Neutron Irradiation Tests Research Articles

Neutron irradiation test of depleted CMOS pixel detector prototypes

Charge collection properties of depleted CMOS pixel detector prototypes produced on p-type substrate of 2 kΩ cm initial resistivity (by LFoundry 150 nm process) were studied using Edge-TCT method before and after neutron irradiation. The test structures were produced for investigation of CMOS technology in tracking detectors for experiments at HL-LHC upgrade. Measurements were made with passive detector structures in which current pulses induced on charge collecting electrodes could be directly observed. Thickness of depleted layer was estimated and studied as function of neutron irradiation fluence. An increase of depletion thickness was observed after first two irradiation steps to 1 · 1013 n/cm2 and 5 · 1013 n/cm2 and attributed to initial acceptor removal. At higher fluences the depletion thickness at given voltage decreases with increasing fluence because of radiation induced defects contributing to the effective space charge concentration. The behaviour is consistent with that of high resistivity silicon used for standard particle detectors. The measured thickness of the depleted layer after irradiation with 1 · 1015 n/cm2 is more than 50 μm at 100 V bias. This is sufficient to guarantee satisfactory signal/noise performance on outer layers of pixel trackers in HL-LHC experiments.

The preparation of the Shutdown Dose Rate experiment for the next JET Deuterium-Tritium campaign

The assessment of the Shutdown Dose Rate (SDR) due to neutron activation is a major safety issue for fusion devices and in the last decade several benchmark experiments have been conducted at JET during Deuterium-Deuterium experiments for the validation of the numerical tools used in ITER nuclear analyses. The future Deuterium-Tritium campaign at JET (DTE2) will provide a unique opportunity to validate the codes under ITER-relevant conditions through the comparison between numerical predictions and measured quantities (C/E). For this purpose, a novel SDR experiment, described in the present work, is in preparation in the frame of the WPJET3-NEXP subproject within EUROfusion Consortium. The experimental setup has been accurately designed to reduce measurement uncertainties; spherical air-vented ionization chambers (ICs) will be used for on-line ex-vessel decay gamma dose measurements during JET shutdown following DT operations and activation foils have been selected for measuring the neutron fluence near ICs during operations. Active dosimeters (based on ICs) have been calibrated over a broad energy range (from about 30keV to 1.3 MeV) with X and gamma reference beam qualities. Neutron irradiation tests confirmed the capability of active dosimeters of performing on-line decay gamma dose rate measurements, to follow gamma dose decay at the end of neutron irradiation as well as insignificant activation of the ICs.

Progress in the Design and Testing of In-Vessel Magnetic Pickup Coils for ITER

This paper presents the results of the R&D activities recently performed to achieve the preliminary design of electromagnetic transducers for in-vessel local magnetic field measurements at low frequency (<30 kHz) for ITER. The study is based on thermoelectrical and electromagnetic bench tests performed on a batch of 40 sensor prototypes manufactured with the low temperature cofired ceramic (LTCC) technology. Also, the outcomes of a first neutron irradiation test on LTCC sensors are presented. The development of an alternative concept of a magnetic sensor for ITER, based on mineral insulated cables winding is also reported, with suitable thermomechanical and electromagnetic numerical analyses performed to assess the reliability of such sensors within the ITER operating conditions.

Exploring design diversity redundancy to improve resilience in mixed-signal systems

Redundancy is the most popular technique to add fault tolerance at system level to electronic systems. Redundancy with hardware and software diversity of digital computers is currently employed in safety critical applications, as, for example, in spacecrafts and commercial aircrafts, to increase the reliability of such systems. This work presents a study of the design diversity redundancy technique in the context of mixed-signal systems, identifying the advantages and associated costs of applying this technique to subsystems with both analog and digital parts. The discussion is based on three case studies: two data acquisition systems and a low-pass filter, all of them prototyped in mixed-signal programmable platforms. In these systems, different combinations regarding the number of modules (double or triple modular redundancy) and specific issues related to the applied diversity modes are considered. Based on the results of fault injection campaigns by hardware emulation and one neutron irradiation test, the achieved reliability level of each studied system is discussed, as well as the tradeoffs of applying design diversity redundancy to mixed-signal systems.

Characterizing Alpha- and Neutron-Induced SEU and MCU on SOTB and Bulk 0.4-V SRAMs

We experimentally characterized and compared the soft error rates of 65-nm bulk and silicon on thin buried oxide (SOTB) SRAMs by conducting accelerated alpha and neutron irradiation tests. Measurement results show that an SOTB SRAM has better soft error immunity than a bulk SRAM. In particular, the number of 2-bit multiple cell upsets (MCUs) of SOTB SRAM was smaller by two orders of magnitude than that of bulk SRAM, and the number of 3-bit or larger MCUs decreased further. In addition, the reverse body bias (RBB) reduced the soft error rate of SOTB SRAM to two-thirds of zero body bias (ZBB). To investigate this dependence on body bias, we evaluated the sensitive cross sectional area for ZBB and RBB with 3D technology computer aided design device simulations. The simulation results show that the RBB decreases the sensitive cross-sectional area of an SOTB device for small linear energy transfer (LET) ions, which is consistent with the measured dependence on body bias.

Production and Neutron Irradiation Tests on a New Epoxy/Molybdenum Composite

Molybdenum powder was added in an epoxy matrix to increase the neutron-shielding capacity of pure epoxy. FLUKA and GEANT4 Monte Carlo programs were used to design new neutron-shielding material. After finding the epoxy/Mo ratio for the best shielding capacity, neutron equivalent dose rate measurements were performed. Results were compared to commonly used neutron-shielding materials such as paraffin, steel, concrete, and B4C. The produced new sample has a high neutron shielding capacity and it can be used for neutron protection purposes.

The ATLAS liquid argon calorimeter: upgrade plans for the HL-LHC

The ATLAS detector was designed and built to study proton-proton collisions produced at the LHC at centre-of-mass energies up to 14 TeV and instantaneous luminosities up to 1034 cm−2s−1. Liquid argon (LAr) sampling calorimeters are employed for electromagnetic and hadronic calorimetry. The luminosity for the proposed High Luminosity LHC phase (HL-LHC) will increase up to 5×1034 cm−2s−1 with the goal of accumulating an integrated luminosity of 3000 fb−1. This is well beyond the values for which the detectors were designed. The electromagnetic and hadronic calorimeters will be able to tolerate the increased particle flux, but the performance of the forward calorimeter (FCal) will be affected. Two possible solutions for keeping the current performance are being discussed. The readout electronics will also need to withstand larger radiation environment. In the hadronic endcap calorimeter (HEC) cold GaAs preamplifiers are located inside the endcap cryostats. The properties of these devices have been investigated in recent proton and neutron irradiation tests to determine whether they must be replaced. In addition, the entire front-end readout system is not expected to survive the integrated luminosity at the HL-LHC and will be replaced. The description of the new readout system is presented.

Exploring Well-Configurations for Minimizing Single Event Latchup

This work experimentally studies single event latchup (SEL) prevention by altering well configurations. The well structures under consideration in this paper are ordinary twin-well structure, triple-well structure with deep N-well (DNW) and triple-well structure with deep P-well (DPW). Doping profiles are also varied in our experiments. Neutron irradiation tests for test chips fabricated in 55-nm and 90-nm bulk Si CMOS processes show that SEL can be suppressed with a DPW or a DNW well configuration and a high-dose implantation in the well. Among these, DPW was the most effective to eliminate SEL, and no SEL was observed throughout our irradiation tests in the SRAM with DPW in both 55-nm and 90-nm processes. In addition, DPW brings a desirable side effect of single event upset (SEU) reduction. A disadvantage is a cost to develop a DPW process. DNW is a common process option and hence it is easily adopted for SEL prevention, but we need to pay attention to the fact that DNW increases SEU rate. Increasing well doping in twin-well structure reduced SEL by 60%.

GPUs Reliability Dependence on Degree of Parallelism

A higher Degree of Parallelism decreases the code execution time. However, a higher scheduler strain is necessary to manage the increased number of parallel processes, which have the countermeasure of increasing the graphics processing unit (GPU) cross section. This hypothesis is confirmed by extensive neutron irradiation testing to study how the Degree of Parallelism affects GPU reliability. Moreover, the cache distribution forced by different Degrees of Parallelism is proved to influence the application error rate. Finally, the Mean Executions Between Failures metric is introduced to evaluate the amount of data computed correctly by the GPU on a practical application.

Flexible heat-resistant neutron and gamma-ray shielding resins

Flexible heat-resistant neutron and gamma-ray shielding resins have been successfully developed through the use of a polymer resin. The production process involves a new mixing technique of the resin and materials for neutron absorber/gamma-ray attenuation using a new cold-setting method. The process allows for easy onsite fabrication. The materials are B4C powder for neutron shield, Colemanite powder for neutron/gamma-ray shield and FeW powder for gamma-ray shield, respectively. We assessed a basic property and neutron penetration performance of the neutron/gamma-ray shielding resin and carried out a neutron irradiation test of the resin using Japan Research Reactor 3. Gamma-ray shielding performance of the developed resin with FeW powder was performed by using a Monte-Carlo calculation code. The neutron and gamma-ray shielding resins can be used in a high-temperature environment (~200 oC). These resins will be applied around tokamak fusion devices as an additional shielding: they can reduce neutron and gamma-ray streaming from the device.

Soft-Error in SRAM at Ultra-Low Voltage and Impact of Secondary Proton in Terrestrial Environment

This paper presents soft-error measurement results through neutron and alpha irradiation tests and simulation in SRAM at ultra-low voltages, down to 0.19 V. Soft-error-rate at 0.19 V is higher than at 1.0 V by two orders of magnitude. This measurement result supported by simulation clarifies that direct ionization from secondary protons generated by nuclear reaction with neutron collision contribute to a dramatic increase in SRAM soft-error-rate at ultra-low voltages in terrestrial environment.

Mitigating Multi-Bit-Upset With Well-Slits in 28 nm Multi-Bit-Latch

This paper proposes a technique that mitigates multi-bit-upset (MBU) in multi-bit-latch (MBL) without performance degradation by applying well-slits. The area overhead in an MBL macro for processor design, which includes a clock buffer and a checker, is only 5.4% in a 28 nm technology. Sixty-hour accelerated neutron irradiation test observed no MBUs in the MBL with well-slits. The proposed mitigation technique achieved excellent robustness against MBU without any increase in SBU rate. The MBL with the proposed mitigation technique helps improve reliability of electronic devices.

Radiation-tolerant joining technologies for silicon carbide ceramics and composites

Silicon carbide (SiC) for nuclear structural applications, whether in the monolithic ceramic or composite form, will require a robust joining technology capable of withstanding the harsh nuclear environment. This paper presents significant progress made towards identifying and processing irradiation-tolerant joining methods for nuclear-grade SiC. In doing so, a standardized methodology for carrying out joint testing has been established consistent with the small volume samples mandated by neutron irradiation testing. Candidate joining technologies were limited to those that provide low induced radioactivity and included titanium diffusion bonding, Ti–Si–C MAX-phase joining, calcia–alumina glass–ceramic joining, and transient eutectic-phase SiC joining. Samples of these joints were irradiated in the Oak Ridge National Laboratory High Flux Isotope Reactor at 500 or 800°C, and their microstructure and mechanical properties were compared to pre-irradiation conditions. Within the limitations of statistics, all joining methodologies presented retained their joint mechanical strength to ∼3dpa at 500°C, thus indicating the first results obtained on irradiation-stable SiC joints. Under the more aggressive irradiation conditions (800°C, ∼5dpa), some joint materials exhibited significant irradiation-induced microstructural evolution; however, the effect of irradiation on joint strength appeared rather limited.

Experimental Assessment of Cache Memory Soft Error Rate Prediction Technique

In this paper, we explain the validation of the Cache Analyzer prediction technique thanks to accelerated test experiments. The technique, described in one of our previous works and targeted towards end-user exploitation, focuses on the analysis of cache memory transactions. This paper presents the experimental setup, including the fault detection system used to detect errors in cache memories during the physical validation experiments, and to link them with application failures. We verified that our prediction tool would have correctly predicted the failures. Results obtained during neutron and proton irradiation tests are in accordance with the Cache Analyzer predictions.

Performance studies of Micro Pixel Chamber for the ATLAS upgrade

The Micro Pixel Chamber (μ-PIC) is being developed as a muon chamber of the ATLAS experiment in an HL-LHC environment. In the ATLAS muon system, a high flux of fast neutron background causes instability operation of the detectors. We performed neutron irradiation tests with μ-PIC to optimize the operation gas and detector structure. In addition, we studied neutron interactions with the detector, in order to understand the effect of fast neutrons.

Development of GEM-based detector for thermal neutron

We have developed a two-dimensional imaging detector with a gas electron multiplier (GEM) for thermal neutron detection. The basic characteristics of the GEM-based detector have already been measured. In order to improve the detector performance such as the nγ discrimination capability and the position resolution, a neutron irradiation test was performed at BL21 in the Materials and Life Science Experimental Facility (MLF). This paper describes the potential for improving the detector performance on the basis of the results of the neutron irradiation test.

Thermal performance of carbon foams used as heat sink for the pixel MVD PANDA

The Micro Vertex Detector (MVD) for the PANDA experiment is designed and optimized to reconstruct the D mesons secondary vertices and to provide the maximum acceptance close to the interaction point. The experimental physics goals and setup require sophisticated solutions for the detector integration in order to minimise the material budget. The thermal power produced by the “on board” read-out electronics is fast removed using carbon foam as heat sink. Two types of carbon foam are under evaluation. The mechanical and thermal property behaviors after neutron irradiation test with neutrons have been studied. Results from finite element thermal analyses and test bench are also presented.

Modelling radiation-effects and annealing in semiconductor lasers for use in future particle physics experiments

Optical link components used in future particle physics experiments will typically be exposed to intense radiation fields during the lifetime of the experiment and the qualification of these components in terms of radiation tolerance is thus required. We have created a model that describes the degradation of the L-I characteristic of a semiconductor laser undergoing irradiation with the annealing processes taken into account. This model can be used to predict the behaviour of a laser being irradiated with the different particle fluxes at different locations inside a particle physics experiment. The robustness of the model has been checked against the experimental data obtained during high-fluence (in excess of 1015 particles/cm2) neutron and pion irradiation testing in 2009 and 2010.

Present status of refurbishment and irradiation technologies in JMTR

The Japan Materials Testing Reactor (JMTR) of the Japan Atomic Energy Agency is a testing reactor for various neutron irradiation tests on nuclear fuels and materials, as well as for radioisotope production. The operation of JMTR stopped temporarily in August 2006 for refurbishment and improvement. The renewed JMTR will resume operation in Japanese fiscal year 2011. The renewal of aged reactor components, the preparation of new irradiation facilities, and the development of irradiation technologies have been carried out for the resumption of the new JMTR. The new JMTR with the new irradiation facilities and the irradiation technologies will be utilized for the research and development of fission and fusion reactor fuels and materials. This paper describes the present status of the refurbishment and the irradiation technologies focused on instrumentation such as the multi-paired thermocouple which is applicable to irradiation temperature control and a ceramic oxygen sensor in JMTR.

Modelling radiation-effects in semiconductor lasers for use in SLHC experiments

Optical link components in the SLHC inner detectors are to be exposed to intense radiation fields during operation, and, hence, their qualification in terms of radiation tolerance is required. We have created a model that describes a semiconductor laser undergoing irradiation to enable the extrapolation to full lifetime total fluences from lower fluence radiation tests. This model uses a rate-equation approach with modified gain calculation that takes thermal rollover into account. The model is used to fit experimental data obtained during high-fluence (in excess of 1015 particles/cm2) neutron and pion irradiation tests and evaluate its prediction capability.