نشریه سنجش و ایمنی پرتو
سال سوم شماره 2 (پیاپی 10، بهار 1394)

In this study, a mixture of waste lead mine Nakhlak and cement with different percentages of boric acid are used to construct a proper shield for gamma and neutron radiations emitted from the Am-Be source. Neutron dose rate reduction ​​by the prepared samples was investigated by thermal neutron irradiation system of Isfahan University, TLD 600 and TLD 700. Neutron dose rate changes, compressive strength and sample activation induced by the neutron irradiation were measured. The effect of various amounts of boric acid in the prepared shield on total mass attenuation coefficient of gamma radiation was investigated by WINXCOM software. Using genetic algorithm, the optimum amounts of boric acid and neutron dose rate were calculated 53.15% and 90.1% respectively. Also, for the shield with the optimum amount of boric acid, total mass attenuation coefficient for 4.438 MeV gamma radiation and compressive strength were obtained 0.03262 cm2/g and 120.36 Kg/cm2 respectively.

Upon increasing needs and vast application of neutron detectors, especially in nuclear reactors and growing number of linear accelerators, design and manufacturing of neutron detectors is a serious demand. The aim of this project is building neutron detectors capable of compensating gamma and temperature response in a radiation media. A special thermocouple coated with Boron carbide at the junction is developed. In a neutron flux, the nuclear reaction between neutron and Boron carbide which produces alpha particles, induce a voltage across the junction which is proportional to neutron density. To eliminate the effect of gamma and temperature of the medium, a thermocouple coated with Aluminum used as a differentiation mode in the detector, because of close atomic number, density, conduction coefficient and heat coefficient of Boron carbide and Aluminum. Detector is placed into thermal column of TRR. The threshold of measured flux was found to be using indium foil.

Radon, a progeny of 238U is formed from the radioactive decay of radium. One of the main sources of radon is the emanation from ground water. Radon gas dissolves in groundwater when it moves from the bed of volcanic rocks which contain radioactive elements such as uranium and thorium and then diffuse into spaces. In closed places, the accumulated radon that decays to radioactive particles can cause an increased health risk. In this case study, Sarein hot mineral water pools chosen to investigate radon concentration diffused from groundwater into the air specially covered space. Both experimental and numerical works were done on this case study. CR-39 detectors were used to measure radon concentration. Fluent as powerful software is used to investigate radon gas concentration in different parts of a sample closed space of hot spring pool. Comparison of both results gained from experimental work and numerical analysis shows good agreement between them.

With the development of science and technology in the medical field and need more than ever to accuracy and quality of treatment has been causer increase different radiotherapy methods. Almost the past two decade’s intraoperative radiation therapy (IORT) as one of the new techniques used to treat cancer patients. One of the problems with this method is obtaining accurate dosimetry, because neither before nor after surgery ray images taken from the area of patient data do not match exactly. Therefore, dosimetric characteristics for intraoperative dedicated radiation therapy accelerators in comparison of conventional accelerators are difficult. The main objective of this study was to investigate the LIAC head a light and portable intraoperative radiation therapy accelerator and dosimetry calculate its features. For this purpose, the LIAC head was simulated using Monte Carlo (MCNP). Then the percentage depth dose curves obtained for reference applicator (10 cm) in all accelerator energies using experimental measurements, simulation model was validated. All experimental measurements were done by 12MeV models of LIAC accelerator. Finally, some dosimetric parameters such as maximum absorbed dose (Dm), maximum depth dose (dm), R50, practical range (Rp), dose profile and other dosimetric parameters evaluated for reference applicator in the all LIAC electron beam energies.The results of this work show that the LIAC accelerator is designed for intraoperative radiation therapy method.

In this research, Pure Sodium chloride (NaCl) Nano and micro particles were produced for the first time by using the surfactant in co-precipitation method. X-ray diffraction (XRD) and scanning electron microscope (SEM) were utilized to analyze the shape and size of the synthesized material. The role of CTAB surfactant on morphology of particles was also investigated. The results show that CTAB surfactant has important role on controlling the particle size, such that an increase in the surfactant content, increases termoluminescence (TL) sensitivity. Thermoluminescence general order kinetics model was employed in a computer program for obtaining the kinetics parameters. TL glow curve of bulk phosphors exhibit four overlapping glow peaks at 367, 378, 432 and 479 °K and for nanophosphors, three overlapping glow peaks are observed at 360, 398 and 451°K. Prepared nanoparticles exhibit a linear dose response up to 1000 Gy following gamma irradiation with 60Co source. Also, the micro scaled particles are less sensitive than those of nanoparticles.

Porous silicon (PS) samples are obtained by electrochemical anodization of Si wafers in HFು solution. The hydrogen complex components are formed on the inner surface walls of porous silicon. In this work the depth profile of porous silicon is estimated by measurement of hydrogen content in the depth of the sample. Since the well-known ion beam analysis simulation programs are inappropriate for simulating porous materials, a Monte-Carlo simulation program is developed to obtain the most consistent depth profiles with the experimental ones. Hydrogen content in the depth of the sample is considered to be proportional to the porosity of the sample. The results indicate that the maximum porosity of the sample is 90% for 69-139 nm depth of the sample.

Biological effects of radiation are due to energy deposition arising from the alpha particles hits with cell nuclei. A simulation has been done to calculate the flux density of Radon progeny alpha particles induced from uniform inner surface source distributed in lung cylindrical airway using Monte Carlo method. Number of hits, transformation frequency and dose has been calculated using obtained flux density by MCNPX simulation in various depths. The results have been verified by comparison with those of other models and experimental data. This was for the first time that the flux density has been accounted as an effective parameter to calculate number of hits, transformation frequency, dose and makes these calculations simpler and faster.