Radiation-induced Current Research Articles

Application of InGaP space solar cells for a radiation dosimetry at high dose rates environment of Fukushima Daiichi nuclear power plant

ABSTRACT Decommissioning the Fukushima Daiichi nuclear power plant (1F) after the accident caused by a tsunami in 2011 requires characterization of the fuel debris by dose distribution measurement. This paper describes the experimental and theoretical behavior of a radiation detector applied with InGaP solar cells is investigated and allow the localization and characterization of the fuel debris. In the irradiation test, it was observed that the radiation-induced current output of the InGaP solar cells increases linearly with increasing dose rates of 60Co γ-rays. For measurements at low dose rates, it becomes clear that the minimum detectable dose rate and resolution can be determined by analyzing the noise characterization. The maximum detectable level of radiation dosimetry for the InGaP solar cell was found to be higher than the highest γ-ray dose rate observable at the reactor core for 1F plants. Additionally, as an analysis of the radiation-induced current, it is attempted to express a relational expression between the absorbed dose rate and the creation of radiation-induced current pairs in the solar cells. The experimental and simulation results suggest that solar cells can be powerful tools for radiation dosimetry in high dose rate environments near the debris of the 1F plant.

First results from the CMS SiPM-based hadronic endcap calorimeter

The CMS hadronic calorimeter employs a plastic-scintillator-based endcap detector. In early 2017, a 20° wedge of the endcap was upgraded with silicon photomultipliers (SiPMs) and readout electronics based on the QIE11 digitizer. Based on the excellent experience with this 20° pilot system in 2017, the entire endcap detector was upgraded with SiPMs in early 2018. We report on the first ever operation of SiPMs in a high-rate collider detector.We compare SiPM performance to that of the previous hybrid photodiode / QIE8-based readout and describe how the factor three improvement in photon-detection efficiency, increased longitudinal segmentation, and improved response stability allow for mitigation of scintillator radiation damage and simplified calibration. We report in situ measurements of radiation-induced SiPM dark current. Overall, we show that the upgraded SiPM-based system brings more than 50% improvement in radiation-induced response degradation.

Improved Model for Excess Base Current in Irradiated Lateral p-n-p Bipolar Junction Transistors

An improved total ionizing dose model for lateral p-n-p bipolar junction transistors is described. The model captures the impact of charged defects on radiation-induced excess base current. Failure to incorporate this mechanism in model underestimates gain degradation.

Damage Factor for Radiation-Induced Dark Current in InGaAs Photodiodes

In this paper, a compendium of InGaAs photodiode irradiation test results is presented. These photodiodes were irradiated either with γ-rays, protons, neutrons, electrons, pions, alpha particles, or carbon ions of various energies. The displacement damage dose formalism was found to be effective in describing the radiation-induced dark current increase of any of the studied InGaAs photodiodes. The exploitation of capacitancebias voltage and current-bias voltage measurements also allows us to deduce a damage factor that can be used to assess the radiation-induced dark current in a great number of radiation environments.

Atypical Effect of Displacement Damage on LM124 Bipolar Integrated Circuits

LM124 operational amplifiers from three different manufacturers are irradiated with 60Co gamma rays and neutrons. During neutrons irradiation, one of the three integrated circuits exhibits an unexpected slew rates increase while its open loop gain and supply bias current follow the usual monotonic decrease as described in the literature. Analysis at circuit level shows that this phenomenon is due to an increase in the radiation-induced base current of the transistor used as buffer stage in the amplification chain. It is then demonstrated that a slight modification of the buffer transistor design, which is not implemented on the two other devices, enhances this phenomenon. Finally, the impact of the buffer transistor design on displacement damage and total ionizing dose response is investigated.

THz Wave Detection by Antenna-Coupled Nanoscale Thermoelectric Converters

We present a terahertz (THz) wave detector based on antenna-coupled single-metal nanoscale thermocouples. The dipole antenna is tuned to receive 600-GHz electromagnetic waves, and the nanoscale thermoelectric converter (NTEC) converts the heat, generated by the dissipated antenna currents to electrical signals. The measured polarization- and thermopile-length-dependent responses of these THz detectors, configured in thermopiles with various lengths, confirms that the measured signal is the result of the heating caused by the radiation-induced antenna currents and detected by the NTEC.

170 keV Proton radiation effects on low-frequency noise of bipolar junction transistors

ABSTRACTIn this paper, the electrical properties and low-frequency noise for bipolar junction transistors irradiated by 170 keV proton are examined. The result indicates that for the sample under proton irradiation with fluence 1.25 × 1014 p/cm2, base current IB in low bias range (VBE < 0.7 V) increases due to superimposition of radiation-induced recombination current, while the gain decreases significantly. Meanwhile, the low-frequency noise increases in the proton-irradiated sample. By analysis of evolution of parameters extracted from low-frequency noise power spectra, it is demonstrated that radiation-induced noise is mainly originated from carrier fluctuation modulated by generation–recombination centers (G–R centers) located at the interface of Si/SiO2, which are introduced by proton-radiation-induced defects. It is also confirmed that the electrical properties and noise behavior of irradiated sample are mostly affected by the carrier recombination process caused by G–R centers at the interface of Si/SiO2 than by G–R centers in EB junctions.

Nanoantenna arrays for infrared detection with single-metal nanothermocouples

Antenna-coupled nanothermocouples (ACNTC) for infrared detection have been widely studied. It has been shown that dipole antennas receive incident infrared radiation, and radiation-induced antenna currents heat the hot junction of the nanothermocouple, thus producing an electrical potential by the Seebeck effect. We have already demonstrated small thermopiles constructed from the series connection of ACNTCs. Here we study the infrared response of large-scale (N>500) nanoantenna arrays constructed from ACNTCs, where the antennas are spaced over a range of 25–300% of the incident wavelength. COMSOL simulations show temperature oscillations, and both simulations and experiments show corresponding open-circuit voltage oscillations as a function of antenna spacing. When the distance between the antennas is less than 2λ, constructive and deconstructive interference leads to an enhancement or attenuation of the antenna currents. Our simulations and experimental results are in excellent agreement, and show that the open-circuit voltage response of the array depends on the inter-column distance of the array and the separation between the hot and cold junctions. Furthermore, we report polarization- and array-size-dependent measurements to confirm that the responses of the arrays are the result of the heating of the hot junction by the radiation-induced antenna currents.

Time dependent modeling of single particle displacement damage in silicon devices

An approach combining molecular dynamics simulations with Kinetic Monte Carlo simulations is proposed to model the temporal evolution of single particle displacement damage in silicon. The three dimensional distributions of primary defects induced by Si recoils within 10ps are obtained by molecular dynamics simulations and subsequently the long-term evolution (over 105s) of multiple types of defects is simulated with Kinetic Monte Carlo technique fed by molecular simulation results. Based on classical Shockley–Read–Hall theory, the annealing factors of radiation-induced dark current related to the evolution of defects are predicted for photodiodes of 0.18μm CMOS image sensors under neutron irradiation. The calculation results are consistent with the experimental data.

Shape engineering of antenna-coupled single-metal nanothermocouples

We study the thermal response of antenna-coupled nanothermocouples (NTC) for long-wave infrared (IR) detection based on a single-metal nanostructure and shape engineering. The influence of the shape of the NTC junctions on the electrical and IR response of the sensor is studied. In particular, we compare detectors with abrupt and tapered junctions. We find that the thermoelectric behaviors of the two different NTC designs are identical when one of the junctions is selectively heated by a nanoscale heater to produce an open-circuit voltage. However, the IR responses are significantly different when the junctions are heated by the radiation-induced antenna current. Both simulations and experiments demonstrate that the tapered junction is more efficiently heated by the antenna, which results in nearly twice as large IR response compared with detectors having abrupt junctions.

Injection deep level transient spectroscopy: An improved method for measuring capture rates of hot carriers in semiconductors

An improved method for measuring the cross sections for carrier trapping at defects in semiconductors is described. This method, a variation of deep level transient spectroscopy (DLTS) used with bipolar transistors, is applied to hot carrier trapping at vacancy-oxygen, carbon-oxygen, and three charge states of divacancy centers (V2) in n- and p-type silicon. Unlike standard DLTS, we fill traps by injecting carriers into the depletion region of a bipolar transistor diode using a pulse of forward bias current applied to the adjacent diode. We show that this technique is capable of accurately measuring a wide range of capture cross sections at varying electric fields due to the control of the carrier density it provides. Because this technique can be applied to a variety of carrier energy distributions, it should be valuable in modeling the effect of radiation-induced generation-recombination currents in bipolar devices.

Towards thin-film self-powered radiation detectors employing disparate conductive layers

A new class of self-powered thin film radiation detectors is experimentally explored via their IV-curve characteristics. These detectors are parallel-plane microstructures composed of disparate atomic number (Z) thin-film electrodes separated by air gaps. Large radiation-induced electron currents (RIC) are observed for zero external voltage bias. Compared to ionization chambers (composed of macroscopic non-disparate low-Z electrodes), this anomalous behavior is due to two independent effects: traversal of fast electrons leaking from the high-Z cathodes and the auto-collection of ionization electrons from the air gap due to the presence of contact potential. The zero voltage current reaches up to 80% of the saturation current measured for non-zero bias voltages. The magnitude of saturation currents increases with the total anode and cathode atomic numbers. The stopping potentials (i.e., external voltage bias resulting in zero RIC current) correspond to the differences in the electrodes’ work functions (the contact potential) modified by the contributions from the fast electron current formed by the leaking electrons. These features make the thin film detector attractive for applications in x-ray medical or industrial imaging, dosimetry and radiation protection.

Current mode response of phototransistors to gamma radiation

This paper investigates the current mode response of four commercial NPN phototransistors under gamma radiation exposure from Co-60 source, with the aim to evaluate their applicability for gamma radiation dosimetry. The radiation-induced collector current was measured while the phototransistors were successively biased with 10 V and 20 V between collector and emitter. The main aspects analyzed in the experiment were the stability of the induced current, dependence of the induced current with respect to dose rate, short-term repeatability of the induced current and relation between the induced charge and the absorbed dose. The current response of all samples was stable during the 2-min irradiation sessions at the dose rates from 0.65 Gy/h to 32.1 Gy/h, with the relative uncertainty less than 5% in all cases, and the variation of the mean effective current as a function of dose rate was well fitted with the standard power relation. During the three consecutive 2-min irradiation sessions at the dose rate of 32.1 Gy/h, the repeatability of the induced charge was very good for all samples with the relative uncertainty below 3%. However, for continuous irradiation up to the absorbed dose of 20 Gy (10-min irradiation at the dose rate of 60 Gy/h), all samples exhibited significant current fall which can be attributed to the radiation-induced current gain degradation. As a result of the current degradation, the relationship between the induced charge and the absorbed dose was non-linear and it was demonstrated that the second order polynomial can be used as a calibration equation for determination of absorbed dose. The obtained results have shown that only one of the examined phototransistors may be a suitable candidate for gamma radiation dosimetry employing Co-60 source, since it has exhibited the highest current sensitivity, best linearity of the induced current with respect to dose rate and smallest dose rate dependence of the charge sensitivity.

Using RADFET for the real-time measurement of gamma radiation dose rate

RADFETs (RADiation sensitive Field Effect Transistors) are integrating ionizing radiation dosimeters operating on the principle of conversion of radiation-induced threshold voltage shift into absorbed dose. However, one of the major drawbacks of RADFETs is the inability to provide the information on the dose rate in real-time using the conventional absorbed dose measurement technique. The real-time monitoring of dose rate and absorbed dose can be achieved with the current mode dosimeters such as PN and PIN diodes/photodiodes, but these dosimeters have some limitations as absorbed dose meters and hence they are often not a suitable replacement for RADFETs. In that sense, this paper investigates the possibility of using the RADFET as a real-time dose rate meter so that it could be applied for simultaneous online measurement of the dose rate and absorbed dose. A RADFET sample, manufactured by Tyndall National Institute, Cork, Ireland, was tested as a dose rate meter under gamma irradiation from a Co-60 source. The RADFET was configured as a PN junction, such that the drain, gate and source terminals were grounded, while the radiation-induced current was measured at the bulk terminal, whereby the bulk was successively biased with 0 , 10 , 20 and 30 V. In zero-bias mode the radiation-induced current was unstable, but in the biased mode the current response was stable for the investigated dose rates from 0.65 to 32.1 Gy h−1 and up to the total absorbed dose of 25 Gy. The current increased with the dose rate in accordance with the power law, whereas the sensitivity of the current read-out was linear with respect to the applied bias voltage. Comparison with previously analyzed PIN photodiodes has shown that the investigated RADFET is competitive with PIN photodiodes as a gamma radiation dose rate meter and therefore has the potential to be employed for the real-time monitoring of the dose rate and absorbed dose.

Analysis of single-event upset of magnetic tunnel junction used in spintronic circuits caused by radiation-induced current

This paper describes the possibility of a switching upset of a magnetic tunnel junction (MTJ) caused by a terrestrial radiation-induced single-event-upset (SEU) current in spintronic integrated circuits. The current waveforms were simulated by using a 3-D device simulator in a basic circuit including MTJs designed using 90-nm CMOS parameters and design rules. The waveforms have a 400 -μA peak and a 200-ps elapsed time when neutron particles with a linear energy transfer value of 14 MeV cm2/mg enter the silicon surface. The authors also found that the SEU current may cause soft errors with a probability of more than 10−12 per event, which was obtained by approximate solution of the ordinary differential equation of switching probability when the intrinsic critical current (IC0) became less than 30 μA.

Radiation-Induced Currents in 4H-SiC Dosimeters for Real-Time Gamma-Ray Dose Rate Monitoring

In order to test the response of radiation-induced current with wide range of dose rate, a Silicon Carbide (SiC) dosimeter is exposed to gamma-rays emitted from a 60Co source. The SiC dosimeter in this study is made of a high purity semi-insulating 4H-SiC with nickel and aluminum electrodes. We have successfully demonstrated that the radiation-induced currents in the dosimeter show a linear relationship with the dose rate, and are repeatable and stable.

Reset Tree-Based Optical Fault Detection

In this paper, we present a new reset tree-based scheme to protect cryptographic hardware against optical fault injection attacks. As one of the most powerful invasive attacks on cryptographic hardware, optical fault attacks cause semiconductors to misbehave by injecting high-energy light into a decapped integrated circuit. The contaminated result from the affected chip is then used to reveal secret information, such as a key, from the cryptographic hardware. Since the advent of such attacks, various countermeasures have been proposed. Although most of these countermeasures are strong, there is still the possibility of attack. In this paper, we present a novel optical fault detection scheme that utilizes the buffers on a circuit's reset signal tree as a fault detection sensor. To evaluate our proposal, we model radiation-induced currents into circuit components and perform a SPICE simulation. The proposed scheme is expected to be used as a supplemental security tool.

Effect of radiation induced current on the quality of MR images in an integrated linac‐MR system

In integrated linac-MRI systems, the RF coils are exposed to the linac's pulsed radiation, leading to a measurable radiation induced current (RIC). This work (1) visualizes the RIC in MRI raw data and determines its effect on the MR image signal-to-noise ratio (SNR) (b) examines the effect of linac dose rate on SNR degradations, (c) examines the RIC effect on different MRI sequences, (d) examines the effect of altering the MRI sequence timing on the RIC, and (e) uses a postprocessing method to reduce the RIC signal from the MR raw data. MR images were acquired on the linac-MR prototype system using various imaging sequences (gradient echo, spin echo, and bSSFP), dose rates (0, 50, 100, 150, 200, and 250 MU∕min) and repetition times (TR) with the gradient echo sequence. The images were acquired with the radiation beam either directly incident or blocked from the RF coils. The SNR was calculated for each of these scenarios, showing a loss in SNR due to RIC. Finally, a postprocessing method was applied to the image k-space data in order to remove partially the RIC signal and recover some of the lost SNR. The RIC produces visible spikes in the k-space data acquired with the linac's radiation incident on the RF coils. This RIC leads to a loss in imaging SNR that increases with increasing linac dose rate (15%-18% loss at 250 MU∕min). The SNR loss seen with increasing linac dose rate appears to be largely independent of the MR sequence used. Changing the imaging TR had interesting visual effects on the appearance of RIC in k-space due to the timing between the linac's pulsing and the MR sequence, but did not change the SNR loss for a given linac dose rate. The use of a postprocessing algorithm was able to remove much of the RIC noise spikes from the MR image k-space data, resulting in the recovery of a significant portion, up to 81% (Table II), of the lost image SNR. The presence of RIC in MR RF coils leads to a loss of SNR which is directly related to the linac dose rate. The RIC related loss in SNR is likely to increase for systems that are able to provide larger than 250 MU∕min dose. Some of this SNR loss can be recovered through the use of a postprocessing algorithm, which removes the RIC artefact from the image k-space.

Ratchet effects in two-dimensional systems with a lateral periodic potential

Radiation-induced ratchet electric currents have been studied theoretically in graphene with a periodic noncentrosymmetric lateral potential. The ratchet current generated under normal incidence is shown to consist of two contributions, one of them being polarization-independent and proportional to the energy relaxation time, and another controlled solely by elastic scattering processes and sensitive to both the linear and circular polarization of radiation. Two realistic mechanisms of electron scattering in graphene are considered. For short-range defects, the ratchet current is helicity-dependent but independent of the direction of linear polarization. For the Coulomb impurity scattering, the ratchet current is forbidden for the radiation linearly polarized in the plane perpendicular to the lateral-potential modulation direction. For comparison, the ratchet currents in a quantum well with a lateral superlattice are calculated at low temperatures with allowance for the dependence of the momentum relaxation time on the electron energy.

Radiation induced current in the RF coils of integrated linac‐MR systems: The effect of buildup and magnetic field

In integrated linac-MRI systems, a measurable radiation induced current (RIC) is caused in RF coils by pulsed irradiation. This work (1) tests a buildup method of RIC removal in planar conductors; (2) validates a Monte Carlo method of RIC calculation in metal conductors; and (3) uses the Monte Carlo method to examine the effects of magnetic fields on both planar conductor and practical cylindrical coil geometries. The RIC was measured in copper and aluminum plates, taken as the RF coil conductor surrogates, as a function of increasing thickness of buildup materials (teflon and copper). Based on the Penelope Monte Carlo code, a method of RIC calculation was implemented and validated against measurements. This method was then used to calculate the RIC in cylindrical coil geometries with various air gaps between the coil conductor and the enclosed water phantom. Magnetic fields, both parallel and perpendicular to the radiation beam direction, were then included in the simulation program. The effect of magnetic fields on the effectiveness of RIC removal with the application of buildup material was examined in both the planar and the cylindrical geometries. Buildup reduced RIC in metal plate conductors. For copper detector∕copper buildup case, the RIC amplitude was reduced to zero value with 0.15 cm copper buildup. However, when the copper is replaced with teflon as buildup atop the copper conductor, the RIC was only reduced to 80% of its value at zero buildup since the true electronic equilibrium cannot be obtained in this case. For the aluminum detector∕teflon buildup case, the initial amplitude of the RIC was reduced by 90% and 92% in planar aluminum conductor and a surface coil, respectively. In case of cylindrical coils made of aluminum, teflon buildup around the coil's outer surface was generally effective but failed to remove RIC when there was an air gap between the coil and the phantom. Stronger magnetic fields (>0.5 T) perpendicular to the beam direction showed a modest decrease in the RIC for planar conductors with buildup. In the cylindrical geometries, the effect of magnetic fields was very small compared to the effect of introducing air gaps. Loss in signal-to-noise ratio (SNR) due to RIC was reduced from 11% to 5% when a simple buildup was applied to the solenoid in a preliminary experiment. The RIC in RF coils results from the lack of electronic equilibrium in the coil conductor as the RIC in planar conductor was completely removed by identical buildup of adequate thickness to create electronic equilibrium. The buildup method of RIC removal is effective in cylindrical coil geometry when the coil conductor is in direct contact with the patient. The presence of air makes this method of RIC removal less effective although placing buildup still reduces the RIC by up to 60%. The RIC Monte Carlo simulation is a useful tool for practical coil design where radiation effects must be considered. The SNR is improved in the images obtained concurrently withradiation if buildup is applied to the coil.