1,721,106 research outputs found
Conferenza internazionale sulle moderne tecniche di radioterapia : progressi e sfide nella radioprotezione del paziente : resoconto ed impressioni
No full textScintillators and semiconductor detectors
No full textVarious processes occur during the detection of ionizing radiation within a scintillator, and proper detection designs are needed [1, 2, 3]. As a consequence of the interaction of radiation with the scintillation material, ionisation and excitation processes arise, and the energy (or part of it) of the incoming radiation is transferred to the atoms and molecules of the scintillator. Following deexcitation processes, photons originate in the ultraviolet/visible (UV/VIS) region of the electromagnetic spectrum, light that must be collected and converted in a suitable electric signal. In many cases, light collection simply may be obtained by coupling the scintillator directly with an optical detector, typically a photomultiplier tube (PMT). In other cases, depending on the particular application or measurement geometry, a light guide is required, which efficiently transmits the light emitted by the scintillator to the optical device. Finally, light photons are converted into electrons, and the resulting basic electric signal is amplified and properly processed. Let us consider in more detail the scintillation conversion mechanism in a wide band-gap material. This process may be explained by considering the energy band structure of an activated crystalline scintillator. An inorganic scintillator is indeed usually a crystalline solid containing a small amount of dopant, acting as a luminescent centre, which creates energy levels within the forbidden band between the valence band and the conduction band. Moreover, the natural impurities and defects present in the crystal are the origination of other energy levels, which may act as traps during the charge transport
Photo-transferred thermoluminescence from deep traps in quartz
No full textPhoto-transferred thermoluminescence (PTTL) measurements were performed on analytical grade quartz with the aim to study the dependence of the PTTL signal on preheat temperature and light-exposure time. The results proved that, in addition to the well-known contribution due to the electron traps related to the 325 °C thermoluminescence peak, a non-negligible role was played by deep thermally disconnected traps. Moreover, the shape of the time-response curve for the PTTL signal of quartz samples preheated at high temperature values suggested that recombination processes of optically stimulated electrons from deep traps involved also a non-radiative recombination centre
Rare earth doped silica optical fibre sensors for dosimetry in medical and technical applications
Full text linkRadioluminescence optical fibre sensors are gaining importance since these devices are promising in several applications like high energy physics, particle tracking, real-time monitoring of radiation beams, and radioactive waste. Silica optical fibres play an important role thanks to their high radiation hardness. Moreover, rare earths may be incorporated to optimise the scintillation properties (emission spectrum, decay time) according to the particular application. This makes doped silica optical fibres a very versatile tool for the detection of ionizing radiation in many contexts. Among the fields of application of optical fibre sensors, radiation therapy represents a driving force for the research and development of new devices. In this review the recent progresses in the development of rare earth doped silica fibres for dosimetry in the medical field are described. After a general description of advantages and challenges for the use of optical fibre based dosimeter during radiation therapy treatment and diagnostic irradiations, the features of the incorporation of rare earths in the silica matrix in order to prepare radioluminescent optical fibre sensors are presented and discussed. In the last part of this paper, recent results obtained by using cerium, europium, and ytterbium doped silica optical fibres in radiation therapy applications are reviewed
The thermoluminescence peaks of quartz at intermediate temperatures and their use in dating and dose reconstruction
No full textThermoluminescence properties of the quartz peaks occurring at intermediate temperature range were studied. Two main peaks (named peak I and peak II), placed at approximately 150°C and 200°C using a heating rate of 2°C/s were observed. They proved to have a linear dose response up to approximately 1 Gy; for higher doses non-linear behaviours were observed. Moreover, sensitisation phenomena occurred as consequences of successive cycles of irradiations and heating treatments. Lifetimes of 720±70 days and 580±70 years (at a temperature of 15°C) for peak I and II respectively were derived. Thermal activation energy and frequency factor of these two glow peaks were equal to (1.22±0.02) eV and to (3.39±1.46)·1013 s-1 for peak I, and to (1.36±0.02) eV (2.23±0.75)·1013 s-1 for peak II. The quartz glow peaks at intermediate temperatures were then used in TL dating of three building materials samples (one brick and two tiles) of age in the range 55-75 years. The total dose absorbed by the samples was assessed by using different procedures such as regeneration dose method, additive dose and single aliquot regeneration dose. The various components of annual dose rate were estimated using different and complementary techniques, such as beta dosimetry, alpha counting, gamma spectrometry and flame photometry. The results obtained demonstrate that the quartz glow peaks at intermediate temperatures can be successfully used in TL dating of young samples (i.e. samples having an age of few decades). Moreover, the precision of the method makes the use of these peaks promising in dose reconstruction applications, for the assessment of accidental dose values of some tens of milliGrays
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
Caratterizzazione dosimetrica di cristalli e ceramiche di Lu3Al5O12 drogati con cerio tramite luminescenza termicamente stimolata
No full textIl granato di Alluminio e Lutezio (comunemente abbreviato con LuAG, formula molecolare Lu3Al5O12) è noto per le sue proprietà di scintillazione. Può essere drogato con varie terre rare ed essere prodotto sia in forma di cristallo singolo che di ceramica trasparente. Le proprietà ottiche, spettroscopiche e di scintillazione di questo cristallo sono state ampiamente investigate negli ultimi anni e le relative informazioni sono disponibili nella recente letteratura (Liu et al., 2016; Djebli et al., 2017). Limitati sono invece gli studi inerenti le proprietà dosimetriche di LuAG (Yanagida, 2017). In questo lavoro verrà presentata una caratterizzazione dosimetrica di cristalli e ceramiche di LuAG drogati con cerio (LuAG:Ce) mediante la tecnica di Luminescenza Termicamente Stimolata (TSL), in vista di possibili impieghi di questo materiale come dosimetro passivo. Nello specifico, verranno mostrati i risultati di misure di riproducibilità del segnale TSL, di linearità con la dose nell’intervallo 0-25 Gy, di stabilità nel tempo e dell’effetto dell’esposizione a sorgenti luminose di varie lunghezze d’onda sulla forma ed intensità della glow curve
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