Time filter

Source Type

Deevband M.R.,Tarbiat Modares University | Abdolmaleki Dr. P.,Tarbiat Modares University | Kardan M.R.,Nuclear Science Research School | Khosravi H.R.,Iranian Nuclear Regulatory Authority | And 4 more authors.
Iranian Journal of Radiation Research | Year: 2011

Background: The Poly-Allyl Diglycol Carbonate (PADC) detector is of particular interest for development of a fast neutron dosimeter. Fast neutrons interact with the constituents of the CR-39 detector and produce H, C and O recoils, as well as (n, α) reaction. These neutron- induced charged particles contribute towards the response of CR-39 detectors. Material and Methods: Electrochemical etching was used to enlarge track diameter which was made by low energy recoil protons. Before electrochemical etching, a chemical etching was performed for 1 hour. The responses were also calculated by Monte Carlo simulations, using MCNPX code in different energy bins considering H, C and O recoils. The total registered efficiency and partial contributions of the efficiency, due to interactions with each constituent of CR-39, were calculated. Results: The optimized condition of etchant was obtained to be 6N KOH 15kV.cm-1, and 6 hours etching time. The obtained results show that track efficiency of CR-39 was a function of incident neutron energy. The tracks caused by O and C recoil nuclei were negligible for neutron energies lower than 1 MeV. At neutron energies lower than 1 MeV, only recoil protons would have sufficient energy to leave visible tracks. But, O and C recoils had important contributions in overall response of PADC at neutron energies of few MeV. Conclusion: The efficiency of a CR-39 based dosemeter could be calculated by MCNPX code and the results were in a good agreement with experimental results in energy range of 241Am - Be bare source and 241Am-Be was softened with a spherical polyethylene moderator of radius of 20 cm. Source

Rehani M.M.,International Atomic Energy Agency | Ciraj-Bjelac O.,Vinca Institute of Nuclear Sciences | Al-Naemi H.M.,Hamad Medical Corporation | Al-Suwaidi J.S.,Dubai Hospital | And 7 more authors.
European Journal of Radiology | Year: 2012

Recognizing the lack of information on image quality and patient doses in most countries in Asia, the International Atomic Energy Agency (IAEA) initiated a project to assess the status of imaging technology, practice in conventional radiography, mammography, computed tomography (CT) and interventional procedures, and to implement optimisation actions. A total of 20 countries participated. Obsolete practices of use of fluoroscopy for positioning, photofluorography, chest fluoroscopy and conventional tomography were reported by 4 out of 7 countries that provided this information. Low-kV technique for chest radiography is in use in participating countries for 20-85% of cases, and manual processing is in 5-85% of facilities in 5 countries. Instances of the use of adult CT protocol for children in three participating countries were observed in 10-40% of hospitals surveyed. After implementation of a Quality Control programme, the image quality in conventional radiography improved by zero to 13 percentage points in certain countries and dose reduction was from 10% to 85%. In mammography, poor quality, ranging from 10 to 29% of images in different countries was observed. The project increased attention to dose quantities and dose levels in computed tomography, although doses in most cases were not higher than reference levels. In this study 16-19% of patients in interventional cardiology received doses that have potential for either stochastic risk or tissue reaction. This multi-national study is the first of its kind in the Asia, and it provided insight into the situation and opportunities for improvement. © 2012 Elsevier Ireland Ltd. Source

Paydar R.,Tehran University of Medical Sciences | Takavar A.,Tehran University of Medical Sciences | Kardan M.R.,Nuclear Science Research School | Babakhani A.,Iranian Nuclear Regulatory Authority | And 3 more authors.
International Journal of Radiation Research | Year: 2012

Background: The radiation doses resulting from diagnostic X-ray examinations are routinely measured in terms of entrance surface dose (ESD) and effective dose (ED). In this study, for the purpose of radiation protection, the radiation doses received from Digital chest X-ray examination were evaluated in terms of ESD and ED. Material and Methods: The ED was calculated by using the MCNP Monte Carlo code and an adult hermaphrodite mathematical phantom. The effects of both operating high voltage and projection geometry on the effective dose were investigated. The absolute values of the ED were calculated for digital and conventional Posterior-Anterior (PA) and Lateral (LAT) projections of chest radiography. Results: The results show ED for PA projection in digital chest radiography in some major hospitals is higher than National Diagnostic Reference Level (NDRL). Conclusion: Therefore optimization process should be considered seriously at national level to reduce patient exposure in digital chest radiography in Iran. Source

Ahmadi Jeshvaghane N.,Iranian Nuclear Regulatory Authority | Paydar R.,Iranian Nuclear Regulatory Authority | Fasaei B.,Iranian Nuclear Regulatory Authority | Pakneyat A.,Iranian Nuclear Regulatory Authority | And 4 more authors.
Radiation Protection Dosimetry | Year: 2011

External dose rate (ED) and residual activity (RA) of patients treated with. 131I sodium iodide are two main factors, to consider before release of patients. In this study, six nuclear medicine centres out of total seven centres in Iran were selected and measurements have been done on 330 patients. ED of patients was measured by physicists of the centres for 6 months (May-November 2009) at a 1 m distance from the thyroid of each patient on the first, second and third days after administration by a calibrated survey meter. The maximum and minimum values of ED were 21 (SD=18) and 11 (SD=4) μSv h. -1, respectively. Furthermore, the maximum and minimum values of RA during release of patient were 720 and 250 MBq, respectively. According to the study, we recommend a release activity limit of 500 MBq (14 mCi) or a dose rate level of 20 μSv h. -1 at 1 m from the patient to be set instead of a release activity limit of 1100 MBq (30 mCi) as it is now for the country. © The Author 2011. Published by Oxford University Press. All rights reserved. Source

Hashemi S.M.,Nuclear Science and Technology Research Institute, Iran | Raisali G.,Nuclear Science and Technology Research Institute, Iran | Taheri M.,Iranian Nuclear Regulatory Authority | Majdabadi A.,Nuclear Science and Technology Research Institute, Iran | Ghafoori M.,Nuclear Science and Technology Research Institute, Iran
Nukleonika | Year: 2011

Medical linacs used in radiotherapy produce bremsstrahlung spectra. In the energy range from 8 to 25 MV medical linacs produce, besides the clinically useful electron and photon beams, secondary neutrons. The aim of this study was to investigate the effect of an external wedge filter on the photoneutron dose equivalent produced by a medical linac at patient plane. Polycarbonate (PC) films were used for the determination of photoneutron dose equivalent produced by a Varian 2100 C/D linac working at 18 MV photon mode. Neutron dose equivalent was measured at distances 0, 10, 20 and 50 cm from the center of the X-ray beam for open field and after inserting a wedge filter. It was noted that by inserting the external wedge in the path of the X-ray beam, the photoneutron dose equivalent was increased compared to open field. It can be concluded that an external wedge, made from heavy materials may act like the other components of linac head, producing undesired photoneutrons and thus increasing patient dose. Source

Discover hidden collaborations