Radiation Physics and Engineering

Abstract ‎The concentration of naturally occurring radioactive materials (NORM) in surface water and irrigation wells is measured using gamma ray spectrometry by HPGe detector‎. ‎Measurement was carried out for samples that were collected over seventeen points in Tehran city and its suburbs‎. ‎The samples were prepared in compliance with the principles from irrigation wells of city‎. ‎The specific radioactivity of Ra-226‎, ‎Th-232 and K-40 were measured and the results from different locations covered a range with the minimum being below "minimum detectable activity‎" ‎up to maximum of 4.04‎, ‎and 6.85 and 4.7 Bq per liter of water‎, ‎respectively‎. ‎The accumulation of radioactive materials in the samples from southern areas of Tehran was more than that of central areas‎. ‎Also‎, ‎concentration of Ra-226 in all the samples was less than the Derived Release Limit of Canada and Environmental Protection Agency standard threshold‎.

Abstract ‎18F-FDG PET/CT is commonly used for evaluation and diagnostic of many types of cancer‎, ‎such as; tumor diagnosis‎, ‎treatment monitoring‎, ‎and radiation therapy planning‎. ‎Accurate diagnostic is needed in meticulous patient preparation‎, ‎including restrictions of diet and activity and management of blood glucose levels in diabetic patients‎, ‎as well as an awareness of the effect of medications and environmental conditions‎. ‎All of these conditions play important roles toward obtaining good-quality images‎, ‎which are essential for accurate interpretation‎. ‎This article introduces the new synthesis and quality control method for obtaining the best quality FDG which is used as radiopharmaceutical‎. ‎All the reactions are carried out and completed in one reaction vessel without any replacement‎. ‎The paper is including details of synthesis‎, ‎quality control and transportation step‎. ‎It is the first time that the alkaline FDG synthesis is introducing by details in Iran‎.

Abstract ‎Utilizing radioactive stents is a usual method for treatment of advanced esophageal cancer‎. ‎It is necessary to investigate the dose distribution of radioactive esophageal stents before the clinical use‎. ‎This study presents a dosimetric comparison between three radioactive esophageal stents‎: ‎I-125 seed-loaded stent‎, ‎iodine-eluting stent and double-layered iodine-eluting stent‎. ‎Depth-dose and angular dose distributions were carried out using Geant4 toolkit‎. ‎Moreover‎, ‎the effect of interval distance between two adjacent seeds on the dose distribution was investigated‎. ‎Esophageal stents loaded with I-125 seeds seems to be better than iodine-eluting stents‎, ‎with the distance less than 15 mm between two adjacent seeds‎.

Abstract ‎Numerical solution of the multi-group static forward and adjoint neutron diffusion equation (NDE) using the Finite Elements Method (FEM) is investigated in detail‎. ‎A finite element approach based on the generalized least squares method is applied for the spatial discretization of the NDE in 3D-XYZ geometry‎. ‎A computer code called GELES was also developed based on the described methodology covering linear or quadratic tetrahedral elements generated via the mesh generator for an arbitrary shaped system‎. ‎A number of test cases are also studied to validate the proposed approach‎. ‎Moreover‎, ‎to assess the output dependency to the number of elements‎, ‎a sensitivity analysis is carried out at the end‎.

Abstract ‎In this paper‎, ‎dose uniformity ratio in irradiation cell of GC-220 is specifiedutilizing an analytical method based on the multipole moment expansion‎. ‎In this method‎, ‎the values of monople‎, ‎dipole and quadrupole moments for source arrangements of GC-220 are calculated by numerical integrating‎. ‎Appling these values‎, ‎the dose uniformity ratio in the irradiation cell of GC-220 is calculated equal to 1.92‎. ‎Monte Carlo simulation is applied to validate calculations‎. ‎There is a relative difference about 12% between the results obtained from the analytical calculation and Monte Carlo simulation‎, ‎which confirm the used method‎. ‎In comparison with Monte Carlo methods‎, ‎this method is not time consuming‎, ‎so‎, ‎this method can be used for the conceptual designing and the source load planning of irradiators‎.

Abstract ‎A second shutdown system (SSS) is designed for the Tehran Research Reactor (TRR) completely independent and diverse from the existing First Shutdown System (FSS)‎. ‎Given limitations‎, ‎specifications‎, ‎and requirements of the reactor‎, ‎the design of SSS is based on the injection of liquid neutron absorber‎. ‎The plan has the ability to satisfy the major criterion of required negative reactivity worth‎, ‎to transfer the reactor to subcritical state in needed time‎, ‎with necessary shutdown margin and for the required duration‎. ‎Design calculations are performed using the stochastic code MCNPX2.6.0‎, ‎deterministic code PARET and Pipe Flow Expert software‎. ‎The ORIGEN2 code and HotSpot health physics code are also used for simulation of environmental pollution release‎. ‎The SSS chambers cause a decrease of about 5% and 15% in total and thermal neutron flux‎, ‎respectively‎. ‎To demonstrate the SSS role in enhancing reactor safety‎, ‎the probable accident of core meltdown is investigated‎. ‎As a consequence of this accident‎, ‎the radioactive pollution in and out of reactor containment is released‎. ‎Without existing the SSS and in case of failure of FSS‎, ‎the residents within 58000 m² of the reactor perimeter would receive about 1 mSv which is more than the annual limit of absorbed dose for the community‎.