Irradiated Zone Research Articles

Multifunctional nanoparticles potentiate in-situ tumor vaccines via reversing insufficient Photothermal therapy by disrupting tumor vasculature

Photothermal therapy can trigger immunogenic cell death and release personalized in-situ tumor vaccine, activating immune responses to eliminate systemic tumors beyond the irradiated zone. However, the immune response of the in-situ tumor vaccines is often undermined by the residual tumor cells and their induced immunosuppressive tumor microenvironment (TME), which is attributed to insufficient photothermal effects stemming from the limited accumulation of photosensitizers. To overcome these limitations, we developed multi-functional nanoparticles (VI@Gd-NPs) that integrate a tumor vasculature-specific disrupting agent (Vadimezan, Phase III clinical drug), a photosensitizer (Indocyanine Green, ICG), and a magnetic resonance imaging contrast agent (Gadolinium, Gd) through chemical self-assembly. By selectively disrupting the tumor vasculature, these nanoparticles enhance the intratumoral delivery of photosensitizers (ICG and blood cells), and Gd. With the guidance of Gd-enhanced MRI, the improved delivery facilitates comprehensive photothermal ablation and regulates the TME, further initiating the in-situ tumor vaccine. Notably, this approach significantly enhances anti-tumor immune responses, improves survival rates, and reduces tumor recurrence and metastasis in various animal models. Moreover, depleting CD8+ T cells reverses these therapeutic benefits, highlighting the critical role of adaptive T cell immunity. Therefore, the VI@Gd-NPs treatment holds great potential for reigniting the in-situ tumor vaccine of photothermal therapy.

Estimating the design parameters of a space-based radio surveillance system

Currently, small spacecraft with both optoelectronic and radar imaging equipment are becoming increasingly common. The purpose of the work is to improve the efficiency of preliminary assessment of achievable characteristics of radio surveillance payloads at the initial stages of design of small spacecraft. The paper describes the advantages of using radar imaging equipment, as well as the main trends in its development. The main areas of application of spacecraft with radar of different frequency ranges are given; the advantages of each frequency range are described. The methodology of determining the parameters of the trajectory signal when the platform moves in a circular orbit, taking into account the assumptions associated with estimating the size of the irradiation zone in azimuth is considered. Based on the considered methodology, a program is developed in Python programming language that makes it possible to estimate the length of synthesized aperture, synthesis time and azimuthal resolution of the target equipment on the basis of mass and dimensional characteristics of the antenna and spacecraft orbit parameters. A graphical user interface has been developed for the program which allows the user to interactively vary the initial data for calculation and evaluate the graphical representation of the result. The developed software system can be used for calculation of the main design parameters of small spacecraft with radar imaging equipment at the preliminary design stage.

Dual-Modal Near-Infrared Organic Nanoparticles: Integrating Mild Hyperthermia Phototherapy with Fluorescence Imaging.

Our study seeks to develop dual-modal organic-nanoagents for cancer therapy and real-time fluorescence imaging, followed by their pre-clinical evaluation on a murine model. Integrating NIR molecular imaging with nanotechnology, our aim is to improve outcomes for early-stage cutaneous melanoma by offering more effective and less invasive methods. This approach has the potential to enhance both photothermal therapy (PTT) and Sentinel Lymph Node Biopsy (SLNB) procedures for melanoma patients. NIR-797-isothiocyanate was encapsulated in poly(D,L-lactide-co-glycolide) acid (PLGA) nanoparticles (NPs) using a two-step protocol, followed by thorough characterization, including assessing loading efficiency, fluorescence stability, and photothermal conversion. Biocompatibility and cellular uptake were tested in vitro on melanoma cells, while PTT assay, with real-time thermal monitoring, was performed in vivo on tumor-bearing mice under irradiation with an 808 nm laser. Finally, ex vivo fluorescence microscopy, histopathological assay, and TEM imaging were performed. Our PLGA NPs, with a diameter of 270 nm, negative charge, and 60% NIR-797 loading efficiency, demonstrated excellent stability and fluorescence properties, as well as efficient light-to-heat conversion. In vitro studies confirmed their biocompatibility and cellular internalization. In vivo experiments demonstrated their efficacy as photothermal agents, inducing mild hyperthermia with temperatures reaching up to 43.8 °C. Ex vivo microscopy of tumor tissue confirmed persistent NIR fluorescence and uniform distribution of the NPs. Histopathological and TEM assays revealed early apoptosis, immune cell response, ultrastructural damage, and intracellular material debris resulting from combined NP treatment and irradiation. Additionally, TEM analyses of irradiated zone margins showed attenuated cellular damage, highlighting the precision and effectiveness of our targeted treatment approach. Specifically tailored for dual-modal NIR functionality, our NPs offer a novel approach in cancer PTT and real-time fluorescence monitoring, signaling a promising avenue toward clinical translation.

Impact of adding high-concentration neutron poisons to reactor moderator system for guaranteed shutdown

To ensure a reliable shutdown of the proposed advanced heavy water reactor (AHWR) of Indian origin during emergency conditions, it is imperative to use an increased concentration of liquid neutron poison for injection into the moderator system due to its higher reactivity. The sudden injection of this liquid poison may cause a surge in radiolytic product (H2O2 and H2) yield, posing safety risks. If H2/D2 yield exceeds 4 % (v/v), a combustible mixture with oxygen can be formed and presence of oxidizing H2O2 can enhance corrosion. Hence, accurate estimation of H2O2 and H2 is imperative from the reactor safety point of view. We investigated gadolinium and boron (two liquid neutron poisons) at varying concentrations through high energy electron beam and gamma radiolysis. The radiolytic yields from both the liquid neutron poisons of equivalent concentrations at a constant dose and operating moderator conditions in electron beam and gamma radiolysis were compared. The molecular product yield was observed to be concentration and dose-rate-dependent for both the neutron poisons. Electron radiolysis exhibited a higher yield of H2O2, whereas gamma radiolysis resulted in a greater H2 yield. In electron radiolysis, the H2O2 yield decreased with increasing B concentration. These results give an overall estimation of radiolytic products for a particular dose rate, total dose and effect of head space volume over liquid irradiation zone from these two liquid poisons of a particular concentration. These insights will aid in selecting suitable poisons and managing their effects effectively to avoid hydrogen deflagrations after emergency shutdown.

Abstract Mo073: Elucidating the Role of Cardiac Radiotherapy on the Sympathetic Nervous System as a Treatment for Ventricular Tachycardia

Ventricular tachycardia (VT) is a dangerous arrhythmia that occurs in structurally and electrically heterogenous regions of the diseased heart, leading to sudden cardiac arrest and death if left untreated. One of the main drivers underlying the arrhythmogenic substrate is abnormal remodeling of the autonomic nervous system after cardiac injury, resulting in a heterogenous distribution of sympathetic innervation and subsequent ventricular arrhythmia. In patients with VT refractory to conventional therapy, noninvasive cardiac stereotactic body radiotherapy (SBRT) has emerged as a promising new treatment. Here, we investigated whether cardiac radiotherapy homogenizes the arrhythmogenic substrate through induction of cardiac sympathetic nerve innervation and activity in a closed-chest ischemia reperfusion murine model of ischemic heart failure. Using single nucleus-RNA sequencing, we identified global transcriptomic changes in the left ventricle 6 weeks after 25 Gray (Gy) cardiac X-ray radiation. Notably, these changes included increased expression of neurotrophins such as brain derived neurotrophic factor, a growth factor essential for neuronal survival and development, in irradiated hearts compared to sham controls. Consequently, Western blot and immunofluorescence showed increased expression of the sympathetic neuronal markers tyrosine hydroxylase and neuropeptide Y at the scar border zone of irradiated mice. Similar immunofluorescence results were observed at the irradiated border zone from the explanted heart of a patient previously targeted with 25 Gy compared to a nontargeted remote region within the same heart. These findings suggest a novel role for radiation-induced remodeling of the sympathetic nervous system in the anti-arrhythmic response to SBRT.

Air disinfection performance of upper-room ultraviolet germicidal irradiation (UR-UVGI) system in a multi-compartment dental clinic

Multi-compartment dental clinics present significant airborne cross-infection risks. Upper-room ultraviolet germicidal irradiation (UR-UVGI) system have shown promise in preventing airborne pathogens, but its available application data are insufficient in multi-compartment dental clinics. Therefore, the UR-UVGI system's performance in a multi-compartment dental clinic was comprehensively evaluated in this study. The accuracy of the turbulence and drift flux models was verified by experimental data from ultrasonic scaling. The effects of the ventilation rate, irradiation zone volume, and irradiation flux on UR-UVGI performance were analyzed using computational fluid dynamics coupled with a UV inactivation model. Different patient numbers were considered. The results showed that UR-UVGI significantly reduced virus concentrations and outperformed increased ventilation rates alone. At a ventilation rate of six air changes per hour (ACH), UR-UVGI with an irradiation zone volume of 20% and irradiation flux of 5 μW/cm2 achieved a 70.44% average virus reduction in the whole room (WR), outperforming the impact of doubling the ventilation rate from 6 to 12 ACH without UR-UVGI. The highest disinfection efficiency of UR-UVGI decreased for WRs with more patients. The compartment treating patients exhibited significantly lower disinfection efficiency than others. Moreover, optimal UR-UVGI performance occurs at lower ventilation rates, achieving over 80% virus disinfection in WR. Additionally, exceeding an irradiation zone volume of 20% or an irradiation flux of 5 μW/cm2 notably reduces the improvement rates of UR-UVGI performance. These findings provide a scientific reference for strategically applying UR-UVGI in multi-compartment dental clinics.

Modeling of rabbit femoral artery occlusion by high-intensity focused ultrasound

One of the effective methods of artery and vein occlusion used in experimental studies and in clinical practice for certain diseases is local exposure of vessels to high-intensity focused ultrasound (HIFU). The wide use of this method in our country is limited by the lack of appropriate domestic equipment. At the Peter the Great St. Petersburg Polytechnic University, in the Laboratory of Ultrasound Technologies of the Center for Advanced Research, a stand for HIFU effects on various biological objects has been developed. There is no experience in using this device in angiology yet. The purpose of our research was to study the possibility of using Medusa 008, a high-tech mobile medical device designed for ultrasound diagnosis and personalized HIFU therapy, to model vascular occlusion and stop blood flow during irradiation. Materials and methods. The object of the study is the femoral artery of a rabbit. The source of HIFU is Medusa 008, the high-tech mobile medical device designed for ultrasound diagnostics and personalized HIFU-therapy with radiation frequency of 2 MHz (prototype). The following irradiation modes were used in the research: irradiation duration - 50 ms, pause between exposures – 10 ms, number of pulses – 20, 30, 40. The following energy values corresponded to these modes: 58 J, 87 J, 116 J. Irradiation of the femoral artery of an anesthetized rabbit was performed percutaneously. We used ultrasound to visualize the arteries and measure the blood flow velocity. According to ultrasound data, after HIFU irradiation, blood flow in the artery stopped. The factor contributing to arterial occlusion is the cessation of blood flow during irradiation. A histological examination of the area of the irradiated artery revealed structural changes in all layers of the vascular wall. Results. HIFU irradiation with intensity of 87 and 116 J has a significant dose-dependent destructive effect on the muscular arterial wall. The more intense damaging irradiation (116 J) causes smooth muscle cell necrosis. The time of direct influence on the vessel wall structures did not exceed 3 sec. During the experiment, we found that HIFU in the used modes causes temperature increase up to 45–60 оC, which is enough for thermal damage of cells in the irradiation zone. Conclusion. Thus, as a result of the above experiments, it was shown that Medusa 008, the high-tech mobile medical device designed for ultrasound diagnostics and personalized HIFU-therapy can be used to simulate vascular occlusion.

ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ СОСТОЯНИЯ КОЖИ ОБЛАСТИ РТА ЖИВОТНЫХ ПОСЛЕ ВОЗДЕЙСТВИЯ СТОМАТОЛОГИЧЕСКИХ ДИОДНЫХ ФОТОПОЛИМЕРИЗАТОРОВ

Aim of the study: studying the effect of light radiation from dental photopolymerizers on the soft tissues of the mouth area (regio oralis A01.2.01.018). Materials and methods. Experimental studies were carried out on 50 eight months male rats, randomly divided into 4 groups: 3 main (15 animals each), the fourth - control (5 animals). Under Zoletil anesthesia, the incisors of the lower jaw of experimental animals were exposed twice to light (wavelength 395 - 480 nm) from a dental photopolymerization device. Three photopolymerization modes were used: main group No. 1 – diode photopolymerizer with a luminous flux power of 1000 mW/cm2, main group No. 2 – diode photopolymerizer with a luminous flux power of 1400 mW/cm2; main group No. 3 – diode photopolymerizer with a luminous flux power of 3200 mW/cm2. Animals in the control group were not exposed to light radiation from dental photopolymerizers. After one, three and seven days, animals from groups No. 1 – 3, seven days – animals from the control group were subjected to ether anesthesia and removed from the experiment by decapitation. For pathomorphological studies, a fragment of skin from the mouth area was isolated. The material was fixed with a 15% aqueous neutral solution of formalin and embedded in paraffin. Histological sections were stained with hematoxylin and eosin, according to the van Gieson method, and Alcian blue; performed the CHIC reaction. The vascular bed and its elements were studied using the Gabu-Dybanu method. A standardized comparative microscopic study of skin tissue adjacent to the irradiation zone was carried out using the ZEISS Axio Imager A2 hardware and software complex at magnifications of 1:100 and 1:200. A descriptive method was used to evaluate the results obtained. Results. Microscopy of preparations of the skin of the lips of experimental animals allowed us to come to the conclusion that the primary reaction of tissues to the effects of light radiation from photopolymerizers is of the same type and does not depend on their technical characteristics. Hyperkeratosis and acanthosis of the epithelium, congestion of the microvasculature, the presence of edema and diffuse infiltration of the dermis were detected. Quantitative and qualitative changes in mast cells were observed - an increase in the degree of their degranulation and the number of process forms, which is a marker of tissue damage in response to irradiation. The described changes, which in general are pathomorphological signs of acute inflammation, were determined on the first and third days after irradiation. Further dynamics indicated a decrease in the described reactive changes by the third day when using the photopolymerization mode: wavelength 395 – 480 nm, power 1000 mW/cm2, exposure 10 sec. When using the photopolymerization mode: wavelength 395 - 480 nm, power 1400/3200 mW/cm2, exposure 3 seconds - by the seventh day of observation there was a positive dynamics in the relief of pathological processes, but signs of inflammation remained. Conclusion. Experimental data indicate the possible development of negative photochemical reactions in the skin of the lips after exposure to light from dental photopolymerizers during the treatment of patients with pathology of hard dental tissues. The results obtained can be used to substantiate the prevention of pathological processes in the tissues of the perioral area. Further in vitro, in vivo, and clinical studies are needed to determine the optimal irradiation intensity, irradiation time, and other aspects to ensure the safety and effectiveness of light curing agents.

In vivo X-ray microtomography locally affects stem radial growth with no immediate physiological impact.

Microcomputed tomography (µCT) is a nondestructive X-ray imaging method used in plant physiology to visualize in situ plant tissues that enables assessments of embolized xylem vessels. Whereas evidence for X-ray-induced cellular damage has been reported, the impact on plant physiological processes such as carbon (C) uptake, transport, and use is unknown. Yet, these damages could be particularly relevant for studies that track embolism and C fluxes over time. We examined the physiological consequences of µCT scanning for xylem embolism over 3 mo by monitoring net photosynthesis (Anet), diameter growth, chlorophyll (Chl) concentration, and foliar nonstructural carbohydrate (NSC) content in 4 deciduous tree species: hedge maple (Acer campestre), ash (Fraxinus excelsior), European hornbeam (Carpinus betulus), and sessile oak (Quercus petraea). C transport from the canopy to the roots was also assessed through 13C labeling. Our results show that monthly X-ray application did not impact foliar Anet, Chl, NSC content, and C transport. Although X-ray effects did not vary between species, the most pronounced impact was observed in sessile oak, marked by stopped growth and stem deformations around the irradiated area. The absence of adverse impacts on plant physiology for all the tested treatments indicates that laboratory-based µCT systems can be used with different beam energy levels and doses without threatening the integrity of plant physiology within the range of tested parameters. However, the impacts of repetitive µCT on the stem radial growth at the irradiated zone leading to deformations in sessile oak might have lasting implications for studies tracking plant embolism in the longer-term.

Domain shape evolution under multiple IR laser irradiation in lithium niobate

In this work, we have studied the shape evolution of the isolated domains in domain array in congruent lithium niobate crystals under the action of pyroelectric fields arising during multiple irradiation by laser pulses. The loss of the circle shape with the pulse number was obtained in the arrays of isolated domains arising at the edges of the irradiated zone. The simulation of the domain growth under the action of the pyroelectric field allowed revealing two stages of domain shape evolution in the regular domain array. An important role of the neighboring domains was revealed.

ВИЗНАЧЕННЯ ТЕХНОЛОГІЧНИХ ПАРАМЕТРІВ ЛАЗЕРНОГО ВИПРОМІНЕННЯ ДЛЯ ОТРИМАННЯ СУБМІКРО- ТА НАНОСТРУКТУР У ЗМІЦНЮВАЛЬНИХ ПОКРИТТЯХ НА СТАЛЯХ

Using the previously developed model of theoretical processes in the zone of laser irradiation, where thermal and thermomechanical processes are described, including the influence of crystallization energy and other internal energies during the formation of nanostructures at various temperature levels, further investigation of the thermal and thermomechanical characteristics of different structural steels during the formation of nanostructures on their surfaces using laser irradiation was conducted. To validate the model, temperature fields were determined in the zone of laser irradiation on steel 20 (Fig. 1a) and steel 50 (Fig. 1b), considering both heating and cooling processes. Calculations were performed for heat flux densities and durations of exposure close to those necessary for obtaining nanostructures (500...2000 K) and with temperature rise rates exceeding 10^7 K/s. As a result of calculations using the refined thermal model, temperature distributions at a depth of 1 μm during laser irradiation on steel with different carbon contents (steel 20, 38Х, 50, and У8) at various peak heat flux densities in the surface layer were obtained. A spatiotemporal distribution of temperatures along the radius of the laser spot and over time during laser irradiation with a heat flux density of q=3∙10^8 W/m^2 at a spot radius of 0.1 mm was constructed. Zones of nanostructure formation were identified depending on the heat flux density over the duration of laser irradiation. Theoretical investigations using the updated thermal model confirmed the need to consider the temperature rise rate, as exceeding it increases the likelihood of thermomechanical failure. At the same time, due to insufficient temperature rise rates during laser nanostructure formation in the surface layers of carbon steels, more micro- and sub microstructures are formed.

Influence of Temperature on Properties and Dynamics of Gas-Solid Flow in Fluidized-Particle Tubular Solar Receiver

A fluidized particle single-tube solar receiver has been tested for investigating the gas-particle characteristics that enable the best operating conditions in a commercial-scale plant. The principle of the solar receiver is to fluidize the particles in a vessel – the dispenser – in which the receiver tube is plunged. The particles are flowing upward in the tube, irradiated over 1-meter height, by applying an overpressure in the dispenser. Experiments with a concentrated solar flux varying between 188 and 358 kW/m² are carried out, and the particle mass flux varied from 0 to 72 kg/(m²s). The mean particles and external tube wall temperatures in the irradiated zone are heated from the ambient to respectively 700°C and 940°C. It is shown that the temperature rise leads to a decrease of the particle volume fraction. Furthermore, a self-regulation of the system is evidenced with a short transient regime. This characteristic is essential from the operational viewpoint. The thermal efficiency of the receiver increases with the particle flow rate, reaching between 60 and 75% above 30 kg/(m²s). Several fluidization regimes are identified thanks to pressure signal analyses, like slugging, turbulent and fast fluidization, showing that regimes transitions are strongly affected by the temperature.

INFRARED THERMAL IMAGING CONTROL OF RADIATION DERMATITIS DYNAMICS.

Radiation-induced dermatitis impairs the quality of life of cancer patients and may lead to the need of interrupting radiotherapy. The grade of dermatitis is subjectively assessed by the visual examination. There is an urgent need for both objective and quantitative methods for assessing the current grade of dermatitis and predicting its severity at an early stage of radiotherapy. The aim of the study was to evaluate the advantages and limitations of infrared thermography for monitoring the current level of radiation-induced dermatitis and predicting its severity by quantitative analysis of the thermal field dynamics in the irradiated zone. 30 adult patients were examined by infrared thermography during the course of 2D conventional radiotherapy for malignant tumors of various types and localizations. Our approach for quantifying the thermal field caused by dermatitis alone was applied. A statistical (correlation and ROC) analysis was performed. Dermatitis of varying severity was observed in 100% of the patients studied. The dynamics in the intensity of the anomalous thermal fields in the irradiated zone correlated with the dynamics of dermatitis grades, excluding the case of a radiosensitive tumor (correlation coefficient 0.74÷0.84). It was found that the maximum toxicity (dermatitis grade ≥ 3) develops in patients who how significant hyperthermia in the area of interest (≥ 0.7 °C) at an early stage of radiotherapy. The ROC analysis demonstrated the "good quality" of the prognosis method (AUC = 0.871). The non-invasive and cheap infrared thermography is a suitable tool for objective quantitative monitoring the current dermatitis grade during radiotherapy as well as predicting its severity for any tumor location.

Influence of the pulse duration at the laser processing of nitride ceramics

This paper presents results on laser ablation of AlN and Si3N4 ceramics by laser pulses with different duration. Three types of laser systems, a Nd:YAG one, operated at wavelength of 1064 nm and pulse duration of 15 ns, a Nd:YAG, operated at wavelength of 1064 nm and pulse duration of 10 ps, and a femtosecond laser system, operated at 800 nm, with a pulse duration of 75 fs, are used for experiments. Details on the ablation efficiency, surface morphology, and the chemical composition of the irradiated zones as a function of the pulse duration are given and discussed. It is demonstrated that the ablation rate (ablation depth per pulse) is highest for processing with nanosecond pulses and it is lowest for the femtosecond regime. The laser ablation results in significant change of the surface morphology, as its characteristics are influenced by the pulse duration. For all pulse durations conditions for formation of ripples structures are found. The ablation process is realized by decomposition of the ceramics and the composition of the remaining surface layer is governed by oxidation and carbonization.

CHANGES IN THE STRUCTURE AND PHASE STATE OF ALUMINUM ALLOY 2014, WHICH OCCURRED AS A RESULT OF IRRADIATION WITH AN ELECTRON BEAM

The use of aluminum alloys in nuclear power is limited by the properties of these alloys in the irradiation zone. The use of electron accelerators is an effective technique for simulating real operating conditions. As a result of irradiation, a whole complex of factors begins to work in the targets, which change the properties of these targets. Pulsed electric and magnetic fields appear, shock waves are generated, and gradient heating occurs. All this together changes the structure and properties of the targets. To irradiate the samples, electron beams with an energy of 8.2...8.3 MeV and a beam current of 0.8 mA were used. The work studied changes in the structural-phase state of an aluminum alloy of type 2014. For samples, before and after irradiation, an analysis of changes in mechanical characteristics (hardness, ultimate strength, proof strength) was carried out. Diffractometric studies were performed. These studies made it possible to determine changes in the phase composition. The intensity values of the diffraction lines were obtained.

Determination of the property evolution in rock after laser irradiation by nanoindentation and nuclear magnetic resonance

Laser technology, as a novel approach to rock breaking, holds great promise for accessing resources in deep, hard rock layers. Therefore, it is crucial to conduct microscopic testing and analysis of rocks following laser irradiation. In this study, the changes in minerals and elements of the rocks after laser irradiation are clarified using X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Additionally, the primary temperature range for rock weight loss is determined through thermogravimetric analysis (TGA). The rocks' microscopic features after irradiation are observed using a scanning electron microscope (SEM) and nuclear magnetic resonance (NMR), while the micromechanical properties of the rocks after irradiation are analyzed using nanoindentation techniques. New components such as Ca(OH)2 and CaO are generated in the laser irradiation zone. There is a decrease in the mass percentage of carbon (C), from 10.10 % without laser irradiation to 9.70 % with irradiation, and a decrease in the mass percentage of oxygen (O), from 46.38 % without irradiation to 43.99 % with irradiation. The percentage of large and medium-sized pores is evenly distributed, accounting for more than 50 % of the total after laser irradiation. The small pores occupy 18.85 % and 18.08 % within the size range of 0.0025–0.01 μm and 0.01–0.025 μm, respectively, accounting for a combined total percentage of slightly over 35 %. In the nanoindentation test, the laser irradiation area exhibits more significant deformation, with an average maximum indentation depth increase of 139.4 % compared to non-irradiated areas. The average microscopic modulus of elasticity of the rocks decreases from 36.69 GPa without laser irradiation to 10.06 GPa with laser irradiation, representing a reduction of 72.58 %. Moreover, the average hardness of the rocks decreases from 1.67 GPa without laser irradiation to 0.47 GPa with laser irradiation, indicating a decrease of 71.86 %. This study provides valuable foundational data for potential engineering applications.

The Role of Carbides in Forming the Steels Structure and Properties under Pulsed Laser Irradiation

Introduction. At present, in scientific publications, there is no unambiguous understanding and reasoned metal physical justification of the role of the carbide phase of irradiated materials in forming the required structure and achieving a given degree of hardening of surface layers of steels during pulsed laser treatment, especially in the zone of laser hardening from a solid (austenitic) state. The solution to this issue is of great importance, since it allows us to reasonably and purposefully design the required structure of surface layers of products of various functional purposes with high performance properties. The complexity and insufficiently detailed study of the process of structure formation in the surface layers of steels under extreme thermal effects of pulsed laser radiation required a series of metal physical experiments to study the fine structure of steels after high-speed high-temperature hardening. The aim of this article was to obtain, quantify and critically analyze the array of results of metal physical studies and to assess the degree of influence of the carbide phase on the formation of structure and properties of surface layers of steels in the process of pulsed laser hardening in different modes, that is, with and without melting the surface of the samples. Materials and Methods. In the work, carbon and alloyed tool steels were subjected to surface laser irradiation at a Kvant 16 installation. The radiation power density was 70–200 MW/m2. Optical, scanning probe and electron microscopy were used in conducting metal physical studies, as well as methods of diffractometric, spectral and durometric analysis of steels before and after laser treatment. Results. It was shown that laser treatment of steels with a radiation power density of 130–200 MW/m2 led to a local change in the chemical composition in the laser-fused areas of the spot, partial or complete dissolution of carbides present in the irradiated metal and an increase in the amount of residual austenite in the fused areas up to 40–60 %. It was found that on P6M5 steel, the maximum possible hardness of the irradiated zones was achieved by dissolving 30 % of carbides, on 9XC, HVG steels — 60–70 %. It was shown that under pulsed laser irradiation with q=70–125 MW/m2, that is, without melting the steel surface, "white zones" formed around carbide inclusions under the influence of thermo-deformation stresses at the boundaries of the "carbide – steel matrix" composition. They had irretrievability, dispersion of the structure and increased hardness (10–12 GPa). It was determined that the maximum hardness of laser-hardened metal in the zones of laser hardening from a solid state was achieved if the "white zones" occupied 40 % of the irradiated area of steel. It was found that the dispersion of carbides in this case was 0.5–1.5 microns. Discussion and Conclusion. The results of the conducted studies indicate that in order to obtain the best combination of hardness and viscosity of the irradiated zones during laser treatment with melting of the surface of steels of different chemical composition, it is necessary to dissolve different amounts of carbides. The dispersed structure of laser-fused steel zones, along with a sufficiently high content of residual austenite, predetermine the possibility of improving the operational characteristics of irradiated materials, especially under conditions of external shock loads. The analysis of the conducted metal physical studies irradiated without melting the surface of steels allows us to conclude that in order to obtain a high degree of hardening, it is necessary and expedient to ensure the presence of a certain volume of dispersed carbides in the structure of the irradiated steel. The structural composition of "white zones" formed during laser treatment without melting the steel surface contributes to obtaining a unique level of operational properties. The results of the performed studies contribute to the theory of steel structure formation under conditions of extreme heat exposure and allow for a rational choice of modes of surface laser processing of products and their operability.

Research on the design of a radiation biodevice based on a compact D-D neutron generator

ABSTRACT In this research, we used a self-developed compact D-D neutron generator and designed a neutron radiation biological device. The research results showed that lead was the material with the best neutron permeability; thus, hard lead was selected as the structural material for this device. Our research disclosed a phenomenon that differed from conventional wisdom, namely, the dose contribution of the neutrons reflected from the hard lead material at the top of the device was about twice that of the polyethylene material. Therefore, hard lead was also selected for the material of the top reflector in this device. The study also showed that the device had good dose uniformity, and the standard neutron absorption dose in each irradiation zone could be obtained according to the simulation results. This device may further promote the development of future research work such as neutron radiation biological effects and mutation breeding.

Numerical modeling to predict threshold fluence for material ejection in Laser-Induced forward transfer of metals

Laser-induced forward transfer (LIFT) uses a pulsed laser beam to propel material from a donor (containing a glass coated with a thin material film) onto a receiving substrate, resulting in pixellated material deposition. The deposition characteristics depend on the material ejection modes that vary with film thickness and laser parameters. This study develops a computational model based on the finite volume method for LIFT of gold films using nanosecond pulses, which captures two different ejection modes for droplet depositioncap ejection and jet ejection. The model computes the temperature distribution and predicts potential ejection regimes for different film thicknesses, providing an understanding of the material removal process. Cap ejection occurs at lower laser fluences when the entire film thickness in the irradiated zone is in the molten phase. In comparison, jet ejection occurs at higher laser fluences caused by vapor pocket formation at the glass-film interface. The model predicts threshold fluences with greater than 90% accuracy for film thickness less than 583 nm. However, for the film thickness of more than 583 nm, the simulations underpredict the threshold fluence, suggesting that laser absorption by the film decreases due to vapor formation at the glass-film interface. Besides, it is observed that higher fluences can cause melting and vaporization of the glass at the interface leading to possible contamination of the deposited material. The proposed model can be used to choose the operating window for laser parameters for droplet deposition in LIFT, which otherwise is challenging using experiments.

Simulation study on the effect of different wavelengths of laser on graphitization of diamond surface

A temperature field simulation study of CVD diamonds under nanosecond laser processing was carried out to investigate the characteristics of diamond graphitization and material removal mechanisms during nanosecond laser processing. Experimental results show that diamond undergoes significant burn and graphitization during laser processing. The graphite layer thickness and width of the diamond surface were measured to determine the regularity of nanosecond laser-induced diamond graphitization. Analysis of the simulation results for the diamond temperature profile shows that the nanosecond laser irradiation energy is mainly distributed over the diamond surface, and the thermal effect zone of nanosecond laser irradiation on the diamond is small, resulting in a graphite layer thickness of about 3.25 μm.