Understanding Of Radiation Effects Research Articles

Radiation tolerance of piezoelectric bulk single-crystal aluminum nitride.

For practical use in harsh radiation environments, we pose selection criteria for piezoelectric materials for non-destructive evaluation (NDE) and material characterization. Using these criteria, piezoelectric aluminum nitride is shown to be an excellent candidate. The results of tests on an aluminum-nitride- based transducer operating in a nuclear reactor are also presented. We demonstrate the tolerance of single-crystal piezoelectric aluminum nitride after fast and thermal neutron fluences of 1.85 x 10(18) neutron/cm(2) and 5.8 x 10(18) neutron/ cm(2), respectively, and a gamma dose of 26.8 MGy. The radiation hardness of AlN is most evident from the unaltered piezoelectric coefficient d33, which measured 5.5 pC/N after a fast and thermal neutron exposure in a nuclear reactor core for over 120 MWh, in agreement with the published literature value. The results offer potential for improving reactor safety and furthering the understanding of radiation effects on materials by enabling structural health monitoring and NDE in spite of the high levels of radiation and high temperatures, which are known to destroy typical commercial ultrasonic transducers.

Discussion on the Structural Origins of the Fracture Toughness and Hardness Changes in Rapidly Quenched Borosilicate Glasses: A Molecular Dynamics Study

Understanding radiation effects in nuclear glasses is important in order to assess their long term behaviour in a geological repository. In this paper, the results obtained by classical molecular dynamics about the mechanical properties of a simplified SiO2 – B2O3 – Na2O glass with the same molar proportions as in the real French nuclear glass were reviewed. A pristine and a disordered structure, representative of the irradiated one, were prepared in order to address the question of the radiation effects on the fracture toughness and hardness.In a first step, fracture simulations were performed to compare the atomistic mechanisms in the pristine and disordered glasses. In a second step, nanoindentation was simulated using a diamond tip and again the pristine and disordered glass behaviors were compared.The depolymerisation associated to the glass disordering, in particular the increase of the tri-coordinated boron concentration relative to the tetra-coordinated boron concentration improves the fracture resistance by favouring the plastic flows. On the contrary, the swelling of the disordered glass limits the fracture resistance by facilitating the cavity formation. The first effect is dominant in the case of the glass investigated here because, experimentally, the fracture toughness increases after irradiation.Concerning the hardness, both the decrease of the boron coordination in parallel with non-bridging oxygen formation and free volume accumulation lead to a hardness decrease because the more disordered and open structure facilitates the tip penetration.

Radiation as an Immune Modulator

Radiation therapy is currently one of the most widely utilized treatment strategies in the clinical management of cancer. Classically, radiation therapy was developed as an anticancer treatment on the basis of its capacity to induce DNA double strand breaks in exposed cancer cells, ultimately resulting in tumor cell death. Recently, our understanding of radiation effects has expanded widely in terms of the consequences of radiation-induced tumor cell death and the pertinent cells, signaling pathways, and molecular sensors that modify the tumor response to radiation. It is now well accepted that inflammation plays a complex dual role in promoting or inhibiting tumor growth. The capacity of inflammatory responses to alter the tumor response to radiation therapy, and vice versa, is now the subject of intense scientific and clinical investigation. Herein, we review the concepts regarding the immunostimulatory properties of radiation therapy with particular focus on the effects of radiation therapy on the tumor microenvironment.

Compromised hematopoiesis and increased DNA damage following non-lethal ionizing radiation of a human hematopoietic system reconstituted in immunodeficient mice

Purpose: Precise understanding of radiation effects is critical to development of new modalities for the prevention and treatment of radiation-induced damage. In this study, we evaluated the effects of non-lethal doses of X-ray irradiation on human hematopoietic stem and progenitor cells (HSPC) reconstituted in NOD/Shi-scid, IL2Rγnull (NOG) immunodeficient mice.Materials and methods: We transplanted cord blood CD34+ HSPC into NOG mice irradiated with 2.0 Gy via tail veins. At the 12th week after transplantation, the NOG mice were irradiated with 0, 0.5, 1.0, 2.0, or 4.0 Gy, and the radiation effects on human HSPC in vivo were evaluated.Results: Although a majority of the mice irradiated with 2.0 Gy or more died in 12 weeks after irradiation, the mice that were exposed to 0.5 or 1.0 Gy of irradiation survived and were subjected to analysis. The chimerism of human CD45+ hematopoietic cells in peripheral blood and bone marrow (BM) of the recipient mice was reduced in an X-ray dose-dependent manner after irradiation. Percentages of human CD34+ HSPC as well as human CD34+CD38− HSC in BM similarly declined. CD34+CD38− HSC purified from the humanized mice at the 12th week after irradiation showed significantly increased numbers of phosphorylated H2AX (γH2AX) foci, a marker of DNA breaks, in an X-ray dose- dependent manner. Expression of p16INK4A, a hallmark of aging of HSC, was also detected only in HSPC from irradiated mice.Conclusions: With further refinement, the humanized mouse model might be effectively used to study the biological effects of non-lethal radiation in vivo.

Swift heavy ion-induced amorphization of CaZrO3 perovskite

Perovskite, ABO3, structures are an important class of ceramics with a large variety of derivative structure-types (cubic, tetragonal, hexagonal, orthorhombic, and rhombohedral). Radiation damage in perovskites is of interest due to their potential as actinide waste forms and to understand radiation effects in uranium- and thorium-bearing phases. Powder CaZrO3 perovskite was irradiated with 940-MeV Au ions up to 1.5×1013ions/cm2. Changes in the crystal structure were followed in situ as function of fluence by means of a sequence of X-ray diffraction (XRD) measurements. Ion-induced amorphization is evidenced by a decrease in diffraction intensity and an increase in diffuse scattering. Based on XRD measurements, as well as transmission electron microscopy (TEM), CaZrO3 is completely amorphized at a fluence of 1.5×1013ions/cm2. From the evolution of the integrated XRD-maxima intensities with fluence, the diameter of the amorphous tracks is estimated to be 6.0±0.6nm, which is independently confirmed by bright-field TEM images: 6.7±0.4nm. Changes in the positions of diffraction maxima may be caused by at least two processes. Broadening of the diffraction maxima is analyzed using a Williamson–Hall plot. Strain-induced broadening is the dominant process.

Radiation Effects in MOS-based Devices and Circuits: A Review

Radiation effects in microelectronic components have been studied for several decades for military and space applications. Understanding radiation effects in electronics is a complex and continually evolving challenge. In this paper, we present an extensive literature review pertaining to the state-of-the-art issues in radiation effects and radiation-hardened circuit design. Various research papers, books and application notes were referred, which take care of various aspects of understanding of radiation effects. In particular, this review gives a bibliographical survey of the current research efforts in the area of radiation effects in metal-oxide-semiconductor based devices and circuits. The paper also presents some of the challenges anticipated in the years to come and enlists further scope for research. A full description of the various methods is beyond the scope of this article; instead, the focus is on providing primary developments that have taken place in the area of radiation effects.

Radiation Therapy for Head and Neck Cancers

To provide an overview of the state of the art in the management of head and neck cancers with radiation therapy (RT) and review issues concerning dose-fractionation, concurrent systemic treatment as well as acute and chronic toxicity. Published peer-reviewed research articles, technical documents, and patient management guidelines. Modern RT techniques can use technical advances to precisely target regions involved by the tumor, while sparing normal structures. This has significant implications for treatment decisions and anticipated treatment toxicities. Our understanding of radiation effects on tumor and normal tissues and their optimal care are continuously evolving. Nurses need to be aware of the basic principles underlying the technical advances in RT in order to be able to counsel patients during their decision-making and treatment. They also need to stay updated on the pathophysiology and current management of acute and chronic toxicities of radiation treatment in order to provide optimal supportive care.

An exploratory study to determine applicability of nano-hardness and micro-compression measurements for yield stress estimation

The superior properties of ferritic/martensitic steels in a radiation environment (low swelling, low activation under irradiation and good corrosion resistance) make them good candidates for structural parts in future reactors and spallation sources. While it cannot substitute for true reactor experiments, irradiation by charged particles from accelerators can reduce the number of reactor experiments and support fundamental research for a better understanding of radiation effects in materials. Based on the nature of low energy accelerator experiments, only a small volume of material can be uniformly irradiated. Micro and nanoscale post irradiation tests thus have to be performed. We show here that nanoindentation and micro-compression testing on T91 and HT-9 stainless steel before and after ion irradiation are useful methods to evaluate the radiation induced hardening.

RD50 status: Developing radiation tolerant materials for ultra radiation-hard tracking detectors

The need for ultra-radiation hard semiconductor detectors for the tracker regions in high energy physics experiments at a future high luminosity hadron collider, like the proposed LHC Upgrade, has led to the formation of the CERN RD50 collaboration. The R&D directions of RD50 follow two paths: understanding radiation effects and finding mitigation through the use of new silicon materials, device engineering and optimised operations, all of which are covered in this paper. An emerging picture of a possible design of a future tracking detector is presented.

Microstructural evolution of proton irradiated T91

Understanding radiation effects in ferritic–martensitic alloys is critical for their success in advanced reactor and transmutation systems. The objective of this work is to evaluate the microstructural and mechanical property changes in irradiated ferritic–martensitic alloy T91. Irradiations were conducted with 2.0 MeV protons to doses of 3, 7, and 10 dpa at a dose rate of 2 × 10 −5 dpa/s and at temperatures of 400 °C, 450 °C, and 500 °C. The post irradiation microstructure contained a high density of black-dots and a 0〈1 0 0〉 dislocation loops in addition to precipitates and tangled dislocations that were present in the unirradiated condition. The irradiated dislocation microstructure is sensitive to the heat treatment. Results show that the irradiated microstructure did not contain any voids or evidence of second phase formation. Hardness increases with dose and tends to saturate around 5 dpa for 400 °C irradiation. Only a portion of irradiation hardening can be accounted for by the observable microstructural features. An initial investigation of the effect of irradiation on prior austenite grain boundary microchemistry revealed that Cr is enriched by 4.7 wt%, V by 0.6 wt% (nearly 300%), and Fe is depleted by 5.3 wt% relative to the bulk values. No segregation was observed in the unirradiated condition. No radiation-induced segregation was observed at martensite lath boundaries. Overall, the irradiated microstructure is consistent with reactor and spallation system experiments.

Nanodosimetric cluster size distributions of therapeutic proton beams

As we move into the new millennium, it is important that we improve our understanding of radiation effects on humans and nanoelectronic systems. This understanding is essential in a number of areas including radiation therapy for cancer treatment and extended human presence in outer space. Nanodosimetry in low-pressure gases enables measurement of the energy deposition of ionizing radiation on a scale equivalent to the dimensions of the DNA molecule. This is extremely important for not only biological applications but also electronic applications, as the effect of radiation on nanoelectronics needs to be determined before they are installed and deployed in complex radiation fields. However, before nanodosimetry can be widely applied, further investigation is required to link the output of gas-based nanodosimeters to the actual effect of the radiation on a biological or electronic system. The purpose of this research is to conduct nanodosimetric measurements of proton radiation fields at the proton accelerator of Loma Linda University Medical Center (LLUMC) and to develop a Monte Carlo simulation system to validate and support further developments of experimental nanodosimetry. To achieve this, measured ion cluster size distributions are compared to the output from the Monte Carlo simulation system that simulates the characteristics of the LLUMC beam line and the performance of the nanodosimeter installed on one of LLUMC's proton research beam lines.

Track formation and electron emission in swift ion collisions with condensed matter

Electron ejection from target atoms is one of the basic processes when ionizing radiation interacts with matter. The primary electrons and their subsequent secondary interactions lead to the deposition of energy around the ion trajectory. The detailed knowledge of the structure of these ion tracks is a key issue for our understanding of radiation effects in condensed matter, an important example being calculations of the RBE of heavy particles, where doubly differential electron ejection cross sections are a key input parameter. Usually, data obtained from single collisions, i.e. with gas targets, are used, but condensed matter effects may considerably alter the emission patterns. Therefore, we will focus on the primary ionization (binary encounter and soft electron emission), which is common to single atoms (gas targets) and condensed matter. Then, special emphasis will be given to discuss effects, which are only seen in condensed matter (electron transport and multiple scattering effects, jet-like structures, wake effects due to collective excitation of plasmons), but not in gaseous targets (single collisions).

The linear no-threshold model does not hold for low-dose ionizing radiation.

Almost all of the data on the biological effects of ionizing radiation come from studies of high doses. However, the human population is unlikely to be exposed to such doses. Regulatory limits for radiation exposure are based on the linear no-threshold model, which predicts that the relationship between biological effects and radiation dose is linear, and that any dose has some effect. Chromosomal changes are an important effect of ionizing radiation because of their role in carcinogenesis. Here we exposed pKZ1 mice to single whole-body X-radiation doses as low as 1 microGy. We observed three different phases of response: (1) an induction of inversions at ultra-low doses, (2) a reduction below endogenous inversion frequency at low doses, and (3) an induction of inversions again at higher doses. These results do not fit a linear no-threshold model, and they may have implications for the way in which regulatory standards are presently set and for understanding radiation effects.

Electron ejection by heavy particles as precursor of track formation in condensed matter

The detailed knowledge of the structure of ion tracks is a key issue for our understanding of radiation effects in condensed matter. Important examples are the radial energy deposition profile by electronic excitation for numerical simulations of track formation (via “Coulomb explosion” or “thermal spike”) in inert matter, and calculations of the RBE (relative biological effectiveness) of heavy particles in living matter (with important applications in dosimetry and hadrontherapy). In both cases, differential electron ejection cross sections are used as input parameter. The precursor of track formation is thus electron ejection from target atoms, or from the projectile itself. These primary electrons and their subsequent secondary interactions lead to the deposition of energy along and around the ion trajectory. We first briefly discuss “primary ionization” (binary encounter and soft electron emission, multiple collision sequences: “Fermi shuttle”) common to single atoms (gas targets) and condensed matter. Then, specific effects in condensed matter (electron transport, jet-like electron spikes, wake effects due to collective excitation of plasmons and emission of shock wave electrons) will be presented. Finally, we concentrate on effects connected to the high density of deposited energy and strong perturbation induced by heavy particles such as heavy ions and clusters (reduction effects due to screening, transport and “sweeping away”, multiple ionization, electronic temperatures from Auger spectroscopy).

Expression profiling of irradiated human lung endothelial cells using a large DNA chip

Purpose/Objective: Until recently, radiation research has mainly focused on the tumor cell compartment. However, the genetically more stable microenvironment including the endothelial cell compartment has now been widely recognized to play a key role in radiation effects in vivo. One way to better understand radiation effects is the identification of genes regulated in response to radiation, which can affect the cell cycle, DNA repair, apoptosis, metastasis and angiogenesis. DNA microarray technology is now considered as an emerging technology to potentially explore cellular pathways. In order to better understand the effects of radiation on endothelial cells, we investigate here the gene expression profile of endothelial cells in response to ionizing radiation using a DNA chip.

Extracellular signaling through the microenvironment: a hypothesis relating carcinogenesis, bystander effects, and genomic instability.

Cell growth, differentiation and death are directed in large part by extracellular signaling through the interactions of cells with other cells and with the extracellular matrix; these interactions are in turn modulated by cytokines and growth factors, i.e. the microenvironment. Here we discuss the idea that extracellular signaling integrates multicellular damage responses that are important deterrents to the development of cancer through mechanisms that eliminate abnormal cells and inhibit neoplastic behavior. As an example, we discuss the action of transforming growth factor beta (TGFB1) as an extracellular sensor of damage. We propose that radiation-induced bystander effects and genomic instability are, respectively, positive and negative manifestations of this homeostatic process. Bystander effects exhibited predominantly after a low-dose or a nonhomogeneous radiation exposure are extracellular signaling pathways that modulate cellular repair and death programs. Persistent disruption of extracellular signaling after exposure to relatively high doses of ionizing radiation may lead to the accumulation of aberrant cells that are genomically unstable. Understanding radiation effects in terms of coordinated multicellular responses that affect decisions regarding the fate of a cell may necessitate re-evaluation of radiation dose and risk concepts and provide avenues for intervention.

The Production of Strong Blast Waves through Intense Laser Irradiation of Atomic Clusters

An understanding of radiation effects on the evolution of shock waves is of great importance to many problems in astrophysics. Shock waves driven by a laser-heated plasma are attractive for laboratory investigation of these phenomena. Recent studies of intense short-pulse laser interactions with gases of atomic clusters indicate a potential avenue to access this regime of radiative hydrodynamics. We have measured the energy absorption efficiency of high-intensity, picosecond laser pulses in low-density gases composed of large atomic clusters and find that the energy absorption can be very high (> 95%), producing a high-temperature plasma filament which consequently produces a strong blast wave. Interferometric characterization of these shock waves indicates that in high-Z gases such as Xe, radiation transport plays an important role in the evolution of the shock wave.

Nature of the Fine-Scale Defects and Radiation Hardening in Stainless Steels Neutron-Irradiated at 550K

ABSTRACTOur understanding of radiation effects in stainless steels irradiated at temperatures below annealing stage V (<573K) remains unclear. The microstructure under these conditions has been loosely described in terms of Frank loops and “black spot” damage, the latter of which is typically considered to be 4-5 nm or less in size. To further clarify the nature of these defects, 6 stainless steels heats neutron irradiated at 550K from 0.6 to 13.3 dpa have been characterized by TEM. The microstructure is comprised of a very high density of small Frank loops present in sizes as small as 1 nm and perhaps lower, which could be of both vacancy and interstitial-type. The density of the visible loops is already established at the lowest dose available, however, the microstructure continues to evolve as the dose increases. The size distributions of the Frank loops change from a narrow symmetric distribution to a much broader size distribution with a bimodal distribution beginning to form at the higher doses.

Microchemistry and microstructure of proton-irradiated austenitic alloys: toward an understanding of irradiation effects in LWR core components

Over 1200 measurements of grain boundary composition and microstructure have been made on 14 different austenitic Fe–Cr–Ni alloys following proton irradiation in the temperature range 200–600°C and in the dose range 0.1–3.0 dpa. From these data, a greater understanding of radiation induced segregation (RIS) and microstructure development has been gained. Grain boundary composition measurements revealed that Cr depletes at grain boundaries, Ni enriches and Fe can either enrich or deplete depending on alloy composition. Analysis of temperature and composition dependence of RIS revealed that the magnitude and direction of grain boundary segregation depends on alloy composition because the values of migration enthalpy of the alloy constituents are not the same, and diffusivities of the alloy constituents are composition-dependent. The dose dependence of segregation revealed ordering in Ni-base alloys and temperature dependence was used to show that RIS is consistent with a vacancy exchange mechanism. The dependence of segregation on composition is consistent with all known, relevant neutron data. RIS was found to be related to the development of the dislocation and void microstructures. Alloys in which the microstructure develops slower with dose also show slower changes in RIS. Similarly, it was shown that the dependence of swelling on composition is the same for neutron, ion and proton irradiation and all can be explained by the effect of RIS on defect diffusivity at the void nuclei. This paper illustrates the value of conducting carefully chosen irradiation experiments over several, well-controlled variables to elucidate the mechanisms underlying the microchemical and microstructural changes.

Total-dose effects of γ-ray irradiation on SOI-MOS transistors

A measurement of total-dose radiation effects of SOI-MOS transistors is presented. The motivation of this study is to understand radiation effects of a single transistor, which is fabricated with the same structure (BESOI) as a preamplifier planned to be used for the silicon vertex detector in the KEK BELLE experiment. Results are given with the threshold voltage shift (ΔV th), mobility degradation and increase of the 1/f noise. We decomposed ΔVth into the oxide trap and interface trap components. Using this decomposition result, we found good agreement of data for the mobility degradation versus interface traps and the 1/f noise increase versus oxide trapped charges with the empirical relations.