Papers by HERNAN OLAYA DAVILA
Nucleation and Atmospheric Aerosols, 2016
Using the Geant4 based simulation framework SciFW1, a detailed simulation was performed for a det... more Using the Geant4 based simulation framework SciFW1, a detailed simulation was performed for a detector array in the hybrid tomography prototype for small animals called ClearPET / XPAD, which was built in the Centre de Physique des Particules de Marseille. The detector system consists of an array of phoswich scintillation detectors: LSO (Lutetium Oxy-ortosilicate doped with cerium Lu2SiO5:Ce) and LuYAP (Lutetium Ortoaluminate of Yttrium doped with cerium Lu0.7Y0.3AlO3:Ce) for Positron Emission Tomography (PET) and hybrid pixel detector XPAD for Computed Tomography (CT). Simultaneous acquisition of deposited energy and the corresponding time - position for each recorded event were analyzed, independently, for both detectors. interference between detection modules for PET and CT. Information about amount of radiation reaching each phoswich crystal and XPAD detector using a phantom in order to study the effectiveness by radiation attenuation and influence the positioning of the radioactive source 22Na was ob...
Ciencia en Desarrollo, Mar 30, 2012
En este trabajo hemos implementado un modelo basado en Monte Carlo para la interacdon de neutro... more En este trabajo hemos implementado un modelo basado en Monte Carlo para la interacdon de neutrones en agua, el cual considera la interaccion elastica entre el neutron y los nucleos blancos del medio, mediante el estudio de la interaccion de una fuente puntual monoenergetica de 5, 1 O y 15 MeV, en un medio infinito de agua. Las distribuciones de dosis entregadas al medio se determinan analizando la dependencia de las mismas con la energia. Adicionalmente, calculamos la distribucion de distancias de la fuente a los puntos de absorcion de los neutrones para las mismas energias y las distribuciones del numero de colisiones que sufren los neutrones antes de ser absorbidos por el medio. Palabras claves: Interaccion elastica, fuente puntual monoenergetica. Abstract In this work we have implemented a model based on Monte Carlo for the interaction of neutrons with the water, which considers the elastic interaction between the neutron and the core nucleus of the medium, by studying the interaction of the monoenergetic point source, of 5, 10 and 15 MeV, in an infinite medium of water. The dose distributions given to the medium were determined analyzing their dependence with the energy. Additionally, the distribution of distances were calculated from the source to the points of absorption of the neutrons for the same energy and the distributions of the number of collisions suffered by the neutrons befare being absorbed by the medium. Keywords: Elastic i nteraction, source punctual monoenergetic.
Ciencia en Desarrollo, May 31, 2017
Monte Carlo calculations were carried out with radioactive sources of monoenergetic positron-emit... more Monte Carlo calculations were carried out with radioactive sources of monoenergetic positron-emitters used in compounds, like FDG (18 F), Acetate (11 C), and Ammonium (13 N), were incorporated into a soft tissue volume, in the aim to estimate the type of particles produced their energies, their mean free paths, and the absorbed dose at different distances with respect to the center of the volume. The volume was modeled with a radius larger than the maximum range of positrons in order to produce 0.511 MeV annihilation gamma-ray photons. With the obtained results the absorbed dose, in various organs and tissues able to metabolize different radiopharmaceutical drugs, can be estimated. The simulation code used was Geant4.
Applied Radiation and Isotopes, Aug 1, 2018
We developed an experimental setup by using a continuous emission X-ray (Pantak DXT-3000) and thr... more We developed an experimental setup by using a continuous emission X-ray (Pantak DXT-3000) and three types of Pb aprons, with thicknesses of 0.25, 0.5, and 0.75 mm, coated with Mylar fiber on their surface. Aprons were placed at a distance of 2.5 m from the focus. Aluminum filtration was performed at the beam output to reproduce the qualities of narrow beams, N40 (E effective =33 keV), N80 (E effective =65 keV), and N100 (E effective =83 keV), according to the ISO standard 4037 (1-3). Each apron was fixed with 10 thermoluminescent dosimeters (TLDs) over its surface, five dosimeters before and five dosimeters after irradiation with X-rays. Dosimeter readings were noted, and the attenuation coefficients for each effective energy were calculated. To confirm the method of effective energy of ISO-4037 and evaluate the effectiveness of aprons according to the energy range required for different medical practices, a Monte Carlo simulation using GEANT4 code was performed. Thus, the fluence and the absorbed dose in each of the dosimeters were determined, and then the coefficients of linear attenuation were calculated and compared with the experimental data and with those reported by the National Institute of Standards and Technology. Results were consistent between theoretical calculations and experimental measures. This work will serve to make assessments for other personalized radiation protectors made of Pb.
XIII Encuentro Facultad de Ciencias-UPTC I Encuentro Internacional, Nov 20, 2018
Journal of Nuclear Physics, Material Sciences, Radiation and Applications, 2020
Radon gas diffusion and progeny transport in air, are mechanisms to be considered in retrospectiv... more Radon gas diffusion and progeny transport in air, are mechanisms to be considered in retrospective glass dosimetry. With the aim to contribute to the understanding of the Rn progeny recoil energy role in this dosimetry methodology, we carried out a simulation employing GEANT4 code. In that, we assumed the chemical compound of the glass that is used commonly in households. Results are compared to experimentally measured 210Bi concentration to show that the recoil energy helps the progenies incrustation, mainly for the 218,214Po alpha emitters but do not influence bismuth-210 diffusion directly. A significant difference exists between our results and measured values; that is interpreted as due to atomic displacement by primary knock-on atoms. The SiO2 molecule binding energy breaks and the following ion recombination, induce a structural modification between the atom by e.g. cavities formation in such a way that reduces significantly the radon progeny diffusion speed.
Applied Radiation and Isotopes, 2019
In a bimodal PET/CT system X-ray photons being scattered in a phantom has been estimated using Mo... more In a bimodal PET/CT system X-ray photons being scattered in a phantom has been estimated using Monte Carlo method. • Calculations were carried out with the Geant4 code where a detail model of PET/CT system was built.
Universal Journal of Physics and Application, 2017
Based on The National Electrical Manufacturers Association (NEMA), using the AMINE software to co... more Based on The National Electrical Manufacturers Association (NEMA), using the AMINE software to construction of sinograms and using a positron emission source of 22 Na, were made calculations to determine the spatial resolution of a ring array system of phoswich detectors of positron emission tomograph included in the CLEAR PET-XPAD3/CT prototype for small animals, made in the laboratories of CCPM and whose project is led by the research group ImXgam. The radioactive source 22 Na of approximately 9 MBq of activity, with spherical shape and diameter of 0.57mm is immersed in a plexiglas disc that was located at the geometric center of tomographic system with a Field of View (FOV) of 35 mm in the axial and transverse directions. Displacements of radioactive source were performed on the three cartesian axes and was rebuilt a sinogram for each axis. The shape of sinogram allows describe the correct position and the maximum efficiency of each detector. Subsequently, was carried out a scanning in each one of three spatial axes taking enough distance to cover the dimensions of radioactive source. Data for each phoswich detector were recorded. The process was repeated for other axes and then radioactive source was centered with respect to the FOV and were calculated FWHM (Full Width at Half Maximum) and FWTM (Full Width at Tenth Maximum) values and performing statistics of these values with parabolic fitting, the latter setting allows to obtain parameters of spatial resolution of system.
Applied Radiation and Isotopes, 2018
A bimodal tomographic system with a RTW MCBM 65B-50Mo X-ray tube and a XPAD3s semiconductor camer... more A bimodal tomographic system with a RTW MCBM 65B-50Mo X-ray tube and a XPAD3s semiconductor camera that contains 8 bars, each one with 67200 hybrid pixels are modeled in GEANT4 simulation code. Several conical X-ray spectra were simulated, particularly a spectrum with a peak energy of 17.4 keV used in tomography on small animals. Three phantoms located in the tomographic center were added to the simulation to evaluate the image quality and its magnification based on the simulation of different photon fluences and the rotation effect of the tomographic system with an average angular velocity of 360o per minute. The images were recorded and analyzed in 2D through ROOT software toolkit in virtual XPAD3 detector. The quantitative method 20%-80% of the maximum intensity of radiation was used for obtain the contouring of the phantoms, this method is used in radiotherapy and radiodiagnosis imaging. For this purpose, the images were taken to DICOM format in order to estimate the optical density of the contours and to evaluate the optimum and minimum photon fluence to be used in the tomographic system in order to reduce the absorbed doses in the individuals. This study allowed to determine the optimal fluence to validate it with realistic fluences used in the tomographic prototype ClearPET /XPAD-CT and to make an intercomparison with the absorbed doses measured with detectors located in the tomographic center.
A bimodal tomographic system with a RTW MCBM 65B-50Mo X-ray tube and a XPAD3s semiconductor camer... more A bimodal tomographic system with a RTW MCBM 65B-50Mo X-ray tube and a XPAD3s semiconductor camera that contains 8 bars, each one with 67,200 hybrid pixels are modeled in GEANT4 simulation code. Several conical X-ray spectra were simulated, particularly a spectrum with a peak energy of 17.4 keV used in tomography on small animals. Three phantoms located in the tomographic center were added to the simulation to evaluate the image quality and its magnification based on the simulation of different photon fluences and the rotation effect of the tomographic system with an average angular velocity of 360o per minute. The images were recorded and analyzed in 2D through ROOT software toolkit in virtual XPAD3 detector. The quantitative method 20–80% of the maximum intensity of radiation was used for obtain the contouring of the phantoms, this method is used in radiotherapy and radiodiagnosis imaging. For this purpose, the images were taken to DICOM format in order to estimate the optical density of the contours and to evaluate the optimum and minimum photon fluence to be used in the tomographic system in order to reduce the absorbed doses in the individuals. This study allowed to determine the optimal fluence to validate it with realistic fluences used in the tomographic prototype ClearPET /XPAD-CT and to make an intercomparison with the absorbed doses measured with detectors located in the to-mographic center.
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Papers by HERNAN OLAYA DAVILA