High Energy and Thermal Neutrons Sensitivity of Google Tensor Processing Units

In this article, we investigate the reliability of Google’s coral tensor processing units (TPUs) to both high-energy atmospheric neutrons (at ChipIR) and thermal neutrons from a pulsed source [at equipment materials and mechanics analyzer (EMMA)] and from a reactor [at Thermal and Epithermal Neutron Irradiation Station (TENIS)]. We report data obtained with an overall fluence of 3.41×1012n/cm2 for atmospheric neutrons (equivalent to more than 30 million years of natural irradiation) and of 7.55×1012n/cm2 for thermal neutrons. We evaluate the behavior of TPUs executing elementary operations with increasing input sizes (standard convolutions or depthwise convolutions) as well as eight convolutional neural networks (CNNs) configurations (single-shot multibox detection (SSD) MobileNet v2 and SSD MobileDet, trained with COCO dataset, and Inception v4 and ResNet-50, with ILSVRC2012 dataset). We found that, despite the high error rate, most neutron-induced errors only slightly modify the convolution output and do not change the detection or classification of CNNs. By reporting details about the error model, we provide valuable information on how to design the CNNs to avoid neutron-induced events to lead to misdetections or classifications

Optimisation of Storage Rings and RF Accelerators via Advanced Optical-Fibre Based Detectors

In particle accelerators, diverse causes may lead to the unwanted deviation of the beam particles from the nominal beam orbit and their loss in the machine. To protect from danger- ous beam losses and provide valuable information on the accelerator operation, Beam Loss Monitors (BLMs) are being employed. Conventional BLMs are localised detectors, with a wide range of characteristics, depending on which, the appropriate monitor for each application is selected. The optical fibre BLM is an alternative type of detector, used and examined in various facilities for its ability to cover and effectively protect long parts (of the order of 100 m) of an accelerator. The Compact Linear Collider (CLIC) is a proposal for a future $e^− − e^+$ collider, based on the simultaneous operation of two parallel beam lines, aiming to reach a 3 TeV center of mass energy at approximately 48 km of machine length. In the present work an optical fibre based detector was developed, consisting of a quartz optical fibre coupled with an Silicon Photon Multiplier (SiPM), to be studied as a beam loss monitor for RF accelerators, such as CLIC, and storage rings. A dedicated housing was fabri- cated for the photosensor and the related electronics, which optimised the system in terms of sensitivity, low noise and robustness. Instead of the most commonly used, for such detectors, Photo Multiplier Tubes (PMTs), this study made use of the SiPMs taking advantage of their insensitivity to magnetic fields and their efficiency in terms of cost and required power. The developed system was characterised for its capabilities as a BLM in the CLIC Test Facility 3 (CTF3) and in the Australian Synchrotron Light Source (ASLS). A remarkable intrinsic time resolution of 260 ps was measured, and a discrimination in beam losses with a 25 cm spacing between them was demonstrated for single bunch beams. For 350 ns long electron beams, in order to distinguish simultaneous beam losses on different locations, a distance of 3 m between them was required. The ability of the detector to monitor steady state losses was validated, and a method to assess all beam loss locations utilising only one initially identified, was demonstrated. The limitations introduced to BLMs from the beam loss crosstalk effect in parallel beam lines was investigated, while the sensitivity limitations induced by the RF cavity electron field emission background were estimated as not significant. The optical fibre based detector, combined with appropriate localised detectors at high risk locations, was proven a promising system for the monitoring of beam losses, for both linear accelerators and storage rings. Finally, a modified, highly sensitive version of the detector was introduced as an advanced RF cavity diagnostics tool. This was proven able of monitoring RF breakdowns and field emitted electrons along with estimating the Fowler-Nordheim field enhancement factor. Additionally, both measurements and simulations confirmed the presence of high energy electrons in the radiation environment of accelerating structures due to electron field emission

Study of MicroMegas Detector in neutron and photon field with the simulation toolkit Geant4

119 σ.Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Φυσική και Τεχνολογικές Εφαρμογές”Οι ανιχνευτές αερίου, βασισμένοι στην τεχνολογία του MicroMegas, χρησιμοποιούνται ευρέως σε διάφορα πειράματα ατομικής, πυρηνικής και σωματιδιακής φυσικής. Επιπλέον έχουν ιδιαίτερα χαμηλό κόστος κατασκευής, παρουσιάζουν ανθεκτικότητα σε περιβάλλον υψηλής ακτινοβολίας, ενώ συνδυάζουν ικανότητες σκανδαλισμού και προσδιορισμού τροχιάς. Οι παραπάνω ιδιότητες τους καθιστούν ιδανικούς υπ[οψήφιους για την αναβάθμιση του συστήματος ανίχνευσης μιονίων, ως αντικαταστάτες των ανιχνευτών Cathode Strip Chabmers(CSC), του πειράματος ATLAS. Στο πείραμα αυτό συγκρούονται δέσμες πρωτονίων με αποτέλεσμα την παραγωγή καταιγισμό σωματιδίων, συμπεριλαμβανομένων νετρονίων. Για τον λόγο αυτό είναι απραίτητη η μελέτη της συμπεριφοράς του MicroMegas σε περιβάλλον νετρονίων έτσι ώστε να προβλεφθεί η απόκριση του ανιχνευτή στον σωματιδιακό θόρυβο, δεδομένου ότι το ενδιαφέρον εστιάζεται στην ανίχνευση μιονίων. Για τις ανάγκες της μελέτης χρησιμοποιήθηκε το πακέτο προσομοίωσης Monte Carlo, Geant4 με το οποίο μελετήθηκε η εναπόθεση ενέργειας νετρονίων 5.5MeV σε δύο διαφορετικούς τύπους ανιχνευτή microMegas, σε διαφορετικές αναλογίες αερίου και σε διαφορετικές κατευθύνσεις. Επίσης πραγματοποιήθηκε εικονικό πείραμα με φωτόνια χαμηλών ενεργειών, προκειμένου να μελετηθεί η λειτουργία του ανιχνευτή σε τέτοια πεδία καθώς και η σημαντική συμβολή των υλικών κατασκευής του.Gaseous detectors based on the Micromegas principle have already been used in several atomic, nuclear and particle physics experiments. Moreover, they have low construction cost and are resistant to high levels of radiation. They also succeed in combining triggering and tracking properties. Consequently, they provide an excellent candidate for replacing the Cathode Strip Chambers (CSC) of the ATLAS muon spectrometer in the very forward/backward region. In the ATLAS experiment, two proton beams collide, producing article showers, including neutrons. Therefore it is vital that the performance of the detectors in a neutron radiation field be studied, in order to redict the response of the detector to the particle "noise", taking into consideration the fact that the purpose of the detector is to detect muons. To meet this end, the MonteCarlo simulation toolkit Geant4 has been utilized in the present work, in order to study the energy eposition of 5.5 MeV neutrons on two different types of Micromegas detectors, with different proportion of gases and at different direction. n addition to that, a virtual experiment with low energy photons has been held, in order to study the function of the detector in such fields as well as the significant contribution of its construction materials.Μαρία Μ. Καστριώτο

Impact of Temperature on Neutron Irradiation Failure-in-Time of Silicon and Silicon Carbide Power MOSFETs

Accelerated neutron tests on silicon (Si) and silicon carbide (SiC) power MOSFETs at different temperatures and drain bias voltages were performed at the ChipIr facility (Didcot, UK). A super-junction silicon MOSFET and planar SiC MOSFETs with different technologies made by STMicroelectronics were used. Different test methods were employed to investigate the effects of temperature on neutron susceptibility in power MOSFETs. The destructive tests showed that all investigated devices failed via a single-event burnout (SEB) mechanism. Non-destructive tests conducted by using the power MOSFET as a neutron detector allowed measuring the temperature trend of the deposited charge due to neutron interactions. The results of the destructive tests, in the −50 °C–180 °C temperature range, revealed the lack of a common trend concerning the FIT temperature dependence among the investigated SiC power MOSFETs. Moreover, for some test vehicles, the FIT-temperature curves were dependent on the bias condition. The temperature dependence of the FIT values, observed in some SiC devices, is weaker with respect to that measured in the Si MOSFET. The results of the non-destructive tests showed a good correlation between the temperature trends of the deposited charge with those of FIT data, for both Si and SiC devices

Challenges of arbitrary waveform signal detection by Silicon Photomultipliers as readout for Cherenkov fibre based beam loss monitoring systems

Silicon Photomultipliers (SiPMs) are well recognised as very competitive photodetectors due to their exceptional photon number and time resolution, room-temperature low-voltage operation, insensitivity to magnetic fields, compactness, and robustness. Detection of weak light pulses of nanosecond time scale appears to be the best area for SiPM applications because in this case most of the SiPM drawbacks have a rather limited effect on its performance. In contrast to the more typical scintillation and Cherenkov detection applications, which demand information on the number of photons and/or the arrival time of the light pulse only, beam loss monitoring (BLM) systems utilising Cherenkov fibres with photodetector readout have to precisely reconstruct the temporal profile of the light pulse. This is a rather challenging task for any photon detector especially taking into account the high dynamic range of incident signals (100K – 1M) from a few photons to a few percents of destructive losses in a beam line and presumably an arbitrary temporal distribution of photons (localisation of losses). Nevertheless, a number of advantages and ongoing improvements of SiPM technology are considered to be a reasonable ground for this feasibility study of SiPM application in BLM systems. Transient SiPM responses to light pulses over a wide range of intensities have been measured and an analytical model has been applied to describe the results. Non-linearity of SiPMs due to the limited number of pixels and non-instant pixel recovery time is found to be a source of transient and history-dependent distortions of output signals

An Optical Fibre BLM System at the Australian Synchrotron Light Source

Increasing demands on high energy accelerators are triggering R&D into improved beam loss monitors with a high sensitivity and dynamic range and the potential to efficiently protect the machine over its entire length. Optical fibre beam loss monitors (OBLMs) are based on the detection of Cherenkov radiation from high energy charged particles. Bearing the advantage of covering more than 100m of an accelerator with only one detector and being insensitive to X-rays, OBLMs are ideal for electron machines. The Australian Synchrotron comprises an 100 MeV 15m long linac, an 130m circumference booster synchrotron and a 3 GeV, 216m circumference electron storage ring. The entire facility was successfully covered with four OBLMs. This contribution summarises a variety of measurements performed with OBLMs at the Australian Synchrotron, including beam loss measurements during the full booster and measurements of steady-state losses in the storage ring. Different photosensors, namely Silicon Photo Multipliers (SiPM) and fast Photo Multiplier Tubes (PMTs) have been used and their respective performance limits are discussed

Study of the Deposited Energy Spectra in Silicon by High-Energy Neutron and Mixed Fields

The energy deposition spectra in a silicon detector have been measured at chip irradiation (ChipIr) and Cern High energy AcceleRator Mixed field (CHARM) facilities. The measurement was possible thanks to a fast electronic chain that can cope with high instantaneous fluxes. A computational study of the energy deposition in a silicon detector allows for the comparison of high-energy spallation facilities dedicated to the irradiation of microelectronics and for the validation of radiation transport models. The measured time structure of the facilities pulses is also presented with an example on how to use this result to correct in the case of large dead times (DTs)

Thermal-to-high-energy neutron SEU characterization of commercial SRAMs

Several commercial SRAMs have been tested by the CERN R2E project with neutrons of various energy. The test data are used to cross-compare facilities and to analyze variabilities within SRAMs from the same manufacturer. FIT for atmospheric and ground applications are provided as well as predictions for accelerator soft error rates

Emulating the Effects of Radiation-Induced Soft-Errors for the Reliability Assessment of Neural Networks

Convolutional Neural Networks (CNNs) are currently one of the most widely used predictive models in machine learning. Recent studies have demonstrated that hardware faults induced by radiation fields, including cosmic rays, may significantly impact the CNN inference leading to wrong predictions. Therefore, ensuring the reliability of CNNs is crucial, especially for safety-critical systems. In the literature, several works propose reliability assessments of CNNs mainly based on statistically injected faults. This work presents a software emulator capable of injecting real faults retrieved from radiation tests. Specifically, from the device characterisation of a DRAM memory, we extracted event rates and fault models. The software emulator can reproduce their incidence and access their effect on CNN applications with a reliability assessment precision close to the physical one. Radiation-based physical injections and emulator-based injections are performed on three CNNs (LeNet-5) exploiting different data representations. Their outcomes are compared, and the software results evidence that the emulator is able to reproduce the faulty behaviours observed during the radiation tests for the targeted CNNs. This approach leads to a more concise use of radiation experiments since the extracted fault models can be reused to explore different scenarios (e.g., impact on a different application).peerReviewe

An Analysis of the Significance of the 14N(n, p) 14C Reaction for Single-Event Upsets Induced by Thermal Neutrons in SRAMs

The thermal neutron threat to the reliability of electronic devices caused by $^{10}\text{B}$ capture is a recognized issue that prompted changes in the manufacturing process of electronic devices with the aim of limiting as much as possible the presence of this isotope nearby device sensitive volumes (SVs). $^{14}\text{N}$ can also capture thermal neutrons and release low-energy protons (LEPs; through the $^{14}\text{N}$ (n, p) $^{14}\text{C}$ reaction) that have high enough linear energy transfer (LET) to cause single-event upsets (SEUs). Typically, nitrogen is used in thin barrier layers made of TaN or TiN or even as insulator in the form of Si3N4. Numerical simulations on SVs calibrated on proton and ion experimental data and with an accurate description of the metallization layer on top of the sensitive region show that the presence of nitrogen in these thin barrier layers can be enough to justify the experimentally observed thermal neutron SEU cross Section for a static random access memory (SRAM) sensitive to LEPs. Nevertheless, the expected SEU cross Section from thermal neutrons is usually a few orders of magnitude lower than that of high-energy particles, therefore, not representing an important threat in atmospheric applications. At the same time, for high-energy accelerators, the contribution to the total soft error rate (SER) could become substantial, though easy to handle by margins