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Ocena niezawodności systemu transportowego z wykorzystaniem metody dynamicznego drzewa niezdatności

Szkoda M., Kaczor G.

Autobusy : technika, eksploatacja, systemy transportowe

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2016

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R. 17, nr 6

1593--1598

PL

W przedstawionej pracy zwrócono uwagę na potrzebę modelowania systemów transportowych w aspekcie oceny ich niezawodności. Uwzględnienie zależności czasowych między elementami systemu transportowego w celu dokładniejszego odzwierciedlenia warunków rzeczywistych wymaga dokonania wyboru właściwej metody analizy. Jedną z takich metod jest metoda dynamicznego drzewa niezdatności (DFTA), która opiera się na klasycznej metodzie drzewa niezdatności (FTA), uzupełnionej o bramki logiczne z zależnościami czasowymi. Z uwagi na skomplikowane procedury obliczeniowe, metoda DFTA jest trudna do zastosowania w ujęciu analitycznym. Z tego też powodu korzysta się m.in. z technik symulacyjnych, takich jak np. symulacja Monte Carlo. Jest ona często stosowana w ocenie niezawodności obiektów technicznych, jednak w przypadku systemów o wysokim stopniu złożoności wspierana dodatkowo przez specjalistyczne oprogramowanie komputerowe. Niniejsza praca dotyczy oceny niezawodności przykładowego systemu transportowego, którego model stanowi dynamiczne drzewo niezdatności. Za pomocą symulacji Monte Carlo wyznaczono wybrane miary, mogące służyć do oceny niezawodności. Realizację procedury obliczeniowej wykonano przy pomocy oprogramowania firmy Reliasoft.

EN

The presented paper focuses on the need for modelling of the transportation systems in terms of the reliability assessment. Taking into account the time dependencies between the elements of the system in order to develop the more accurate model needs to choose the appropriate analysis method. One of the methods is Dynamic Fault Tree Analysis (DFTA), which extends the classical Fault Tree Analysis (FTA)by adding the logical gates with time dependencies. Due to the sophisticated calculation procedures, DFT may be difficult to solve it analytically. For this reason the simulation methods are often applied, such as the Monte Carlo Simulation method. It is commonly used for assessing the reliability of the technical objects, but in the case of the complex systems it is supported by a specialized software. This work is aimed at reliability assessment of the given transportation system. Created Dynamic Fault Tree of the system was solved using the Monte Carlo Simulation method. We obtained the selected measures, which can be used to assess the reliability. Performed Calculations were supported by the Reliasoft’s software.

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Tumor dose enhancement by gold nanoparticles in a 6 MV photon beam: a Monte Carlo study on the size effect of nanoparticles

Pakravan D., Ghorbani M., Momennezhad M.

Nukleonika

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2013

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Vol. 58, No. 2

275--280

EN

In this study after benchmarking of Monte Carlo (MC) simulation of a 6 MV linac, the simulation model was used for estimation of tumor dose enhancement by gold nanoparticles (GNPs). The 6 MV photon mode of a Siemens Primus linac was simulated and a percent depth dose and dose profiles values obtained from the simulations were compared with the corresponding measured values. Dose enhancement for various sizes and concentrations of GNPs were studied for two cases with and without the presence of a flattening filter in the beam’s path. Tumor dose enhancement with and without the presence of the flattening filter was, respectively 1–5 and 3–10%. The maximum dose enhancement was observed when 200 nm GNPs was used and the concentration was 36 mg/g tumor. Furthermore, larger GNPs resulted in higher dose values in the tumor. After careful observation of the dose enhancement factor data, it was found that there is a poor relation between the nanoparticle size and dose enhancement. It seems that for high energy photons, the dose enhancement is more affected by the concentration of nanoparticles than their size.

3

Incrustation of alpha-particle emitters in the source backing: influence on activity measurements

Jurado-Vargas M., Fernández-Timón A.

Nukleonika

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2012

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Vol. 57, No. 4

569-573

EN

Alpha particles emitted from radioactive sources are often measured using a 2pi counting geometry in order to determine the activity with a low deviation. The ratio C2pi/A (counting rate/activity) can, however, deviate from the theoretical value of 0.5 because of backscattering in the backing material, scattering and absorption of alpha particles in the source. The experimental counting rates are, therefore, corrected for these effects (backscattering for all sources, plus self-absorption for sources of non-negligible thickness) to determine the real source activity. However, the corrections needed for situations corresponding to alpha-particle sources in which the radionuclides are not deposited but incrusted in the backing material have not been considered. The aim of the present work was therefore to study the influence that incrustation in the backing can have on the total detection efficiency, and hence on the activity estimated for the source. To this end, we used the Monte Carlo computer code SRIM to model the behaviour of the alpha particles in the backing material.

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Development of the technique embedded into a Monte Carlo transport system for calculation of photonuclear isotope yield

Nikiforov V. I., Uvarov V. L.

Nukleonika

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2012

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Vol. 57, No. 1

75-80

EN

The paper describes two methods that use Monte Carlo transport code for computing the photonuclear isotope yield for arbitrary target activation conditions. One of them is based on a direct simulation of new nuclei generation events (DSE method). The other one involves a step-by-step calculation of isotope microyield along the photon trajectories (SBSM method). The techniques have been realized in the computer codes using the PENELOPE package of 2001, 2006 and 2008 versions. The program benchmarking was performed using experimental data on the activity distributions of 67Cu isotope produced in the 68Zn(gamma,p)67Cu reaction in thick zinc targets. Both approaches have shown to give similar results at an appreciably greater speed of the SBSM method. The results of simulation based on the PENELOPE 2006 and 2008 codes are in excellent agreement with all experimental data. At the same time, the PENELOPE 2001 computations give good agreement with the experimental results for target activation by the electron beam, but in the case of target exposed to bremsstrahlung systematic underestimation of about 15% has been observed.

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Assessment of the staff absorbed dose related to cyclotron operation and service in the production of 18F radiopharmaceuticals

Sadat-Eshkevar S. M., Karimian A., Mirzaii M.

Nukleonika

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2012

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Vol. 57, No. 3

407-410

EN

Cyclotron accelerators are used to produce medical radioisotopes. One of the most important problems which may be encountered is malfunction of a part of the target or beam line which requires stopping of the bombardment and making a repair. The decision about doing the repair depends on the whole body dose rate in a target room. In this work, dosimetric conditions related to the production of 18FDG radiopharmaceutical were simulated by the Monte Carlo (MC) method. Independently, the dose rates were measured by 7 ICRU spherical body phantoms placed inside the liquid target room and the maze of the cyclotron. The radiation dose rate inside the target room depends on the duration of the bombardment and the time passed after stopping the bombardment. The correlation between duration of the bombardment and required time after stopping the bombardment to reach the absorbed dose rate less than 25 mi Sv/h, was calculated for the presence and absence of the irradiated target. The results showed that the repair can be started immediately after stopping of the proton bombardment only if the target has been ejected from the target room and the duration of bombardment has not taken more than 10 min.