نشریه سنجش و ایمنی پرتو
سال ششم شماره 1 (پیاپی 21، زمستان 1396)

Reduction of background track in solid state nuclear track detectors is an important topic in dosimetry. The main objective of this research is to optimize the reduction of background track using the chemical pre-etching process for removal of surface layer of the detector followed by electrochemical etching process. In this regard, the chemical reaction between a polycarbonate detector and ethylenediamine solution with various density portion of 20%, 30%, 40%, and 50% is studied. Accordingly, some empirical relationships between removed layer thickness and etching time in different solution density are derived. The results of experiments illustrate that best outcome in the uniformity of etching can be achieved at density of 40% with 50% of background track reduction.

In the present work a microdosimeter designed for measurement of neutrons dose-equivalent, is evaluated in the mixed neutron-gamma fields of 241Am-Be and 252Cf sources. The microdosimeter is considered as an array of 259 similar sensitive volumes to increase the sensitivity to neutrons. Each sensitive volume is a cylinder of 5 mm in diameter and height filled with the tissue-equivalent gas at 0.11 atm pressure to simulate 1 µm of tissue. Dose-equivalent values of neutrons are determined using the microdosimetric distributions calculated by Geant4 simulation toolkit and also considering the separation limit of 3.5 keV/µm between the neutron and gamma contributions in these distributions. Obtained results reveal that the dose-equivalent values of above sources deviate by 9% and 17% from H*(10) values, respectively. Paying attention to the no need for dose calibration of microdosimeters separately in different fields and their trustworthy responses in unknown fields, it can be concluded that the designed microdosimeter can be used in every mixed neutron-gamma field with the maximum energy of 11 MeV in order to measure the dose-equivalent of neutrons.

One of the most important issues in a reactor core, at the time of radioactive material leakage, is detection and management of failed fuel assembly among all of assemblies. The purpose of this study is to provide a quick and efficient method compared to the non-destructive techniques, and common sipping tests to identify a failed fuel. The current method is based on sampling a coolant passing through the damaged FAs and evaluating the gamma spectrum obtained to measure the activity ratio of desired leaked fission fragments. Using the 134Cs/137Cs activity ratio and considering the history factor of each FA the maximum power peaking factor can be found. Also, by measuring the 133I × 135I /133Xe activity ratio the position of the core where failed-fuel is located can be predicted. In order to investigate the current method, a sample of the cooling water which passes through the failed fuel, located in the test sipping of the Tehran Research Reactor, was studied to measure the activity ratio of the desired isotopes. Then, the gamma spectrum at different cooling times (after leakage time) was studied. Considering the activity ratio of 134Cs/137Cs (0.1212) and the history of the relevant fuel (2.1023), the burnup of damaged-fuel was anticipated to be 33.92%. In addition the code calculations were carried out and we found that the suggested fuel assembly burnup is equal to 33.12%. Comparing the experimental as well as the calculational procedures gives a fairly good consistency of the herein method.

The aim of this research is to investigate the effects of the band width of magnetic resonance imaging (MRI) on the response of the PAGATUG polymer gel dosimeter. Sampling time decreases by increase in receive band width. Therefore, the scan time can decrease by increase in receive band width. Hence, the cost of gel dosimetry reduces by proper choose of MRI receive band width. To this aim the PAGATUG polymer gel dosimeter was prepared. The polymer gel cuvettes were irradiated using a clinical 60Co one day after preparation. Afterward, the gels responses were readout using a 1.5 T MRI system. Receive band widths of 60, 80, 90, 100 and 120 Hz/pixel were selected for imaging protocols. It was found that the R2 responses and the R2 sensitivities were not changed significantly by varying the receive band width. However, for receive band widths more than 90 Hz/pixel the dose resolution was decreased significantly. It is suggested to select the receive band width of 90 Hz/pixel for PAGATUG polymer gel dosimeters scanning. Theoretical calculations show that a receive band width of 90 Hz/Pixel causes a chemical shift of 0.82 mm which is of order of one pixel dimension. By using this receive band width the scanning time were reduced by 22% from receive band width of 60 Hz/pixel.

Many public health agencies rank residential radon exposure as the second risk factor of lung cancer after smoking. Due to the presence of children in the indoor (especially schools after homes) for a long time, and high respiratory rate, they are exposed to higher risk from radon than adults. Therefore, in this research, indoor radon measurement was conducted randomly in some of primary schools in Yazd city. For this purpose, measuring device of radon gas (RAD7) were placed in appropriate classes of 23 elementary schools. This device measured radon gas concentration for 24 hours in 16 cycles each for 1.5 hours. Finally, average radon concentration with standard deviation for each of the school was obtained. Radon levels were in the range of 13 to 145 Bq/m³. The average radon concentration in all schools, 47.87 Bq/m³ with standard error equals 1.73 were lower than introduced action level by the EPA (148 Bq/m³).

The aim of this paper is to design and study the manufacturing feasibility of a Bremsstrahlung spectrometer for measuring hard X-ray emission spectrum of Damavand Tokamak. For this purpose, a set of lead filters with increasing cut-off energies and GR-200 thermoluminescence dosimeters were used. The matrix equation which describes the relation between energy spectrum of hard X-ray emission and absorbed dose in thermoluminescence dosimeters was extracted by applying superposition principle and the values of coefficient matrix are obtained by performing a simulation procedure using Monte Carlo N Particle (MCNP) code. Irradiation was performed using Damavand tokamak and the hard X-ray emission spectrum was measured by unfolding method. The results show that the proposed diagnostic tool can be used as a photon spectrometer for unfolding energy spectrum of hard X-ray radiation of Damavand tokamak at 100keV-2MeV energy range.

In this paper, cellular S-values for monoenergetic electron sources with energy from 1 to 70keV and the Auger-electron emitting radionuclides Tc-99m and In-111 were calculated in liquid water using the Geant4 Monte Carlo toolkit with the low energy extension Geant4-DNA. The results were compared to corresponding MIRD database and the differences were calculated. Differences between Geant4-DNA and MIRD results up to 70% were found; However, for the present monoenergetic sources and radionuclides, they mostly remain below 20%. Calculated S-values in this paper, were in good agreement to S-values obtained in the other literatures. This study is an important step for performing cellular dosimetry which the results would improve the treatment planning in the country.