نشریه سنجش و ایمنی پرتو
سال سوم شماره 4 (پیاپی 12، پاییز 1394)

In regard with increasing use of brachytherapy for treatment of cancer, especially prostate cancer, dosimetry of the organs surrounding prostate is necessary. The received dose by prostate is relatively high and the healthy organs surrounding prostate are potentially at a risk of high dose too. In this paper, the doses delivered to the prostate and organs of interest were calculated by MCNP4C code. Moreover, the effects of scattering from legs on dose distribution of the related organs were evaluated. First, the imparted energies to the organs delivered by 125I were obtained. Then the doses per transformations were calculated by using the volumes and densities of the organs and as a result, the doses to the organs were determined using the activity of the source. Dose to the prostate as a source of radiation was obtained in excess of 100 Gy. Bladder, testes and sigmoid Colon received higher dose than the other organs due to proximity to the prostate. The values of them were 9.45, 4.83 and 2.88 Gy, respectively. The differences between the dose with scattering from the legs of the phantom and without it for testes and sigmoid colon were the highest because of their proximity to the prostate and obtained to be 14.5% and 6.3%. This difference was not considerable for the other organs.

Cadmium tungstate nano powder (CdWO4) was synthesized with co-precipitation method. Two different types of material (based on acetate and nitrate) were used as precursors. The synthesized powder was characterized by X-ray powder diffraction (XRD)¡ scanning electron microscopy (SEM)¡ Fourier transfer Infrared absorption (FTIR) spectrum¡ and photoluminescent (PL) spectrum. According to the XRD pattern¡ two samples¡ nitrate based and acetate based were synthesizedwith average size of 31.0 and 30.0 nm¡ respectively. Besides¡ the response of two samples to the alpha particles was measured by using 3330 Bq241Am source. The respond of two samples to the alpha particles was acceptable and the central channels for them were occurred at the same channel. However¡ the count rate of the acetate based sample was 17.7% higher than the nitrate based sample. Since the sensitivity of two samples regarding to response to the alpha particles was acceptable¡ these two samples can be used as counter of the alpha particles.

The radioisotope Technetium-99m has unique chemical and nuclear properties; which is widely used in the field of nuclear medicine. This isotope has a half-life of 6.04 hours and the emitted gamma ray has energy of 140.5 keV. This radioisotope is not normally found in nature, but is obtained from radioisotope molybdenum99 decay. molybdenum99 has half-life of 66 hours, and 740 keV Gamma-ray. Mother and daughter isotopes separation performed in the 99Mo-99mTc generator. When milking generator, some of molybdenum99 may penetrate to Technetium-99m solution in generators that impact on the quality of the images and Patients may receive higher doses which is recommended. we measured the amount of molybdenum99 breakthrough from the generators. The results show generators with 600 mCi capacity have more Molybdenum99 contamination than generators with 400 mCi capacity.

In Radiation processing of products by high energy electrons, scattered electrons reduce at the edges of the product and the absorbed dose is low at this regions. Dose reduction in edges, affects some system parameters such as dose uniformity ratio, Energy utilization efficiency and mass throughput.In this paper,the 3-D dose distribution in the sample product was determined by MCNP computer code and experimental data were measured by CTA dosimeters. Calculated and measured data weredeterminedfor one-sided irradiation by TT-200 Rhodotron electron beam accelerator. Also the effect of dose reduction in the product edges on system parameters was investigated. Calculated and measured data were in a good agreement.The results indicate that the dose reduction in the edges of product decreases the minimum absorbed dose and consequently increases the dose uniformity ratio and reduces the efficiency in utilization of energy from 0.70 to 0.48. Also this effect decreases the mass throughput by a factor of 0.68.

This research work introduces a new method for synthesizing CER.M-PAN composite to be used as 137Cs absorbent from nuclear waste water. The granular morphology and crystal structure of the synthesized compound were determined using various methods such as IR, SEM and BET. The impact of important elements such as interfering ions in the uptake of cesium by the pellets and the temperature distribution was evaluated on distribution coefficient. It is shown how to use the synthetic adsorbent following Freundlich relations as well as performing as a multi-layer insulation. The cesium absorption performance of synthesis granules is very good due to its porous structure. The product stability against high doses of radiation (100-200kGy) was investigated. The cobalt-60 radiation source with gamma irradiation energies 1.17Mev and 1.33Mev is used. The result shows that the synthesized granules have a very good stability against radiation dose as 200KGy and maintains its original structure.

Neutron response Induced in Thermoluminescence Dosimeter TLD-700 chips due to reactions of thermal neutrons with slab phantom and Badge Dosimeter TLD-600,700 materials in a neutron-gamma mixed field was measured. Using the linear relationship between thermal neutron fluence and the thermal neutrons induced TL response with slab phantom, Badge-TLD Materials, an empirical relationship was introduced to obtain the thermal neutron induced additional dose. Measurements in two different neutron-gamma mixed field indicated, that use of this method, depends on the growth of thermal neutron fluence, reduces error in the ambient gamma dose assessment several times.

Nanoparticles of Yb-doped SrF2 were synthesized by co-precipitation method. The formation of nanostructures was confirmed by X-ray diffraction (XRD) pattern. The particle size of about 46 nm was calculated from XRD data. The shape and size of SrF2:Yb nanoparticles were also observed by scanning electron microscope (SEM). The computerized glow curve deconvolution (CGCD) method was employed to determine the number of component glow peaks and kinetic parameters of the synthesized nanoparticles. Its thermoluminescence (TL) glow curve contains three overlapping glow peaks at around 394, 435 and 488 K. TL response of this nanophosphor was studied for different Yb concentrations and the maximum sensitivity was found at 0.5 mol% of Yb impurity.