MeV Neutron Equivalent Fluence Research Articles

Characterization of SiPM performance in a small satellite in low earth orbit using LabOSat-01

In this work, the performance of SensL MicroFC-60035 SiPM devices was studied during a 1460-day mission in Low Earth Orbit (LEO) using the LabOSat-01 characterization payload. Two of these platforms, carrying two SiPMs each, were integrated into the ÑuSat-7 satellite (COSPAR-ID: 2020-003B). Analysis revealed that these SiPMs experienced an increase in dark current over time due to damage from trapped and solar proton radiation. The total ionizing dose received by the payload and the SiPMs was measured using p-MOSFET dosimeters, with a resulting value of 5 Gy, or a 1 MeV neutron equivalent fluence of ϕn=5⋅109 n/cm2. The dark current was observed to increase up to 500 times. Parameters such as Gain and Photon Detection Efficiency remained unchanged throughout the mission. These findings align with previous performance reports involving different SiPMs irradiated with various particles and energies.

Monolithic HV-CMOS sensors for a beam monitoring system of therapeutic ion beams

Nowadays, cancer treatment with ion beam is well established and studied. This method allows to deposit the maximum dose to the tumor and minimize the damage to healthy tissue, due to the Bragg peak of the ion energy deposition near the end of the particle range. During the treatment, it is possible to provide volumetric dose delivery by changing the particle energy (penetration depth) and adjusting the beam position via a magnetic system. For the beam monitoring system, the precise measurement of the beam direction, shape and fluence in real time becomes crucial to provide effective and safe dose delivery to the tumor. Additionally, the system should work for beam intensities up to 1010 s-1 for protons, be tolerant to 1 MeV neutron equivalent fluences up to 1015 cm-2 per year and be to tolerant to magnetic fields (for MR-guided ion beam).The studies presented in this article are focused on the application of the HitPix sensor family with counting electronics and frame-based readout for such a beam monitoring system. The HitPix sensors are monolithic pixelated silicon sensors based on HV-CMOS technology and have been developed at the ASIC and Detector Lab (ADL, KIT). Recent measurements with ion beams and a multi-sensor readout as well as future developments are discussed.

Synergistic Radiation Effects in PPD CMOS Image Sensors Induced by Neutron Displacement Damage and Gamma Ionization Damage.

The synergistic effects on the 0.18 µm PPD CISs induced by neutron displacement damage and gamma ionization damage are investigated. The typical characterizations of the CISs induced by the neutron displacement damage and gamma ionization damage are presented separately. The CISs are irradiated by reactor neutron beams up to 1 × 1011 n/cm2 (1 MeV neutron equivalent fluence) and 60Co γ-rays up to the total ionizing dose level of 200 krad(Si) with different sequential order. The experimental results show that the mean dark signal increase in the CISs induced by reactor neutron radiation has not been influenced by previous 60Co γ-ray radiation. However, the mean dark signal increase in the CISs induced by 60Co γ-ray radiation has been remarkably influenced by previous reactor neutron radiation. The synergistic effects on the PPD CISs are discussed by combining the experimental results and the TCAD simulation results of radiation damage.

Evaluation of planar silicon pixel sensors with the RD53A readout chip for the Phase-2 Upgrade of the CMS Inner Tracker

The Large Hadron Collider at CERN will undergo an upgrade in order to increase its luminosity to 7.5 × 1034 cm-2s-1. The increased luminosity during this High-Luminosity running phase, starting around 2029, means a higher rate of proton-proton interactions, hence a larger ionizing dose and particle fluence for the detectors. The current tracking system of the CMS experiment will be fully replaced in order to cope with the new operating conditions. Prototype planar pixel sensors for the CMS Inner Tracker with square 50 μm × 50 μm and rectangular 100 μm × 25 μm pixels read out by the RD53A chip were characterized in the lab and at the DESY-II testbeam facility in order to identify designs that meet the requirements of CMS during the High-Luminosity running phase. A spatial resolution of approximately 3.4 μm (2 μm) is obtained using the modules with 50 μm × 50 μm (100 μm × 25 μm) pixels at the optimal angle of incidence before irradiation. After irradiation to a 1 MeV neutron equivalent fluence of Φeq = 5.3 × 1015 cm-2, a resolution of 9.4 μm is achieved at a bias voltage of 800 V using a module with 50 μm × 50 μm pixel size. All modules retain a hit efficiency in excess of 99% after irradiation to fluences up to 2.1 × 1016 cm-2. Further studies of the electrical properties of the modules, especially crosstalk, are also presented in this paper.

First characterization results of ARCADIA FD-MAPS after X-ray irradiation

The ARCADIA collaboration is developing fully-depleted (FD) Monolithic Active Pixel Sensors (MAPS) in a 110 nm CMOS process in collaboration with LFoundry. The sensor design incorporates an n+ collection node within a n-type epi-layer on top of a high-resistivity n-type substrate and p+ backside. Thus, the pn-junction sits on the backside and through an applied backside bias, the full substrate gets depleted. The targeted applications of this technology range from future high energy physics experiments to space applications, and medical and industrial scanners. Together, these applications set the minimum requirements on the detector: data collection at hit rates of (10–100) MHz/cm2, full signal processing within (1–10) μs, maximum power consumption (5–20) mW/cm2 and radiation tolerances of up to 3.4 Mrad or 6.2 × 1012 1 MeV neutron equivalent fluence. In order to proof the performance of the technology, a demonstrator chip of 512 × 512 pixels with 25 μm pitch was designed and fabricated in a first engineering run in 2021, together with additional test structures of pixel and strip arrays with different pitches and sensor geometries. The production run has produced functional passive and active pixel matrices. Earlier studies have shown that positive oxide charges and traps at the Si-SiO2 interface, introduced by ionising radiation, affect the depletion region around the collection electrode, increasing the pixel capacitance. By varying the gap size between collection node and pwells, the geometry can be optimised to keep the capacitance low also after irradiation. To study the performance after irradiation, of the optimised diode designs, the passive pixel matrices were irradiated with doses up to 10 Mrad (SiO2) using a X-ray tube with a Tungsten anode. The measurements are complemented by TCAD simulations. The maximum capacitance increase after irradiation was found to reach 6 and 12 fF/pixel for pixel pitches of 25 and 50 μm, respectively. The relative capacitance increase after irradiation has hereby been found to reach up to 250% after a dose of 10 Mrad.

Influence of neutron/gamma irradiation on damage and scintillation of Ga-doped ZnO thin films

As a new type of inorganic scintillator, ZnO crystal doped with Ga has been used for Ultra-fast scintillating detectors with fast response to detect X-ray, gamma, neutron, and charged particles. Moreover, due to the large bandgap energy and high threshold displacement energy, ZnO: Ga has a strong radiation resistance in theory. However, there is a lack of experimental studies on the change of scintillation properties of ZnO: Ga under an intense irradiation environment. This study deposited thin Ga-doped ZnO films on α-Al2O3(0001) substrate by dual-target reactive magnetron sputtering. The ZnO: Ga samples were irradiated by neutrons from 1010 to 7.1 × 1014 neutrons/cm2 (1 MeV neutron equivalent fluence) and γ rays from 500 to 10,000 Gy, respectively. The structural and optical properties of all irradiated samples were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), optical transmittance (TS), and effective light output at room temperature. The results indicated that all the irradiated samples are still in both hexagonal wurtzite structure and c-axis orientation. Compared with unirradiated samples, it is found that the samples' optical transmittance, energy resolution, and effective light output have little change due to irradiation, which has fully proved that the ZnO: Ga scintillation films have good radiation resistance under neutron and gamma irradiation. Hence, ZnO: Ga is an attractive candidate for radiation detectors with ultra-fast responses under extreme radiation environments.

Design and testing of LGAD sensor with shallow carbon implantation

The low gain avalanche detectors (LGADs) are thin sensors with fast charge collection which in combination with internal gain deliver an outstanding time resolution of about 30 ps for Minimum Ionizing Particles (MIP). High collision rates and consequent large particle rates crossing the detectors at the upgraded Large Hadron Collider (LHC) in 2028 will lead to radiation damage and deteriorated performance of the LGADs. The main consequence of radiation damage is loss of gain layer doping (acceptor removal) which requires an increase of bias voltage to compensate for the loss of charge collection efficiency and consequently time resolution. The Institute of High Energy Physics (IHEP), Chinese Academy of Sciences (CAS) has developed a process based on the Institute of Microelectronics (IME), CAS capability to enrich the gain layer with carbon to reduce the acceptor removal effect by radiation. After 1 MeV neutron equivalent fluence of 2.5 × 1015 neq/cm2, which is the maximum fluence to which sensors will be exposed at ATLAS High Granularity Timing Detector (HGTD), the IHEP-IME second version (IHEP-IMEv2) 50μm LGAD sensors already deliver adequate charge collection >4 fC and time resolution <50 ps at voltages <400 V. The operation voltages of these 50μm devices are well below those at which single event burnout may occur.

CMS Phase-2 Inner Tracker Upgrade

The HL-LHC conditions of instantaneous peak luminosity up to 7.5x1034 cm-2s-1 and an integrated luminosity of the order of 300 fb-1/year is expected to result in 1 MeV neutron equivalent fluence of 2.3 x 1016 neq/cm2 and a total ionizing dose (TID) of 12 MGy (1.2 Grad) at the center of the CMS Experiment, where its innermost component, the Phase-2 Pixel Detector will be installed. This detector has to survive the above radiation dose, handle hit rates of 3.2 GHz/cm2 in the layers closest to the beam line, be able to track and separate particles in extremely dense collisions, deal with a pileup of 140-200 collisions per bunch crossing and have a high impact parameter resolution. This translates into a highly granular detector design with thinner sensors and smaller pixels, and a faster and more radiation hard electronics compared to the Phase-1 detector. This contribution reviews the Phase-2 upgrade of the (silicon-based) CMS Inner Tracker focusing on the features of the detector layout and on developments of pixelated devices.

Hadron-Induced Radiation Damage in Fast Heavy Inorganic Scintillators

Fast and heavy inorganic scintillators with suitable radiation tolerance are required to face the challenges presented at future hadron colliders of high energy and intensity. Up to 5 GGy and 5 × 1018 neq/cm2 of one-MeV-equivalent neutron fluence is expected by the forward calorimeter at the Future Hadron Circular Collider. This paper reports the results of an investigation of proton- and neutron-induced radiation damage in various fast and heavy inorganic scintillators, such as LYSO:Ce crystals, LuAG:Ce ceramics, and BaF2 crystals. The experiments were carried out at the Blue Room with 800 MeV proton fluence up to 3.0 × 1015 p/cm2 and at the East Port with one MeV equivalent neutron fluence up to 9.2 × 1015 neq/cm2, respectively, at the Los Alamos Neutron Science Center. Experiments were also carried out at the CERN PS-IRRAD proton facility with 24 GeV proton fluence up to 8.2 × 1015 p/cm2. Research and development will continue to develop LuAG:Ce ceramics and BaF2:Y crystals with improved optical quality, F/T ratio, and radiation hardness.

Characterisation of planar sensors for the inner tracker of the CMS experiment

The Compact Muon Solenoid (CMS) experiment is expected to collect an integrated luminosity of 3000 fb−1 during the High Luminosity phase of the Large Hadron Collider (HL-LHC). This scenario comes with a high number of collisions per bunch crossing, and in turn, a high level of radiation for the innermost layer of the CMS tracker. Simulations estimate a 1 MeV neutron equivalent fluence, Φeq, of 2.3 × 1016 cm−2 at a distance of 2.8 cm from the collision point. The inner tracker of the CMS detector is required to withstand this range of fluence and maintain tracking performance. Planar pixel sensors with an active thickness of 150 μm and pixel sizes of 25 × 100 μm2 or 50 × 50 μm2 have been produced by Hamamatsu Photonics (HPK) and Fondazione Bruno Kessler (FBK). The sensors were bump bonded to the RD53A readout chip prototype. The sensor-chip modules were irradiated with 23 MeV protons to the 1 MeV neutron equivalent fluence of up to 2.4 × 1016 cm−2 at the Zyklotron AG (ZAG).Non-irradiated and irradiated modules were tested in the DESY II beam test facility. The spatial resolution as a function of the incidence angle and hit efficiency as a function of the bias voltage of the sensors were determined from these measurements. It is shown that for the highest fluence, the planar modules still reach 98% hit efficiency at bias voltages below 800 V.

The fast beam condition monitor as standalone luminometer of the CMS experiment at the HL-LHC

For the Phase-2 CMS upgrade for the High-Luminosity LHC, a luminosity uncertainty of 1% is targeted. To achieve this goal, measurements from multiple luminometers with orthogonal systematics are required. A standalone luminometer, the Fast Beam Condition Monitor (FBCM) is being designed for the online bunch-by-bunch luminosity measurement. The sampling time resolution of ∼0.7 ns also enables the measurement of beam-induced backgrounds. In this paper, the hardware architecture and the readout protocol of the FBCM are described. The expected performance with a simple behavioral model of the front-end comprising a constant fraction discriminator is discussed, although the final implementation in the ASIC is still under discussion. Simulation results show that the FBCM will provide the required statistical uncertainty and deviation from linearity by employing 336 silicon-pad sensors, each with an area of about 3 mm2. In addition, the front-end with sensitivity to as low as 6000 electrons will satisfy the longevity constraints for an exposure of 1 MeV neutron equivalent fluence of 3.5 × 1015 per cm2.

Can the electric field in radiation-damaged silicon pad diodes be determined by admittance and current measurements?

A method is proposed for determining the electric field in highly-irradiated silicon pad diodes using admittance-frequency (Y−f), and current measurements (I). The method is applied to Y−f and I data from square n+p diodes of 25 mm2 area irradiated by 24 GeV/c protons to four 1 MeV neutron equivalent fluences between 3×1015 cm−2 and 13×1015 cm−2. The measurement conditions were: Reverse voltages between 1 V and 1000 V, frequencies between 100 Hz and 2 MHz and temperatures of −20 °C and −30 °C. The position dependence of the electric field is parameterised by a linear dependence at the two sides of the diode, and a constant in the centre. The parameters as a function of voltage, temperature and irradiation fluence are determined by fits of the model to the data. For voltages below about 300 V all data are well described by the model, and the results for the electric field agrees with expectations: Depleted high-field regions towards the two faces and a constant low electric field in the centre, with values which agrees with the field in an ohmic resistor with approximately the intrinsic resistivity of silicon. For conditions at which the low field region disappears and the diode is fully depleted, the method fails. This happens around 300 V for the lowest irradiation fluence at −30 °C, and at higher voltages for higher fluences and lower temperatures. In the conclusions the successes and problems of the method are discussed.

Effect of deep gain layer and Carbon infusion on LGAD radiation hardness

The properties of 50 μm thick Low Gain Avalanche Diode (LGAD) detectors manufactured by Hamamatsu photonics (HPK) and Fondazione Bruno Kessler (FBK) were tested before and after irradiation with neutrons. Their performance were measured in charge collection studies using β-particles from a 90Sr source and in capacitance-voltage scans (C-V) to determine the bias to deplete the gain layer. Carbon infusion to the gain layer of the sensors was tested by FBK in the UFSD3 production. HPK instead produced LGADs with a very thin, highly doped and deep multiplication layer. The sensors were exposed to a 1 MeV neutron equivalent (neq/cm2) neutron fluence from 4× 1014 neq/cm2 to 4× 1015 neq/cm2. The collected charge and the timing resolution were measured as a function of bias voltage at −30 C, furthermore the profile of the capacitance over voltage of the sensors was measured. The deep gain layer (HPK-3.2) and the Carbon infusion (FBK3+C) both show reasonable performance up to 3× 1015 neq/cm2. Furthermore the correlation between the time resolution and the gain is found to be independent from the sensor type, given the same thickness, and from the fluence. Finally a correlation is shown between the bias voltage to deplete the gain layer and the bias voltage needed to reach a certain amount of gain in the sensor.

Charge collection and electrical characterization of neutron irradiated silicon pad detectors for the CMS High Granularity Calorimeter

The replacement of the existing endcap calorimeter in the Compact Muon Solenoid (CMS) detector for the high-luminosity LHC (HL-LHC), scheduled for 2027, will be a high granularity calorimeter. It will provide detailed position, energy, and timing information on electromagnetic and hadronic showers in the immense pileup of the HL-LHC. The High Granularity Calorimeter (HGCAL) will use 120-, 200-, and 300-μm-thick silicon (Si) pad sensors as the main active material and will sustain 1 MeV neutron equivalent fluences up to about 1016 neq cm−2. In order to address the performance degradation of the Si detectors caused by the intense radiation environment, irradiation campaigns of test diode samples from 8-inch and 6-inch wafers were performed in two reactors. Characterization of the electrical and charge collection properties after irradiation involved both bulk polarities for the three sensor thicknesses. Since the Si sensors will be operated at −30̂C to reduce increasing bulk leakage current with fluence, the charge collection investigation of 30 irradiated samples was carried out with the infrared-TCT setup at −30̂C. TCAD simulation results at the lower fluences are in close agreement with the experimental results and provide predictions of sensor performance for the lower fluence regions not covered by the experimental study. All investigated sensors display 60% or higher charge collection efficiency at their respective highest lifetime fluences when operated at 800 V, and display above 90% at the lowest fluence, at 600 V. The collected charge close to the fluence of 1016 neq cm−2 exceeds 1 fC at voltages beyond 800 V.

Radiation damage study of SensL J-series silicon photomultipliers using 101.4 MeV protons

Radiation damage of J-series silicon photomultipliers (SiPMs) has been studied in the context of using these photodetectors in future space-borne scintillation detectors. Several SiPM samples were exposed to 101.4 MeV protons, with 1 MeV neutron equivalent fluence ranging from 1.27×108 neq/cm2 to 1.23×1010 neq/cm2. After the irradiation, the SiPMs experienced a large increase in the dark current and noise, which may pose problems for long-running space missions in terms of power consumption, thermal control and detection of low-energy events. Measurements performed with a CeBr3 scintillator crystal showed that after exposure to 1.23×1010 neq/cm2 and following room-temperature annealing, the dark noise of a single 6 mm square SiPM at room temperature increased from 0.1 keV to 2 keV. Because of the large SiPM noise, the gamma-ray detection threshold increased to approximately 20 keV for a CeBr3 detector using a 4-SiPM array and 40 keV for a detector using a 16-SiPM array. Only a small effect of the proton irradiation on the average detector signal was observed, suggesting no or little change to the SiPM gain and photon detection efficiency.

Characterization of the radiation tolerance of cryogenic diodes for the High Luminosity LHC inner triplet circuit

Cryogenic bypass diodes are part of the baseline powering layout for the circuits of the new ${\mathrm{Nb}}_{3}\mathrm{Sn}$ based final focus magnets of the high luminosity Large Hadron Collider. They will protect the magnets against excessive transient voltages during a nonuniform quenching process. The diodes are located inside an extension to the magnet cryostat, operated in superfluid helium and exposed to ionizing radiation. Therefore, the radiation tolerance of different types of diodes has been tested at cryogenic temperatures in CERN's CHARM irradiation test facility during its 2018 run. The forward bias characteristics, the turn-on voltage and the reverse blocking voltage of each diode were measured weekly at 4.2 K and 77 K, as a function of the accumulated radiation dose. The diodes were submitted to a total dose close to 12 kGy and a 1 MeV neutron equivalent fluence of $2.2\ifmmode\times\else\texttimes\fi{}{10}^{14}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}$. After the end of the irradiation program the annealing behavior of the diodes was tested by increasing the temperature slowly to 293 K. This paper describes the experimental setup, the measurement procedure and the analysis of the measurements performed during the irradiation program as well as the results of the annealing study.

Influence of radiation damage on the absorption of near-infrared light in silicon

The absorption length, λabs, of light with wavelengths between 0.95 and 1.30 μm in silicon irradiated with 24 GeV/c protons to 1 MeV neutron equivalent fluences up to 8.6×1015 cm−2 has been measured. It is found that λabs decreases with fluence due to radiation-induced defects. A phenomenological parametrization of the radiation-induced change of λabs as a function of wavelength and neutron equivalent fluence at room temperature is given. The observation of the decrease of λabs with irradiation is confirmed by edge-TCT measurements on irradiated silicon strip detectors. Using the measured wavelength dependence of λabs, the change of the silicon band-gap with fluence is determined.

Performance of 5-[formula omitted]m PIN diamond diodes as thermal neutron detectors

Diamond PIN diodes with an approximately 5-μm thick i-layer and coated with a thin boron nitride (BN) layer have been tested with a thermal neutron beam. For a flux of 4.4 × 106 n/s/cm2, count rates were on the order of 30–100 counts per second depending on the thickness of the BN neutron converter layer. Pulse height spectra showed features associated with α and 7Li fission products consistent with the thickness of the BN layer. An irradiation test with a 1 MeV neutron equivalent fluence of 1015 n/cm2 showed no significant alteration in the count rate of the tested detector.

Nuclear analysis of the ITER torus cryopumps

The ITER Tokamak will feature six torus cryopumps (TCP) to maintain the vacuum requirements inside the vacuum vessel for plasma operation. They will be connected to the ITER vacuum vessel through the lower ducts, which have limited shielding to ensure an efficient pumping. Therefore, these ducts will represent a relevant path for radiation to travel from the plasma and affect diverse aspects of the ITER facility, such as the electronics allocation or the maintenance operations during the machine shutdown. Previous analyses have addressed these important aspects. Nonetheless, limitations in those studies and design evolution have justified a new analysis, specifically dedicated to the TCP final design review. The results of the nuclear analysis are presented here focusing on the B1 level port cell #4. The TCP design and the associated and neighboring equipment have evolved and updated models have been considered. The TCP modelling has required an explicit heterogeneous treatment of the internal parts. The radiation source from the divertor cooling water pipes running along the port cell ceiling has been considered with the latest available source definition. In terms of methodology, one major improvement has been the modelling of the radiation transmission from C-model to the Tokamak Complex model. Another important improvement has been the consideration of D1SUNED for the determination of shutdown dose rates, covering a broader fraction of the radioactive inventory than in previous studies. The following quantities have been determined: neutron flux, absorbed dose to silicon, 1 MeV equivalent neutron fluence and shutdown dose rates (SDDR) after 106 s of cooling time. Finally, a set of proposals have been made to considerably mitigate the SDDR after 106 s of cooling. This work represents a realistic and matured source of information of the radiation environment in the ITER TCP port cells as presented in the final design review.

Photon detectors and front-end electronics for RICH detectors in high particle density environments

Abstract Photon detectors capable of operating in high photon rate environments are required for next generation ring imaging Cherenkov (RICH) detectors at high luminosity accelerators, like HL-LHC. These photodetectors will have to sustain single photon rate in excess of 1 GHz∕cm 2 , while being able to resist to high radiation levels of several Mrad and a 1 MeV-equivalent neutron fluence up to 10 14 n eq ∕ cm 2 . The characteristics of latest models of commercial silicon photomultipliers (SiPMs) and micro-channel plates photomultiplier tubes (MCP-PMT) are investigated in order to verify whether they satisfy the required performance, with particular emphasis on radiation hardness and high rate operation. Their innovative characteristics require tailored front-end electronics, whose architecture can be adapted to deal with higher pixel occupancy, as it will be described.