ناهید حاجیلو

In this research, water equivalent ratios (WER) at helium ion beam energy ranging 25-250 MeV/u for four potential plastic dosimetric materials: polycarbonate (PC), polypropylene (PP), polymethyl methacrylate (PMMA), and paraffin have been calculated using MCNPX Monte Carlo code. Among studied materials, PC and PP with 0.979 and 1.177 show minimum and maximum differences with water respectively. In mentioned materials by increasing mass density, WER values increase and by decreasing mass density they decrease. Calculated values are in good agreement with the results published in literatures.

The shadow cone technique is one of the methods which is used for determining the contribution of scattered particles on the response of neutron detectors. This technique is used for neutron field calibration in Agriculture, Medicine and Industry Research School (AMIRS). In this investigation, we have designed and constructed an optimized shadow cone. According to the calculated neutron dose equivalent attenuation factors, a cone with 20 cm of iron and 30 cm of polyethylene has been found as optimum. For this cone, the neutron dose equivalent attenuation factor for 241Am/Be neutron source, is 0.00035 for which the contribution of scattered neutrons in AMIRS neutron calibration laboratory according to the calculation and measurement results, can be evaluated with less than 0.5% of error. 

Thallium-201 is one of the medical radioisotopes produced in Nuclear Research Center for Agriculture and Medicine via 203Tl (p, 3n) 201Pb reaction, using protons from cyclotron Cyclone 30. Due to high intensity of the neutrons produced from the thallium target and its copper substrate, protection against this radiation is a necessity. The radiation shield is the concrete walls of the target room accessible from outside through a multi-bend maze. In this work, we have calculated the streaming of neutrons through the maze of the target room using MCNP Monte Carlo radiation transport code. The target has been bombarded with 145 µA of 28.5 MeV protons. Equivalent dose rate of neutrons in various positions in the maze has been calculated and compared with the measured values. The maximum deviation between the calculated and measured values is found to occur at the farthest position from the source, namely at the entrance door of the maze, for which the neutron equivalent dose has been calculated as 93 mSv/hr and the corrected measured value upon using the energy spectrum weighted correction factor is 136 mSv/hr. These values are in good agreement with each other according to the shielding point of view.