Radiation Damage Studies Research Articles

Real-time study of radiation damage in monocrystalline diamond sensors

Being an excellent radiation hard material, diamond is preferred as an ionizing radiation sensor in radiation harsh environments. In this study, radiation damage from a beam of 67.5 MeV protons at the Crocker Nuclear Laboratory on the campus of the University of California, Davis, was used to determine exposure lifetime in detectors made from a thinned (∼ 40 μm) monocrystalline CVD (chemical vapor deposition) diamond substrate. The sensor response was sampled in real time as the sensor was exposed to a total fluence of ∼ 4×1016 / cm2, yielding an overall damage constant of k = (3.3 ± 0.3) × 10-18 cm2 / p-μm. Damage levels were later confirmed using a non-destructive x-ray technique at the LINAC Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory. Results are presented on the real-time degradation of the charge collection efficiency as a function of proton fluence.

Behavior of Foreign Interstitial Hydrogen and Helium Atoms at Tungsten/Beryllium Interface from First-Principles Calculations

The behavior of foreign interstitial hydrogen and helium atoms and its effect on the physical properties of the tungsten/beryllium interface structure were computationally studied by first-principles calculations. Briefly, as part of our study of helium irradiation damage and hydrogen detention, the following properties were calculated: (1) the electronic properties of the tungsten/beryllium interface structure with a single interstitial hydrogen or helium atom and Hen vacancy or Hn vacancy complexes, and (2) the isotropy (polycrystalline) elastic modulus (bulk, torsion, Young’s modulus), anisotropy factor and minimum thermal conductivity of the previously described tungsten/beryllium interface systems. This study found that defect atoms are more likely to be concentrated in beryllium, but the tungsten layer is more sensitive to changes in mechanical properties caused by interstitial atoms. The ability of the beryllium vacancies to capture interstitial atoms is smaller than that of the tungsten vacancies. Based on the computational results, a preliminary assumption of the judgment of the tungsten/beryllium interface structure on the resistivity for plasma-facing materials is introduced. These computational studies provide a critical evaluation of the radiation resistivity and hydrogen retention of tungsten/beryllium interface materials. The calculated interface properties can be incorporated into radiation damage resistance property evaluation systems to develop and test tungsten-based composite materials.

A Review of Cluster Dynamics in Studying Radiation Damage: Dominant Factors and Practical Implications

A Review of Cluster Dynamics in Studying Radiation Damage: Dominant Factors and Practical Implications

Gamma‐Ray‐Induced Photoelectric Field Exacerbating Irradiation Damage in Ceramic Capacitors

Ceramic capacitors are widely used in radioactive environments and are known to take irradiation damages, but most of previous studies of its reliability focus on thermal or electrical issues, and much less is known about the microscopic mechanism of its irradiation damaging process. Herein, it is shown that the capacitance of ceramic capacitors can change significantly under continuous gamma‐ray irradiation. Moreover, it is noticed that ex situ measurements will underestimate the effect comparing with the in situ one. Herein, it is discovered that this difference is due to the gamma‐ray‐induced photoelectric field, which dissipate rapidly in ex situ measurements. While the impact of the photoelectric field on the capacitance can be seen in situ, due to the recombination of photogenerated carriers and annealing of defects after irradiation, ex situ measurements only account for a part of the irradiation damage. This discovery indicates that ex situ measurements, which are prevailing in irradiation damage studies, can miss critical information, and in situ measurements are necessary for revealing the mechanism of the process.

Study of irradiation damage in silicon at different scales

In this work we focus on the simulation of radiation effects on silicon under proton irradiation at different scales. Two models of the Monte Carlo displacement damage calculation method in the Particle and Heavy Ion Transport code System (PHITS) were first used: the Torrens displacements per atom (NRT-DPA) model and a thermal recombination corrected dpa (arc-DPA), the prediction result of the final arc-DPA model is about 1/3 lower than the traditional NRT-DPA model; we also compared the difference between the two calculated values at the same dose of irradiation. When presenting a molecular dynamics study of the generation and evolution of silicon defects under irradiation, we simulated a 10 keV displacement cascade at room temperature. By post-processing the simulation results, the changes in the distribution and number of defects, as well as the evolution of defect clusters, were analyzed, where both the number of point defects and vacancy clusters show a tendency to increase and then decrease. Finally, first-principles were used to simulate and analyze the energy band structures, DOS, effective mass, the dielectric function, reflection and transmission spectra of silicon after introduction of defects. In order to obtain more accurate value of the bandgap, the HSE06 hybridization generalization is used so that the bandgap is not underestimated, while the clear bandgap facilitates fine analysis of the band structures of the defect states. We found that although the width of the energy band is reduced, which will lead to a increase of intrinsic carrier concentration. At the same time, the effective mass of the electron and hole are greatly reduced, which ultimately leads to a reduction of carrier mobility, and this will finally cause series of performance degradations.

TEM study of neutron radiation damage in tungsten

TEM study of neutron radiation damage in tungsten

Molecular dynamics study of primary radiation damage in TiVTa concentrated solid-solution alloy

The primary radiation damage in pure V and TiVTa concentrated solid-solution alloy (CSA) was studied using a molecular dynamics method. We have performed displacement cascade simulations to explore the generation and evolution behavior of irradiation defects. The results demonstrate that the defect accumulation and agglomeration in TiVTa CSA are significantly suppressed compared to pure V. The peak value of Frenkel pairs during cascade collisions in TiVTa CSA is much higher than that in pure V due to the lower formation energy of point defects. Meanwhile, the longer lifetime of the thermal spike relaxation and slow energy dissipation capability of TiVTa CSA can facilitate the recombination of point defects. The defect agglomeration rate in TiVTa CSA is much lower due to the lower binding energy of interstitial clusters and reduced interstitial diffusivity. Furthermore, the occurrence probability of dislocation loops in TiVTa CSA is lower than that in pure V. The reduction in primary radiation damage may enhance the radiation resistance of TiVTa CSA, and the improved radiation tolerance is primarily attributed to the relaxation stage and long-term defect evolution rather than the ballistic stage. These results can provide fundamental insights into irradiation-induced defects evolution in refractory CSAs.

Opportunities for high-energy neutron- and deuteron-induced measurements for fusion technology at the Soreq applied research accelerator facility (SARAF)

The Soreq Applied Research Accelerator Facility (SARAF) will be based on a 40 MeV, 5 mA CW (continuous wave) proton/deuteron superconducting linear accelerator, currently under construction at Soreq Nuclear Research Center in Yavne, Israel. It is planned to commence operation during 2025. Experiments at SARAF could provide data on high-energy deuteron- and neutron-induced cross-sections, yields and radiation damage, which are invaluable for the design and operation of the International Fusion Materials Irradiation Facility-DEMO-Oriented NEutron Source (IFMIF-DONES), and fusion technology in general. Pulsed beams (∼1 nsec) of variable energy deuterons will irradiate a lithium target and generate pulsed neutron beams with energy up to ∼55 MeV, which will be used to measure energy-dependent neutron-induced differential cross-sections, utilizing time of flight techniques. Impinging continuous wave (CW) 40 MeV deuteron beams on a unique gallium-indium (GaIn) liquid-jet target, will generate a neutron rate of more than 1 × 1015 n/sec, with energies up to ∼45 MeV. We plan to use this high rate to measure integral neutron-induced reaction yields of all channels simultaneously, employing an original novel method that will identify the reaction-produced nuclei via accurate mass measurement. The neutron-energy dependence of the yields could be deduced by combining measurements at various deuteron energies. The measured cross-sections and yields at SARAF may predict the activation characteristics of construction materials of IFMIF-DONES and future fusion reactors. The deuteron beams will also be used directly to measure cross-sections via in-beam and offline methods. The high neutron and deuteron rates will extend SARAF’s reach to rare materials. The deuteron beam power density on the liquid GaIn target will be 100 kW/cm2(similar to IFMIF-DONES) on a 2 cm2spot. The resulting neutron flux on small secondary samples will be in the 1013 n/cm2/s level, only an order of magnitude less than IFMIF-DONES. Therefore, SARAF may serve as a pilot facility for fusion-related radiation damage studies, providing important information towards the design of IFMIF-DONES.

Modeling and countering the effects of cosmic radiation using bioengineered human tissues

Cosmic radiation is the most serious risk that will be encountered during the planned missions to the Moon and Mars. There is a compelling need to understand the effects, safety thresholds, and mechanisms of radiation damage in human tissues, in order to develop measures for radiation protection during extended space travel. As animal models fail to recapitulate the molecular changes in astronauts, engineered human tissues and “organs-on-chips” are valuable tools for studying effects of radiation in vitro. We have developed a bioengineered tissue platform for studying radiation damage in individualized settings. To demonstrate its utility, we determined the effects of radiation using engineered models of two human tissues known to be radiosensitive: engineered cardiac tissues (eCT, a target of chronic radiation damage) and engineered bone marrow (eBM, a target of acute radiation damage). We report the effects of high-dose neutrons, a proxy for simulated galactic cosmic rays, on the expression of key genes implicated in tissue responses to ionizing radiation, phenotypic and functional changes in both tissues, and proof-of-principle application of radioprotective agents. We further determined the extent of inflammatory, oxidative stress, and matrix remodeling gene expression changes, and found that these changes were associated with an early hypertrophic phenotype in eCT and myeloid skewing in eBM. We propose that individualized models of human tissues have potential to provide insights into the effects and mechanisms of radiation during deep-space missions and allow testing of radioprotective measures.

Review of optical reporters of radiation effects in vivo: tools to quantify improvements in radiation delivery technique.

Radiation damage studies are used to optimize radiotherapy treatment techniques. Although biological indicators of damage are the best assays of effect, they are highly variable due to biological heterogeneity. The free radical radiochemistry can be assayed with optical reporters, allowing for high precision titration of techniques. We examine the optical reporters of radiochemistry to highlight those with the best potential for translational use in vivo, as surrogates for biological damage assays, to inform on mechanisms. A survey of the radical chemistry effects from reactive oxygen species (ROS) and oxygen itself was completed to link to DNA or biological damage. Optical reporters of ROS include fluorescent, phosphorescent, and bioluminescent molecules that have a variety of activation pathways, and each was reviewed for its in vivo translation potential. There are molecular reporters of ROS having potential to report within living systems, including derivatives of luminol, 2'7'-dichlorofluorescein diacetate, Amplex Red, and fluorescein. None have unique specificity to singular ROS species. Macromolecular engineered reporters unique to specific ROS are emerging. The ability to directly measure oxygen via reporters, such as Oxyphor and protoporphyrin IX, is an opportunity to quantify the consumption of oxygen during ROS generation, and this translates from in vitro to in vivo use. Emerging techniques, such as ion particle beams, spatial fractionation, and ultra-high dose rate FLASH radiotherapy, provide the motivation for these studies. In vivo optical reporters of radiochemistry are quantitatively useful for comparing radiotherapy techniques, although their use comes at the cost of the unknown connection to the mechanisms of radiobiological damage. Still their lower measurement uncertainty, compared with biological response assay, makes them an invaluable tool. Linkage to DNA damage and biological damage is needed, and measures such as oxygen consumption serve as useful surrogate measures that translate to in vivo use.

Charging of Vitreous Samples in Cryogenic Electron Microscopy Mitigated by Graphene.

Cryogenic electron microscopy can provide high-resolution reconstructions of macromolecules embedded in a thin layer of ice from which atomic models can be built de novo. However, the interaction between the ionizing electron beam and the sample results in beam-induced motion and image distortion, which limit the attainable resolutions. Sample charging is one contributing factor of beam-induced motions and image distortions, which is normally alleviated by including part of the supporting conducting film within the beam-exposed region. However, routine data collection schemes avoid strategies whereby the beam is not in contact with the supporting film, whose rationale is not fully understood. Here we characterize electrostatic charging of vitreous samples, both in imaging and in diffraction mode. We mitigate sample charging by depositing a single layer of conductive graphene on top of regular EM grids. We obtained high-resolution single-particle analysis (SPA) reconstructions at 2 Å when the electron beam only irradiates the middle of the hole on graphene-coated grids, using data collection schemes that previously failed to produce sub 3 Å reconstructions without the graphene layer. We also observe that the SPA data obtained with the graphene-coated grids exhibit a higher b factor and reduced particle movement compared to data obtained without the graphene layer. This mitigation of charging could have broad implications for various EM techniques, including SPA and cryotomography, and for the study of radiation damage and the development of future sample carriers. Furthermore, it may facilitate the exploration of more dose-efficient, scanning transmission EM based SPA techniques.

MD Simulations of Collision Cascades in α-Ti. The Residual Number of Radiation Defects, Cascade Relaxation Time and Displacement Cascade Region Morphology

Molecular dynamics (MD) simulations were applied to study radiation damage formation in collision cascades created by the recoil of primary knock-on atoms (PKA) with PKA energies Epka = 5, 10, 15, 20 and 25 keV in α-Ti at temperatures T = 100, 300, 600 and 900 K. A series of 24 collision cascades with the same set of (Epka, T) parameters has been simulated to generate representative sampling. Sapling size was justified a posteriori. The number of Frenkel pairs Nfp and cascade relaxation time were obtained as functions of (Epka, T). It was shown that the average ⟨Nfp(Epka,T)⟩ fits within 0.3NRT, provided the threshold displacement energy is chosen in 28-40 eV range depending on the irradiation temperature. Under high PKA energy/low irradiation temperature conditions, displacement cascade region splits into subcascades expended along high-energy recoil trajectories. Cascade relaxation time does not depend on Epka in this case. Contrary, under low PKA energy/ high temperature simulation conditions, most of collision cascades possess equiaxial shape, and their relaxation time grows with PKA energy increase.

Radiation Damage by Heavy Ions in Silicon and Silicon Carbide Detectors.

While silicon has been a steadfast semiconductor material for the past 50 years, it is now facing competition from other materials, especially for detector design. In that respect, due to its high resistance to radiation damage, silicon carbide is one of the most promising materials. In this work, we discuss the radiation damage studies of a new, large area, p-n junction silicon carbide device developed by the SiCILIA collaboration. We have studied the general performances of several devices, as a function of fluence, irradiated in different experimental conditions with different beams. A standard p-n junction silicon detector was also irradiated for comparison. The new detectors manifest excellent performance in terms of stability of the main parameters, linearity, defect distribution, charge collection efficiency, energy resolution, leakage current, etc. Experimental results evidence a radiation resistance of SiC devices more than two order of magnitude higher than Si devices. The new construction technology applied to silicon carbide material has made it possible to create very robust devices with excellent performance. These devices will soon be available for all those scientific projects where a high resistance to radiation damage is required.

A comprehensive study on intrinsic alpha corpuscular radiation damage in monazite crystals using picometer-scale imaging, coupled with SCXRD and Raman spectroscopy

We have investigated monazite crystals, known to experience lattice distortions due to alpha particle emission from their atomic nuclei. Our aim in this investigation is to study the complex relationship between the lattice parameters and Raman spectra of monazite crystals. Through this study, we seek to understand the interdependency between these physical parameters and their influence on one another for an improved understanding of radiation-induced damage in these crystals. In addition to this, we also attempted to establish a correlation between these properties and their picometer-scale images to gain a deeper understanding of the structural changes that occur at the atomic scale. We conducted our study on four monazite samples withstanding intrinsic alpha decay radiation, denoted as M1, M2, M3, and M4, with crystal unit cell volume ranging from 299.961 Å3 to 301.96 Å3. Our Pearson statistical analysis revealed a correlation R2 (0.96) between the SCXRD-derived Ce–P Distance of monazite and the FWHM of PO4 band active mode in Raman spectra. This indicated lattice distortions due to alpha decay radiation impacting the Raman spectra. While Raman PO4 band broadening can be a consequence of impurities, dopants, and radiation damage, HRTEM scrutiny of the samples at picometer scales revealed the presence of point defects, plane rotation, and lattice distortions within the samples, suggesting the impact of alpha decay on the crystal lattice. HRTEM analysis has added additional confirmation that the major contribution to PO4 band broadening is due to alpha radiation damage in these samples. Through our study, we conclude a multiple-approach correlation is necessary to accurately study radiation damage dynamics at atomic scales.

Near-infrared study of radiation damage in cerium dioxide

Radiation damage is studied in electron-irradiated cerium dioxide (CeO2) single crystals. Near Infra-red (NIR) spectra are recorded at room temperature between 2800 and 11,000 cm−1 (i.e. ∼0.9–3.57 µm in wavelength and ∼0.35–1.36 eV in photon energy). Measurements were carried out in the transmission mode for the single crystals and diffuse reflectivity mode for sintered CeO2 and (Ce, Gd)O2-x reference un-irradiated samples. The ceria single crystals were irradiated with 1.4-MeV and 2.5-MeV electrons for high fluences up to 3 × 1016 cm−2. Five broad absorption bands centered at 3600, 4100, 4600, 6000, and 7100 cm−1 (i. e. ∼0.44, 0.51, 0.57, 0.74, and 0.88 eV) are deduced from fits for the 2.5-MeV electron irradiation, whereas no absorption band is recorded for the 1.4-MeV electron energy. Those bands are consistent with the broad 0.9-eV band (7260 cm−1, 1.37 µm) in the UV–visible range associated with the change in color from light blue to deep green for the 2.5-MeV energy. Optical absorption arises from point-defect formation by elastic collisions for electron irradiation above the threshold energy near 1.4 MeV corresponding to the onset of cerium atom displacement. No defect bleaching occurs after isothermal annealing at 700 °C. No such bands are recorded for the virgin (Ce, Gd)O2-x samples for 5, 10, and 15 mol% Gd2O3 with an increasing amount of oxygen vacancies. The origin of absorption bands in the NIR range is discussed in relation to the available experimental data and ab-initio calculations of point defects in CeO2 and other dioxides with the cubic fluorite-like structure. Absorption bands are tentatively assigned to electronic transitions involving cerium vacancy levels in the band gap.

Low-temperature radiation damage studies in single-walled carbon nanotube bundles by hopping conductance

The paper shows the results of studying radiation defects in single-walled carbon nanotube bundles at low temperatures. The data were obtained in a unique experiment that inseparably combines 1 MeV electron irradiation at a temperature of ∼10 K and electrical conductivity measurements over a wide temperature range of 5–300 K. The experiment allowed us to reveal and separate the influence of stable and unstable radiation defects on the electrical properties of SWCNTs. It is shown that the 2D Mott variable range hopping conduction regime exhibits resistance to electron irradiation. The hopping conductivity is the dominant charge transfer mechanism in the temperature range of 5–50 K in both the pristine and irradiated SWCNT samples. It was found that the parameters of hopping transport demonstrate high sensitivity to the introduction and annealing of radiation defects. The low-temperature electron irradiation revealed the possibility of the emergence of an additional conduction channel in the irradiated SWCNTs. This channel demonstrates thermally activated behavior with a low activation energy of ∼0.5 meV at temperatures of 5–50 K. The obtained data indicate that unstable radiation defects create conditions for the possibility of impurity band conduction in SWCNT bundles.

Molecular Dynamics Studies of Primary Irradiation Damage in α‐Type Ti35 Alloy

α‐type Ti35 alloy (Ti‐6 wt%Ta) has been recommended as one of the candidate materials for advanced nuclear reactors due to its excellent overall performance. Nonetheless, irradiation effects on the alloy remain scarcely understood by far. Herein, the primary irradiation damage of Ti35 alloy is investigated from multiple perspectives using atomistic simulations. Results show that with the increasing energy of the primary knock‐on atom (2 keV ≤ E PKA ≤ 10 keV), the number of Frenkel pairs (N FP) gradually increases independent of the incident direction of PKA (IDPKA) and the ambient temperature (100 K ≤ T ≤ 700 K), while it exhibits a downtrend at each IDPKA as the T elevates. The magnitude of E PKA can affect the anisotropy of IDPKA on irradiation damage. Unrelated to E PKA, IDPKA, and T, di‐interstitial clusters and N vacancy > 3 clusters respectively account for the largest proportion of their categories, highlighting their stability. In any case, vacancies are more prone to cluster than interstitials. The increase of E PKA has a greater effect on vacancy clustering than interstitial clustering but can promote the increase in both the clustering fractions. An important insight into the understanding of the irradiation damage behaviors for the alloy has been provided.

Role of direct interactions in (d, p) and (d, 2p) reactions

Accurate cross sections of deuteron–induced reactions within an enlarged energy range up to 50 MeV are definitely involved by demands of on-going strategic research programs (ITER, IFMIF, SPIRAL2-NFS) using deuteron beams. Among them, the (d, p) and (d, 2p) reaction cross sections leading to hydrogen– gas bubble accumulation in the structural materials are very important for radiation damage studies. In contrast to the case of neutrons, systematics of deuteron activation cross sections, including those leading to hydrogen, triton, and helium–gas accumulation, is modest while even the newest evaluations show apparent discrepancies. Thus, the present work is devoted to the comparative analysis of measurements, model calculations, and evaluation corresponding to (d, p), and (d, 2p) activation cross sections, to improve the description of existing data and to provide trustful predictions where no measured data exist.

Analog performance of the CROCv1 pixel readout chip for the CMS Phase-2 Tracker Upgrade

The CROCv1 front-end (FE) chip was designed by the RD53 collaboration for the CMS Phase-2 Inner Tracker Upgrade. It is designed to cope with the extreme radiation and hit rates of the HL-LHC and it is based on the 65 nm CMOS technology and a novel analog FE design featuring linear charge to Time-over-Threshold conversion. In this contribution, the characterization measurements of the analog part of the chip are presented with a special focus on the linear analog FE, including Total Ionizing Dose radiation damage studies.

Developing Waste Forms for Transuranic Elements: Quaternary Neptunium Fluorides of the Type NaxMNp6F30 (M = Ti, V, Cr, Mn, Fe, Co, Ni, Al, Ga)

A series of quaternary Np(IV) fluorides was synthesized using a mild hydrothermal synthesis approach. The compositions are all of the type NaxMNp6F30, where M = Ti(III), V(III), Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Al(III), and Ga(III) and x = 4 for divalent metals, x = 3 for trivalent metals. The compounds all crystallize in the P-3c1 space group and are isotypic with actinide analogues NaxMAn6F30 (An = Ce, U, Th, Pu). Structure data from the neptunium crystals were combined with data from the other actinide analogues to establish the tetravalent, nine-coordinated ionic radii of neptunium (1.030(2) Å), plutonium (1.014(1) Å), and cerium (1.012(2) Å). Radiation damage studies were also carried out on a surrogate material, the cerium analogue Na3AlCe6F30, which indicates that the structure type has low resistance to amorphization. Density functional theory calculations were carried out to compute the band gaps and enthalpies of formation variations among the isotypic cerium and actinide structures to compare the stability of the structures.