1,721,020 research outputs found
Microdosimetry at nanometric sites of charged Helium, Carbon and Oxygen beams with an advanced Tissue Equivalent Proportional Counter
No full textThe effectiveness of radiotherapy, particularly hadron therapy, is closely tied to the interactions of radiation at the cellular and sub-cellular levels. Understanding the local energy deposition of charged particles is essential for accurately predicting their biological effects. Traditional dosimetric approaches, based on absorbed dose, fail to describe the stochastic nature of energy deposition at micrometric and nanometric scales. This study investigates the micro- and nano-dosimetric properties of Helium, Carbon, and Oxygen ion beams at 62 MeV/u using an advanced Tissue Equivalent Proportional Counter (TEPC). This TEPC, designed to simulate site sizes ranging from 0.5 μm to 25 nm, was placed at various depths across the Bragg peaks of the ion beams at the INFN-LNS facility in Catania (Italy). Results show a clear dependence of microdosimetric distributions on both simulated site size and position across the depth-dose profile. Smaller site sizes shift the distribution toward higher lineal energies, especially at proximal depths, suggesting that microdosimetric spectra at nanometric scale can offer different insights on the radiation interaction with tissue. This study also underlines the role of secondary electrons and fragmentation effects, which vary with the atomic number of the ion, producing different effects for Helium, Carbon and Oxygen ions. These findings may have significant implications for improving relative biological effectiveness (RBE) models in hadron therapy. By extending microdosimetric analysis to the nanometric scale, this research provides new data for a possible improvement of the predictive accuracy of radiation-induced biological effects. The novel TEPC used in this study bridges the gap between microdosimetry and nanodosimetry, offering a more refined assessment of radiation quality
Numerical modeling of the gas gain of low-pressure Tissue-Equivalent Proportional Counters
No full textProportional counters are radiation detectors widely used in many applications. The design of the counter, to best fit each application, needs an accurate knowledge and physical modeling of the electron avalanche process. A particular proportional counter is the tissue-equivalent proportional counter (TEPC), the reference detector for experimental microdosimetry, which consists of a spherical or cylindrical chamber filled with low-density tissue-equivalent gas to simulate the energy deposition in tissue sites of micrometric size. The lower operation limit of standard TEPCs operated in the pulse-height analysis mode is about 0.3μm. In order to overcome this technological limit, different avalanche-confinement nano-microdosimetric TEPCs capable of measuring microdosimetric spectra in the nanometric domain were designed and constructed. In this work, a novel numerical tool developed for the Monte Carlo simulation of the electron avalanche process inside a low-pressure TEPC is described. The Monte Carlo code allows to simulate complex 3D electric field configurations exploiting COMSOL finite elements analysis. Several models for the electron interactions (i.e. scattering and ionization) are included in the code. The code has been benchmarked with the experimental results of a wall-less avalanche-confinement TEPC in terms of absolute gas gain for different operating conditions (i.e. gas pressures and electrode voltages). The results show that the code is capable of reproducing the absolute value of the gas gain for the avalanche-confinement TEPC simulating some tenths of nanometers in site size. Moreover, the code can reproduce both the extension and the shape of the proportional counter working windows. The code was also applied for simulating the probability of absorption of electrons by the central third electrode: the helix. The results show a non-negligible probability of absorption in the common range of operation. This code will be further applied for optimizing the TEPC design, capable of simulating site sizes closer to the nanometer region
DIAMON: A portable, real-time and direction -aware neutron spectrometer for field characterization and dosimetry
No full textAn innovative portable detection system based on real-time spectrometry was developed for neutron field characterization and dosimetry. This system, called DIAMON (Direction-aware Isotropic and Active neutron MONitor with spectrometric capabilities), relies on a multi-detector geometry and a built-in unfolding code to provide in real time all field and operational quantities of interest. A patent pending design provides a quasi-ideal isotropic response and an optimized spectrometric performance from thermal to high energies. Furthermore, the custom signal processing and acquisition system is conceived for deriving continuously the 3D directional distribution of incoming neutrons. This work describes the characterization of DIAMON performances carried out at the neutron calibration facility of Politecnico di Milano. Neutron spectra, field quantities and dosimetric values are reported and compared with those assessed by a reference, calibrated, Bonner Sphere System. The overall variability of the DIAMON angular response and the gamma sensitivity are presented and discussed. An example of the continuous monitoring capabilities is also shown. Results demonstrate DIAMON is an all-in-one detection system able to characterize accurately all neutron field properties in real-time
Solid state microdosimetry of a 148 MeV proton spread-out Bragg peak with a pixelated silicon telescope
Full text linkA constant value of the Relative Biological Effectiveness (RBE), equal to 1.1, to weight the physical dose of proton therapy treatment planning collides with the experimental evidence of an increase of effectiveness along the depth dose profile, especially at the end of the particle range. In this context, it is desirable to develop new optimized treatment planning systems that account for a variable RBE when weighting the physical dose. In particular, due to the increasing interest on microdosimetry as a possible methodology for measuring physical quantities correlated with the biological effectiveness of the therapeutic beam, the development of new Tissue-Equivalent Proportional Counters (TEPCs) specifically designed for the clinical environment are in progress. In this framework, the silicon technology allows to produce solid state detectors of real micrometric dimensions. This is a valid alternative to the TEPC from a practical point of view, being simple, easy-of-use and more versatile. The feasibility of a solid state microdosimeter based on a monolithic double stage silicon telescope has been previously proposed and deeply investigated by comparing its response to the one obtained by reference TEPCs in various radiation fields. The device is constituted by a matrix of cylindrical elements, 2 μm in thickness and 9 μm in diameter, coupled to a single E stage, 500 μm in thickness. Each segmented ΔE stage acts as a solid state microdosimeter, while the E stage gives information on the energy of the impinging proton up to about 8 MeV. This work is dedicated to the description of the microdosimetric characterization of the 148 MeV energy-modulated proton beam at the radiobiological research line of the Trento Proton Therapy Centre by means of a pixelated silicon microdosimeter. All measurements were carried out at different positions across the spread-out Bragg peak (SOBP) and the corresponding microdosimetric distributions were derived by applying a novel extrapolation algorithm. Finally, microdosimetric assessment of Relative Biological Effectiveness was carried out by weighting the dose distribution of the lineal energy with the Loncol's biological weighting function. Benefits and possible limitations of this approach are discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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