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(a) Equi-potential and electric field lines simulation at 4 kV. (b) Illustration of electron incidence angle.
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Ultrasoft X-ray characteristic aluminum K alpha line (Al Kα with energy of 1.5 keV) is used in radiobiological experiments to study the effect of radiation on biological matter. A simple method to generate a continuous beam of those X-ray radiations is to bombarding an aluminum target with accelerated electrons using high voltage (HV). In this work...
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... distributions of air kerma, we have simulated the electric field lines between the cathode and the anode with the aim to visualize the electron beam that interacts with the Al foil. The shape of this latter may be linked to the spatial distribution of USX pho- tons. The simulation is performed based on COMSOL™ Multi- physics code calculations; Fig. 7 shows the electric field lines at voltage 4 kV that imposes the shape of the electron beam. A very similar shape for the electric field lines was obtained at 2 ...
Citations
... According to the findings of this study, air tension falls as tube voltage rises and exposure falls. Air kerma has been measured and reported on by researchers in the medical and industrial sectors [7][8][9][10][11][12][13][14][15]. These analyses did not include the rest of the X-ray tube's radiation field in their estimation of air kerma at the tube's core. ...
The air kerma, which is the amount of energy given off by a radioactive substance, is essential for medical specialists who use radiation to diagnose cancer problems. The amount of energy that a photon has when it hits something can be described as the air kerma (the amount of energy that was deposited in the air when the photon passed through it). Radiation beam intensity is represented by this value. Hospital X-ray equipment has to account for the heel effect, which means that the borders of the picture obtain a lesser radiation dosage than the center, and that air kerma is not symmetrical. The voltage of the X-ray machine can also affect the uniformity of the radiation. This work presents a model-based approach to predict air kerma at various locations inside the radiation field of medical imaging instruments, making use of just a small number of measurements. Group Method of Data Handling (GMDH) neural networks are suggested for this purpose. Firstly, a medical X-ray tube was modeled using Monte Carlo N Particle (MCNP) code simulation algorithm. X-ray tubes and detectors make up medical X-ray CT imaging systems. An X-ray tube’s electron filament, thin wire, and metal target produce a picture of the electrons’ target. A small rectangular electron source modeled electron filaments. An electron source target was a thin, 19,290 kg/m3 tungsten cube in a tubular hoover chamber. The electron source–object axis of the simulation object is 20° from the vertical. For most medical X-ray imaging applications, the kerma of the air was calculated at a variety of discrete locations within the conical X-ray beam, providing an accurate data set for network training. Various locations were taken into account in the aforementioned voltages inside the radiation field as the input of the GMDH network. For diagnostic radiology applications, the trained GMDH model could determine the air kerma at any location in the X-ray field of view and for a wide range of X-ray tube voltages with a Mean Relative Error (MRE) of less than 0.25%. This study yielded the following results: (1) The heel effect is included when calculating air kerma. (2) Computing the air kerma using an artificial neural network trained with minimal data. (3) An artificial neural network quickly and reliably calculated air kerma. (4) Figuring out the air kerma for the operating voltage of medical tubes. The high accuracy of the trained neural network in determining air kerma guarantees the usability of the presented method in operational conditions.
... The key achievement of this investigation was demonstrating the reduction in the air kerma by increasing the voltage and decreasing the exposure. In [7][8][9][10][11][12][13][14], the amount of air kerma was calculated and reported for both the industry and medicine areas. In the abovementioned research, the focus was only on the determination of the air kerma in the center of the X-ray beam. ...
The air kerma is a key parameter in medical diagnostic radiology. Radiologists use the air kerma parameter to evaluate organ doses and any associated patient hazards. The air kerma can be simply described as the deposited kinetic energy once a photon passes through the air, and it represents the intensity of the radiation beam. Due to the heel effect in the X-ray sources of medical imaging systems, the air kerma is not uniform within the X-ray beam’s field of view. Additionally, the X-ray tube voltage can also affect this nonuniformity. In this investigation, an intelligent technique based on the radial basis function neural network (RBFNN) is presented to predict the air kerma at every point within the fields of view of the X-ray beams of medical diagnostic imaging systems based on discrete and limited measured data. First, a diagnostic imaging system was modeled with the help of the Monte Carlo N Particle X version (MCNPX) code. It should be noted that a tungsten target and beryllium window with a thickness of 1 mm (no extra filter was applied) were used for modeling the X-ray tube. Second, the air kerma was calculated at various discrete positions within the conical X-ray beam for tube voltages of 40 kV, 60 kV, 80 kV, 100 kV, 120 kV, and 140 kV (this range covers most medical X-ray imaging applications) to provide the adequate dataset for training the network. The X-ray tube voltage and location of each point at which the air kerma was calculated were used as the RBFNN inputs. The calculated air kerma was also assigned as the output. The trained RBFNN model was capable of estimating the air kerma at any random position within the X-ray beam’s field of view for X-ray tube voltages within the range of medical diagnostic radiology (20–140 kV).
... They indicated that an increase in tube voltage with a decrease in exposure (product of tube current and time) would lead to significant air kerma reduction. More studies about calculation of air kerma parameter in the two fields of medicine and industry can be found in references (Alonso et al., 2018;Haba et al., 2016;Kwon et al., 2011;Bushberg et al., 2012;Perera et al., 1994;Oliveira et al., 2000;Liu et al., 2016;Ounoughi et al., 2015). ...
... Les solutions complexes sont exposées en environnement atmosphérique à la raie Kα de l'aluminium à l'aide d'un générateur de rayons X à cathode froide dont le faisceau a été caractérisé finement [9,10,11]. Le dispositif complet est schématisé en figure 1, il est piloté via une interface LabVIEW. Les paramètres d'opération sont une tension d'accélération de 4 kV, un courant de 2 mA, et une pression interne au tube de 0,07 mbar. ...
... In the present case, the substrate is composed of freshly cleaved HOPG foils. The USX source is the Al K line (1.5 keV) generated by using a lab-bench cold-cathode system (Ounoughi et al., 2013), with a well characterized beam, both spatially and energetically (Groetz et al., 2014), (Ounoughi et al., 2015). ...
In this paper we present in a first part the latest results of our group which are in relation with the study of DNA damages inflicted by low energy electrons (0-20 eV) in ultra-high vacuum as well as in air under atmospheric conditions. A short description of the drop-casting technique we developed to produce thin and nanometre-scaled DNA layers onto graphite sheets is given. We provide the absolute cross-section for loss of supercoiled topology of plasmid DNA complexed with 1,3-diaminopropane (Dap) in the vacuum under 10 eV electron impact and suggest a specific pathway for the dissociation of the transient negative ion formed by resonant capture of such a low energy electron (LEE) by the DNA's phosphate group when complexed to Dap. Well-gauged DNA-Dap layers with various nanometre-scaled thicknesses are used to evaluate the effective attenuation length of secondary photo-LEEs in the energy range (0-20 eV). The values of 11-16 nm for DNA kept under atmospheric conditions are in good agreement with the rare literature data available and which are stemming from computer simulations. In a second part, we describe the method we have developed in order to expose liquid samples of plasmid DNA to ultra-soft X-rays (Al Kα line at 1.5 keV) under hydroxyl radical scavenging conditions. We provide an experimentally determined percentage of indirect effects in aqueous medium kept under standard conditions of 94.7 ± 2.1% indirect effects; in satisfactory agreement with the data published by others (i.e. 97.7%) relative to gamma irradiation of frozen solutions (Tomita et al., 1995).
... Les solutions complexes sont exposées en environnement atmosphérique à la raie Kα de l'aluminium à l'aide d'un générateur de rayons X à cathode froide dont le faisceau a été caractérisé finement [9,10,11]. Le dispositif complet est schématisé en figure 1, il est piloté via une interface LabVIEW. Les paramètres d'opération sont une tension d'accélération de 4 kV, un courant de 2 mA, et une pression interne au tube de 0,07 mbar. ...
The chemical environment of DNA in real biological situation is complex notably due to the presence of histones, i.e. nuclear proteins which are linked approximately in equal mass balance to the DNA macromolecule to form chromatin. Histones have numerous terminal tails made up of basic (positively charged) amino acids arginine and lysine while DNA is a macro-anion which holds one negative charge per phosphate moiety all along the double-helix. As a first attempt, in this study, the complexity of the nuclear chromatin structure is mimicked through the formation of complexes made up of the basic amino acids Arg, His, Lys (which apart from His are protonated at physiological pH) and a DNA plasmid used as a probe. Those three amino acids, when free in aqueous solution are known to be effective radical scavengers, notably for the hydroxyl radical, they might therefore protect DNA against indirect effects when exposed to ionizing radiations. At fixed concentration, the scavenging capacities of free amino acids, σ, for the hydroxyl radical are typically such that σHis ≈σArg > σLys (σLys ≈ 0,1 × σArg). We have measured the yields of single strand breaks per plasmid and per Gray (X) during exposure of aqueous solutions of complexes [amino acid –plasmid DNA]
to ultra-soft X-rays (1,5 keV). At equal concentrations, the three complexed amino acids which also are present in large excess in the solutions do not exhibit DNA protection capabilities that are in line with their scavenging capacities ; we find indeed single strand break yields that follow the order XHis > XArg > XLys (XLys ≈ 0,01 × XArg). After having detailed our experimental protocol, we analyze the specific features of basic amino acids interactions with DNA, based on a bibliographic survey. The specificity of Arg interaction with DNA, especially
its propensity to create bidentate contacts with bases (principally with the G base) makes it possible to propose a way by which high DNA single strand break damage is favored in the presence of Arg. An inter-molecular radical transfer is suggested which also seems to hold for the Lysine amino acid. As for the unexpected high single strand break yields observed with His, we suggest some possible pathways but complementary experiments still will have to be performed.
The dose distribution is a crucial evaluation to ensure radiation safety once using a Crookes tube in the teaching of science in Japan. In this study, the spatial dose distribution surrounding the Crookes tube was estimated using TLDs. The results showed that the high dose distribution predominated in front of the Crookes tube with a range of 0.23–0.46 mSv/h at a distance of 1 m. From the experimental data, the present study made some recommendations for radiation protection and operational condition on these apparatuses. These results will contribute as a radiation safety database on Crookes tube serving in radiological education in Japan.
The air kinetic energy released per unit of mass (air kerma) quantity is of importance in both medicine and industry for evaluating the radiation field of X-ray tubes and also for calibrating the reference instruments. The air kerma spatial distribution inside the X-ray tube's radiation field is not uniform because of the heel effect phenomenon. In this paper, a combination of Monte Carlo N Particle eXtended (MCNPX) simulation code and artificial neural network (ANN) has been utilized to estimate the air kerma inside the radiation field of X-ray tube for a wide range of tube voltages (50–600 kV) which covers both medical and industrial applications. At first, an X-ray tube with an anode angle of 20° was simulated using MCNPX code. Next, in order to provide the required data for training the network, 1375 point detectors were placed in different positions inside the conical radiation field of the simulated X-ray tube and then the air kerma was calculated for tube voltages in the range of 50–600 kV with a step of 50 kV. The tube voltage and point detector's spherical coordinates including distance from target, tangential angle and polar angle were utilized as the 4 inputs and the air kerma was used as the output of the ANN. After training the ANN, the proposed ANN model could estimate the air kerma in every position inside the radiation field of X-ray tube for a wide range of voltages (50–600 kV) with a mean relative error (MRE) of less than 0.67%.
This study aimed to calculate the Conversion Coefficients (CC) of Equivalent and Effective doses by air kerma considering Total Body Irradiation scenarios with Varian linear accelerator with photon beams energy of 4, 6, 10, 15, 18, and 25 MV. The simulations were performed in the MCNPX code and the University of Florida (UF) phantoms were used to represent exposed lying down adult patients in the AP, PA, RLAT, and LLAT irradiation geometries. Lead attenuators were inserted in the scenarios for the preservation of organs of risk and their contribution were analyzed for CC. For most counts, the statistical uncertainty was approximately 5%. For the gonads, CC values for the male phantom decreased with the increase of energy in the AP geometry, which did not occur for the female phantom. As the beam becomes more penetrating, the ovary absorbs more energy because of its internal position. Considering the lung, an organ of risk in TBI, the insertion of the attenuators in the scenarios caused the CC values to reduce by more than 30%. For organs and tissues such as skin and male breasts, the attenuators caused the dose to increase. As for the active bone marrow, which is the TBI target tissue, it was not possible to obtain a good estimate for CC at 15, 18, and 25 MV due to a limitation of the method used to calculate the dose in the bone areas. Nevertheless, for lower energies the CC values for the marrow were valid.
L’environnement chimique de l’ADN en situation biologique est complexe notamment en raison de la présence d’histones, protéines nucléaires, associées en quantité approximativement égales à l’ADN pour former la chromatine. Les histones possèdent de nombreux radicaux basiques arginine et lysine chargés positivement et dont la majorité se trouve sur les chaînes émergentes, l’ADN présente quant à lui des charges négatives sur ses groupements phosphates localisés tout au long de la double hélice. Dans cette étude, la complexité de la structure de la chromatine nucléaire est dans un premier temps mimée en solution aqueuse par la formation de complexes entre un ADN plasmidique sonde et les trois acides aminés basiques, Arg, His, Lys, qui, mis à part His, sont protonés au pH physiologique. Ces acides aminés libres en solution sont réputés être des capteurs efficaces de radicaux libres, notamment pour le radical hydroxyle, conférant ainsi un pouvoir protecteur vis-à-vis des effets indirects sur l’ADN en situation d’exposition aux rayonnements ionisants. A concentration fixée, les capacités de capture des acides aminés libres, , pour le radical hydroxyle sont typiquement les suivantes His ≈Arg > Lys (Lys ≈ 0,1 × Arg). Nous avons mesuré les taux de cassures simple brin par plasmide et par Gray () lors d’expositions de solutions aqueuses de complexes [acide aminé – ADN plasmidique] aux rayons X ultra-mous (1,5 keV). A concentrations égales, les trois acides aminés complexés et présents en large excès ne manifestent pas une capacité de protection de l’ADN proportionnelle à leur capacité de capture libre et en solution ; on trouve en effet des taux de cassures dans l’ordre suivant His > Arg >Lys (Lys ≈ 0,01 × Arg). Après avoir détaillé le mode opératoire de ces mesures, nous analyserons sur des bases bibliographiques, les modes spécifiques d’interaction des acides aminés basiques avec l’ADN. La spécificité des liaisons de l’arginine avec l’ADN et plus particulièrement sa propension à être un ligand bidentate qui se lie aux bases (principalement G) de l’ADN nous permet d’expliquer les taux de cassures simple brin particulièrement élevés observés avec Arg. Un mécanisme de transfert de radical intermoléculaire est suggéré pour Arg. Un raisonnement globalement similaire peut être tenu pour la lysine. Pour l’histidine, nous suggérons quelques voies possibles qui conduiraient à expliquer les taux de cassure anormalement élevés observés, mais cela demandera des expériences complémentaires.
