Position-sensitive Silicon Detectors Research Articles

High event rate analysis technique for the dual-axis duo-lateral position-sensitive silicon detectors of FAUST

The dual-axis duo-lateral (DADL) position-sensitive silicon detector was developed to obtain precise position and energy information for detected charged particles. The Forward Array Using Silicon Technology (FAUST) is currently equipped with 68 DADL detectors backed by CsI(Tl) scintillators for the study of charged particle correlations in heavy-ion collisions where precise position and energy information is essential. When conventional signal processing electronics were used for the DADL detectors, a position dependence of the measured energy as well as distortions in the calculated particle positions were observed. In previous work, waveforms from the detector after preamplification were studied to better understand the features that give rise to these distortions; therein, a waveform analysis technique was developed to improve the energy resolution and linearity in position reconstruction. However, the reading and writing of waveforms for an entire detector array limits data collection rates and adds significant burden in data storage and analysis speed. In this work, the integrators of a Struck SIS3316 ADC were utilized to process 228Th source data to develop and optimize a new analysis method that captures the benefits of the waveform analysis technique while circumventing the waveform writing requirement. This integrator method – capable of 59keV (FWHM) energy resolution – was used in the collection of 35 MeV/nucleon 28Si + 12C collision data using FAUST to investigate exotic decays of highly excited highly deformed nuclei. In this data, a position resolution of 0.4mm (FWHM) was obtained for 25MeV α-particles; for α-particles near this energy that originate from 8Be ground state decays, a 8Be ground state width of 30keV (FWHM) was obtained. The impact of the energy-dependent DADL position resolution emergent from electronic noise on the quality of excited state measurement was modeled and compared to the experimental data.

SoC-FPGA based data acquisition system for position sensitive silicon detectors

The System-on-a-Chip Field-Programmable Gate Array (SoC-FPGA) based Data Acquisition System (DAQ) is an autonomous measurement system for the Silicon beam profilometer, the Silicon beam tracker and Silicon modules test benches at the Baryonic Matter at Nuclotron (BM@N) experiment. The DAQ system provides detector signals digitization, storage and transfer of packaged data to a computer, processing and visualization of decoded information. The system is composed of the multichannel Front-end Electronics (FEE), the SoC-FPGA based Control Unit Carried Board equipped with two 8 channels analog-to-digital converters (ADCs), the Control and Analysis Software (C&A Software). The paper presents the DAQ system structure, the SoC-FPGA design, and the Silicon beam tracker test results.

Intra- and inter-fraction relative range verification in heavy-ion therapy using filtered interaction vertex imaging

Heavy-ion therapy, particularly using scanned (active) beam delivery, provides a precise and highly conformal dose distribution, with maximum dose deposition for each pencil beam at its endpoint (Bragg peak), and low entrance and exit dose. To take full advantage of this precision, robust range verification methods are required; these methods ensure that the Bragg peak is positioned correctly in the patient and the dose is delivered as prescribed. Relative range verification allows intra-fraction monitoring of Bragg peak spacing to ensure full coverage with each fraction, as well as inter-fraction monitoring to ensure all fractions are delivered consistently. To validate the proposed filtered interaction vertex imaging (IVI) method for relative range verification, a 16O beam was used to deliver 12 Bragg peak positions in a 40 mm poly-(methyl methacrylate) phantom. Secondary particles produced in the phantom were monitored using position-sensitive silicon detectors. Events recorded on these detectors, along with a measurement of the treatment beam axis, were used to reconstruct the sites of origin of these secondary particles in the phantom. The distal edge of the depth distribution of these reconstructed points was determined with logistic fits, and the translation in depth required to minimize the χ 2 statistic between these fits was used to compute the range shift between any two Bragg peak positions. In all cases, the range shift was determined with sub-millimeter precision, to a standard deviation of the mean of 220(10) μm. This result validates filtered IVI as a reliable relative range verification method, which should be capable of monitoring each energy step in each fraction of a scanned heavy-ion treatment plan.

A new waveform analysis technique to extract good energy and position resolution from a dual-axis duo-lateral position-sensitive detector

The dual-axis duo-lateral position-sensitive silicon detector was developed to detect charged particles with high quality position and energy resolution. When these detectors were used with conventional signal processing electronics, an empirically determined correction was used to improve energy resolution. In this work, the waveforms from the detector after preamplification are studied in detail to investigate position information contained in the waveforms. A 7.22 MeV/nucleon alpha particle beam was impinged directly on a masked dual-axis duo-lateral detector. Data obtained using a 228Th alpha particle source was also used. By studying the waveform characteristics that give rise to the position-dependent distortions, a new summed trigger analysis method has been developed to significantly improve linearity in position reconstruction without sacrificing energy resolution.

Performance of position-sensitive resistive silicon detectors in the Forward Array Using Silicon Technology (FAUST)

The silicon telescopes of the Forward Array Using Silicon Technology (FAUST) have been recently upgraded with silicon detectors which use resistive charge-splitting to measure the position of charged particles. This is in addition to the measurement of the total energy that these charged particles deposit in the detector. The upgrade results in increased angular resolution with a much smaller number of signals than silicon strip detectors with similar resolution. A novel method of calibration has been used to demonstrate the efficacy of these position-sensitive detectors, and the detectors have been used in a commissioning experiment.

New segmented target for studies of neutron unbound systems

The study of neutron-unbound systems using invariant mass spectroscopy is often performed using low-intensity radioactive ion beams. Low reaction yields can be countered by using thick targets but at the expense of larger uncertainties in the reconstructed invariant mass. We present a new segmented target designed to address this trade-off. It is composed of three ∼4 mm thick passive beryllium targets interleaved between four 140μm thick position sensitive silicon detectors. In the first experiment to use this new system the half-life of two-neutron unbound 26O was measured to be T1∕2=5.0−2.2+1.7 (stat)±1.7 (syst) ps, which agrees with a previous measurement made by the MoNA Collaboration.

Study of position sensitive silicon detector (PSD) for SiW-ECAL at ILC

For the past few years we have been developing position sensitive silicon detectors (PSDs) which have an electrode at each of four corners so that incident position of a charged particle can be obtained with signal from the electrodes. It is expected that the position resolution of the silicon-tungsten electromagnetic calorimeter (SiW-ECAL) of the International Large Detector (ILD) will be improved by introducing PSDs to detection layers. In the previous production we found that the charge separation is not optimal due to the readout impedance. To solve the issue, we produced new PSDs with higher surface resistance with an additional resistive layer on the surface. We also implemented several techniques to decrease position distortion and increase signal-to-noise ratio which are essential for optimal position resolution. We present first measurements of the performance of one new PSD using a strontium 90 source, and using the Skiroc2-CMS ASIC.

Reasons for high charge collection efficiency of silicon detectors at HL-LHC fluences

Position sensitive silicon detectors are more resilient to radiation then predicted from extensive measurements over the R&D phase for Large Hadron Collider. It was demonstrated over the past few years that they can be successfully operated also at the upgraded LHC (HL-LHC) and even beyond. A review of silicon properties affecting charge collection after irradiation will be given with special emphasis on their changes in very harsh radiation environments such as HL-LHC. Mainly three reasons: charge multiplication, high electric fields in undepleted bulk and saturation of trapping probabilities lead to better than expected performance of the silicon detectors. Initial acceptor removal, important for novel detector technologies such as Low Gain Avalanche Detectors and depleted CMOS sensors, will be also addressed.

Radiation damage study of thin YAG:Ce scintillator using low-energy protons

Radiation hardness of a 50 μ m thin YAG:Ce scintillator in a form of dependence of a signal efficiency on 3.1 MeV proton fluence was measured and analysed using X-ray beam. The signal efficiency is a ratio of signals given by a CCD chip after and before radiation damage. The CCD chip was placed outside the primary beam because of its protection from damage which could be caused by radiation. Using simplified assumptions, the 3.1 MeV proton fluences were recalculated to:⋅ 150 MeV proton fluences with intention to estimate radiation damage of this sample under conditions at proton therapy centres during medical treatment, ⋅ 150 MeV proton doses with intention to give a chance to compare radiation hardness of the studied sample with radiation hardness of other detectors used in medical physics, ⋅ 1 MeV neutron equivalent fluences with intention to compare radiation hardness of the studied sample with properties of position sensitive silicon and diamond detectors used in nuclear and particle physics. The following results of our research were obtained. The signal efficiency of the studied sample varies slightly (± 3%) up to 3.1 MeV proton fluence of c. (4 − 8) × 1014 cm−2. This limit is equivalent to 150 MeV proton fluence of (5 − 9) × 1016 cm−2, 150 MeV proton dose of (350 − 600) kGy and 1 MeV neutron fluence of (1 − 2) × 1016 cm−2. Beyond the limit, the signal efficiency goes gradually down. Fifty percent decrease in the signal efficiency is reached around 3.1 MeV fluence of (1 − 2) × 1016 cm−2 which is equivalent to 150 MeV proton fluence of around 2 × 1018 cm−2, 150 MeV proton dose of around 15 MGy and 1 MeV neutron equivalent fluence of (4 − 8) × 1017 cm−2. In contrast with position sensitive silicon and diamond radiation detectors, the studied sample has at least two order of magnitude greater radiation resistance. Therefore, YAG:Ce scintillator is a suitable material for monitoring of primary beams of particles of ionizing radiation.

Integrated cooling channels in position-sensitive silicon detectors

We present an approach to construct position-sensitive silicon detectors with an integrated cooling circuit. Tests on samples demonstrate that a very modest liquid flow very effectively cool the devices up to a power dissipation of over 10 W/cm2. The liquid flow is found to have a negligible impact on the mechanical stability. A finite-element simulation predicts the cooling performance to an accuracy of approximately 10%.

An improved method of energy calibration for position-sensitive silicon detectors**Supported by ‘100 Person Project’ of the Chinese Academy of Sciences and the National Natural Science Foundation of China (11405224 and 11435014)

Energy calibration of resistive charge division-based position-sensitive silicon detectors is achieved by parabolic fitting in the traditional method, where the systematic variations of vertex and curvature of the parabola with energy must be considered. In this paper we extend the traditional method in order to correct the fitting function, simplify the procedure of calibration and improve the experimental data quality. Instead of a parabolic function as used in the traditional method, a new function describing the relation of position and energy is introduced. The energy resolution of the 8.088 MeV α decay of 213Rn is determined to be about 87 keV (FWHM), which is better than the result of the traditional method, 104 keV (FWHM). The improved method can be applied to the energy calibration of resistive charge division-based position-sensitive silicon detectors with various performances.

Measurements from The Heavy-Ion Telescope at The ISS Kibo Exposed Facility

Space radiation such as solar energetic particles, galactic cosmic rays (GCR), and trapped particles affect space activities. Heavy ions, in particular, have high linear energy transfer (LET) that exacerbates the risk of radiation exposure for astronauts and affects the electrical circuits of satellites. The Japan Aerospace Exploration Agency (JAXA) has operated the Space Environment Data Acquisition Equipment - Attached Payload (SEDA-AP) at the International Space Station (ISS) Japanese Experiment Module (Kibo) - Exposed Facility, since 2009. The heavy-ion telescope (HIT) is one of the SEDA-AP instruments, which comprises two position-sensitive silicon detectors and 16 silicon detectors. Based on the ΔE × E particle-identification method, HIT measures fluxes of energetic ions from Li to Fe and calculates the loss of energies at each sensor. The HIT results are consistent with the general GCR model and other ISS experiments in terms of elemental abundances and LET distributions. In addition, HIT might have detected heavy ions from a X5.4 solar flare. Moreover, there is the possibility of detecting the anomalous cosmic rays (ACR) from the ADEOS satellite observations; however, ACR was not observed because the pitch angle was not in the field of view of HIT or no distribution of ACR exists at 400 km altitude.

Silicon detectors for monitoring neutron beams in n-TOF beamlines.

During 2014, the second experimental area (EAR2) was completed at the n-TOF neutron beam facility at CERN (n-TOF indicates neutron beam measurements by means of time of flight technique). The neutrons are produced via spallation, by means of a high-intensity 20 GeV pulsed proton beam impinging on a thick target. The resulting neutron beam covers the energy range from thermal to several GeV. In this paper, we describe two beam diagnostic devices, both exploiting silicon detectors coupled with neutron converter foils containing (6)Li. The first one is based on four silicon pads and allows monitoring of the neutron beam flux as a function of the neutron energy. The second one, in beam and based on position sensitive silicon detectors, is intended for the reconstruction of the beam profile, again as a function of the neutron energy. Several electronic setups have been explored in order to overcome the issues related to the gamma flash, namely, a huge pulse present at the start of each neutron bunch which may blind the detectors for some time. The two devices were characterized with radioactive sources and also tested at the n-TOF facility at CERN. The wide energy and intensity range they proved capable of sustaining made them attractive and suitable to be used in both EAR1 and EAR2 n-TOF experimental areas, where they became immediately operational.

A method to simulate the observed surface properties of proton irradiated silicon strip sensors

During the scheduled high luminosity upgrade of the LHC, the world's largest particle physics accelerator at CERN, the position sensitive silicon detectors installed in the vertex and tracking part of the CMS experiment will face a more intense radiation environment than the present system was designed for. To upgrade the tracker to the required performance level, extensive measurements and simulation studies have already been carried out. A defect model for the bulk properties of proton irradiated silicon has been created with the Synopsys Sentaurus TCAD simulation package which produces simulated results that closely match the measured properties of silicon strip detectors. However, the expected behaviour due to increased surface damage is not so well predicted by the model. The solution requires an approach that does not affect the accurate bulk properties produced by the proton model, but only adds to it the required radiation induced properties close to the surface. These include the observed position dependence of the strip detector's charge collection efficiency (CCE). In this paper a procedure to find a defect model that reproduces the correct CCE loss, along with other surface properties of a strip detector up to a fluence 1.5×1015 1 MeV neq cm−2 (Φeq), will be presented. When applied to CCE loss measurements at different fluences, this method may provide a means for the parametrization of the accumulation of oxide charge at the SiO2/Si interface as a function of dose.

Automation of experiments at the Dubna gas-filled separator of recoil nuclei: Part II

An application developed in Builder C++ (Windows) for the offline analysis of experimental data from the spectrometer of the gas-filled separator of recoil nuclei (Flerov Laboratory of Nuclear Reactions) based on the double-sided silicon strip detector is discussed. The automatic express method developed for calibrating 48 strips of the silicon position-sensitive detector based on the three most energetic spectral lines from the natYb + 48Ca▭*Th reaction is compared to the results produced by more rigorous calibration methods. The examples of spectra for this reaction and the results of filtering for the proposed calibration algorithm are given.

Charge collection efficiency simulations of irradiated silicon strip detectors

During the scheduled high luminosity upgrade of LHC, the world's largest particle physics accelerator at CERN, the position sensitive silicon detectors installed in the vertex and tracking part of the CMS experiment will face a more intense radiation environment than the present system was designed for. Thus, to upgrade the tracker to the required performance level, comprehensive measurements and simulation studies have already been carried out.Essential information of the performance of an irradiated silicon detector is obtained by monitoring its charge collection efficiency (CCE). From the evolution of CCE with fluence, it is possible to directly observe the effect of the radiation induced defects on the ability of thedetector to collect charge carriers generated by traversing minimum ionizing particles (MIPs).In this paper the numerically simulated CCE and CCE loss between the strips of irradiated silicon strip detectors are presented. The simulations based on the Synopsys Sentaurus TCAD framework were performed before and after irradiation for fluences up to 1.5 × 1015 neqcm−2 for n-on-p sensors. A two level defect model and non-uniform three level defect model were applied for the proton irradiation simulations, and a two levelmodel for neutrons. The results are presented together with the measurements of strip detectorsirradiated by different particles and fluences and show considerable agreement for both CCE and its position dependency.

Color sensing ability of an amorphous silicon position sensitive detector array system

The color sensing ability of a data acquisition prototype system integrating a 32 linear array of 1D amorphous silicon position sensitive detectors (PSD) was analyzed. Besides being used to reproduce a 3D profile of highly reflective surfaces, here we show that it can also differentiate primary red, green, blue (RGB) and derived colors. This was realized by using an incident beam with a RGB color combination and adequate integration times taking into account that a color surface mostly reflects its corresponding color. A mean colorimetric error of 25.7 was obtained. Overall, we show that color detection is possible via the use of this sensor array system, composed by a simpler amorphous silicon pin junction.

α-decay studies of the francium isotopes198Fr and199Fr

Very neutron deficient francium isotopes have been produced in fusion evaporation reactions using ${}^{60}$Ni ions on ${}^{141}$Pr targets. The gas-filled recoil separator RITU was employed to collect the fusion products and to separate them from the scattered beam. The activities were implanted into a position sensitive silicon detector after passing through a gas-counter system. The isotopes were identified using spatial and time correlations between the implants and the decays. Two $\ensuremath{\alpha}$-particle activities, with ${E}_{\ensuremath{\alpha}}=7613(15)$ keV and ${T}_{1/2}$ $=$ (${15}_{\ensuremath{-}5}^{+12}$) ms and ${E}_{\ensuremath{\alpha}}=7684(15)$ keV and ${T}_{1/2}$ $=$ (${16}_{\ensuremath{-}5}^{+13}$) ms were identified in the new isotope ${}^{198}$Fr. In addition, the half-life and $\ensuremath{\alpha}$-particle energy of ${}^{199}$Fr were measured with improved precision. The measured decay properties deduced for ${}^{199}$Fr and ${}^{198}$Fr suggest that there is an onset of ground-state deformation at $N=112$ in the Fr isotopes.

A detection system with broad angular acceptance for particle identification and angular distribution measurements

A new detection system for time-optimized heavy-ion angular distribution measurements has been designed and constructed. This device is composed by an ionization chamber with a segmented-grid anode and three position-sensitive silicon detectors. This particular arrangement allows identifying reaction products emitted within a 30° wide angular range with better than 1° angular resolution. As a demonstration of its capabilities, angular distributions of the elastic scattering cross-section and the production of alpha particles in the 7Li+27Al system, at an energy above the Coulomb barrier, are presented.

Recent Experimental Results from HELIOS

The renewed emphasis on nuclear structure far from stability, studied with nucleon-transfer reactions that utilize radioactive beams, has led to many new and exciting results. Accompanying these developments are, however many technical challenges that confront studies of transfer reactions in inverse kinematics. Amongst these are the identification of reaction products and the resolution of states in the residual nuclei. A new device, HELIOS (the HELIcal Orbit Spectrometer) has been constructed to solve many of the problems encountered with such reactions. The device uses a uniform magnetic field produced by a large, superconducting solenoid to transport light reaction products from the target to a linear array of position-sensitive silicon detectors. In operation since August of 2008, HELIOS has been used to study a variety of (d,p) reactions with beams of stable and unstable ions with masses ranging from A=11 to 136.