scholarly journals Influence of head cover on the neutron dose equivalent in Monte Carlo simulations of high energy medical linear accelerator

2018 ◽  
Vol 33 (2) ◽  
pp. 217-222
Author(s):  
Hrvoje Brkic ◽  
Mladen Kasabasic ◽  
Ana Ivkovic ◽  
Dejan Agic ◽  
Ivana Krpan ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Medical Personnel ◽  
High Energy ◽  
Medical Professional ◽  
Linear Accelerators ◽  
Flux Change ◽  
Place Of Origin ◽  
The One ◽  
Head Cover

Neutron contamination of radiotherapeutic photon beam occurs when energies higher than 10 MeV are used in radiotherapy. To correctly assess the neutron doses that medical personnel and patients receive, it is highly important to know the spectra of the produced photoneutrons. One of the most common ways to determine such spectrum is to perform Monte Carlo simulations of the accelerator. Major issue in the Monte Carlo modelling is that the manufacturers often does not provide full specifications of the accelerators head, so some parts of the head are omitted from the simulation. Within this paper we present a model that includes head cover compared to the one where it is omitted, as it can often be found in the references. Neutron fluxes, spectra, mean energies and place of origin are compared in isocenter, at the point 1 m above target and the point 1 m aside from the target, in both models. In all the considered planes the flux change was found to be more than 20 %, with a significantly change in neutron energy, what is also important in neutron dosimetry. Ignoring the head cover in the Monte Carlo modelling of the high energy electron linear accelerators in radiotherapy, will introduce a large uncertainty of neutron doses assessing a patient, or a medical professional.

scholarly journals A fractional generalization of the dirichlet distribution and related distributions

2021 ◽  
Vol 24 (1) ◽  
pp. 112-136
Author(s):  
Elvira Di Nardo ◽  
Federico Polito ◽  
Enrico Scalas
Keyword(s):  
Monte Carlo ◽  
Probability Density Function ◽  
Monte Carlo Simulations ◽  
Probability Density ◽  
Dirichlet Distribution ◽  
One Dimensional ◽  
Reasonable Approximation ◽  
Generalized Dirichlet Distribution ◽  
The One ◽  
Generalized Dirichlet

Abstract This paper is devoted to a fractional generalization of the Dirichlet distribution. The form of the multivariate distribution is derived assuming that the n partitions of the interval [0, Wn ] are independent and identically distributed random variables following the generalized Mittag-Leffler distribution. The expected value and variance of the one-dimensional marginal are derived as well as the form of its probability density function. A related generalized Dirichlet distribution is studied that provides a reasonable approximation for some values of the parameters. The relation between this distribution and other generalizations of the Dirichlet distribution is discussed. Monte Carlo simulations of the one-dimensional marginals for both distributions are presented.

Topological defects in nematic films between planar degenerate surfaces. A Monte Carlo study

2021 ◽  
pp. 2250016
Author(s):  
Cesare Chiccoli ◽  
Paolo Pasini ◽  
Luiz Roberto Evangelista ◽  
Rodolfo Teixeira de Souza ◽  
Claudio Zannoni
Keyword(s):  
Monte Carlo ◽  
Boundary Conditions ◽  
Monte Carlo Simulations ◽  
Defect Structure ◽  
Topological Defects ◽  
Monte Carlo Study ◽  
Geometric Parameters ◽  
Molecular Organization ◽  
The One

The molecular organization of a nematic film sandwiched between two planar randomly aligned surfaces is studied by means of detailed Monte Carlo simulations. The formation as well as the evolution of topological defects induced by these particular boundary conditions are investigated. The resulting defect structure is compared with the one induced by hybrid aligned surfaces. The observation of such defects and some features of their structures can be associated with geometric parameters of the film and with properties of the confining surfaces.

In-Situ Measurement of Artificial Nuclides in Seabed Sediments Based on Monte Carlo Simulations and an Underwater HPGe Detector

2019 ◽  
Vol 53 (3) ◽  
pp. 16-22
Author(s):  
Jinzhao Zhang ◽  
Hongzhi Li ◽  
Xianguo Tuo
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Energy Resolution ◽  
Hpge Detector ◽  
High Energy ◽  
In Situ Measurement ◽  
Energy Calibration ◽  
High Energy Resolution ◽  
Seabed Sediments

AbstractIn-situ measurement of marine sediment radioactivity does not destroy the stratification of radionuclides in the sediment. We develop a novel seabed sediment radioactive measurement technique using a High Purity Germanium (HPGe) detector. The overall measurement system is designed, and the detector energy calibration is performed. The efficiency is calculated based on Monte Carlo simulations using the MCNP5 code. We compared the efficiency and energy resolution with the NaI(Tl) detection through experiments. NaI(Tl) detection is incapable of identifying the 137Cs artificial nuclides in seabed sediments due to the energy resolution limit. Hence, underwater HPGe detection is utilized due to its high energy resolution, which enables the detection of artificial nuclides 137Cs. The proposed method is of great significance in evaluating marine radioactive pollution.

Energy spectrum from single TGFs detected by ASIM

2020 ◽  
Author(s):  
Anders Lindanger ◽  
Martino Marisaldi ◽  
Nikolai Østgaard ◽  
Andrey Mezentsev ◽  
Torstein Neubert ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Spectral Analysis ◽  
Energy Spectrum ◽  
Monte Carlo Simulations ◽  
Energy Range ◽  
Gamma Ray ◽  
High Energy ◽  
Energy Calibration ◽  
Energy Detector ◽  
Instrumental Effects

<p>Terrestrial Gamma-ray Flashes (TGFs) are sub milliseconds bursts of high energy photons associated with lightning flashes in thunderstorms. The Atmosphere-Space Interactions Monitor (ASIM), launched in April 2018, is the first space mission specifically designed to detect TGFs. We will mainly focus on data from the High Energy Detector (HED) which is sensitive to photons with energies from 300 keV to > 30 MeV, and include data from the Low Energy Detector (LED) sensitive in 50 keV to 370 keV energy range. Both HED and LED are part of the Modular X- and Gamma-ray Sensor (MXGS) of ASIM.<br><br>The energy spectrum of TGFs, together with Monte Carlo simulations, can provide information on the production altitude and beaming geometry of TGFs. Constraints have already been set on the production altitude and beaming geometry using other spacecraft and radio measurements. Some of these studies are based on cumulative spectra of a large number of TGFs (e.g. [1]), which smooth out individual variability. The spectral analysis of individual TGFs has been carried out up to now for Fermi TGFs only, showing spectral diversity [2]. Crucial key factors for individual TGF spectral analysis are a large number of counts, an energy range extended to several tens of MeV, a good energy calibration as well as knowledge and control of any instrumental effects affecting the measurements.</p><p>We strive to put stricter constraints on the production altitude and beaming geometry, by comparing Monte Carlo simulations to energy spectra from single ASIM TGFs. We will present the dataset and method, including the correction for instrumental effects, and preliminary results on individual TGFs.</p><p>Thanks to ASIM’s large effective area and low orbital altitude, single TGFs detected by ASIM have much more count statistics than observations from other spacecrafts capable of detecting TGFs. ASIM has detected over 550 TGFs up to date (January 2020), and ~115 have more than 100 counts. This allows for a large sample for individual spectral analysis.</p><p>References:</p><ol><li>Dwyer, J. R., and D. M. Smith (2005), A comparison between Monte Carlo simulations of runaway breakdown and terrestrial gamma-ray flash observations, Geophys. Res. Lett., 32, L22804, doi:10.1029/2005GL023848.</li> <li>Mailyan et al. (2016), The spectroscopy of individual terrestrial gamma-ray flashes: Constraining the source properties, J. Geophys. Res. Space Physics, 121, 11,346–11,363, doi:10.1002/2016JA022702.</li> </ol>

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