نشریه سنجش و ایمنی پرتو
سال پنجم شماره 4 (پیاپی 20، پاییز 1396)

One of the factors which can kill or decrease the viability of bioleaching bacteria is the creation of toxicity due to the process of metal release from mine stone. This toxicity is partly due to the presence of arsenic in mine stone. In the present study mutagenesis method was used to improve the bioleaching process performance by using UV and gamma rays. The influence of radiations (UV& gamma rays) on growth and death of Thiobacillus ferrooxidans bacteria were investigated at different time exposures. Afterwards, a defined concentration of arsenic salt (NaAsO5) was added to the remaining bacteria until mutant bacteria with arsenic resistance were separated. The results showed that irradiation time of 180 second and 120 minute of gamma and UV rays, causes the number of bacteria to increase by 20% and 45%, respectively.

Jaundice or hyperbilirubinemia is frequently observed in newborn infants. In most cases a Phototherapy tool is used for treatment. In this way light with wavelengths in the range of 420- 470 nanometers (nm) is used to convert bilirubin so that it can be excreted in the urine and feces. Since high levels of bilirubin can cause deafness and brain damage, it is very important to care it soon, so the used wavelength is important.
50 phototherapy lamps with different brands, but with the same power were considered. By using a spectroradiometer, the spectrums of all lamps were prepared in the same situation. Then the ratio of light intensity in 200-400 nm ultraviolet range (unwanted) to the total intensity (first ratio), and the ratio of light intensity in 420- 474 nm (useful range) to the total intensity (second ratio) were calculated for each lamp, and these ratios were compared.
The amounts of first ratio for 20 % of the lamps are near average values, for 50 % are more than average values, while for 30 % of the lamps fall under average ratio. It is also shown that the amounts of second ratio for 31% of the lamps are near average values, for 22% fall under average and for remaining 47% are more than average value.
Finally it is suggested that when importing phototherapy lamps, it is better to compare the mentioned two ratios with average values to be able to choose justifiable ones.

Brachytherapy is a therapeutic approach in which radioactive sources are used to irradiate malignant tumors from near distance. In this study, the comparison of dose distribution in iodine-125 source, STM 1251 and Oncoseed 6711 models was performed using the Monte Carlo Geant4 code. The results obtained from the Monte Carlo calculations have been compared with the TG43U1 formulation and also with the available experimental results. According to the TG43U1 formula, the dose distribution of the STM 1251 has a greater influence than Oncoseed 6711. Also, this trend was observed in the region near the phantom surface that was not balanced with radiation distribution conditions. In this region, there was no significant difference between TG43U1 protocol and experimental values ​​and calculated results in this study. Therefore, the selection of the source model can be done based on the results of the Geant4 code.

One of the main characteristics of heavy water research reactors is their high production of plutonium. This work demonstrates the possibility of reduction of plutonium production and other actinides in heavy water research reactors. Among the many ways for reducing plutonium production in a heavy water reactor, in this research, changing the fuel from natural uranium to thorium-uranium mixed fuel was focused. For this purpose, different compositions of thorium-uranium fuel were used in our calculations. Natural uranium oxide was regarded as the reference fuel. Neutronic parameters for each fuel were calculated by MCNPX2.6 code linked to a fuel depletion code (CINDER90). The obtained results indicated that thorium-uranium fuels have some advantages compared to natural uranium fuel. Thorium-Uranium fuels could dramatically reduce plutonium production up to 90% in a year, compare to natural uranium fuels for heavy water moderated reactors. Also, the quality of produced nuclear wastes can be improved significantly compare to natural uranium fuel because they contain less minor actinides.

The coastal area of ​​Ramsar in northern of Iran located in the province of Mazandaran has been known as the highest levels of natural radiation background in the world. The background radiation is mainly due to the presence of radioactive isotopes of the radium element and its decay products, which is brought to the surface by hot springs. In this study, the indoor gamma dose rate in Ramsar was directly measured and the public annual effective dose due to indoor gamma radiation was calculated. To measure the gamma dose rate, a portable gamma spectrometer with sodium iodide detector (Na I) was used. 100 houses are randomly selected and the measurements were carried out at one meter height above the ground surface in each place, which was mostly occupied by people in each house. The public annual effective dose due to indoor gamma exposure was calculated. The maximum, minimum, and average dose rates were 222 nSv h-1, 44 nSv h-1 and 94 nSv h-1, respectively. The highest, lowest, and average public annual effective dose of Ramsar residents due to indoor gamma exposure were 1.55, 0.31 and 0.66 mSv, respectively. The results of this study indicate that average of the public annual effective dose of Ramsar people due to indoor gamma exposure is equal to 0.66 mSv and it is approximately 1.6 times greater than the worldwide average exposure to indoor gamma radiation reported by the United Nations Scientific Committee on the Effects of Atomic Radiation (0.41 mSv). In addition, it is not significantly different from the other reported results (average of 0.7 mSv) for the homes in normal radiation background areas in Ramsar.

In this paper, the ratio of adsorbed dose to the tissues of muscle, blood and bone to water for medical accelerators of Electa 25MV and Siemens 6MV is calculated using an analytical method based on cavity theory and Monte Carlo simulation. To confirm the validation of these methods, the ratio of absorbed dose to air to water was determined experimentally for radiation field of 60Co in Secondary Standard Dosimetry Laboratory (SSDL). The relative difference between the measured value and calculated values was less than 10% which confirms the validation of analytical and simulation methods.
The ratio of absorbed dose to muscle and blood to water is close to unity due to their atomic composition and density similar to water. The ratio of absorbed dose to bone to absorbed dose to water is calculated 0.96 and 0.91 for radiation fields of Electa 25MV and Siemens 6MV, respectively due to the discrepancy between atomic composition and density of bone and water. Further, the obtained results reveals that the ratio of absorbed dose to different tissues to absorbed dose to water is depended on radiation field energy. The results of this paper can be useful to determine the absorbed dose delivered to an organ in a treatment planning systems.

Double-exposure digital holographic interferometry is a powerful and widespread technique for fine measurement of the induced changes in special physical properties, like density, refractive index and etc. In this paper, application of this technique for measuring the absorbed dose from an electron radiation source in poly (methyl methacrylate) material is studied through modeling. The method of applying this technique for interpretation of the resulted fringe pattern and obtaining the pattern of isodose regions and the percent depth dose curve, that are ubiquitously used for treatment planning and monitoring of the absorbed dose, is investigated. Our results prove the capability of this optical technique for online monitoring of the absorbed dose from a radiation source through interpreting the formed fringe pattern.