Segmented Silicon Research Articles

Monitoring electron and proton beam profiles with segmented silicon sensors

The FRIDA INFN project characterized thin silicon sensors for monitoring electron FLASH beams, showing a response linearity up to ∼10 Gy/pulse on 9 MeV electrons. The use of segmented silicon configurations could provide the spatial resolution useful in Spatially Fractionated Radiotherapy (SFRT). Within the MIRO INFN project, a strip sensor integrated with a multichannel readout chip is being developed and tested for monitoring FLASH and SFRT electron and proton beams. One hundred and twenty-eight strips are independently read by two front-end TERA chips. Preliminary tests were performed on 6–10 MeV electron beams at the LINAC at Physics Department of the University of Torino, with and without using a tungsten minibeam collimator, and on 62–226 MeV proton beams at CNAO (Pavia). The capability to spatially resolve electron and proton beams at conventional dose-rates has been proved.

Numerical Modeling on Ballistic Impact Analysis of the Segmented Sandwich Composite Armor System

This research delves into the design, modeling, and finite element impact analysis of the segmented sandwich composite armor system subjected to impact loading, considering different parameters such as materials to be used, armor height, and armor design configuration. Initial studies were performed to select the ideal model that will provide the best impact resistance at the least weight and with minimal fabrication requirements. Material type, thickness, and overall model configuration were defined during the initial model development period. Once the final design was defined, finite element analysis was performed using 2017 ABAQUS software to observe the performance of the model and to validate the efficiency of the chosen armor. Based on the results from the material selection and thickness validation, the optimal design with the best impact resistance was noted as 1.2 mm thick rectangular segmented silicon carbide tiles, serving as the top layer that covers the three-level gradient core composed of a titanium metal honeycomb frame filled with silicon carbide inserts, and finally a 2 mm thick glass epoxy composite layer made from four laminas in a 0/45/90/-45-degree configuration serving as the last layer of the armor.

Performance of LGAD strip detectors for particle counting of therapeutic proton beams

Objective. The performance of silicon detectors with moderate internal gain, named low-gain avalanche diodes (LGADs), was studied to investigate their capability to discriminate and count single beam particles at high fluxes, in view of future applications for beam characterization and on-line beam monitoring in proton therapy. Approach. Dedicated LGAD detectors with an active thickness of 55 μm and segmented in 2 mm2 strips were characterized at two Italian proton-therapy facilities, CNAO in Pavia and the Proton Therapy Center of Trento, with proton beams provided by a synchrotron and a cyclotron, respectively. Signals from single beam particles were discriminated against a threshold and counted. The number of proton pulses for fixed energies and different particle fluxes was compared with the charge collected by a compact ionization chamber, to infer the input particle rates. Main results. The counting inefficiency due to the overlap of nearby signals was less than 1% up to particle rates in one strip of 1 MHz, corresponding to a mean fluence rate on the strip of about 5 × 107 p/(cm2·s). Count-loss correction algorithms based on the logic combination of signals from two neighboring strips allow to extend the maximum counting rate by one order of magnitude. The same algorithms give additional information on the fine time structure of the beam. Significance. The direct counting of the number of beam protons with segmented silicon detectors allows to overcome some limitations of gas detectors typically employed for beam characterization and beam monitoring in particle therapy, providing faster response times, higher sensitivity, and independence of the counts from the particle energy.

Silicon Subwavelength Grating Slot Waveguide based Optical Sensor for Label Free Detection of Fluoride Ion in Water

Recently, Subwavelength Grating Waveguides (SWG WG) attract a lot of attention for sensing applications because it offers better sensitivity than conventional WGs. The sensitivity of SWG WG is greatly improved due to the interaction between the analyte and guiding mode in the SWG segments. In this study, a highly sensitive sensor based on a silicon SWG slot waveguide (SWGSW) is proposed for detecting low-concentration fluoride contaminations in water. The gap called as “slot” between the silicon slab along with cladding and the spaces between the segmented silicon rail waveguide is filled with fluoride ion-contaminated water samples as analyte for strong light–matter interaction between guiding modes of the SWG structure, resulting in greater sensitivity of the proposed sensor. The sensitivity of the proposed structure is estimated by numerical simulations as S = 615.38 nm/RIU which is comparable to the existing reported optical sensor structures based on optical waveguide and optical fibre with a smaller footprint. Additionally, the effect of variation of geometrical parameters on the transmission resonances of the proposed structure is also analyzed for the optimization of a SWG WG structure. The obtained results will be helpful to realize and design highly sensitive sensors based on the SOI platform.

Test Bench for Highly Segmented GRIT Double-Sided Silicon Strip Detectors: A Detector Quality Control Protocol

This work deals with the characteristics of highly segmented double-sided silicon detectors. These are fundamental parts in many new state-of-the-art particle detection systems, and therefore they must perform optimally. We propose a test bench that can handle 256 electronic channels with off-the-shelf equipment, as well as a detector quality control protocol to ensure that the detectors meet the requirements. Detectors with a large number of strips bring new technological challenges and issues that need to be carefully monitored and understood. One of the standard 500 μm thick detectors of the GRIT array was investigated, undergoing studies that revealed its IV curve, charge collection efficiency, and energy resolution. From the data obtained, we calculated, among other things, the depletion voltage (110 V), the resistivity of the bulk material (9 kΩ·cm), and the electronic noise contribution (8 keV). We present, for the first time, a methodology called “the energy triangle’’ to visualize the effect of charge sharing between two adjacent strips and to study the hit distribution with the interstrip-to-strip hit ratio (ISR).

Transmission of 120 Gbaud QAM With an All-Silicon Segmented Modulator

Segmenting a silicon modulator can substantially increase its electro-optic bandwidth without sacrificing modulation efficiency. We demonstrate a segmented silicon IQ modulator and experimentally explore both modulator design and operating point to optimize systems trade-offs in coherent detection. An electro-optic bandwidth of greater than 40 GHz is measured for a 4-mm-long segment, and greater than 60 GHz for a 2-mm-long segment. We evaluate optical transmission experimentally at 120 Gbaud for 16-ary quadrature amplitude modulation (QAM) and 32QAM. The segments are operated in tandem with identical data at each segment. We present an experimental method to align data timing between the segments. Through the optimization of segment biasing and linear compensation, we have achieved a bit error rate (BER) of 16QAM well below the 20% forward error correction (FEC) threshold ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2\times 10^{-2}$</tex-math></inline-formula> ). Adding nonlinear pre-compensation allows for 32QAM with a BER below the 24% FEC threshold ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$4.5\times 10^{-2}$</tex-math></inline-formula> ), enabling a net rate of 483 Gbs per polarization. The modulator can also be operated as an optical digital analogy converter for complex optical signal generation, for which 100 Gbs is achieved for a proof of concept.

Characterisation of irradiated and non-irradiated silicon sensors with a table-top two photon absorption TCT system

A tabletop Two Photon Absorption-Transient Current Technique (TPA-TCT) set-up built at CERN was used to investigate a non-irradiated PIN diode, an irradiated PIN diode, and a non-irradiated 5 × 5-multipad HPK LGAD. The intrinsic three dimensional spatial resolution of this method is demonstrated under normal incidence of the laser probe. A charge collection versus depth profile of the non-irradiated PIN diode is presented, where reflection on the rear silicon-air interface was observed. It is found that the time-over-threshold versus depth profile is particularly suitable to determine the boundaries of the DUT’s active volume. A depth scan of the irradiated PIN diode is discussed and a method to omit the single photon absorption background is presented. Finally, a charge collection measurement in the inter-pad region of the 5 × 5-multipad HPK LGAD is presented and it is demonstrated that TPA-TCT can be used to image the implantation and the electric field of segmented silicon devices in a three dimensional manner.

Machine learning based event classification for the energy-differential measurement of the [formula omitted]C(n,p) and [formula omitted]C(n,d) reactions

The paper explores the feasibility of using machine learning techniques, in particular neural networks, for classification of the experimental data from the joint natC(n,p) and natC(n,d) reaction cross section measurement from the neutron time of flight facility n_TOF at CERN. Each relevant ΔE−E pair of strips from two segmented silicon telescopes is treated separately and afforded its own dedicated neural network. An important part of the procedure is a careful preparation of training datasets, based on the raw data from Geant4 simulations. Instead of using these raw data for the training of neural networks, we divide a relevant 3-parameter space into discrete voxels, classify each voxel according to a particle/reaction type and submit these voxels to a training procedure. The classification capabilities of the structurally optimized and trained neural networks are found to be superior to those of the manually selected cuts.

Measurements of charge sharing in a hybrid pixel photon counting CdTe detector

Hybrid pixel radiation detectors working in a single-photon counting mode have gained increasing attention due to their noiseless imaging and high dynamic range. Due to the fact that sensors of different materials can be attached to the readout circuit, they allow operation with a wide range of photon energies. The performance of the single photon counting detectors is limited by pile-up. To allow a detector to work under high flux conditions, the pixel size is reduced, which minimizes detector dead time. However, with smaller pixel sizes the charge sharing effect, a phenomenon that deteriorates both detection efficiency and spatial resolution is more profound.The influence of charge sharing on the detector performance can be quantified using parameterization of the s-curve obtained in the spectral response measurements. The article presents the measurements of the response function of a hybrid pixelated photon counting detector for certain primary energy, which corresponds to the probability of detecting a photon as a function of its energy deposition. The measurements were carried out using an X-ray tube by performing a threshold scan during illumination with X-ray photons of a 1.5 mm and 0.75 mm thick CdTe detector with 100 µm pixel pitch. The charge size cloud depends on the sensor material, the bias voltage, and the sensor thickness. Therefore, the experimental data from a sensor biased with different bias voltages are compared to the theoretical results based on a cascaded model of a single-photon counting segmented silicon detector. The study of the charge sharing influence on the spatial resolution of the CdTe detector will serve for a further study of the possible implementations of the algorithms achieving subpixel resolution, in which the charge sharing becomes the desired effect since the charge division in the pixels is used to interpolate the photon interaction position.

The DAQ system of the 12,000 channel CMS high granularity calorimeter prototype

The CMS experiment at the CERN LHC will be upgraded to accommodate the 5-fold increase in the instantaneous luminosity expected at the High-Luminosity LHC (HL-LHC) [1]. Concomitant with this increase will be an increase in the number of interactions in each bunch crossing and a significant increase in the total ionising dose and fluence. One part of this upgrade is the replacement of the current endcap calorimeters with a high granularity sampling calorimeter equipped with silicon sensors, designed to manage the high collision rates [2]. As part of the development of this calorimeter, a series of beam tests have been conducted with different sampling configurations using prototype segmented silicon detectors. In the most recent of these tests, conducted in late 2018 at the CERN SPS, the performance of a prototype calorimeter equipped with ≈12,000 channels of silicon sensors was studied with beams of high-energy electrons, pions and muons. This paper describes the custom-built scalable data acquisition system that was built with readily available FPGA mezzanines and low-cost Raspberry Pi computers.

Neutral tritium gas reduction in the KATRIN differential pumping sections

The KArlsruhe TRItium Neutrino experiment (KATRIN) aims to measure the effective electron anti-neutrino mass with an unprecedented sensitivity of $0.2\,\mathrm{eV}/\mathrm{c}^2$, using $\beta$-electrons from tritium decay. The electrons are guided magnetically by a system of superconducting magnets through a vacuum beamline from the windowless gaseous tritium source through differential and cryogenic pumping sections to a high resolution spectrometer and a segmented silicon pin detector. At the same time tritium gas has to be prevented from entering the spectrometer. Therefore, the pumping sections have to reduce the tritium flow by more than 14 orders of magnitude. This paper describes the measurement of the reduction factor of the differential pumping section performed with high purity tritium gas during the first measurement campaigns of the KATRIN experiment. The reduction factor results are compared with previously performed simulations, as well as the stringent requirements of the KATRIN experiment.

Runaway electron diagnostics using silicon strip detector

We present a proof-of-principle measurement of runaway electrons in a small tokamak using a silicon strip detector. The detector was placed inside the diagnostic port of the tokamak vessel and detected the runaway electron signal directly. The measured signal was compared to the signal provided by other tokamak diagnostics, especially the hard X-ray scintillation detector, which detects secondary photons created by interaction of accelerated electrons with tokamak walls (indirect detection of runaway electrons). The preliminary results show that when not saturated, direct detection with a segmented silicon strip detector provides promising new diagnostic information including spatial and temporal distribution of the runaway electron beam, and the measurement results are in good agreement with hard X-ray measurements with a scintillation detector.

SPIDER: A Silicon PIe DEtectoR for low-energy Coulomb-excitation measurements

SPIDER is a new array of segmented silicon detectors for low-energy Coulomb-excitation experiments, designed as an ancillary device for modern γ-ray spectrometers such as GALILEO and AGATA. Currently, it is used at the INFN Legnaro National Laboratories (LNL) for experiments with the GALILEO γ-ray array and the stable beams provided by the Tandem-XTU, ALPI-PIAVE accelerator complex. In this paper, a detailed description of SPIDER is presented, as well as the outcomes from the first in-beam experiment of the array coupled with GALILEO. In particular, radiation damage and cross-talk/charge-sharing effects induced by energetic heavy ions in SPIDER are investigated and the capabilities of the array to perform on-line Rutherford back-scattering analysis of the exploited target are presented. The material reported here can be used to plan future experiments with the GALILEO-SPIDER setup with the presently available stable beams at LNL and paves the way for future experimental campaigns with the radioactive beams provided in the near future by the SPES facility at LNL.

Consideration of ferromagnetic anisotropy in electrical machines built of segmented silicon steel sheets

Electrical steel shows a distinct non-linear and anisotropic behaviour even for non-oriented steel. The flux guidance in electrical machines is realised by ferromagnetic steel sheets, and therefore it is necessary to consider the anisotropy in the simulation to have reliable and accurate results. Due to the fact that the reduction of silicon steel waste in the production process of electrical machines is crucial, and to enhance the material utilisation the segmentation is employed in the construction of electrical machines. The segmentation further allows to enhance the magnetic behaviour of the machine by considering the easy magnetisation axis in the design process. Nowadays, consideration of ferromagnetic anisotropy in the simulation of electrical machines is not accurate. To cope with these inaccuracies, in this contribution, a vectorial anisotropy model based on two-dimensional measurements is employed to the simulation of a segmented electrical machine, which is not state of the art in current machine computation. With the presented methodology, it is possible to simulate and design segmented electrical machines in an accurate fashion taking the ferromagnetic anisotropy into account.

Performance of n-on-p planar pixel sensors with active edges at high-luminosity environment

Future high-energy physics experiments require highly segmented silicon sensors of increased geometrical efficiency with the ability to withstand extremely high radiation damage. The performance of planar n-on-p sensors with active edges is simulated at high radiation fluences up to 1 × 1016 neq/cm2, using a three-level trap model for p-type silicon material. Taking advantage of the secondary ion mass spectrometry (SIMS) technique, an accurate representation of the structure was obtained in terms of doping profile. The breakdown voltage, leakage current, hole density and electric field distributions as well as the charge collection efficiency (CCE) are studied as a function of radiation fluence.

Linear and nonlinear viscoelastic properties of segmented silicone-urea copolymers: Influence of the hard segment structure

The linear and non-linear viscoelastic behaviors of 5 segmented silicone copolymers - with low fraction of 1,6-hexamethylene diisocyanate (HDI), 4,4′-methylenebis (cyclohexyl isocyanate) (HMDI), 1,3-bis(1-isocyanato-1-methylethyl)benzene (TMXDI), 2,4-tolylene diisocyanate (TDI) or isophorone diisocyanate (IPDI) as hard segments (HS) - are compared, in relation with their microstructure. When the HS are non-symmetrical, the materials nanostructuration is weak and has a limited impact on the mechanical response: two mechanical relaxations occur after the α relaxation of the polydimethylsiloxane (PDMS), the first related to the “unfreezing” of the HS-HS bonds, and the second one to the sticky reptation of the polymer chains. Conversely, when the HS are symmetrical, their self-organization is favored and the long range ordering of the HS is possible. The materials are then semi-crystalline like, with a low crystallinity (due to the low weight percentage of HS) and their flow, possible above their melting temperature (Tm), depends also on the HS dynamics, which is the most rapid for HDI.

Estimates of TPR spectrometer instrumental signal-to-background ratios and count rate limits for ITER like plasmas

The work presented is a realistic simulation of the response function for a detection efficiency optimized Thin-foil proton recoil (TPR) neutron spectrometer. The TPR spectrometer consists of a thin foil acting as neutron-to-proton converter followed by ΔE-E detectors operating in coincidence mode. In this work, two different spectrometer designs were considered using segmented silicon detectors. Design 1 has slightly better resolution while design 2 is more compact and has higher efficiency. The TPR spectrometer response functions were simulated in the energy range 8–18 MeV in steps of 40 keV for the two designs using the dedicated Monte Carlo code GEANT4. The resulting simulated response functions were broadened using experimentally determined energy resolutions of the detectors, in order to produce more realistic response functions. Using these broadened response functions together with an ITER like neutron spectrum and neutron induced background simulations ΔE/E energy deposition plots were created. The energy-cuts, for 14 MeV neutron signal identification, were applied to the ΔE-E plots leading to an estimate of the expected signal-to-background ratio. In addition, pile-up fraction and maximum expected count rates were estimated. Results show that the ΔE-E energy cuts show a great prospect of increasing the signal-to background ratio for the TPR spectrometer. In addition the TPR spectrometer has energy resolution (FWHM/E) of around 5% for 14 MeV neutrons for both investigated designs. The spectrometer can cope with maximum count rate expected and have a sufficient signal-to-background ratio in the neutron energy range of interest to perform fuel ion ratio measurements. However an increase of acquisition channels would be beneficial to limit the pile-up rate.

Monolithically Integrated Silicon Photodiode-Based FIR Filter in 65 nm CMOS Technology

This letter presents a finite impulse response (FIR) filter utilizing segmented silicon (Si) photodiodes as a part of the filter for equalization. The filter utilizes an integrated Si photodiode divided into three segments which serve as current sources and capacitors, and realizes a high-pass FIR that partially compensates for the frequency-dependent gain loss due to the physical and the electrical bandwidths of Si photodiode. This technique is well-suited for low-power applications since it uses only passive components. The photodiode-based FIR filter is implemented in a standard 65-nm CMOS technology utilizing an n-well to p-substrate junction photodiode with 12 fingers. The photodiode has a measured physical bandwidth of 15 MHz and a simulated electrical bandwidth of 5.9 GHz. The filter compensates for the photodiode gain loss by 8.7 dB in the frequency range from 1 to 5 GHz.

Performance of the new integrated front-end electronics of the TRACE array commissioned with an early silicon detector prototype

The spectroscopic performances of the new integrated ASIC (Application-Specific Integrated Circuit) preamplifiers for highly segmented silicon detectors have been evaluated with an early silicon detector prototype of the TRacking Array for light Charged Ejectiles (TRACE). The ASICS were mounted on a custom-designed PCB (Printed Circuit Board) and the detector plugged on it. Energy resolution tests, performed on the same detector before and after irradiation, yielded a resolution of 21 keV and 33 keV FWHM respectively. The output signals were acquired with an array of commercial 100-MHz 14-bit digitizers. The preamplifier chip is equipped with an innovative Fast-Reset device that has two functions: it reduces dramatically the dead time of the preamplifier in case of saturation (from milliseconds to microseconds) and extends the spectroscopic dynamic range of the preamplifier by more than one order of magnitude. Other key points of the device are the low noise and the wide bandwidth.

S -wave scattering lengths for the Be7+p system from an R -matrix analysis

The astrophysical $S$-factor for the radiative proton capture reaction on $^7$Be ($S_{17}$) at low energies is affected by the $s$-wave scattering lengths. We report the measurement of elastic and inelastic scattering cross sections for the $^7$Be+p system in the center-of-mass energy range 0.474 - 2.740 MeV and center-of-mass angular range of 70$^\circ$- 150$^\circ$. A radioactive $^7$Be beam produced at Oak Ridge National Laboratory's (ORNL) Holifield Radioactive Ion Beam Facility was accelerated and bombarded a thin polypropylene (CH$_{2}$)$_\text n$ target. Scattered ions were detected in the segmented Silicon Detector Array. Using an $\textit{R}$-matrix analysis of ORNL and Louvain-la-Neuve cross section data, the $s$-wave scattering lengths for channel spins 1 and 2 were determined to be 17.34$^{+1.11}_{-1.33}$ and -3.18$^{+0.55}_{-0.50}$ fm, respectively. The uncertainty in the $s$-wave scattering lengths reported in this work is smaller by a factor of 5-8 compared to the previous measurement, which may reduce the overall uncertainty in $S_{17}$ at zero energy. The level structure of $^8$B is discussed based upon the results from this work. Evidence for the existence of 0$^+$ and 2$^+$ levels in $^8$B at 1.9 and 2.21 MeV, respectively, is observed.