جستجوی مقالات مرتبط با کلیدواژه « طیف سنجی گاما » در نشریات گروه « علوم پایه »

Identifying and measuring the radioactivity of airborne particles are a necessary and very important to recognize and estimate the effect of radioactive contamination on human health and the environment. Gamma-ray spectromety is one of the most useful methods for quantitative and qualitative analysis of samples, like air filters. One of the first and necessary steps in performing sample analysis by Gamma-ray spectrometer is to calibrate this equipment, which requires appropriate standard sources. The purpose of this research is to design and manufacture a suitable standard source considering filter geometry and its quality control and validation. For this purpose, a circular HEPA air filter with a diameter of 60 mm was used. Gamma-ray spectrometry system (HPGe) was calibrated by mentioned standard source. The results of counting and quality control of the manufactured source showed the accuracy of source manufacturing method. The validation of manufacturing method by Spike method showed an acceptable error of 8%.

Safe water is one of the basic needs of humans that must be free of any contamination. One of the water pollutants is radioactive nuclei, which naturally and artificially occur in the environment. Therefore, accurate measurements of water radioactivity are very important. The activity concentration of 226Ra, 232Th, 40K, and 137Cs in 26 drinking water samples from the Isfahan province was measured by gamma spectrometry using a high purity germanium detector (HPGe). Activity concentrations of 226Ra for all samples were below the detection limit. The average specific activity of radionuclides 232Th, 40K and 137Cs were measured as 1.40, 82.23 and 0.0.40 respectively in Bq/l. Annual effective doses as a result of ingestion of water containing 232Th, 40K and 137Cs radionuclides for adults ranged from 0.317 to 1.153 with an average of 0.784, from 0.059 to 0.150 with an average of 0.114 and from 0.001 to 0.016 with an average of 0.003 in μSv/y respectively. The excess lifetime cancer risk was calculated for three age groups, which was 1.59 ×10-6 for adults. The results showed that the annual effective dose as a result of drinking water consumption was lower than the WHO Individual Dose Criterion (100 μSv/y), so it does not pose a threat to the inhabitants of this area and has good quality.

Environmental monitoring, which is an inseparable component of nuclear safety, is always important. The need for regular, accurate and qualified implementation is essential. The gamma spectrometry method is widely used for the detection and measurement of gamma emitting radionuclides in natural samples. In the gamma spectrometry method, like all methods of measurement, the determination of measurement uncertainty is evident. The aim of this study is to measure the gamma-ray radionuclide activity of the soil sample and the correct associated uncertainty. A soil sample in a cylindrical container and weighing 243 grams was used based on the 661 keV peak of cesium and a high-purity germanium detector (80% relative efficiency) for calculations. According to the counting of 72000 second of the soil sample, the amount of cesium activity was 482 Becquerel. Also, the uncertainty of the above activity measurements was calculated 33.4 Becquerels. The results of this study indicate that the measurement of activity of gamma emitting radionuclide with relative uncertainty of 6.9% indicates the high reliability of the results. Also in the total uncertainty, the counting and efficiency uncertainty make the main contribution.

A useful benchmark for the reliability of gamma spectrometry results is to provide measurement uncertainty. Due to the importance and necessity of radiation monitoring in water resources, this research has been oriented toward providing measurements of the gamma- emitting radionuclides along with introducing the expression for the uncertainty that appeared in these measurements. To calculate the uncertainty of the activity measurements in water, a sample, where its radioactive elements were obtained from the PolAtom Company, was used. The calculations were performed based on the 661 keV peak of 137</sup>Cs radionuclide and a high-purity germanium detector (HPGe). The investigations show that the factors affecting the measurement uncertainty are composed of two parts, including counting with the gamma spectroscopy system and sample preparation, where each of these parts comes from several sources of uncertainty such as uncertainties associated with the counting process, efficiency calibration, emission probability, the counting correction factors, and the mass measurement. The results of analyses show that the relative uncertainty is about 3.7% (Coverage factor = 1) for a water sample with an activity of 425 Becquerel from 137</sup>Cs.

Precise calibration of energy and efficiency of gamma spectrometry systems for different geometries is very important. In most cases, preparation of these sources for educational and research centers  is very difficult due to high costs and lack of access to the reactor. The purpose of this paper is to explain the procedure for production of calibration sources 65Zn and 60Co using instrumental neutron activation analysis (INAA) method. These sources are used for calibration of gamma spectrometry systems. To do so, 65Zn (3.83 and 9.38 µCi) and 60Co (3.65 and 3.85 µCi) were produced. The quality control of the sources indicates the acceptable quality of the produced sources.

The precise and timely manner modeling of received photon counts from gamma-ray sources has an important role in providing afore information for Airborne Gamma Ray Spectrometry (AGRS). In this manuscript, the Auto-Regressive Integrated Moving Average (ARIMA) model has been used to model AGRS. The proposed method provides gamma source and environmental disturbances ARIMA model, using known radioactive sources, to arrange the afore information for AGRS process experts to analyze the spectrometry data. The model extraction process and training will be done offline using different sizes and types of radioactive sources. The extracted models then being validated by evaluation functions to determine the type and amount of radionuclides during online AGRS. In order to evaluate the implemented modeling, the proposed ARIMA method is compared with other process modeling methods, including the Auto Regressive Moving Average ARMA in three bias, median absolute deviation (MAD) and the mean square error (MSE) criteria. The results show that the proposed method models the received photon counts much more accurate than other common methods.

The knowledge of concentration of elements in foodstuffs is of significant interest. Wheat is one of the most consumed food stuffs in Iran and zinc is also considered as one of the necessary and vital elements. Since the measurement of some trace elements is not practical by the conventional analytical methods, due to the lower detection limit, the neutron activation analysis (NAA) was applied to determine the zinc in wheat and wheat bran. Food sample of roughly 50mg was irradiated for 24h. After cooling, the interval samples were counted by a gamma spectrometry system. The concentration of zinc in wheat without bran and the wheat bran were 18.444±0.656 and 19.927±0.698 ppm, respectively. The amount of zinc in wheat bran was noticeable so it showed that consuming wheat with bran is more beneficial than the wheat with no bran for the human-beings’ body requirements.

In this paper, an algorithm base on Monte Carlo simulation for pileup effect in gamma spectrum of a detection system is presented whose its code was written in FORTRAN language. The code can be run in paralayzable and nonparalazable mode to obtain the pileup distortion and value of pulses pileup for any detection system. The result show, that the computed spectrum of 137Cs is in good agreement with the experimental spectrum in NaI(Tl) detector. The free of pileup free spectrum and sub-spectra with different degrees of pulses of pileup are calculated. Also, we can apply it to different sources and detectors for pileup correction.

In this project, the activity concentration of some radionuclides in rice samples, collected from Guilan province have been analyzed and the results have been compared with rice samples imported from other countries. For this purpose, sixteen types of rice samples from different region of Guilan and four imported rice samples have been collected. The collected samples have been analyzed in order to determine the activity concentration of number of radionuclides such as 40K, 226Ra, 232Th and 137Cs. A gamma spectroscopy system with a high purity germanium detector (HPGe) has been used for the radioactivity measurement. The highest activity concentration in the rice samples belongs to potassium-40. The mean activity of 40K, 220Ra, 232Th and 137Cs were (30.23±5.51), (3.30±1.75)10-2, (3.78±1.65)10-2 and (2.65±0.99)10-2 Bq.Kg-1, respectively. It can be concluded that all the activity concentrations are comparable with the values that have been, imported for other countries.