Irradiation Fluence Research Articles

Unlocking the performance evolution of GdBCO coated conductors irradiated by deuterium plasma

REBa2Cu3O7-δ (REBCO, RE: rare earth) coated conductors (CCs) can generate a powerful magnetic field and are optimal for sustaining the reaction in fusion devices. However, the REBCO CCs will inevitably be exposed to neutron radiation during device operation. Transmutation produces gas atoms such as hydrogen will affect their properties. In this paper, GdBCO CCs were irradiated by 20 eV deuterium plasma. It was found that the irradiation introduced smaller (2–4 nm) pinning sites that formed a mixed pinning landscape with rare earth oxides (tens of nanometres) in the pristine samples, leading to an improved vortex pinning. At an irradiation fluence of 5.0 × 1018 D cm−2, the J c values of the samples irradiated by deuterium can maintain the best enhancement of in-field performance at 4.2 K. Excess irradiation results in a decrease in J c, a broadening of the superconducting transition width, and an enhanced disorder in GdBCO. This study provides some valuable insights for potential changes in the properties of REBCO CCs irradiated in fusion devices.

Subpicosecond laser ablation behavior of a magnesium target and crater evolution: Molecular dynamics study and experimental validation

Abstract The micro-ablation processes and morphological evolution of ablative craters on single-crystal magnesium under subpicosecond laser irradiation are investigated using molecular dynamics (MD) simulations and experiments. The simulation results exhibit that the main failure mode of single-crystal Mg film irradiated by a low fluence and long pulse width laser is the ejection of surface atoms, which has laser-induced high stress. However, under high fluence and short pulse width laser irradiation, the main damage mechanism is nucleation fracture caused by stress wave reflection and superposition at the bottom of the film. In addition, Mg[0001] has higher pressure sensitivity and is more prone to ablation than Mg [ 10 1 ¯ 0 ] . The evolution equation of crater depth is established using multi-pulse laser ablation simulation and verified by experiments. The results show that, under multiple pulsed laser irradiation, not only does the crater depth increase linearly with the pulse number, but also the quadratic term and constant term of the fitted crater profile curve increase linearly.

Neutron irradiation and polarization effect of 4H–SiC Schottky detector

Neutron irradiation experiments were carried out on a 4H–SiC Schottky detector. The effects of neutron and accompanying γ-rays irradiation on the electrical properties, charge collection efficiency (CCE), energy resolution and crystal defects of 4H–SiC detectors were investigated. The total irradiation fluence was 1.24 × 1014 n/cm2, with an equivalent 1 MeV neutron fluence of 1.33 × 1015 n/cm2. Following neutron irradiation, the turn-on voltage increased significantly, and the capacitance of the Schottky junction no longer varied with the reverse bias voltage. The CCE of the detector decreased from 100% to 90.8%, while the energy resolution increased from 0.79% to 1.49%. The irradiated detector required a higher bias voltage for optimal performance. Additionally, we observed two defect levels, Ec-0.5 eV and Ec-0.35 eV, in the 4H–SiC crystals after irradiation. Their generation is also related to gamma ray irradiation. The detector exhibited a polarization effect, where the energy spectrum split into two distinct components during prolonged measurement of monoenergetic α particles. The peak position gradually shifted towards the lower energy side with increasing testing time. These effects can be mitigated by increasing the bias voltage to enhance the electric field strength in the drift region.

Stability of titanium deuteride films irradiated with pulsed ion beams

Titanium deuteride films are widely used as target materials for neutron generators. Intense pulsed ion beams irradiated titanium deuteride films, and their structure stabilities were investigated by combination with scanning electron microscopy, transmission electron microscopy, grazing incidence angle X-ray diffraction, slow positron beam, scratch test and finite element analysis. The beam energy density was 0.3 J/cm2. Five different irradiation fluences of 3 × 1014, 1 × 1015, 3 × 1015, 1 × 1016, 3 × 1016 cm−2 were performed at room temperature. The adhesion strength between the film and Mo substrate decreased with increasing fluence. Moreover, surface melting and grain growth occurred after the beam irradiation with fluences over 3 × 1015 cm−2. The morphology of scratch tracks shows that the titanium deuteride film suffers a transition from ductile fracture to brittle fracture with increasing fluence. The reason for the decreasing adhesion strength was discussed via the introduction of thermal stress and lattice structure recovery. The research result is critical for evaluating the lifetime of titanium deuteride films based on failures in structures and a decrease in concentration of the inner deuterium.

Swift heavy ion irradiation-driven energy band engineering and its profound influence on the photoresponse of β-Ga2O3 ultraviolet photodetectors

Swift heavy Ta ions with an ultra-high energy of 2896 MeV are utilized for irradiation of β-Ga2O3 photodetectors. Noteworthy variations in device performance under different wavelengths are observed. Under 254 nm light illumination, the photocurrent of the devices exhibit degradation at low ion fluences but gradually recover and even surpass the performance of non-irradiated devices at the irradiation fluence of 1 × 1010 cm−2. Conversely, under 365 nm light illumination, photocurrent increases at low fluence but slightly decreases at the same high fluence of 1 × 1010 cm−2. Cathodoluminescence spectra and first-principles calculations elucidate the mechanism underlying the evolution of device performance with irradiation fluence. At low irradiation fluence, the introduction of point defects such as oxygen vacancies and gallium vacancies leads to an expansion of the bandgap, resulting in a decline in photocurrent under 254 nm light illumination. Additionally, deep defect levels are generated by these point defects, promoting an enhancement of photocurrent under 365 nm light illumination. Higher fluences transform these point defects into complex defects such as Ga–O pair vacancies, resulting in a reduction in the bandgap. Consequently, an increase in photocurrent is observed for devices illuminated with 254 nm light. However, at high irradiation fluences, charge recombination induced by the presence of deep defect levels becomes more significant, leading to a decrease in photocurrent when exposed to 365 nm light. No matter what, at 1 × 1010 cm−2 fluence, β-Ga2O3 photodetectors still maintain excellent performance, implying their strong radiation resistance and immense potential for application in space environments.

Optimization of energy parameters for laser-induced photodynamic therapy of cervical tissues using numerical simulation and fluorescent navigation

SignificanceThe main problem in the photodynamic therapy of tumors is insufficient light exposure to tissue depth or the appearance of undesirable surface effects. It is required to investigate the influence of energy density and radiation spot diameter on the photosensitizer photobleaching efficiency by depth. ApproachOptimization of energy parameters for laser-induced photodynamic therapy of cervical tissues was conducted using numerical simulation and fluorescent navigation. ResultsThe laser radiation fluence rate in the near-surface layer of cervical tissue increases relative to the incident radiation fluence rate with increasing spot diameter in the range from 0.2 to 15 mm. The photosensitizer photobleaching increases with an increase in the spot diameter from 5 to 15 mm. ConclusionsThe developed method will improve the efficiency of photodynamic therapy by providing a therapeutic effect throughout the entire depth of tumor invasion without superficial thermal damage.

Selective modulation of electronic transport in VO2 induced by 10 keV helium ion irradiation

Vanadium dioxide (VO2) manifests an abrupt metal–insulator transition (MIT) from monoclinic to rutile phases, with potential use for tunable electronic and optical properties and spiking neuromorphic devices. Understanding pathways to modulate electronic transport in VO2, as well as its response to irradiation (e.g., for space applications), is critical to better enable these applications. In this work, we investigate the selective modulation of electronic transport in VO2 films subject to different 10 keV helium ion (He+) fluences. Under these conditions, the resistivity in the individual monoclinic and rutile phases varied by 50%–200%, while the MIT transformation temperature remains constant within 4 °C independent of irradiation fluence. Importantly, different trends in the resistivity of the monoclinic and rutile phases were observed both as a function of total He fluence as well as in films grown on different substrates (amorphous SiO2/Si vs single crystal Al2O3). Through a combination of measurements including majority carrier sign via Seebeck, low frequency noise, and TEM, our investigation supports the presence of different kinds of point defects (V in; O in), which may arise due to grain boundary defect interactions. Our work suggests the utility of He irradiation for the selective modulation of VO2 transport properties for neuromorphic, in contrast to other established but non-selective methods, like doping.

Radiation hardness of self-powered Si/SiC heterojunction detector under neutron irradiation

When typically confronted with harsh environments in space, semiconductor radiation detectors with low-power consumption and long service life are preferred. To address this concern, a novel Si/SiC heterojunction detector is proposed in this paper. At a neutron irradiation fluence of 1 × 1012 cm−2, the detector has a charge collection efficiency of 96.2% and an energy resolution of 0.95% at 10 V bias at 243Am-244Cm alpha particle detection. It can maintain a charge collection efficiency of 44.2% in the self-powered mode. The detector's performance is improved significantly using the heterojunction structure, extending its carrier lifetime. Due to its exceptional performance in sustaining high charge collection efficiency at low bias or even in self-powered mode following neutron irradiation, the Si/SiC heterojunction detector has been established as a promising option for space radiation detection.

Irradiation resistance of thermo-optical properties of zirconium diboride by 3 MeV electrons

Due to good thermal conductivity and thermal shock resistance, ultra-high temperature ceramics such as zirconium diboride (ZrB2) have been investigated as promising materials to be used in reusable thermal protection systems TPSs are vital to the heat balance of a spacecraft during atmospheric reentry and subsequent operation in space. Hence, the thermal and optical properties are especially critical for such applications. Meanwhile, radiation exposure in space can pose risks of degrading such material properties, especially over a prolonged mission duration. The interaction of electron radiation-which can be found in the outer Van Allen belt, with ZrB2 has not been studied previously and was chosen as the main scope of this study. An electron source of 3 MeV with different radiation exposure time was used. The response of thermo-optical properties of ZrB2 to increasing electron radiation fluences was investigated. ZrB2 samples were made through spark plasma sintering into sintered pellets and then exposed to 3 MeV electron irradiation. These ZrB2 samples were characterized by their microstructure, thermal conductivity, coefficient of thermal expansion (CTE), emittance, absorptivity, and surface roughness before and after irradiation. It was found that ZrB2’s thermo-optical properties showed high radiation resistance at these fluences, and no apparent microstructural change was observed after irradiation. However, the irradiated samples had, on average, a 29% lower surface roughness than the unirradiated samples, possibly originating from electron sputtering.

Synergistic effect of electrical bias and proton irradiation on the electrical performance of β-Ga2O3 p–n diode

The synergistic impact of reverse bias stress and 3 MeV proton irradiation on the β-Ga2O3 p–n diode has been studied from the perspective of the defect in this work. The forward current density (JF) is significantly decreased with the increase in proton irradiation fluence. According to the deep-level transient spectroscopy results, the increase in the acceptor-like trap with an energy level of EC-0.75 eV within the β-Ga2O3 drift layer, which is most likely to be Ga vacancy-related defects, can be the key origin of the device degradation. The increase in these acceptor-like traps results in the carrier concentration reduction, which in turn leads to a decrease in JF. Furthermore, compared with the case of proton irradiation with no bias, the introduction of −100 V electrical stress induced a nearly double decrease in JF. Based on the capacitance–voltage (C–V) measurement, with the support of the electric field, the carrier removal rate increased from 335 to 600 cm−1. Similar to the above-mentioned phenomenon, the trap concentration also increased significantly. We propose a hypothesis elucidating the synergistic effect of electrical stress and proton irradiation through the behavior of recoil nuclei under the electric field.

The effect of nickel additive and ion irradiation on the structural and optical properties of lithium borate glasses

The study investigates the impact of nickel oxide (NiO) doping (0%, 0.1%, 0.2%, and 0.3% wt%) on the glass composition 85B2O3-15Li2O using the melt quenching technique. Both X-ray diffraction (XRD) and FTIR confirm the amorphous nature and functional groups. Density, molar volume, average boron separation, ion concentration, interionic distance, polaron radius,. UV-visible absorption (200–1100 nm) was also recorded before and after nitrogen ion beam irradiation (fluence: 8x1017 and 16x1017 ion/cm2). Results indicate a decrease in the optical energy gap (Eoptical gap) and an increase in Urbach’s energy (EU) with higher NiO content, especially post-irradiation. Nitrogen ion irradiation at higher doses (16x1017 ion/cm2) induces more significant effects, attributed to increased non-bridging oxygen species (NBOs) formation and finally dielectric parameters were measured from 100 Hz to 100 kHz. Overall, the ability to tailor borate glass properties via nitrogen ion irradiation holds promise for diverse technological applications in optoelectronics, photonics, sensors, and radiationdetection

Effect of deformation nanostructuring on ion-beam erosion of copper

The effect of deformation nanostructuring on ion-beam erosion of copper at high fluences of irradiation with 30 keV argon ions was experimentally studied. Deformation nanostructuring by high-pressure torsion was used to form an ultrafine grained structure with a grain size of ~0.4 µm in copper samples with an initial grain size about 2 µm. It was found that when a layer of thickness comparable to the grain size was sputtered, a steady-state cone-shaped relief was formed on the copper surface, the appearance of which did not change with increasing irradiation fluence. It has been shown that the smaller the grain size in copper, the greater the concentration and the smaller the cone height on the surface. The cone inclination angles, close to 82°, as well as the sputtering yield of 9.6 at./ion, practically does not depend on the copper grain size, the thickness of the sputtered layer, and the irradiation fluence. Calculations using the SRIM code showed that when taking into account the sputtering of atoms from the walls of the cones, the sputtering yield of a cone-shaped copper relief Үc, was 3.5 times less than the yield of a single cone, 1.2 times greater than the sputtering yield of a smooth surface, and the value of 9.25 at./ion was close to the experimentally measured one.

Surface modification of ZrC dispersion-strengthened W under low energy He plasma irradiation

ZrC dispersion-strengthened W exhibits high strength/ductility, low ductile-to-brittle transition temperature, and excellent thermal shock resistance, making it a promising candidate plasma-facing material for future fusion devices. In this study, surface modification of 0.5 wt.% ZrC dispersion-strengthened W (WZrC) under low energy and high fluence He plasma irradiation at high temperature was presented. Under the energy of 90 eV and fluence ranging from 6 × 1024 He·m−2–2 × 1026 He·m−2 He irradiation at 920 °C, a typical fuzz nanostructure appeared on the W matrix of WZrC. The thickness of fuzz layer is proportional to the square root of He irradiation fluence. The fuzz showed comparable thickness and structural features to pure W, indicating limited effects of the particle’s addition on resistance to high fluence He irradiation at high temperatures. Under continuous He injection, the fuzz would grow extending onto the particle area, making the particle obscured. Besides, the erosion behavior of particles under He plasma irradiation has been investigated, which is thought to be dominated by a sputtering process. Under the He influence of 6 × 1024 He·m−2, only nanopores were observed in the surface region. With fluence increasing to 5 × 1025 He·m−2, the surface became relatively uneven with larger holes. W aggregated in spots and distributed on the surface of the particle, which might be the result of subthreshold sputtering and deposition. When fluence further increased to 2 × 1026 He·m−2, the particles were eroded completely and covered by the extended fuzz, forming cavities. In addition, distinctive layered nanotendrils were observed above the cavities, which were characterized to consist of inner W-riched skeletons and outer Zr-riched layers. It indicates that the layered nanotendrils should be the result of fuzz extension combined with particle sputtering/deposition.

Incident beam current impact on space-charge retention in electron dynamitron irradiated polymethyl methacrylate

Dielectric charging aboard spacecraft and satellites is a persistent and pressing issue in materials design and applications. This study investigated the effect of electron irradiation on charge trapping and leakage properties in polymethyl methacrylate, which is necessary for determining the maximum permissible fluence of radiation before the material is pushed beyond its breakdown threshold in charged particle radiation-intense environments. It was observed that dielectric breakdown in the form of an electrostatic discharge event cannot be induced under the conditions of this experiment after an amount of time that is dependent on initial electron fluence. This time limit for which an electrostatic discharge can be induced was found to be longer for the lower beam current irradiations. The work presented here discusses the factors affecting charge leakage using a global electric field-driven model.

Influence of swift heavy ion irradiation on structure and morphology of La0.25Pr0.375Ca0.375MnO3 film

The effects of Ag15+ (120 MeV) swift heavy ion (SHI) irradiation on the structural and morphological properties of epitaxial La0.25Pr0.375Ca0.375MnO3 (LPCMO) thin films were investigated by x-ray scattering and atomic force microscopy (AFM) techniques. LPCMO films of thickness ∼ 280 Å were irradiated with an Ag15+ ion beam at different fluences of 1 × 1011, 5 × 1011, and 1 × 1012 ions cm−2. XRD results suggested the development of the tensile stress along the out-of-plane direction of the LPCMO film upon ion irradiation, which increases on increasing the ion fluence. The morphology of the film was also modified with the irradiation and an increase in the fluence of the ion beam enhanced the in-plane height-height correlation length scale (grain size) with a loss of the fractal behaviours. The linear variation of microstrain with ion irradiation fluence in thin LPCMO film can be considered for a possible strain-driven application in modifying functional properties of such a phase separated complex oxide.

HICU PIE results of neutron-irradiated lithium metatitanate pebbles

Lithium metatitanate (Li2TiO3) pebbles were irradiated with neutrons within the HICU (High neutron fluence Irradiation of pebble staCks for fUsion) experiment to investigate their material properties and tritium release behaviour in a post-irradiation examination (PIE). The irradiation temperature is the most significant influence on the material. Besides a higher irradiation temperature, a higher initial Li–6 content tends to lead to an increased tritium generation resulting in the formation of the secondary lithium depleted phase Li4Ti5O12. A pre-compaction of the pebble bed does not have an apparent influence on the material properties. Tritium is released as semi-tritiated water and semi-tritiated hydrogen (HTO and HT) and its release is enhanced at elevated irradiation temperatures.

Different mechanisms of A-site and B-site high entropy effect on radiation tolerance of pyrochlores

The properties of high entropy pyrochlore have been studied extensively, but there is no consistent conclusion on its radiation tolerance. Besides, the mechanism of the high entropy effect on the radiation tolerance of pyrochlore is still unclear. In this work, combined with experiments and calculations of pyrochlores with similar cationic radius ratios, the A-site and B-site high entropy effects on structural evolution under irradiation are analyzed. In situ irradiation experiments were carried out on A-site high entropy pyrochlores such as (La0.2Nd0.2Sm0.2Gd0.2Er0.2)2Zr2O7, B-site Gd2(Ti1/3Sn1/3Zr1/3)2O7, and ternary pyrochlore Sm2Zr2O7 and Gd2Sn2O7 for comparison. The A-site high entropy pyrochlore can maintain a stable structure under high fluence irradiation like corresponding ternary pyrochlore, demonstrated by high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), energy dispersive spectroscopy (EDS) mapping and Raman spectrum. The additional irradiation experiments on A-site high entropy pyrochlores (La1/3Nd1/3Gd1/3)2Zr2O7 and (Nd1/3Sm1/3Gd1/3)2Zr2O7 also confirm the similarity under irradiation between A-site high entropy and ternary pyrochlores. However, the B-site high entropy pyrochlore Gd2(Ti1/3Sn1/3Zr1/3)2O7 becomes amorphous at exceptionally low irradiation fluences, indicating a significantly distinct radiation tolerance compared with the A-site high entropy. The difference between the A-site and B-site high entropy effect is analyzed from cationic lattice distortion, bond strength, and inner electron binding energy by first-principles calculations. The results reveal the role and mechanism of the high entropy effect in pyrochlores and lay a foundation for material design and future applications.

Effects of low fluence 212 MeV Ge swift heavy ion irradiation on the structural and optical properties of β-Ga2O3 epitaxial layers

Considering the future applications of the ultra-wide bandgap semiconductor β-Ga2O3 in high-performance electronic devices and aerospace, the effects of low fluence 212 MeV Ge swift heavy ion (SHI) irradiation on the structural and optical properties of β-Ga2O3 epitaxial layers have been studied in this work. The alternations in Raman scattering properties of the epitaxial layer after Ge SHI irradiation indicate the generation of lattice defects. The increased concentration of oxygen vacancies after irradiation leading to an enhanced area ratio of the yellow-red emission band in the PL spectrum of the β-Ga2O3 epitaxial layer. Simultaneously, the PL intensity quenches as the irradiation fluence increases, attributed to the generation of non-radiative recombination centers. Furthermore, HRTEM analysis provides direct evidence of lattice damage caused by 212 MeV Ge SHI irradiation to the samples. The results demonstrate that the spectral behaviors of β-Ga2O3 epitaxial layers can be modulated by low fluence Ge SHI irradiation with less damage caused to the overall crystalline quality and structure.

1 MeV electron irradiation effect and damage mechanism analysis of flexible GaInP/GaAs/InGaAs solar cells

In this study, the degradation behavior of flexible GaInP/GaAs/InGaAs (IMM3J) solar cells and their metamorphic subcells under 1 MeV electron irradiation was investigated. The remaining factors such as short-circuit current density (Jsc), open-circuit voltage (Voc), and maximum power (Pmax) were 95.62, 85.52, and 79.73%, respectively, at an irradiation fluence of 2 × 1015 e/cm2. The spectral responses of the InGaAs and GaAs subcells degraded significantly, and the InGaAs subcell experienced greater degradation than the GaAs subcell after irradiation. In addition, the current-limiting unit was switched from GaInP to InGaAs after irradiation. Defect analysis by deep-level transient spectroscopy (DLTS) revealed that with increasing irradiation fluence, the defects that had the greatest impact on the performance of GaAs subcells were EV + 0.36 and EV + 0.42 eV. For InGaAs subcells, the defects that had the greatest impact on the performance were EV + 0.29 and EV + 0.24 eV. The decrease in the minority carrier lifetime is the main reason for the decrease in the electrical performance of solar cells, and the variation in the effective minority carrier lifetime (τeff) in the subcells with the irradiation fluence was calculated based on the DLTS results. At a fluence of 2 × 1015 e/cm2, the τeff of the GaAs and InGaAs subcells decreased from 2.93 × 10−10 and 9.10 × 10−10 s to 1.56 × 10−11 and 1.60 × 10−12 s, respectively. These results provide a reference for predicting the degradation of short-circuit current and open-circuit voltage of flexible IMM3J.

Comparative study of dose for different fluence of neutron

The comparative study aims to investigate the dose received by materials exposed to different fluence of neutron radiation. The research is significant in the field of nuclear energy and radiation protection, as neutron radiation is one of the most common types of radiation produced by nuclear reactions. In this study, various materials are exposed to different fluence of neutron radiation, and the dose received by each material was measured using dosimeters. The results showed that the dose received by the materials increased with increasing fluence of neutron radiation. Furthermore, the study found that the dose-response relationship different between different materials, highlighting the importance of material selection in radiation protection. The study concludes that a better understanding of the dose-response relationship for different materials can help in the development of more effective radiation shielding materials and improve radiation safety in various applications.