Radiation-induced Current Research Articles

Diamond energy-dispersive dosimeter for measuring linear energy deposition distributions in clinical carbon beam therapy

A thin diamond membrane energy-dispersive dosimeter 50 μm thick was fabricated for estimating clinical dose distribution. In contrast to conventional semiconductors, diamond wide-bandgap semiconductors are expected to have excellent radiation tolerance and biological compatibility based on the linear relationship of stopping power ratio for clinical carbon particles. Linear energy transfer (LET) spectra were obtained along with the Bragg curve for a clinical carbon beam generated at Gunma University Heavy Ion Medical Center. The relative biological effectiveness (RBE) distributions were estimated from the LET spectra for both the mono-energy and spread-out Bragg peak irradiation configurations. The diamond detector was also used as a solid ionization chamber to obtain the radiation-induced current (RIC) distribution, which represents the physical dose distribution. The clinical dose distribution was estimated from the RIC and RBE distributions as proof of concept for the clinical carbon beam therapy field with a single-chip diamond energy-dispersive dosimeter.

The upgrade of the CMS electromagnetic calorimeter for HL-LHC

The High Luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN aims to achieve unprecedented levels of instantaneous and integrated luminosities, approximately 5 × 1034 cm-2 s-1 and 3000 fb-1, respectively. It is anticipated that each bunch-crossing will result in an average of 140 to 200 collisions (pileup). The lead tungstate crystals and avalanche photodiodes (APDs) in the barrel region of the electromagnetic calorimeter (ECAL) of the Compact Muon Solenoid (CMS) will remain effective. However the readout and trigger electronics will undergo complete replacement to keep the current level of performance. A dual gain trans-impedance amplifier and an application-specific integrated circuit will be installed, providing two 160 MS/s analog-to-digital converter channels, gain selection, and data compression. The increase in noise within the APDs, due to radiation-induced dark current, will be alleviated by reducing the operating temperature of the ECAL. Additionally, the trigger primitive formation will be shifted away from the detector and handled by powerful and flexible field-programmable gate array processors housed on the back-end electronics cards.In this document, the complete ECAL barrel readout chain design and the current state of research and development for each individual component regarding the upgrade will be described. The outcomes of recent test beam campaigns conducted at the CERN SPS, exploiting electron beams with energies of up to 250 GeV, will also be summarized. Notably, measurements pertaining to the energy resolution performance of the latest prototypes of HL-LHC ECAL readout electronics will be presented.

X-ray Induced Electric Currents in Anodized Ta2O5: Towards a Large-Area Thin-Film Sensor.

We investigated the characteristics of radiation-induced current in nano-porous pellet and thin-film anodized tantalum exposed to kVp X-ray beams. We aim at developing a large area (≫cm2) thin-film radiation sensor for medical, national security and space applications. Large area (few cm2) micro-thin Ta foils were anodized and coated with a counter electrode made of conductive polymer. In addition, several types of commercial electrolytic porous tantalum capacitors were assembled and prepared for irradiation with kVp X-rays. We measured dark current (leakage) as well as transient radiation-induced currents as a function of external voltage bias. Large transient currents (up to 50 nA) under X-ray irradiation (dose rate of about 3 cGy/s) were measured in Ta2O5 capacitors. Small nano-porous Ta and large-area flat Ta foil capacitors show similar current-voltage characteristic curve after accounting for different X-ray attenuation in capacitor geometry. The signal is larger for thicker capacitor oxide. A non-negligible signal for null external voltage bias is observed, which is explained by fast electron production in Ta foils. Anodized tantalum is a promising material for use in large-area, self-powered radiation sensors for X-ray detection and for energy harvesting.

On-beam system test of the new readout electronics for the CMS Electromagnetic Calorimeter upgrade

Starting in 2029, the High Luminosity LHC (HL-LHC) at CERN is projected to achieve unparalleled instantaneous luminosity (7.5 × 1034 cm-2s-1) for an integrated luminosities of 4500 fb-1. To cope with the extreme conditions of 200 collisions per bunch crossing (pile-up), both on-detector and off-detector electronics of the CMS Electromagnetic Calorimeter (ECAL) will be upgraded. The new system will incorporate a dual-gain trans-impedance amplifier alongside an Application-Specific Integrated Circuit (ASIC) that includes dual 160 MHz ADC channels and features for gain selection and data compression. The lead tungstate crystals and avalanche photodiodes (APDs) will remain in service due to their proven reliability. To counteract the noise amplification in the APDs, attributed to radiation-induced dark currents, the operational temperature of the ECAL will be reduced from 18°C to roughly 9°C. Preliminary tests of these new electronics have yielded promising results. During tests beams at the CERN H4 beamline using an electron beam, the new electronics met both required energy resolution and linearity and achieved a timing resolution of 30 ps for energies above 50 GeV.

Measurement of radiation-induced current through a SiC Schottky barrier diode in a clinical carbon beam cancer therapy field

Real-time physical dose evaluation was performed using radiation-tolerant SiC Schottky barrier diodes (SBDs). The radiation-induced current (RIC) generated in the SBD was measured under clinical carbon beam irradiation. A SiC SBD semiconductor detector (epitaxial layer, 69 µm thick; impurity concentration, 9.1 × 1014 cm−3; electrodes, 1 mm2) was used. The SiC SBD was irradiated with carbon ions having energy of 290 MeV/n at a maximum flux of therapeutic intensity (1 × 109 particles per second) at the Gunma University Heavy Ion Medical Center. The transition of the RIC value at any depth point in the Bragg curve was evaluated by changing the thickness of a water tank placed in front of the SiC SBD. The RIC from the SiC SBD was obtained with an applied voltage of up to 100 V for each moderator thickness. The physical dose distribution was also measured using a commercial ionization chamber. The Bragg peak was determined from the RIC distribution, and the transition was similar to that observed using the commercial ionization chamber.

The front-end electronics upgrade of the CMS ECAL barrel

The barrel part of the CMS electromagnetic calorimeter (ECAL) consists of 61200 PbWO4 crystals coupled to avalanche photodiodes (APDs). A decrease of the ECAL operating temperature from 18 °C to 9 °C is needed to mitigate the increase in APD noise from radiation-induced dark current in the conditions of the high luminosity upgrade of the LHC. Moreover, a full re-design of the front-end electronics has been undertaken in order to deal with the increase of pileup events and to improve the rejection of anomalous signals generated from direct interaction with the APDs. The VFE (Very Front-End) card will be equipped with two new ASICs: a fast trans-impedance amplifier named CATIA as well as a data conversion and compression ASIC named LiTE-DTU. The VFE will interface with the radiation tolerant LpGBT transceiver and the VTRx+ optical board, while trigger primitive generation will be moved off-detector to FPGA-based processors. The CATIA ASIC has a single input and two differential outputs with different gains in order to have better resolution for low energy signals. CATIA is designed in commercial CMOS 130 nm technology and can be controlled via an I2C interface. The LiTE-DTU ASIC embeds two 12-bit 160 MS/s ADCs, a sample selection logic, a lossless compression digital logic, and a 1.28 Gb/s serializer that will directly interface with the LpGBT e-links. LiTE-DTU is designed in commercial CMOS 65 nm technology. It embeds a PLL for the generation of the low jitter 1.28 GHz clock required by the ADCs and the serializer. Both ASICs have been extensively tested in lab and beam tests. This new system has been verified to fulfill the requirements of the experiment in terms of performance and radiation tolerance. The ASICs are now in the pre-production phase.

Upgrade of the CMS Barrel Electromagnetic Calorimeter for the High Luminosity LHC

The high luminosity upgrade of the LHC (HL-LHC) at CERN will provide unprecedented instantaneous and integrated luminosities of up to 7.5×1034 cm−2s−1 and 4500 fb−1, respectively, from 2029 onwards. To cope with the extreme conditions of up to 200 collisions per bunch crossing, and increased data rates, the on- and off-detector electronics of the CMS electromagnetic calorimeter (ECAL) will be replaced. A dual gain trans-impedance amplifier and an ASIC providing two 160 MHz ADC channels, gain selection, and data compression will be used. The lead tungstate crystals and avalanche photodiodes (APDs) in the current ECAL will keep performing well and will therefore be maintained. The noise increase in the APDs, due to radiation-induced dark currents, will be minimised by reducing the ECAL operating temperature from 18 °C to around 9 °C. Prototype HL-LHC electronics have been tested and have shown promising results. In two test beam periods using the CERN SPS H4 beamline and an electron beam, the new electronics achieved the target energy resolution and a timing resolution consistent that is consistent with our requirements of 30 ps timing for energies greater than 50 GeV.

Analysis of Ion-Induced SEFI and SEL Phenomena in 90 nm NOR Flash Memory

This article mainly focuses on the single event function interruption (SEFI) and single event latch-up (SEL) of 90 nm NOR flash memories. Devices were irradiated by ions with different linear energy transfer (LET) values from 12.9 to $65.8~MeV\cdot cm^{2}$ /mg. SEFI observed in the device is further divided into bit SEFI, column SEFI, and sector SEFI by severity of data corruption. Under irradiation with low LET value ions, SEL propagation-like phenomena were observed in this work, which was recognized as the process from local latch-up to global latch-up in the peripheral circuits. The underlying mechanisms for SEFI and SEL in NOR flash are discussed. Results indicate that the radiation-induced transient current should be responsible for SEFI, and different forms of SEFI depend on in which part of the circuit that transient current occurred. Besides, SEL in NOR flash is considered to be triggered from the peripheral circuits.

Commercial photodiodes and phototransistors as dosimeters of photon beams for radiotherapy.

The response to radiation typically used in radiotherapy treatments has been experimentally evaluated for three samples of two phototransistors (BPW85B and OP505A) and two PIN photodiodes types (VTB8440BH and BPW34S). To that end, a staggered irradiation cycle has been applied which included dose rate values from 0.81 to 4.87cGy/s, achieving a total absorbed dose of 21.4Gy. The samples have been irradiated with a linear accelerator and the relations between the induced photocurrent and the average and instantaneous dose rates, and between the accumulated charge and the absorbed dose, have been determined. The radiation-induced output currents were measured by means of an external interface of the devices to a previously designed readout unit. Experimental results of Si PIN photodiode BPW34S have shown a sensitivity of (13.9±0.5) nC/cGy, slight sensitivity dependence on dose rate, and a high linearity of the current with the average and instantaneous dose rate, requiring only 10V of reverse bias voltage. This device thermal drift has characterized and modeled for temperature effect compensation. Silicon PIN photodiode BPW34S, previously tested for X-rays and Co-60 gamma ray source, can also be a reliable candidate for dose rate and absorbed skin dose determination in typical radiotherapy treatments irradiations. A low sensitivity loss below 2% up to 21.4Gy has been measured, allowing its use as an affordable reusable skin dosimeter. Moreover, no significant difference has been observed between its response to dose-per-pulse and changing pulse repetition frequency in terms of sensitivity and dependence with dose-rate value.

Development and characterization of an LED-based detector for dosimetry in diagnostic radiology

Light-emitting diodes (LEDs) could be a potential dosimetry candidate because they are radiation hard, spectrally selective, direct band gap, and low-cost devices. Thus, an LED-based detector prototype was designed and characterized for dosimetry. A 20 × 20 cm2 array of surface mount device LED chips was sandwiched in photovoltaic mode between two intensifying screens to form a dosimetric system. The system was enclosed in a light-tight air cavity using black vinyl tape. The screens converted diagnostic x-ray beams into fluorescent blue light. LEDs, applied in detector mode, converted the fluorescent light into radiation-induced currents. A digital multimeter converted the analog currents into digital voltage signals. Prototype characterization was executed using (a) IEC 61267’s RQR 7 (90 kVp) and RQR 8 (100 kVp) beam qualities, and (b) low (25 mAs) and high (80 mAs) beam quantities. A standard dosimeter probe was simultaneously exposed with the prototype to measure the prototype’s absorbed dose. In all exposures, the x-ray beams were perpendicularly incident on both the dosimeter and prototype, at a fixed source to detector distance-60 cm. The LED array prototype’s minimum detectable dose was 0.139 mGy, and the maximum dose implemented herein was ∼13 mGy. The prototype was 99.18% and 98.64% linearly sensitive to absorbed dose and tube current–time product (mAs), respectively. The system was ±4.69% energy, ±6.8% dose, and ±7.7% dose rate dependent. Two prototype data sets were 89.93% repeatable. We fabricated an ultrathin (5 mm), lightweight (130 g), and a relatively low-cost LED-based dosimetric prototype. The prototype executed a simple, efficient, and accurate real-time dosimetric mechanism. It could thus be an alternative to the current passive dosimetric systems.

Electrical conductivity and X-ray sensing properties of TiO2:Cr thin film synthesised by chemical bath deposition method

X-ray sensing properties of chromium (Cr) doped titanium dioxide (TiO2) thin films synthesised by a chemical bath deposition method have been reported. Characterisation reports reveal that the films are polycrystalline and possess anatase phase of TiO2. There is no change of its crystalline phase after the doping of Cr. However, the average crystallite size is found to increase from 9 to 10 nm and the optical band gap decreased from 3.26 eV to 3.14 eV after the doping. The doping also enhanced the electrical conductivity of the films. The electrical conductivity under dark condition is increased from 1.11×10−2 to 1.58×10−1 S/(cm) after the doping of 0.10 M Cr. Similarly, the same under X-ray irradiation is also increased from 2.22×10−1 to 5.25×10−1 S/(cm). The doping influenced the detection quality of the films. The rise time of radiation-induced current is found to decrease from 0.91 to 0.84 s whereas the decay time increases from 1.18 to 1.32 s after the doping of 0.10 M Cr. The detection sensitivity of the films is discussed in regards to change in concentration of charge carriers as well as the structural changes occurred after the doping.

Thermoelectric Sensor Coupled Yagi–Uda Nanoantenna for Infrared Detection

We present an experimental demonstration of a thermoelectric sensor coupled with a nanoantenna as an alternative option for detecting infrared energy. Two nanoantenna design (single element and an array) variations based on Yagi-Uda technology and one separate nano-thermoelectric junction array were fabricated and tested. The nanoantennas were tuned to operate and respond at a center wavelength of 1550 nm (193.5 THz) optical C-band window, but they also exhibited a resonance response when excited by lasers of various wavelengths (650 nm and 940 nm). The radiation-induced electric currents in the nanoantennas, coupled with a nano-thermoelectric sensor, produced a potential difference as per the Seebeck effect. With respect to the uniform thermal measurements of the reference nanoantenna, the experiments confirmed the detection properties of the proposed nanoantennas; the single element detected a peak percentage voltage hike of 28%, whereas the array detected a peak percentage voltage hike of 80% at the center wavelength. Compared to state-of-the-art thermoelectric designs, this was the first time that such peak percentage voltages were experimentally reported following a planar design based on the Seebeck principle.

Dual electrical and optical detection of ionizing radiation: Radiation-induced currents and radioluminescence in NaMgF3:Sm

Simultaneous optical and electrical detection of ionizing radiation was achieved using near tissue-equivalent NaMgF3:Sm. The electrical characteristics of the system were capacitive and ohmic and the resistivity of the compound was on the order of 1013 Ω cm. During exposure to X-rays, the compound exhibited both radiation-induced electrical conductivity and radioluminescence from Sm2+ and Sm3+. Initially, strong dose history dependences were observed for both detection methods. The radiation-induced current stabilized after a priming dose and increased with dose rate according to a power law with an exponent Δ = 0.73, and the radioluminescence intensities increased linearly with dose rate. The mobility-lifetime product of the dominant charge carriers was high and estimated to be 1.6 × 10−4 cm2/V. Our results show that dual detection of ionizing radiation is possible using NaMgF3:Sm where the minimum detectable dose rates were 46 μGys−1 and 1.5 mGys−1 for the electrical and optical detection techniques, respectively.

Phosphorus Versus Arsenic: Role of the Photodiode Doping Element in CMOS Image Sensor Radiation-Induced Dark Current and Random Telegraph Signal

This work investigates the role of the phosphorus doping element in the radiation-induced dark current in a CMOS image sensor (CIS) photodiode. The neutron and proton irradiations on shallow arsenic-based photodiode CISs and deep phosphorus-based photodiodes CISs have been performed. The results highlight the applicability of the same dark current increase and random telegraph signal (RTS) models. Already verified on other photodiode structures, these results further extend the universality of these analytic tools. Moreover, it emphasizes that the phosphorus element does not play a significant role either in the radiation-induced dark current increase or in the dark current RTS. The results on RTS after annealing reveal the same recovery dynamic than those already observed in irradiated image sensors, suggesting that the phosphorus element does not play a significant role after annealing. Therefore, this work is a piece of experimental evidence supporting the idea that RTS induced by displacement damage is principally due to defect clusters mainly constituted of intrinsic silicon defects such as clusters of vacancies and interstitials.

CMS ECAL upgrade for precision timing and energy measurements at the High-Luminosity LHC

The High Luminosity upgrade of the LHC (HL-LHC) at CERN will provide unprecedented instantaneous and integrated luminosities of around 5×1034 cm−2s−1 and 3000 fb−1, respectively, from 2025 to 2035. During this operational period, an average of 140 to 200 collisions per bunch-crossing (pile up) is expected, posing a challenge to the event reconstruction. In order to cope with these extreme pile up conditions, harsh environment, and increased data rates, the Compact Muon Solenoid (CMS) detector is undergoing a radical Phase II upgrade program. In the barrel region of the CMS electromagnetic calorimeter (ECAL), the lead tungstate crystals and avalanche photodiodes (APDs) will keep performing well and will therefore be maintained, while the entire readout and trigger electronics will be replaced. A dual gain trans-impedance amplifier and an ASIC providing two 160 MHz ADC channels, gain selection, and data compression will be installed. The noise increase in the APDs, due to radiation-induced dark current, will be contained by reducing the temperature at which ECAL is operated. The trigger decision will be moved off-detector and performed by powerful and flexible FPGA processors, allowing for more sophisticated trigger algorithms to be applied. The upgraded ECAL will be capable of high-precision energy measurements and will greatly improve the time resolution for photons and electrons above 10 GeV. Together with the introduction of a new timing detector designed to perform timing measurements with the resolution of a few tens of picoseconds for minimum ionizing particles, the CMS detector will be able to precisely reconstruct the primary interaction vertex under the described pile up conditions.

Upgrade of the CMS electromagnetic calorimeter for precision timing and energy measurements at the High Luminosity LHC

The high luminosity upgrade of the LHC (HL-LHC) at CERN will provide unprecedented instantaneous and integrated luminosities of around 5 × 1034 cm−2 s−1 and up to 4500 fb−1, respectively, from 2027 to 2035. We predict an average of 140 to 200 concurrent interactions per bunch crossing (pile-up). This poses a major challenge to the event reconstruction. The Compact Muon Solenoid (CMS) detector is therefore undergoing an extensive Phase II upgrade program to prepare for these challenging conditions. The upgrade of the barrel part of the CMS electromagnetic calorimeter (ECAL) for HL-LHC will extend the detector performance to be able to cope with these harsh conditions, particularly the increased trigger and latency requirements at the HL-LHC. The lead tungstate crystals in the ECAL barrel sub-detector will still perform well. The avalanche photodiodes which detect the scintillation light will also continue to be operational with some increase in noise due to radiation-induced dark currents. However the entire readout electronics will need to be replaced. The upgraded detector will have a 25 fold improved trigger granularity and a sampling rate increase by a factor of four. In addition, the upgraded detector will have the new capability to provide precision timing measurements for photons and electrons with energies greater than 10 GeV. This will significantly improve the performance under the predicted pile-up conditions. High precision time resolution will be exploited for pileup mitigation and to permit the assignment of physics objects to their correct vertices. In this report the status of the ongoing R&D activities for the ECAL barrel upgrade will be presented.

In-Core Power Measurement Using SiC Semiconductor Detector

A SiC detector was fabricated and tested in harsh radiation environment of the High Flux Advanced Neutron Application Reactor (HANARO) reactor core at Korea Atomic Energy Research Institute (KAERI). A 4H-SiC with 30 µm thick epitaxial layer was used as the radiation sensor, and the detector was designed to be tolerable against thermal and radiation damages. Alpha response and I-V characteristics of fabricated SiC sensor was measured and detection performance of the SiC detector was evaluated in a neutron field of HANARO ex-core neutron irradiation facility. After preliminary tests, reactor power monitoring using the SiC detector was carried out by inserting it into the HANARO irradiation hole, IP-4. Radiation-induced current of the detector was recorded as reactor power increased up to 10 MWth. Maximum thermal and fast neutron fluxes were 9.4×1012 and 2.5×109 neutrons/cm2/sec, respectively, and total neutron fluence irradiated on the detector was 4.7×1016 neutrons/cm2. The detector showed good linearity of response up to the tested fluence, with R2 = 0.9997. Response speed of SiC detector was compared to that of a Rh self-powered neutron detector (SPND) in terms of signal saturation time. Averaged SiC detector saturation time was 12.8 seconds, approximately 11 times faster that of the Rh SPND.

Method for the differentiation of radiation-induced photocurrent from total measured current in P3HT/PCBM BHJ photodiodes

Thin film radiation-detecting diodes fabricated in the laboratory, such as an organic bulk heterojunction, often contain conductive leads, indium tin oxide traces and metallic interconnects which are exposed to the high-energy photon beam during operation. These components generate extraneous radiation-induced currents, that, if not accounted for, will erroneously be attributed to the detector. In commercial devices, these contributions are mitigated by minimizing the size of these components, an approach that is often not feasible in a research lab. Here we demonstrate a method to measure these extraneous signals, and by subtraction, correct the gross signal to accurately reflect the signal generated in the active volume of the diode itself.The method can effectively correct the extraneous signal.The method showed promise over a range of photon beam energies, dose rates, and field sizes.

Radiation-Induced Transient Currents in Films of Poly(arylene ether ketone) Including Phthalide Moiety.

The electrical properties of thin films of poly(arylene ether ketone) copolymers (co-PAEKs) with a fraction of phthalide-containing units of 3, 5, and 50 mol% in the main chain were investigated by using radiation-induced conductivity (RIC) measurements. Transient current signals and current-voltage (I-V) characteristics were obtained by exposing 20 ÷ 25 μm thick films of the co-PAEKs to monoenergetic electron pulses with energy ranging from 3 to 50 keV in an electric field ranging from 5 to 40 V/μm. The Rose-Fowler-Vaisberg semi-empirical model based on a multiple trapping formalism was used for an analysis of the RIC data, and the parameters of the highly dispersive charge carrier transport were evaluated. The analysis revealed that charge carriers moved in isolation from each other, and the applied electric fields were below the threshold field triggering the switching effect (a reversible high-to-low resistivity transition) in the co-PAEK films. It was also found that the co-PAEK films, due to the super-linear I-V characteristics, are highly resistant to electrostatic discharges arising from the effects of ionizing radiation. This property is important for the development of protective coatings for electronic devices.

Radiation Effects on High-Speed InGaAs Photodiodes

Photodiodes are important components in optical data links, and their performance degradation under irradiation has to be understood in order to guarantee the long-term functionality of the data links in radiation environments of high-energy physics experiments. Indium gallium arsenide (InGaAs) on indium phosphide (InP) photodiodes are attractive candidates for these applications, thanks to their relatively modest radiation-induced responsivity loss when operated at 850 nm. In this paper, we present the results that confirm earlier observed additional sensitivity penalties in InGaAs-based receivers. This behavior is further investigated by carrying out several proton tests where InGaAs photodiodes are irradiated together with alternative photodiode types. The critical parameters—responsivity, dark current, and capacitance—are measured up to fluences exceeding ${1\times 10^{16}}$ p/cm2. Radiation-induced dark current is shown to be orders of magnitude higher in InGaAs photodiodes than in GaAs and InGaAs on GaAs photodiodes. However, instead of the dark current increase, the additional losses with InGaAs photodiodes are shown to arise from strongly increased capacitance, which is a dominant feature only in InGaAs photodiodes. This is confirmed with simulations where the measured capacitance characteristics are used in the device model. Our results show that without precautions in the receiver design, radiation-induced capacitance can limit the use of InGaAs photodiodes in harsh radiation environments.