift mechanism affects the time needed for the photogenerated charge inside the SDD volume to approach the collecting electrode. As a result, the detector output signal shows a rise time limiting usually its timing performances when used with scintillators. In this work, we first developed a simulator to predict the drift time values as a function of charge generation position. Next, we performed the experimental characterization of the SDD timing performances by directly irradiating it with laser light. We carried out spectroscopy measurements for the assessment of the electronics noise of the detector in two readout configurations: 1) single anode and 2) merged anodes. Finally, we experimentally evaluated the timing performances of the SDD at the signal levels expected in the target application, showing sub-ns timing resolution.

Hard x-ray spectrometer calibrations using a portable120kV x-ray source.

A Cauchois transmission-crystal hard x-ray spectrometer was calibrated by using a portable, compact, battery-powered tungsten x-ray source having 120 peak kilovoltage. The source emission region was characterized by recording high-resolution 2D x-ray images and was found to be composed of three emission regions having a 400 µm overall extent. The absolutely calibrated source fluence was measured by using a calibrated silicon drift detector and was in good agreement with the spectrum calculated by the SpekPy code. High-resolution spectra of the W Kα and Kβ lines in the 57-70keV energy range were recorded on image plate detectors by the Cauchois spectrometer and provided excellent calibrations of the spectrometer's dispersion and spectral resolution. The minimal effect of the source size in the spectral lines recorded on the spectrometer's Rowland circle and the source-size broadening of the spatial lines recorded well beyond the Rowland circle were analyzed. The integrated reflectivity of the spectrometer's quartz (101) crystal was measured by using the absolutely calibrated 59.318keVW Kα1 spectral line emission and was in agreement with previous integrated reflectivity measurements performed at the National Institute of Standards and Technology. The well-characterized portable120kV x-ray source provides a convenient and cost-effective way to accurately calibrate the sensitivity, dispersion, spectral resolution, and source-size broadening in the spectra recorded by high-resolution x-ray spectrometers operating in the hard x-ray range. The absolutely calibrated source fluence can also be used to calibrate x-ray detectors at energies in the 40-100keV energy range.