Publication Date: 2006
Iranian Journal of Science and Technology, Transaction A: Science (10286276)30(3)pp. 259-269
A reconnaissance study has been made on the distribution of 238U, 232Th, 40K, 137Cs and geochemical features in soil and sediment samples at various locations on the coast of Bushehr in the Persian Gulf. In this study a gamma-ray spectrometer based on a High Purity Germanium detector and a PC based MCA and X-ray fluorescence (XRF) method were used. Estimation of the measured radionuclide content have been made for the absorbed dose rate of gamma radiation. The Activity concentration (A), the equivalent radium (Req), and the external hazard index (Hex) which resulted from the natural radionuclides in soil and sediment are also calculated. The base-line data of radionuclides and heavy metals in view of the commissioning of nuclear and non-nuclear industries for the coast of Bushehr, which does not yet exist, was obtained. Activity concentration levels due to radionuclides were measured in 50 soil and sediment samples collected from this region. The measurement was performed with respect to their gamma radioactivity for a counting time of 24 hour intervals. From the accumulated spectra, activity concentration were determined for 40K (range from 108 to 520 Bq Kg-1), 137Cs (from 6 to 40 Bq Kg-1), 238U (from 12 to 75 Bq Kg1) and 232Th (from 8 to 33 Bq Kg-1) with the lowest limit detection (LLD) of, respectively, 68, 3.2, 4.3 and 4.3 Bq Kg-1. The dose rate from ambient air at the soil ranges was between 14 to 44 nGy h-1 with an average of 30.56 ± 7.86 nGy h -1. © Shiraz University.
Publication Date: 2006
Journal of Radioanalytical and Nuclear Chemistry (15882780)268(3)pp. 539-544
A nonlinear function was applied in combination with the method of mixing activity calibration for fitting the experimental peak efficiency of HPGe spectrometers in the 50-2614 keV energy range. The preparation of Marinelli beaker standards of mixed gamma- and RG-Set at secular equilibrium with its daughter radionucliedes was studied. Self-absorption was measured for the activity calculation of the gamma-ray lines for daughters of 238U series, 232Th series, as well as 137Cs and 40K in soil samples. Self-absorption in the sample depends on a number of factors including sample composition, density, sample size and gamma-ray energy. Seven Marinelli beaker standards were prepared in different degrees of compaction with bulk density (ρ) of 1.000 to 1.600 g·cm-3. The detection efficiency versus density was obtained and the equation of self-absorption correction factors was calculated for soil samples. © 2006 Akadémiai Kiadó.
Publication Date: 2007
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms (0168583X)263(2)pp. 473-476
In this work thermal neutron self-shielding in aqueous bulk samples containing neutron absorbing materials is studied using bulk sample prompt gamma neutron activation analysis (BSPGNAA) with the MCNP code. The code was used to perform three dimensional simulations of a neutron source, neutron detector and sample of various material compositions. The MCNP model was validated against experimental measurements of the neutron flux performed using a BF3 detector. Simulations were performed to predict thermal neutron self-shielding in aqueous bulk samples containing neutron absorbing solutes. In practice, the MCNP calculations are combined with experimental measurements of the relative thermal neutron flux over the sample's surface, with respect to a reference water sample, to derive the thermal neutron self-shielding within the sample. The proposed methodology can be used for the determination of the elemental concentration of unknown aqueous samples by BSPGNAA where knowledge of the average thermal neutron flux within the sample volume is required. © 2007 Elsevier B.V. All rights reserved.
Publication Date: 2008
Annals of Nuclear Energy (03064549)35(12)pp. 2313-2320
This paper describes the application of a multilayer cellular neural network (CNN) to model and solve the time dependent one-speed neutron transport equation in slab geometry. We use a neutron angular flux in terms of the Chebyshev polynomials (TN) of the first kind and then we attempt to implement the equations in an equivalent electrical circuit. We apply this equivalent circuit to analyze the TN moments equation in a uniform finite slab using Marshak type vacuum boundary condition. The validity of the CNN results is evaluated with numerical solution of the steady state TN moments equations by MATLAB. Steady state, as well as transient simulations, shows a very good comparison between the two methods. We used our CNN model to simulate space-time response of total flux and its moments for various c (where c is the mean number of secondary neutrons per collision). The complete algorithm could be implemented using very large-scale integrated circuit (VLSI) circuitry. The efficiency of the calculation method makes it useful for neutron transport calculations. © 2008 Elsevier Ltd. All rights reserved.
