Lithium-drifted Silicon Detector Research Articles

Low-Noise Analog Channel for the Readout of the Si(Li) Detector of the GAPS Experiment

This work is focused on the design and the experimental characterization of an analog channel developed for the readout of lithium-drifted silicon detectors of the General AntiParticle Spectrometer (GAPS) experiment aimed at the search for dark matter. The instrument is designed for the identification of antideuteron particles from cosmic rays during an Antarctic balloon mission scheduled for late 2022. A low-noise analog front-end, featuring a dynamic signal compression to comply with the wide input range, has been designed in commercial 180-nm CMOS technology. The channel was fabricated in 2018 and is the first building block toward the development of a multichannel readout ASIC. The article will provide a description of the design criteria, the architecture of the channel, and a summary of the results of the experimental characterization.

In-beam internal conversion electron spectroscopy with the SPICE detector

The SPectrometer for Internal Conversion Electrons (SPICE) has been commissioned for use in conjunction with the TIGRESS γ-ray spectrometer at TRIUMF’s ISAC-II facility. SPICE features a permanent rare-earth magnetic lens to collect and direct internal conversion electrons emitted from nuclear reactions to a thick, highly segmented, lithium-drifted silicon detector. This arrangement, combined with TIGRESS, enables in-beam γ-ray and internal conversion electron spectroscopy to be performed with stable and radioactive ion beams. Technical aspects of the device, capabilities, and initial performance are presented.

Overcoming Peak Overlaps in Titanium- and Vanadium-Bearing Materials with Multiple Linear Least Squares Fitting.

The evolution of the energy dispersive spectrometer (EDS) from the lithium-drifted silicon detector [Si(Li)] to the silicon drift detector (SDD) has created new opportunities in the field of electron probe X-ray microanalysis. The SDD permits operation at significantly higher count rates than the Si(Li) and also provides a more stable energy scale. X-ray spectra captured by EDS can now be analyzed qualitatively or quantitatively under the same beam conditions as used for wavelength dispersive spectrometry (WDS). Standards-based quantitative EDS (SB-Quant-EDS) can thus provide analyses that are accurate and precise for an ever growing number of materials measurement problems. In this study, we analyze NIST research glasses with "known" nominal concentrations of titanium (Ti) and vanadium (V) to evaluate the external reproducibility of the SB-Quant-EDS technique in the presence of severe peak overlaps. We additionally analyze several naturally occurring oxide minerals by WDS and EDS simultaneously and evaluate the outputs of these two methods when quantifying the same analytical volume within the sample.

Fully digital readout of segmented solid state detectors

In this work, the digital readout of semiconductor detectors in combination with digital filters was investigated. Both non-segmented high-purity germanium and segmented planar lithium-drifted silicon detectors were used. In each case, photons from a stationary americium (241Am) gamma source were detected. The resulting preamplifier output pulses were digitized at a fixed sampling frequency and stored entirely. Digital filters were applied to the stored waveforms to extract time and energy information. The performance of different digital filters was compared. The optimum energy resolution obtained was comparable with the value resulting from an analogue readout system based on standard nuclear instrumentation module and versatile module Europe bus electronics.

Elemental mapping of microstructures by scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS): extraordinary advances with the silicon drift detector (SDD)

Elemental mapping at the microstructural level by scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDS), while widely applied in science, engineering, and technology, has been limited in performance by the throughput of the lithium-drifted silicon detector [Si(Li)-EDS] which restricts the number of X-ray counts measured per image pixel. The emergence of the silicon drift detector (SDD-EDS) has greatly extended the X-ray throughput, by a factor of 25 to 70 for the same spectral resolution. This improved performance enables practical X-ray spectrum imaging (XSI), in which a complete X-ray spectrum is recorded at each image pixel. By performing complete quantitative corrections for background, peak overlap, and matrix effects to each pixel spectrum, full compositional mapping can be achieved. Various elemental mapping collection strategies are described, including quantitative mapping at the major (concentration C > 0.1 mass fraction), minor (0.01 ≤ C ≤ 0.1), and trace (C < 0.01) constituent levels, extreme pixel density (gigapixel) mapping, rapid mapping (in 10 seconds or less), and high spatial resolution mapping with the thermal field emission gun scanning electron microscope.

Planar Si(Li) detectors with a large active volume

Results of development and investigations of lithium-drifted silicon detectors with a large active volume and an active depth of 4–8 mm for use in multilayer spectrometers are presented. The main performance characteristics of the detectors are described. The detectors have been used to good effect in nuclear radiation spectroscopy, particularly in experimental studies of exotic nuclei at accelerators.

Calibration of 55Fe activity with a lithium-drifted silicon detector

NMIJ participated in the CCRI (II) key comparison of 55Fe activity measurement. A planar-type Si(Li) detector and a liquid-scintillation counter were used to calibrate the activity. The calibration result obtained by the Si(Li) detector agreed with that obtained by the liquid-scintillation counter using the CIEMAT/NIST method within uncertainty. The result was reported to the BIPM in 2006. The activity of 55Fe was also measured by using a 2 π pressurized proportional counter. The result obtained by the 2π pressurized proportional counter agreed with the above results within uncertainty. The measurement by the Si(Li) detector was very simple and its procedure was a combination of conventional methods. The measurement by the liquid-scintillation counter is most popular to calibrate the activity of 55Fe. However the Si(Li) detector is also useful.

Soft x-ray measurement of the toroidal pinch experiment RX reversed field pinch plasma using transition edge sensor calorimeter

A superconductive transition edge sensor (TES) calorimeter is for the first time applied for the diagnostics of the reversed field pinch plasma produced in the toroidal pinch experiment RX (TPE-RX), and the instrumental system is fully described. The first result from the soft x-ray spectroscopy in 0.2–3keV with an energy resolution ∼50eV are also presented. The TES calorimeter is made of a thin bilayer film of titanium and gold with a transition temperature of 151mK and its best energy resolution at our laboratory is 6.4eV, while it was significantly degraded by about a factor of eight during the plasma operation. The TES microcalorimeter was installed in a portable adiabatic demagnetization refrigerator (ADR), which is originally designed for a rocket experiment. The detector box is carefully designed to shield the strong magnetic field produced by the ADR and TPE-RX. The ADR was directly connected to TPE-RX with a vacuum duct in the sideway configuration, and cooled down to 125mK stabilized with an accuracy of 10μK rms using an improved proportional, integral, and derivative (PID) control method. Thin aluminized Toray Lumirror or Parylene-N films were used for the IR to UV blocking filters of the incident x-ray window to allow soft x-rays coming into the detector with good efficiency. TPE-RX was operated with the plasma current of Ip=220kA, and the wave forms of the TES output for every plasma shot lasting ∼80ms were obtained with a digital oscilloscope. The wave forms were analyzed with the optimal filtering method, and x-ray signals were extracted. A total of 3472 counts of x-ray signals were detected for 210 plasma shots during the flat-top phase of t=35–70ms. Combined with the data measured with a lithium drifted silicon detector in the 1.3–8keV range, spectral features are investigated using a spectral fitting package XSPEC. The obtained spectrum is well explained by thermal plasma emission, although an impurity iron-L line emissions at variously ionized states are dominant around 0.7–1.2keV. At least three different temperature components ranging T=350–900eV are required to account for the spectral shape, while the average temperature is consistent with the ruby laser Thomson scattering measurement.

Large-area Si(Li) orthogonal-strip detectors

Segmented lithium drifted silicon detectors are being developed for use in large Compton cameras and for medical imaging. We have successfully fabricated 3.5 mm thick crossed-strip detectors with active areas of 40/spl times/40 mm/sup 2/ with a 2 mm strip pitch. These detectors utilize new contact technology consisting of a boron implanted p-type contact and an amorphous silicon (/spl alpha/-Si) n-type contact. Good energy resolution and excellent strip separation was obtained from both contacts at relatively high operating temperatures. An energy resolution of 2.1 keV FWHM at 122 keV was obtained for the /spl alpha/-Si strip at temperatures up to 200 K and for the boron strip at temperatures up to 240 K. Measurements of the charge sharing between the strips were also performed. When the detector was flood illuminated with 60 keV gamma-rays, a small signal deficit was observed for events in which the signal was shared between two adjacent strips. The amount of deficit depended on the contact type, strip geometry and the operating temperature.

New contact development for Si(Li) orthogonal-strip detectors

At present, the contacts generally used for lithium-drifted silicon detectors consist of a diffused lithium layer (n-type) and a gold surface barrier (p-type). These contacts work well for unsegmented detectors. However, they both have disadvantages if used for segmented detectors. For this reason, we are developing new types of contacts that will be more robust and easier to segment. To replace the lithium n-type contact, we are using a thin layer of amorphous silicon (α-Si) with metalization on top. The new p-type contact consists of boron implanted into the silicon and annealed at the relatively low temperature of 500°C. The implantation and annealing is carried out as the first step in the process, prior to lithium drifting. Detectors have been fabricated using the new contacts both with and without a guard ring. They performed as well as detectors with standard contacts at operating temperatures between 80 and 240K. We will present data on the leakage current vs. temperature, isolation resistance between the guard ring and the center contact versus temperature and bias voltage, electronic noise and energy resolution versus temperature, as well as 57Co spectra.

Going Nondispersive

In February 1968 Ray Fitzgerald, Klaus Keil and myself published in Science a communication titled “Solid-State Energy-Dispersion Spectrometer for Electron Microprobe X-ray Analysis”. The authors describe the use of a lithium-drifted silicon detector for the direct identification of x-rays, without a diffracting crystal, in an electron probe. The subject of this paper was to modify profoundly the development of x-ray microanalysis in the years to follow.Pulse-height analysis of gamma rays detected in scintillation counters was widely used at the time. For radiation of energies below 30 keV, gas proportional counters were also employed. In elementary analysis by x-rays the poor energy resolution of these detectors limited the application of such a procedure, although single-channel pulse height analysis was employed as an adjunct to crystal spectrometers.In 1951, Raymond Castaing in his thesis described his invention of the electron probe microanalyzer, created by adding to a transmission electron microscope a curved-crystal spectrometer which focused the x-rays emitted by the specimen into a Geiger-Muller counter.

Progress in multielement silicon detectors for synchrotron XRF applications (abstract)

Multielement silicon strip detectors, in conjunction with integrated circuit pulse-processing electronics, offer an attractive alternative to conventional lithium-drifted silicon and high purity germanium detectors for high count rate, low noise synchrotron x-ray fluorescence applications. We have been developing these types of detectors specifically for low noise synchrotron applications, such as extended x-ray absorption fine structure spectroscopy, microprobe x-ray fluorescence and total reflection x-ray fluorescence. The current version of the 192-element detector and integrated circuit preamplifier, cooled to −25 °C with a single-stage thermoelectric cooler, achieves an energy resolution of &amp;lt;200 eV FWHM (at 5.9 keV, 2 microseconds peaking time), and each detector element is designed to handle a ∼20 kHz count rate. The detector system will soon be completed to 64 channels using new IC amplifier chips, CAMAC ADCs, CAMAC histogramming modules, and Macintosh-based data acquisition software. We will report on the characteristics of this detector system, the characteristics of the next generation system (192 channels with IC ADCs), and the use of these detector systems in synchrotron XRF applications.

Long-Term Instability of Lithium-Drifted Silicon Detector

Using 1150 nm infrared light, the change in the detector sensitivity was studied. As a simple measure of the states of the detector sensitivity, the time derivative of the photocurrent is proposed. In terms of the derivative, the change is uniquely classified into two categories. Even after the detector is aged, the derivative does not remain constant with respect to time and voltage. The physical mechanisms which cause the change are discussed based on possible effects due to unstable surface states and the accumulation of an oxide layer.

High precision Wölter optic calibration facility

We have developed an off-line facility for very precise characterization of the reflectance and spatial resolution of the grazing incidence Wölter type I x-ray optics used at Nova. The primary component of the facility is a new, very versatile, high brightness x-ray source consisting of a focused DC electron beam incident onto a precision manipulated target-pinhole array. The data are recorded with a selection of detectors. For imaging measurements we use direct exposure x-ray film modules or an x-ray charge-coupled device camera. For energy-resolved reflectance measurements, we use lithium drifted silicon detectors and a proportional counter. An in situ laser alignment system allows precise location and rapid periodic alignment verification of the x-ray point source, the statically mounted Wölter optic, and the chosen detector.

Stability of a Lithium-Drifted Silicon Detector

The instability of a radiation detector has been studied by means of 1150 nm infrared light. The change in the detector sensitivity is exhibited in photocurrent measurements. Several resonancelike bumps were observed in the conductance of the detector when the aging was incomplete. Using the observed data, we discuss the possible mechanisms which affect detector stability.

Developments in X-Ray Detectors and Associated Electronics: A Review of the Technology and Possible Future Trends

The detection of low-energy x rays in a precise and efficient manner is now routinely performed with a range of solid state detectors. These devices have been developed continuously over the past 30 years to the point where current performance closely matches theoretical predictions for resolution and efficiency. To achieve these goals parallel developments in field effect transistors and amplifiers were also required. To fully understand the problems associated with the development and use of these detectors it is necessary to discuss both the generation of x rays and the way in which x rays interact with the available detector materials. The energy range considered is 0-100 keV and a comparison between the successful lithium drifted silicon detector and the more recently re-developed high-purity germanium detectors for these low energy applications is given.

MeV gamma ray detection algorithms for stacked silicon detectors

By making use of the signature of a gamma ray event as it appears in a stack of N=5 to 20 lithium-drifted silicon detectors and applying smart selection algorithms, gamma rays in the energy range of 1 to 8 MeV can be detected with good efficiency and selectivity. Examples of the types of algorithms used for different energy regions include the simple sum mode, the sum-coincidence mode used in segmented detectors, unique variations of sum-coincidence for an N-dimensional vector event, and a new and extremely useful mode for double escape peak spectroscopy at pair-production energies. The latter algorithm yields a spectrum similar to that of the pair spectrometer, but without the need for the dual external segments for double escape coincidence, and without the large loss in efficiency of double escape events. Background events due to Compton scattering are largely suppressed. Monte Carlo calculations were used to model the gamma ray interactions in the silicon in order to enable testing of a wide array of different algorithms on the event N-vectors for a large-N stack. >

Measurement of x-ray absorption spectra of photoresists using a silicon lithium detector

We have developed a simple experimental technique for measuring the absorption spectrum of x-ray photoresists in the region from 1000 to 3000 eV. Knowledge of the absorption characteristics of a photoresist allows selection of the most efficient range of energies to use for performing x-ray exposures. The measurements were performed using the Medical Physics beamline on the University of Wisconsin Aladdin synchrotron source. The beamline is equipped with a lithium-drifted silicon detector that provides an energy resolution of 150 eV. To avoid saturation of the Si(Li) detector, special ‘‘microbeams’’ of approximately 50 circulating electrons in the storage ring were employed. The beam intensity was monitored using a photodiode. The operation of the detector and associated diagnostic equipment will be described. Four by four millimeter square, 1.4 μm thick silicon nitride membranes were used as substrates for the resist films. Photoresist absorption was measured by comparing the transmission of silicon nitride membranes with and without photoresist coatings. Experimental results for both conventional and chemically amplified positive and chemically amplified negative x-ray photoresists are presented.

Energy-dispersive x-ray microanalysis in the earth sciences

The electron microprobe analyser (EMPA) is used extensively for the analysis of the constituent minerals in rocks and the samples generated by experimental petrology apparatus. These analyses, combined with the results of field observations and data from other analytical techniques, are used in petrogenetic studies and hence in the determination of planetary formation and evolution. In turn, this knowledge helps the mining industry in their mineral exploration programs.In the 1960s almost all geological usage of the EMPA was confined to the x-ray spectrometry of L3-K lines of elements of atomic number 11 through 30 (Na through Zn). By the end of this decade semi conductor technology had advanced so that these x-ray lines could be resolved using a lithium-drifted silicon detector working as an energy dispersive spectrometer (EDS). Quantitative EDS software was developed in the early 1970s and it became possible to perform major element analyses of silicates, oxides, carbonates and sulphides using a scanning electron microscope (SEM) fitted with an EDS.

Results from a Si(Li) gamma ray detector stack for future Mars missions

The authors present Monte Carlo analysis and experimental data from a novel lithium-drifted silicon detector stack for gamma ray spectroscopy instrumentation in future Mars surface landers and other planetary missions. The Monte Carlo analysis shows full energy photopeaks even in the range of approximately 100 keV to 2 MeV where. in Si, Compton scattering, dominates the absorption processes. Laboratory data are shown for an experimental detector stack of four planar Si(Li) devices, each 5 mm thick with an active area 2 cm in diameter. All the experimental data were collected with maximum temperature of the stack at 175 K. Background reduction was achieved by using the detector of the stack closest to the source in anticoincidence. Experimental data from the stack are compared with the Monte Carlo model for /sup 137/Cs (662 keV).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>