Thin Silicon Detectors Research Articles

Monitoring of carbon ion therapeutic beams with thin silicon sensors

Single ion counting in particle therapy may lead to new beam monitoring systems, enabling innovative delivery strategies that are faster and more sensitive than those currently used in clinics. Previous studies carried out by the University and the National Institute of Nuclear Physics (INFN) of Turin have demonstrated the feasibility of using thin silicon detectors to count single protons in clinical beams. The aim of this work is to report the performance of a strip-segmented 60-μm thick silicon PIN sensor used for single carbon ion discrimination. All measurements were performed using the CNAO synchrotron at different beam energies covering the clinical energy range (115–399 MeV/u). Signals from the sensor strips were read using a custom amplifier board and sampled with a 5 GS/s digitizer. The carbon ion signals were analyzed in terms of amplitude, duration, and deposited charge at different sensor bias voltages.

First measurements with a new β-electron detector for spectral shape studies

The shape of the electron spectrum emitted in β decay carries a wealth of information about nuclear structure and fundamental physics. In spite of that, few dedicated measurements have been made of β-spectrum shapes. In this work we present a newly developed detector for β electrons based on a telescope concept. A thick plastic scintillator is employed in coincidence with a thin silicon detector. The first measurements employing this detector have been carried out with mono-energetic electrons from the high-energy resolution electron-beam spectrometer at Bordeaux. Here we report on the good reproduction of the experimental spectra of mono-energetic electrons using Monte Carlo simulations. This is a crucial step for future experiments, where a detailed Monte Carlo characterization of the detector is needed to determine the shape of the β-electron spectra by deconvolution of the measured spectra with the response function of the detector. A chamber to contain two telescope assemblies has been designed for future β-decay experiments at the Ion Guide Isotope Separator On-Line facility in Jyväskylä, aimed at improving our understanding of reactor antineutrino spectra.

High-precision 4D tracking with large pixels using thin resistive silicon detectors

The basic principle of operation of silicon sensors with resistive read-out is built-in charge sharing. Resistive Silicon Detectors (RSD, also known as AC-LGAD), exploiting the signals seen on the electrodes surrounding the impact point, achieve excellent space and time resolutions even with very large pixels. In this paper, a TCT system using a 1064 nm picosecond laser is used to characterize RSD sensors produced by Fondazione Bruno Kessler. The paper first introduces the parametrization of the errors in the determination of the position and time coordinates in RSD, then outlines the reconstruction method, and finally presents the results. Three different pixel pitches are used in the analysis: 200 × 340, 450 × 450, and 1300 × 1300 μm2. At gain = 30, the 450 × 450 μm2 pixel achieves a time jitter of 20 ps and a spatial resolution of 15 μm concurrently, while the 1300 × 1300 μm2 pixel achieves 30 ps and 30 μm, respectively. The implementation of cross-shaped electrodes improves considerably the response uniformity over the pixel surface.

Characterizing Low-Energy Charged Particles in the Magnetosphere with the LEM CubeSat Spectrometer Project: Detector Concept and Hardware Characterisation

An accurate flux measurement of low-energy charged particles trapped in the magnetosphere is necessary for space weather characterization and to study the coupling between the lithosphere and magnetosphere, which allows for the investigation of the correlations between seismic events and particle precipitation from Van Allen belts. In this work, the project of a CubeSat space spectrometer, the low-energy module (LEM), is shown. The detector will be able to perform an event-based measurement of the energy, arrival direction, and composition of low-energy charged particles down to 0.1 MeV. Moreover, thanks to a CdZnTe mini-calorimeter, the LEM spectrometer also allows for photon detection in the sub-MeV range, joining the quest for the investigation of the nature of gamma-ray bursts (GRBs) and terrestrial gamma-ray flashes (TGFs). The particle identification of the LEM relies on the ΔE−E technique performed by thin silicon detectors. This multipurpose spectrometer will fit within a 10 × 10 × 10 cm3 CubeSat frame, and it will be constructed as a joint project between the University of Trento, FBK, and INFN-TIFPA. To fulfil the size and mass requirements, an innovative approach, based on active particle collimation, was designed for the LEM; this avoids the heavy/bulky passive collimators of previous space detectors. In this paper, we will present the LEM geometry, its detection concept, the results from the developed GEANT4 simulation, and some characterisations of a candidate silicon detector for the instrument payload.

Beam test results of 25 and 35 mum thick FBK ultra-fast silicon detectors

This paper presents the measurements on first very thin Ultra-Fast Silicon Detectors (UFSDs) produced by Fondazione Bruno Kessler; the data have been collected in a beam test setup at the CERN PS, using beam with a momentum of 12 GeV/c. UFSDs with a nominal thickness of 25 and 35 mum and an area of 1 times 1 text {mm}^2 have been considered, together with an additional HPK 50-mum thick sensor, taken as reference. Their timing performances have been studied as a function of the applied voltage and gain. A time resolution of about 25 ps and of 22 ps at a voltage of 120 and 240 V has been obtained for the 25 and 35 mum thick UFSDs, respectively.

Inter-pad dead regions of irradiated FBK Low Gain Avalanche detectors

Low Gain Avalanche Detectors (LGADs) are a type of thin silicon detector with a highly doped gain layer. LGADs manufactured by Fondazione Bruno Kessler (FBK) were tested before and after irradiation with neutrons. In this study, the inter-pad dead regions (IPDRs), defined as the width of the distances between pads, were measured with a TCT laser system. The response of the laser was tuned using β-particles from a 90Sr source. These insensitive “dead zones” are created by a protection structure to avoid breakdown, the Junction Termination Extension (JTE), which separates the pads. The effect of neutron radiation damage at 1.5 × 1015 neq/cm2, and 2.5 × 1015 neq/cm2 on IPDRs was studied. These distances are compared to the nominal distances given from the vendor, it was found that at the high fluence there is a better matching of the insensitive region to the designed inter-pad region.

An LGAD-Based Full Active Target for the PIONEER Experiment

PIONEER is a next-generation experiment to measure the charged pion branching ratios to electrons vs. muons Re/μ=Γπ+→e+ν(γ)Γπ+→μ+ν(γ) and pion beta decay (Pib) π+→π0eν. The pion to muon decay (π→μ→e) has four orders of magnitude higher probability than the pion to electron decay (π→eν). To achieve the necessary branching-ratio precision it is crucial to suppress the π→μ→e energy spectrum that overlaps with the low energy tail of π→eν. A high granularity active target (ATAR) is being designed to suppress the muon decay background sufficiently so that this tail can be directly measured. In addition, ATAR will provide detailed 4D tracking information to separate the energy deposits of the pion decay products in both position and time. This will suppress other significant systematic uncertainties (pulse pile-up, decay in flight of slow pions) to <0.01%, allowing the overall uncertainty in to be reduced to O (0.01%). The chosen technology for the ATAR is Low Gain Avalanche Detector (LGAD). These are thin silicon detectors (down to 50 μm in thickness or less) with moderate internal signal amplification and great time resolution. To achieve a 100% active region several emerging technologies are being evaluated, such as AC-LGADs and TI-LGADs. A dynamic range from MiP (positron) to several MeV (pion/muon) of deposited charge is expected, the detection and separation of close-by hits in such a wide dynamic range will be a main challenge. Furthermore, the compactness and the requirement of low inactive material of the ATAR present challenges for the readout system, forcing the amplifier chip and digitizer to be positioned away from the active region.

Thin silicon solid-state detectors for energetic particle measurements

Context. Silicon solid-state detectors are commonly used for measuring the specific ionization, dE∕dx, in instruments designed for identifying energetic nuclei using the dE∕dx versus total energy technique in space and in the laboratory. The energy threshold and species resolution of the technique strongly depend on the thickness and thickness uniformity of these detectors. Aims. Research has been carried out to develop processes for fabricating detectors that are thinner than 15 μm, that have a thickness uniformity better than 0.2 μm over cm2 areas, and that are rugged enough to survive the acoustic and vibration environments of a spacecraft launch. Methods. Silicon-on-insulator wafers that have a device layer of the desired detector thickness supported by a thick handle layer were used as starting material. Standard processing techniques were used to fabricate detectors on the device layer, and the underlying handle-layer material was etched away leaving a thin, uniform detector surrounded by a thick, supporting frame. Results. Detectors as thin as 12 μm were fabricated in two laboratories and successfully subjected to environmental and performance tests. Two detector designs were used in the High-energy Energetic Particles Instrument, which is part of the Integrated Science Investigation of the Sun instrument suite on NASA’s Parker Solar Probe spacecraft. These detectors have been performing well for more than two years in space. Conclusions. Thin silicon detectors in d E∕dx versus total energy instruments enable the identification of nuclei with energies down to ~1 MeV nuc−1. This research suggests that detectors at least a factor of two thinner should be achievable using this fabrication technique.

A new detector for the beam energy measurement in proton therapy: a feasibility study

The proof of concept of a new device, capable of determining in a few seconds the energy of clinical proton beams by measuring the time of flight (ToF) of protons, is presented. The prototype consists of two thin ultra fast silicon detector (UFSD) pads, aligned along the beam direction in a telescope configuration and readout by a digitizer. The method developed for extracting the energy at the isocenter from the measured ToF, validated by Monte Carlo simulations, and the procedure used to calibrate the system are also presented and discussed in detail. The prototype was tested at the Centro Nazionale di Adroterapia Oncologica (CNAO, Pavia, Italy), at several beam energies, covering the entire clinical range, and using different distances between the sensors. The measured beam energies were benchmarked against the nominal CNAO energy values, obtained during the commissioning of the centre from the measured ranges in water. Deviations of few hundreds of keV have been achieved for all considered proton beam energies for distances between the two sensors larger than 60 cm, indicating a sensitivity to the corresponding beam range in water smaller than the clinical tolerance of 1 mm. Moreover, few seconds of irradiation were necessary to collect the required statistics. These preliminary results indicate that a telescope of UFSDs could achieve in a short time the accuracy required for the clinical application and therefore encourage further investigations towards the improvement and the optimization of the present prototype.

Test of innovative silicon detectors for the monitoring of a therapeutic proton beam

Beam monitoring in particle therapy is a critical task that, because of the high flux and the time structure of the beam, can be challenging for the instrumentation. Recent developments in thin silicon detectors with moderate internal gain, optimized for timing applications (Ultra Fast Silicon Detectors, UFSD), offer a favourable technological option to conventional ionization chambers. Thanks to their fast collection time and good signal-to-noise ratio, properly segmented sensors allow discriminating and counting single protons up to the high fluxes of a therapeutic beam, while the excellent time resolution can be exploited for measuring the proton beam energy using time-of-flight techniques. We report here the results of the first tests performed with UFSD detector pads on a therapeutic beam. It is found that the signal of protons can be easily discriminated from the noise, and that the very good time resolution is confirmed. However, a careful design is necessary to limit large pile-up inefficiencies and early performance degradation due to radiation damage.

Optimization of an ultra-fast silicon detector for proton and carbon beams using GEANT4 Monte Carlo toolkit.

The purpose of this study was to investigate the crosstalk effects between adjacent pixels in a thin silicon detector with 50um thickness. There are some limitations in the applications of detectors in hadron therapy. So it is necessary to have a detector with concurrent excellent time and resolution. In this work, the GEANT4 toolkit was applied to estimate the best value for energy cutoff in the thin silicon detector in order to optimize the detector. GEANT4 toolkit was applied to simulate the transport and interactions of particles. Calculations were performed for a thin silicon detector (2cm×2cm×0.005cm) irradiated by proton and carbon ion beams. A two-dimensional array of silicon pixels in the x-y plane with 100um×100um×50um dimensions build the whole detector. In the end, the ROOT package is used to interpret and analyze the results. It is seen that by the presence of energy cutoff, pixels with small deposited energy are ignored. The best values for energy cutoff are 0.01MeV and 0.7MeV for proton and carbon ion beams, respectively. By applying these energy cutoff values, efficiency and purity values are maximized and also minimum output errors are achieved. The results are reasonable, good and useful to optimize the geometry of future silicon detectors in order to be used as beam monitoring in hadron therapy applications.

Measurements of radiation quality factor on Mars with the Mars Science Laboratory Radiation Assessment Detector

We report the first long-term measurements of the radiation quality factor of energetic charged particles on the surface of Mars. The Radiation Assessment Detector (RAD) aboard the Mars Science Laboratory rover, also known as Curiosity, has been operating on Mars since 2012. RAD contains thin silicon detectors that record the ionization energy loss of energetic charged particles. The particles are dominantly galactic cosmic rays (GCRs) and the products of their interactions in the Martian atmosphere, with occasional contributions from solar energetic particles (SEPs). The quality factor on the surface of Mars is influenced by two factors: variations in the shielding provided by the atmosphere, and changes in the spectrum of the incident energetic particle flux due to the 11-year solar cycle. The two cannot be easily disentangled using the data alone, but insights can be gained from calculations and Monte Carlo simulations.

The determination of the astrophysical S-factor of the direct 18O(p,$\gamma$)19F capture by the ANC method

The depletion of 18O via the $(\mathrm{p},\gamma)$ capture competes with the $(\mathrm{p}, \alpha)$ capture during the CNO cycles in AGB stars. Despite the fact that the $(\mathrm{p}, \alpha)$ capture is dominant, the $ (\mathrm{p}, \gamma)$ can play an important role in mixing stages of the AGB star evolution. Here, we attempt to determine the astrophysical S-factor of the direct part of the 18O(p,$\gamma$)19F capture by the indirect method of asymptotic normalization coefficients (ANC). We measure the differential cross section of the transfer reaction 18O(3He, d)19F at a 3He energy of 24.6 MeV. The measurement was performed on the cyclotron of the CANAM infrastructure of NPI in Řež, Czech Republic, with the gas target consisting of the high-purity 18O (99.9%). The reaction products were measured by eight $ \Delta E$-E telescopes composed of thin and thick silicon surface-barrier detectors. The parameters of the optical model for the input channel were deduced by means of the code ECIS and the analysis of transfer reactions to 12 levels of the 19F nucleus up to 8.014 MeV was made by the code FRESCO. The deduced ANCs were then used to specify the direct contribution to the 18O(p,$\gamma$)19F capture process and were compared with the mutually different results of two works.

352. Innovative thin silicon detectors for beam monitoring in particle therapy

Purpose For beam monitoring in particle therapy, silicon detectors could overcome the limitations of ionization chambers. In particular, silicon sensors with internal gain (Ultra Fast Silicon Detectors, UFSDs) provide high signal-to-noise ratio and fast collection times ( ∼1 ns in 50 μm thickness). A segmented sensor could allow discriminating and counting single protons up to high fluxes of therapeutic beams. Moreover, the excellent time resolution suggests using time-of-flight techniques for measuring the proton beam energy. Materials and Methods Several 50 μm thick UFSD prototypes, both single pads or segmented in strips, doped with Boron or Gallium, and with different doping concentrations were fully characterized at the Turin university laboratory and tested on the clinical proton beam of the CNAO particle therapy facility, up to fluxes of 109 p/s. Signal-to-noise ratio, pileup probability, internal gain and gain degradation with beam fluence were determined from the offline analysis of the collected waveforms and compared, whenever possible, to the laboratory measurements. Conclusions UFSDs are found to be a viable option for improving the qualification and the monitoring of a therapeutic proton beams. However, a careful design is necessary to avoid large pileup inefficiencies and early performance degradation.

Time-of-flight spectrometry of ultra-short, polyenergetic proton bunches.

A common approach for spectrum determination of polyenergetic proton bunches from laser-ion acceleration experiments is based on the time-of-flight (TOF) method. However, spectra obtained using this method are typically given in relative units or are estimated based on some prior assumptions on the energy distribution of the accelerated ions. In this work, we present a new approach using the TOF method that allows for an absolute energy spectrum reconstruction from a current signal acquired with a sub-nanosecond fast and 10 µm thin silicon detector. The reconstruction is based on solving a linear least-squares problem, taking into account the response function of the detection system. The general principle of signal generation and spectrum reconstruction by setting up an appropriate system response matrix is presented. Proof-of-principle experiments at a 12 MV Tandem accelerator using different nanosecond-short (quasi-)monoenergetic and polyenergetic proton bunches at energies up to 20 MeV were successfully performed. Within the experimental uncertainties of 2.4% and 12.1% for energy and particle number, respectively, reconstructed energy distributions were found in excellent agreement with the spectra calculated using Monte Carlo simulations and measured by a magnetic spectrometer. This TOF method can hence be used for absolute online spectrometry of laser-accelerated particle bunches.

Innovative thin silicon detectors for monitoring of therapeutic proton beams: preliminary beam tests

To fully exploit the physics potentials of particle therapy in delivering dose with high accuracy and selectivity, charged particle therapy needs further improvement. To this scope, a multidisciplinary project (MoVeIT) of the Italian National Institute for Nuclear Physics (INFN) aims at translating research in charged particle therapy into clinical outcome. New models in the treatment planning system are being developed and validated, using dedicated devices for beam characterization and monitoring in radiobiological and clinical irradiations. Innovative silicon detectors with internal gain layer (LGAD) represent a promising option, overcoming the limits of currently used ionization chambers. Two devices are being developed: one to directly count individual protons at high rates, exploiting the large signal-to-noise ratio and fast collection time in small thicknesses (1 ns in 50 μm) of LGADs, the second to measure the beam energy with time-of-flight techniques, using LGADs optimized for excellent time resolutions (Ultra Fast Silicon Detectors, UFSDs). The preliminary results of first beam tests with therapeutic beam will be presented and discussed.

Characterization and optimization of a thin direct electron detector for fast imaging applications

Direct electron detectors are increasingly used to explore the dynamics of macromolecules in real space and real time using transmission electron microscopy. The purpose of this work is to optimize the most suitable detector configuration of a thin silicon detector by Monte Carlo Simulations. Several simulations were performed to achieve an advanced detector geometry that reduces significantly the background signal due to backscattered electrons resulting in an enhanced imaging performance of the detector. Utilizing DEPFET (DEpleted P-channel Field Effect Transistor) technology and the novel ideas for the optimized detector geometry, a unique direct hit electron detector is currently being produced.

The astrophysical S-factor of the direct 18O(p, γ)19F capture by the ANC method

We attempted to determine the astrophysical S-factor of the direct part of the 18 O(p, γ )19 F capture by the indirect method of asymptotic normalization coefficients (ANC). We measured the differential cross section of the transfer reaction 18 O(3 He, d)19 F at a 3 He energy of 24.6 MeV. The measurement was realized on the cyclotron of the NPI in Řež, Czech Republic, with the gas target consisting of the high purity 18 O (99.9 %). The reaction products were measured by eight ∆E-E telescopes composed from thin and thick silicon surface-barrier detectors. The parameters of the optical model for the input channel were deduced by means of the code ECIS and the analysis of transfer reactions to 12 levels of the 19 F nucleus up to 8.014 MeV was made by the code FRESCO. The deduced ANCs were then used to specify the direct contribution to the 18 O(p, γ )19 F capture process and were compared with the mutually different results of two works.

Fabrication of a thin silicon detector with excellent thickness uniformity

We have fabricated and tested a thin silicon detector with the specific goal of having a very good thickness uniformity. SOI technology was used in the detector fabrication. The detector was designed to be used as a ΔE detector in a silicon telescope for measuring solar energetic particles in space. The detector thickness was specified to be 20μm with an rms thickness uniformity of±0.5%. The active area consists of three separate elements, a round centre area and two surrounding annular segments. A new method was developed for measuring the thickness uniformity based on a modified Fizeau interferometer. The thickness uniformity specification was well met with the measured rms thickness variation of 43nm. The detector was electrically characterized by measuring the I–V and C–V curves and the performance was verified using a 241Am alpha source.

Back-thinning process research and characteristics measurement of thin sensor

It is important to develop a thin silicon detector using a large silicon wafer to reduce multiple Coulomb scattering and the material budget. A Si-CsI detector in a large acceptance multi-purpose spectrometer (LAMPS) is considered to identify isotopes. The thickness of the first of three silicon sensors in front of the CsI(Tl) crystal is 100 μm. We aim to establish a manufacturing process for thinning using a 6-inch silicon wafer that provides the characteristics of a photodiode. In this paper, we present a back-thinning process of the photodiode, and comparisons of its electrical characteristics and signal-to-noise ratios before and after the thinning process.