Alpha-particle Irradiation Research Articles

Swelling Mechanisms of UO2 Lattices with Defect Ingrowths.

The swelling that occurs in uranium dioxide as a result of radiation-induced defect ingrowth is not fully understood. Experimental and theoretical groups have attempted to explain this phenomenon with various complex theories. In this study, experimental lattice expansion and lattice super saturation were accurately reproduced using a molecular dynamics simulation method. Based on their resemblance to experimental data, the simulation results presented here show that fission induces only oxygen Frenkel pairs while alpha particle irradiation results in both oxygen and uranium Frenkel pair defects. Moreover, in this work, defects are divided into two sub-groups, obstruction type defects and distortion type defects. It is shown that obstruction type Frenkel pairs are responsible for both fission- and alpha-particle-induced lattice swelling. Relative lattice expansion was found to vary linearly with the number of obstruction type uranium Frenkel defects. Additionally, at high concentrations, some of the obstruction type uranium Frenkel pairs formed diatomic and triatomic structures with oxygen ions in their octahedral cages, increasing the slope of the linear dependence.

Ultraviolet radiation-induced modifications of the optical and registration properties of a CR-39 nuclear track detector

The UV–VIS (ultraviolet–visible) spectra and etching characteristics of poly allyl diglycol carbonate (PADC, a form of the CR-39 polymer) detector films after exposure to UV radiation for various times have been studied. Etching experiments were carried out on the UV-exposed CR-39 detectors after alpha particle and fission-fragment irradiation using a 252Cf source. The bulk and track etch rates were measured using the alpha and fission-fragment track diameters, and the sensitivity and the detection efficiency were also determined. The optical band gap for both indirect and direct transitions was calculated based on the absorption edge of the UV spectra of the pristine and variously UV-exposed detectors. The optical band gap evidently indicates a gradual change in the optical properties of the CR-39 detector that is induced by the UV radiation. This study shows that the UV-exposed CR-39 detectors were demonstrated to be highly sensitive to alpha particles, but proved to be somewhat less sensitive to the fission fragments.

Effects of 5.4 MeV alpha-particle irradiation on the electrical properties of nickel Schottky diodes on 4H–SiC

Current–voltage, capacitance–voltage and conventional deep level transient spectroscopy at temperature ranges from 40 to 300K have been employed to study the influence of alpha-particle irradiation from an 241Am source on Ni/4H–SiC Schottky contacts. The nickel Schottky barrier diodes were resistively evaporated on n-type 4H–SiC samples of doping density of 7.1×1015cm−3. It was observed that radiation damage caused an increase in ideality factors of the samples from 1.04 to 1.07, an increase in Schottky barrier height from 1.25 to 1.31eV, an increase in series resistance from 48 to 270Ω but a decrease in saturation current density from 55 to 9×10−12Am−2 from I–V plots at 300K. The free carrier concentration of the sample decreased slightly after irradiation. Conventional DLTS showed peaks due to four deep levels for as-grown and five deep levels after irradiation. The Richardson constant, as determined from a modified Richardson plot assuming a Gaussian distribution of barrier heights for the as-grown and irradiated samples were 133 and 151Acm−2K−2, respectively. These values are similar to literature values.

The optical, wettability and hardness properties of polyethylene improved by alpha particle irradiations

In this work, the optical, chemical and morphological changes of alpha irradiated low-density polyethylene (LDPE) were investigated using UV/Vis spectroscopy, Fourier transform infrared spectrometer (FTIR) and scanning electron microscope (SEM). In addition to, the wettability and Vicker’s Micro-Hardness have been studied using the contact angle measurements and Vicker’s Micro-Hardness tester. The polymer samples are irradiated with different times of alpha particles. UV/Vis spectra show that the absorbance increases with increase in the irradiation time and the absorption edge shifts toward the higher wavelength. This indicates to a decrease in the optical band gap energy and an increase in number of carbon clusters. FTIR analysis reveals that the formation of CH groups and O–H has been observed and also indicated the presence of unsaturations due to vinyl end groups in the irradiated samples. Noticeable decreases in the contact angle of irradiated samples were observed. This decrease reflects the increase in the wettability and consequently the surface free energy. This behavior is due to the formation of oxidized layer on the irradiated surface polymer. Induced increasing in the Vicker’s hardness in the irradiated polymers was observed, that can be attributed to crosslinking effects in the chain of the polymers.

Simulation study of dose enhancement in a cell due to nearby carbon and oxygen in particle radiotherapy

The aim of this study is to investigate the dose-deposition enhancement due to alpha-particle irradiation in a cellular model by using the carbon and the oxygen chemical compositions. A simulation study was performed to study dose enhancement due to carbon and oxygen for a human cell where the Geant4 code used for alpha-particle irradiation of a cellular phantom. The characteristics of the dose enhancements based on the concentrations of carbon and oxygen in the nucleus and cytoplasm by the alpha-particle radiation was investigated and was compared with those obtained by gold and gadolinium. The results showed that both the carbon- and the oxygen-induced dose enhancements were more effective than those of gold and gadolinium. We found that the dose enhancement effect was more dominant in the nucleus than in the cytoplasm if the carbon or the oxygen were uniformly distributed in the whole cell. For the condition that the added chemical composition was inserted only into the cytoplasm, the effect of the dose enhancement in the nucleus was weak. We showed that high-stopping-power materials offer a more effective dose enhancement efficacy and suggest that carbon nanotubes and oxygenation are promising candidates for dose enhancement tools in particle therapy.

Variation in RBE for Survival of V79-4 Cells as a Function of Alpha-Particle (Helium Ion) Energy

High linear energy transfer (LET) α particles are important with respect to the carcinogenic risk associated with human exposure to ionizing radiation, most notably to radon and its progeny. Additionally, the potential use of alpha-particle-emitting radionuclides in radiotherapy is increasingly being explored. Within the body the emitted alpha particles slow down, traversing a number of cells with a range of energies and therefore with varying efficiencies at inducing biological response. The LET of the particle typically rises from between ~70-90 keV μm(-1) at the start of the track (depending on initial energy) to a peak of ~237 keV μm(-1) towards the end of the track, before falling again at the very end of its range. To investigate the variation in biological response with incident energy, a plutonium-238 alpha-particle irradiator was calibrated to enable studies with incident energies ranging from 4.0 MeV down to 1.1 MeV. The variation in clonogenic survival of V79-4 cells was determined as a function of incident energy, along with the relative variation in the initial yields of DNA double-strand breaks (DSB) measured using the FAR assay. The clonogenic survival data also extends previously published data obtained at the Medical Research Council (MRC), Harwell using the same cells irradiated with helium ions, with energies ranging from 34.9 MeV to 5.85 MeV. These studies were performed in conjunction with cell morphology measurements on live cells enabling the determination of absorbed dose and calculation of the average LET in the cell. The results show an increase in relative biological effectiveness (RBE) for cell inactivation with decreasing helium ion energy (increasing LET), reaching a maximum for incident energies of ~3.2 MeV and corresponding average LET of 131 keV μm(-1), above which the RBE is observed to fall at lower energies (higher LETs). The effectiveness of single alpha-particle traversals (relevant to low-dose exposure) at inducing cell inactivation was observed to increase with decreasing energy to a peak of ~68% survival probability for incident energies of ~1.8 MeV (average LET of 190 keV μm(-1)) producing ~0.39 lethal lesions per track. However, the efficiency of a single traversal will also vary significantly with cell morphology and angle of incidence, as well as cell type.

Alpha particles induce pan-nuclear phosphorylation of H2AX in primary human lymphocytes mediated through ATM

The use of high linear energy transfer radiations in the form of carbon ions in heavy ion beam lines or alpha particles in new radionuclide treatments has increased substantially over the past decade and will continue to do so due to the favourable dose distributions they can offer versus conventional therapies. Previously it has been shown that exposure to heavy ions induces pan-nuclear phosphorylation of several DNA repair proteins such as H2AX and ATM in vitro. Here we describe similar effects of alpha particles on ex vivo irradiated primary human peripheral blood lymphocytes. Following alpha particle irradiation pan-nuclear phosphorylation of H2AX and ATM, but not DNA-PK and 53BP1, was observed throughout the nucleus. Inhibition of ATM, but not DNA-PK, resulted in the loss of pan-nuclear phosphorylation of H2AX in alpha particle irradiated lymphocytes. Pan-nuclear gamma-H2AX signal was rapidly lost over 24h at a much greater rate than foci loss. Surprisingly, pan-nuclear gamma-H2AX intensity was not dependent on the number of alpha particle induced double strand breaks, rather the number of alpha particles which had traversed the cell nucleus. This distinct fluence dependent damage signature of particle radiation is important in both the fields of radioprotection and clinical oncology in determining radionuclide biological dosimetry and may be indicative of patient response to new radionuclide cancer therapies.

Detailed 8-transistor SRAM cell analysis for improved alpha particle radiation hardening in nanometer technologies

Eight-transistor (8T) cells were introduced to improve variability tolerance, cell stability and low-voltage operation in high-speed SRAM caches by decoupling the read and write design requirements. Altogether, 8T-SRAM can be designed without significant area penalty over 6T-SRAM. Ionizing radiation effects are nowadays a major concern for reliability and dependability of emerging electronic SRAM devices, even for sea-level applications. In this paper we demonstrate from experimental results that the 8T-SRAM also exhibits an enhanced overall intrinsic tolerance to alpha particle radiation even though its critical charge values are smaller than conventional 6T cells. We have experimentally found that the soft error rate measured in accelerated experiments with alpha particles in SRAM devices implemented in a 65nm CMOS is 56% better for 8T cells with respect to standard 6T-cells. Even more, we show that this value can be increased up to a 200% through transistor sizing optimization.

Combined effects of depleted uranium and ionising radiation on zebrafish embryos.

In the environment, living organisms are exposed to a mixture of stressors, and the combined effects are deemed as multiple stressor effects. In the present work, the authors studied the multiple stressor effect in embryos of the zebrafish (Danio rerio) from simultaneous exposure to alpha particles and depleted uranium (DU) through quantification of apoptotic signals at 24 h post-fertilisation (hpf) revealed by vital dye acridine orange staining. In each set of experiments, dechorionated zebrafish embryos were divided into 4 groups, each having 10 embryos: Group (C) in which the embryos did not receive any further treatment; Group (IU) in which the embryos received an alpha-particle dose of 0.44 mGy at 5 hpf and were then exposed to 100 µg l(-1) of DU from 5 to 6 hpf; Group (I) in which the embryos received an alpha-particle dose of 0.44 mGy at 5 hpf and Group (U) in which the dechorionated embryos were exposed to 100 µg l(-1) of DU from 5 to 6 hpf. The authors confirmed that an alpha-particle dose of 0.44 mGy and a DU exposure for 1 h separately led to hormetic and toxic effects assessed by counting apoptotic signals, respectively, in the zebrafish. Interestingly, the combined exposure led to an effect more toxic than that caused by the DU exposure alone, so effectively DU changed the beneficial effect (hormesis) brought about by alpha-particle irradiation into an apparently toxic effect. This could be explained in terms of the promotion of early death of cells predisposed to spontaneous transformation by the small alpha-particle dose (i.e. hormetic effect) and the postponement of cell death upon DU exposure.

Effects of Alpha Particle and Proton Beam Irradiation as Putative Cross-Talk between A549 Cancer Cells and the Endothelial Cells in a Co-Culture System.

Background: High-LET ion irradiation is being more and more often used to control tumors in patients. Given that tumors are now considered as complex organs composed of multiple cell types that can influence radiosensitivity, we investigated the effects of proton and alpha particle irradiation on the possible radioprotective cross-talk between cancer and endothelial cells. Materials and Methods: We designed new irradiation chambers that allow co-culture study of cells irradiated with a particle beam. A549 lung carcinoma cells and endothelial cells (EC) were exposed to 1.5 Gy of proton beam or 1 and 2 Gy of alpha particles. Cell responses were studied by clonogenic assays and cell cycle was analyzed by flow cytometry. Gene expression studies were performed using Taqman low density array and by RT-qPCR. Results: A549 cells and EC displayed similar survival fraction and they had similar cell cycle distribution when irradiated alone or in co-culture. Both types of irradiation induced the overexpression of genes involved in cell growth, inflammation and angiogenesis. Conclusions: We set up new irradiation chamber in which two cell types were irradiated together with a particle beam. We could not show that tumor cells and endothelial cells were able to protect each other from particle irradiation. Gene expression changes were observed after particle irradiation that could suggest a possible radioprotective inter-cellular communication between the two cell types but further investigations are needed to confirm these results.

Research on radiation damage in titanium oxide memristors by Monte Carlo method

Nano titanium oxide memristor is expected to be the basic cell of a new generation of resistive memory and applied in the control and data storage systems of spacecrafts that work in a radiation environment. The changes of radiation key factors, such as energy, intensity, direction, and duration etc. probably have an influence on the radiation damage of the titanium oxide memristor. However, there has been no relatively detailed research of it. Based on the SRIM simulation, with the Monte Carlo method used as its core, the main part of cosmic rays——proton and alpha rays and the relevance between the key factors and radiation damage in titanium oxide memristor are quantitatively studied. According to the experimental data, the relations between key factors and R_{ON}, R_{OFF}, the mobility of oxygen vacancies are analyzed. We find that the mobility of oxygen vacancies increases abruptly when the ratio between oxygen vacancies and titanium oxide molecules is greater than 0.16. Moreover, compared with proton radiation, the alpha particle radiation going into the active region in titanium oxide memristor, especially at an oblique incidence angle may cause a greater damage to the device and should be strictly avoided, and the radiation damage increases as the intensity and duration of the radiation are raised. SPICE simulations are further utilized to show the influence of radiation on the characteristics of the coexistence of dopant drift and the tunnel barrier. We also find that the titanium oxide memristor device will gradually turn into a normal resistor with a low resistance and lose its charge-memory ability after persistent radiations. This work provides support for evaluating and reducing radiation damage for titanium oxide memristors, so as to improve the reliability of the device in radiation environment.

ROS/Autophagy/Nrf2 Pathway Mediated Low-Dose Radiation Induced Radio-Resistance in Human Lung Adenocarcinoma A549 Cell

Low-dose ionizing radiation (LDIR) can induce radio-resistance to following high dose radiation in various mammalian cells. The protective role of LDIR has been thought to be associated with the overall outcomes of cancer radiotherapy. NF-E2 related factor 2 (Nrf2) is a transcription factor that plays pivotal roles in maintaining cellular oxidative equilibrium. Since oxidative stress has been indicated to be a mediator of LDIR induced radio-resistance, the role of Nrf2 in this process was investigated in this research. Our results showed that in human lung adenocarcinoma A549 cell, 5cGy alpha particle induced radio-resistance to following 75cGy alpha particle radiation. The expression level of Nrf2 and its target Heme Oxygenase-1(HO-1) increased after 5cGy radiation. Both the shRNA of Nrf2 and the chemical inhibitor of HO-1 suppressed the induced radio-resistance, indicating the involvement of Nrf2 antioxidant pathway in this process. Further, we found 5cGy radiation stimulated autophagy process in A549. Inhibition of the autophagy process resulted in suppression of the radio-resistance and the induced expression of Nrf2 and HO-1. ROS scavenger N-acetyl-L-cysteine (NAC) blocked the autophagy process induced by 5cGy alpha particle, the upregulation of Nrf2 and HO-1, as well as the induced radio-resistance. In conclusion, ROS elevation caused by LDIR promoted Autophagy/Nrf2-HO-1 and conferred radio-resistance in A549.

EReLA: A Low-Power Reliable Coarse-Grained Reconfigurable Architecture Processor and Its Irradiation Tests

In this work, facing pressure from both the increasing vulnerability to single event effects (SEEs) and design constraints of the power consumption, we have proposed a Coarse-Grained Reconfigurable Architecture (CGRA) processor. Our goal is to translate a user programmable redundancy to a guide for balancing energy consumption on the one hand and the reliability requirements on the other. We designed software (SW) and hardware (HW) approaches, coordinating them closely to achieve this purpose. The framework provides several user-assignable patterns of redundancy and the hardware modules to interpret well these patterns. A first version prototype processor, with the name EReLA (Explicit Redundancy Linear Array) has been implemented and manufactured with a 0.18 μm CMOS technology. Stress tests based on alpha particle irradiation were conducted to verify the tradeoff between the robustness and the power efficiency of the proposed schemes.

Cerebrovascular diseases incidence and mortality in an extended Mayak Worker Cohort 1948-1982.

Incidence and mortality from cerebrovascular disease (CVD) [International Classification of Diseases 9th revision (ICD-9) codes: 430-438] was studied in a cohort of 22,377 workers first employed at the Mayak Production Association (Mayak PA) in 1948-1982 and followed up to the end of 2008. The cohort size was increased by 19% and follow-up extended by 3 years over the previous analysis. Radiation doses were estimated using an updated dosimetry system: Mayak Worker Dosimetry System 2008 (MWDS-2008). For the first time, in an analysis of this cohort, quantitative smoking data were used. Workers of the study cohort were exposed occupationally to prolonged external gamma rays and internal alpha particles. The mean (±standard deviation) total dose from external gamma rays was 0.54 ± 0.76 Gy (95% percentile 2.21 Gy) for males and 0.44 ± 0.65 Gy (95% percentile 1.87 Gy) for females. The mean plutonium body burden in the 31% of workers monitored for internal exposure was 1.32 ± 4.87 kBq (95% percentile 4.71 kBq) for males and 2.21 ± 13.24 kBq (95% percentile 4.56 kBq) for females. The mean total absorbed alpha-particles dose to the liver from incorporated plutonium was 0.23 ± 0.77 Gy (95% percentile 0.89 Gy) in males and 0.44 ± 2.11 Gy (95% percentile 1.25 Gy) in females. After adjusting for nonradiation factors (gender, age, calendar period, employment period, facility, smoking, alcohol consumption), there were significantly increasing trends in CVD incidence associated with total absorbed dose from external gamma rays and total absorbed dose to the liver from internal alpha-particle radiation exposure. Excess relative risks per Gy (ERR/Gy) were 0.46 (95% CI 0.37, 0.57) and 0.28 (95% CI 0.16, 0.42), respectively, based on a linear dose-response model. Adjustments for additional factors (hypertension, body mass index, duration of employment, smoking index and total absorbed dose to the liver from internal exposure during the analysis of external exposure and vice versa) had little effect on the results. The categorical analyses showed that CVD incidence was significantly higher among workers with total absorbed external gamma-ray doses greater than 0.1 Gy compared to those exposed to lower doses and that CVD incidence was also significantly higher among workers with total absorbed internal alpha-particle doses to the liver from incorporated plutonium greater than 0.01 Gy compared to those exposed to lower doses. The results of the categorical analyses of CVD incidence were in good agreement with a linear dose response for external gamma-ray doses but for internal alpha-particle doses the picture was less clear. For the first time an excess risk of CVD mortality was seen in workers whose livers were exposed to internal alpha-particle doses greater than 0.1 Gy compared to those workers who were exposed to doses of less than 0.01 Gy. A significant increasing trend for CVD mortality with internal alpha-particle dose was revealed in the subcohort of workers exposed at doses <1.0 Gy after having adjusted for nonradiation factors, ERR/Gy = 0.84 (95% CI, 0.09, 1.92). These updated results provide good evidence for a linear trend in risk of CVD incidence with external gamma-ray dose. The trend for CVD incidence with internal alpha-particle dose is less clear due to the impact of issues concerning the use of dose estimates based on below the limit of detection bioassay measurements.

Identification of gene-based responses in human blood cells exposed to alpha particle radiation.

BackgroundThe threat of a terrorist-precipitated nuclear event places humans at danger for radiological exposures. Isotopes which emit alpha (α)-particle radiation pose the highest risk. Currently, gene expression signatures are being developed for radiation biodosimetry and triage with respect to ionizing photon radiation. This study was designed to determine if similar gene expression profiles are obtained after exposures involving α-particles.MethodsPeripheral blood mononuclear cells (PBMCs) were used to identify sensitive and robust gene-based biomarkers of α-particle radiation exposure. Cells were isolated from healthy individuals and were irradiated at doses ranging from 0-1.5 Gy. Microarray technology was employed to identify transcripts that were differentially expressed relative to unirradiated cells 24 hours post-exposure. Statistical analysis identified modulated genes at each of the individual doses.ResultsTwenty-nine genes were common to all doses with expression levels ranging from 2-10 fold relative to control treatment group. This subset of genes was further assessed in independent complete white blood cell (WBC) populations exposed to either α-particles or X-rays using quantitative real-time PCR. This 29 gene panel was responsive in the α-particle exposed WBCs and was shown to exhibit differential fold-changes compared to X-irradiated cells, though no α-particle specific transcripts were identified.ConclusionCurrent gene panels for photon radiation may also be applicable for use in α-particle radiation biodosimetry.

Gene expression responses in human lung fibroblasts exposed to alpha particle radiation

This study examined alpha (α-) particle radiation effects on global changes in gene expression for the purposes of identifying potential signaling pathways that may be involved in Radon (222Rn) gas exposure and lung carcinogenesis. Human lung fibroblast cells were exposed to α-particle radiation at a dose range of 0–1.5Gy. Twenty-four hours post-exposure, transcript modulations were monitored using microarray technology. A total of 208 genes were shown to be dose-responsive (FDR adjusted p<0.05, Fold change>|2|) of which 32% were upregulated and 68% downregulated. Fourteen of the high expressing genes (>|4| fold) were further validated using alternate technology and among these genes, GDF15 and FGF2 were assessed at the protein level. GDF15, a known marker of lung injury, had expression levels 3-fold higher in exposed cell culture media, 24h post-irradiation as detected by ELISA. Further, pathway analysis of the dose-responsive transcripts showed them to be involved in biological processes related to cell cycle control/mitosis, chromosome instability and cell differentiation. This panel of genes with particular focus on GDF15 may merit further analysis to determine their specific role in mechanisms leading to α-particle induced lung carcinogenesis.

Neutron exposures in human cells: bystander effect and relative biological effectiveness.

Bystander effects have been observed repeatedly in mammalian cells following photon and alpha particle irradiation. However, few studies have been performed to investigate bystander effects arising from neutron irradiation. Here we asked whether neutrons also induce a bystander effect in two normal human lymphoblastoid cell lines. These cells were exposed to fast neutrons produced by targeting a near-monoenergetic 50.5 MeV proton beam at a Be target (17 MeV average neutron energy), and irradiated-cell conditioned media (ICCM) was transferred to unirradiated cells. The cytokinesis-block micronucleus assay was used to quantify genetic damage in radiation-naïve cells exposed to ICCM from cultures that received 0 (control), 0.5, 1, 1.5, 2, 3 or 4 Gy neutrons. Cells grown in ICCM from irradiated cells showed no significant increase in the frequencies of micronuclei or nucleoplasmic bridges compared to cells grown in ICCM from sham irradiated cells for either cell line. However, the neutron beam has a photon dose-contamination of 5%, which may modulate a neutron-induced bystander effect. To determine whether these low doses of contaminating photons can induce a bystander effect, cells were irradiated with cobalt-60 at doses equivalent to the percent contamination for each neutron dose. No significant increase in the frequencies of micronuclei or bridges was observed at these doses of photons for either cell line when cultured in ICCM. As expected, high doses of photons induced a clear bystander effect in both cell lines for micronuclei and bridges (p<0.0001). These data indicate that neutrons do not induce a bystander effect in these cells. Finally, neutrons had a relative biological effectiveness of 2.0±0.13 for micronuclei and 5.8±2.9 for bridges compared to cobalt-60. These results may be relevant to radiation therapy with fast neutrons and for regulatory agencies setting standards for neutron radiation protection and safety.

EBT2 films response to alpha radiation at 48.3 MeV.

To advance the development of a radiobiological experimental set-up for alpha particle irradiations at the Arronax cyclotron, experiments were performed to get the dose response of Gafchomic EBT2 films for alpha particles at 48.3 MeV. A system has been developed using a thin monitor copper foil and an X-ray spectrometer to measure the beam intensity and to calculate the delivered dose. On the other hand, the authors have irradiated EBT2 films, with 6-MV X rays, to get the dose response of EBT2 films for photons. The dose response curve for alpha particles shows an effect of polymerisation saturation compared with the dose response curve for photons.

Properties of thick GEM in low-pressure deuterium

Deuteron inelastic scattering (d, d') provides a promising spectroscopic tool to study nuclear incompressibility. In studies of deuteron inelastic scattering of unstable nuclei, measurements of low-energy recoiled particles is very important. In order to perform these measurements, we are developing a GEM-TPC based gaseous active target, called CAT (Center for nuclear study Active Target), operated with pure deuterium gas. The CAT has been tested with deuterium gas at 1 atm and 100-μm-thick GEMs. The low-pressure operation of CAT is planned in order to improve the detection capability for lower-energy recoil particles. A 400 μm-thick gas electron multiplier (THGEM) was chosen for the low-pressure operation of CAT. However, the properties of THGEM in low-pressure deuterium are currently undocumented. In this work, the performance of THGEM with low-pressure pure deuterium gas has been investigated. The effective gas gain of THGEM has been measured in various conditions using a 5.5-MeV 241Am alpha source. The effective gas gain was measured for 0.2-, 0.3- and 0.4-atm deuterium gas and a gas gain of about 103 was achieved by a double THGEM structure at 0.2 atm. The maximum achieved gain decreased with increasing gas pressure. The dependences of the effective gas gain on the electric field strengths of the drift, transfer and induction regions were investigated. The gain stability as a function of time in hydrogen gas was also tested and a relaxation time of THGEM of about 60 hours was observed with a continuous irradiation of alpha particles, which is significantly longer than previous studies have reported. We have tried to evaluate the gas gain of THGEM in deuterium gas by considering only the Townsend ionization process; however, it turned out that more phenomenological aspects, such as transfer efficiency, should be included in the evaluation. The basic properties of THGEM in low-pressure deuterium have been investigated for the first time.

Impact of Supply Voltage and Frequency on the Soft Error Rate of Logic Circuits

Alpha particle irradiations of 28-nm combinational logic and flip-flop circuits under different supply voltage and frequency operating conditions are investigated. Results indicate that while the supply voltage has a strong impact on the alpha particle soft error rate of flip-flops, the combinational logic error rate is relatively unaffected by supply voltage variation. Simulations are used to explain the results and highlight the differences between low-LET alpha particle irradiation and heavy-ion irradiation as far as voltage dependence of the logic soft error rate is concerned. Moreover, frequency has a much stronger impact on the logic soft error rate as compared to the flip-flop soft error rate. As a result, the frequency at which soft errors from combinational logic circuits will exceed errors from flip-flops decreases as the voltage increases. The impact of these observations is discussed in the context of soft-error mitigation strategies.