Application of sourceless efficiency calibration in activity measurement of gas source in Marinelli beaker / 中国辐射卫生

Objective To optimize the Marinelli beaker with the simulation of Laboratory Sourceless Object Calibration Software (LabSOCS), to investigate the detection efficiency of HPGe detector in measuring noble gas, and to provide a reference for the measurement and optimization of noble gas effluent from nuclear power plants. Methods LabSOCS was used to establish a Marinelli beaker model to investigate the relationship of gamma ray detection efficiency of noble gas with gas components, gas density, size and volume of the Marinelli beaker, and the shape of source container. Results The gas components had little effect on the detection efficiency of the noble gas in the Marinelli beaker. The gas density had a relatively great effect on the detection efficiency of low-energy gamma ray. The Marinelli beaker of appropriate height and radius enabled the HPGe detector to get better measurement results. For the BE5030 HPGe detector, the highest detection efficiency of the Marinelli beakers of different volumes were observed at the location where the radius/height ratio was 0.7, and the optimal values of height and radius were given for the Marinelli beakers of different volumes. Conclusion Choosing Marinelli beaker of the appropriate size can improve the detection efficiency of noble gas in the effluent from nuclear power plants.

Calibration of a CeBr3 based γ-spectrometer for onsite and laboratory radioactivity measurements in sediment samples.

The calibration of an underwater spectrometer, consisting of a CeBr3 crystal, is performed for sediment sample measurements, via experimental data and Monte Carlo simulations. The system was implemented for activity concentration measurements in marine sediment samples in the laboratory. The results were compared with corresponding high resolution measurements and showed that the system provides accurate results, but relatively high uncertainties. Different measurement geometries are theoretically studied via Monte Carlo simulations in order to improve the system performance for such measurements.

Determining of the optimized dimensions of the Marinelli beaker containing source with inhomogeneous emission rate by using genetic algorithm coupled with MCNP and determining distribution type by neural networks.

In order to determine the activity of C137s in soil resulting from nuclear accidents or fallouts, the best choice is to use HPGe detectors due to their best energy resolutions. In this regard, in order to enhance the detection efficiency, the Marinelli beakers have been used to increase the radiation interaction with the sensitive volume of the detector. In previous works, to optimize the dimension of Marinelli beakers, the assumption was that the emission rate of the source is homogeneous in beaker volume. In the present study, to investigate the effect of the inhomogeneous emission rate of the source on the optimum dimensions of the beaker, in a simple case, the beaker was divided into two sections (upper and lower) containing different C137s emission rates. A code based on MCNPX2.6 coupled with genetic algorithm was developed and used to investigate the effects of different emission rates of C137s at the upper and lower section of the beaker on optimum dimensions of the Marinelli with different volumes (300-1500 cm3). The results showed that the inhomogeneity in the emission rate greatly affects the optimal dimensions of the beaker. By using the C137s spectra simulated for a conventional beaker at different emission probabilities in the upper and lower section in training a neural network, the emission probabilities of a beaker containing C137s was estimated.

Optimization of the marinelli beaker dimensions using genetic algorithm.

A computational code, based on the genetic algorithm and MCNPX version 2.6 code was developed and used to investigate the effects of some important parameters of HPGe detector (such as Al cap thickness, dead-layer thickness and Ge hole size) on optimum dimensions of marinelli beaker. In addition, the effects of detector material on optimal beaker dimensions were also investigated. Finally, the optimized beaker dimensions at various beaker volumes (300, 500, 700, 1000 and 1500 cm3) were determined for some conventional Ge detectors with different crystal sizes (16 sizes). These sets of data then were used to drive mathematical formulas (obtained by best fitting to data sets). The results showed that, there is no meaningful correlation between the optimum dimensions of the beaker and each of the dead-layer thickness, Al cap thickness and the Ge-crystal hole size. On the other hand, the optimum beaker radius increases with decreasing the density of the detector material while the beaker height decreases.

Monte Carlo based calibration of an air monitoring system for gamma and beta+ radiation.

Marinelli beaker systems are used to monitor the activity of radioactive samples. These systems are usually calibrated with water solutions and the determination of the activity in gases requires correction coefficients accounting for the different mass-thickness of the sample. For beta+ radionuclides the different distribution of the positrons annihilation points should be also considered. In this work a Monte Carlo simulation based on Geant4 is used to compute correction coefficients for the measurement of the activity of air samples.

Survey of natural radioactivity levels in Ilex paraguariensis (St. Hil.) by gamma-ray spectrometry

The mate tea (Ilex paraguariensis - St. Hil.) is a beverage broadly cultivated and consumed in Brazil. The radioactive traces present in three trademarks of toasted mate tea produced at the south of Brazil were analyzed. Measurements were carried out by gamma-ray spectrometry. The average value for the 40K activity measured for marks A, B and C was 1216 ± 8, 1047 ± 14 and 666 ± 13 Bq.kg-1, respectively. The 137Cs activity was lower than the limit of detection.

Uma bebida amplamente consumida e cultivada no Brasil é o chá-mate (Ilex paraguariensis - St. Hil). Foram analisados os traços radioativos de três marcas comerciais de chá-mate tostado produzidos no sul do Brasil. As medidas foram realizadas por espectrometria gama. Os valores médios para as atividades medidas do 40K, para as marcas A, B e C foram 1216 ± 8, 1047 ± 14 e 666 ± 13 Bq.kg-1, respectivamente. As atividades para o 137Cs foram menores que o limite mínimo de detecção.