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    Wyświetlanie 1-7 z 7
    Tytuł:
    Large Sample Neutron Activation Analysis: correction for neutron and gamma attenuation
    Autorzy:
    Tzika, F.
    Stamatelatos, I.
    Kalef-Ezra, J.
    Bode, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/147265.pdf
    Data publikacji:
    2004
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    neutron activation analysis
    neutron self-shielding
    gamma-ray attenuation
    MCNP code
    Opis:
    A Large Sample Neutron Activation Analysis (LSNAA) facility is under development at the GRR-1 research reactor, NCSR "Demokritos". The LSNAA facility design incorporates sample irradiation in the reactor graphite thermal neutron column and subsequent measurement of the activity induced in a gamma spectroscopy system with gamma ray transmission measurement options included. The Monte Carlo neutron and photon transport code MCNP-4C was used to model the facility. Appropriate correction factors accounting for neutron field perturbation during sample irradiation and high-purity germanium detector efficiency for the volume source were derived. The results of the computations were experimentally verified by measurements for a set of known materials. The LSNAA facility will be used to perform multi-element, non-destructive, contamination-free analysis of large volume samples with high sensitivity and excellent sampling. End-users of the facility will be archaeological, environmental, bio-medical research laboratories and industry.
    Źródło:
    Nukleonika; 2004, 49, 3; 115-121
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Time of soil water thermodynamic equilibrium during retention curve establishment using gamma-ray beam attenuation
    Autorzy:
    Pires, L.
    Bacchi, O.
    Reichardt, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/148674.pdf
    Data publikacji:
    2005
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    gamma-ray attenuation
    time of equilibrium
    pressure chamber
    soil water retention curve
    Opis:
    The soil water retention curve (SWRC) represents a fundamental part of the characterization of the soil hydraulic properties. The establishment of SWRC is usually time-consuming and presents several problems such as the difficulty of a correct judgment of the time of equilibrium. This work presents a new methodology that involves gammaray beam attenuation technique associated with the traditional pressure chambers, having as objective the more precise judgment of the time to attain equilibrium. The gamma-ray source used has an activity of 3.7 GBq consisting of 241Am, with peak energy of 59.54 keV. For the determination of retention curves using the gamma-ray attenuation technique, an acrylic pressure chamber was projected and constructed to be positioned between the source and detector with the gamma-ray beam crossing the center of the chamber and the soil sample during water extraction. The proposed technique allowed, through a specifically elaborated software for data acquisition, to evaluate with precision the exact instant of the equilibrium and, consequently, to obtain the right moment to change the chamber pressure to a new desired level, leading to a reduction of the time required for the whole retention curve determination. The results obtained show that the gamma-ray attenuation technique can be very useful as an auxiliary tool to evaluate SWRC, utilizing the Richards chamber.
    Źródło:
    Nukleonika; 2005, 50, 4; 173-177
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Design, construction and performance of a pressure chamber for water retention curve determination through traditional and nuclear methods
    Autorzy:
    Pires, L.
    Bacchi, O.
    Powiązania:
    https://bibliotekanauki.pl/articles/146181.pdf
    Data publikacji:
    2006
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    soil water potential
    gamma-ray attenuation
    soil water content
    soil physics
    radioisotope application
    Opis:
    We present in this work a detailed design of a small low-pressure chamber outfitted with a ceramic porous plate for evaluating the soil water retention curve (SWRC) in the water potential range from 0 to -100 kPa. The chamber is made of acrylic and permits the use of one unique soil sample each time. The use of this chamber allows quick measurements of soil moisture using nuclear (based on gamma-ray attenuation) and conventional methods and SWRC determinations made with the designed chamber are in agreement with those obtained using a commercial low-pressure chamber. The chamber was designed especially for testing the use of the nuclear method as an auxiliary tool for SWRC determinations but it can be easily adapted for routine investigations and a practical alternative for the conventional SWRC method.
    Źródło:
    Nukleonika; 2006, 51, 4; 225-230
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Designing a simple radiometric system to predict void fraction percentage independent of flow pattern using radial basis function
    Autorzy:
    Roshani, G. H.
    Nazemi, E.
    Shama, F.
    Imani, M. A.
    Mohammadi, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/221419.pdf
    Data publikacji:
    2018
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    two-phase flow
    gamma-ray attenuation
    scintillation detector
    void fraction
    artificial neural network
    Opis:
    The void fraction is one of the most important parameters characterizing a multiphase flow. The prediction of the performance of any system operating with more than single phase relies on our knowledge and ability to measure the void fraction. In this work, a validated simulation study was performed in order to predict the void fraction independent of the flow pattern in gas-liquid two-phase flows using a gamma ray 60Co source and just one scintillation detector with the help of an artificial neural network (ANN) model of radial basis function (RBF). Three used inputs of ANN include a registered count under Compton continuum and counts under full energy peaks of 1173 and 1333 keV. The output is a void fraction percentage. Applying this methodology, the percentage of void fraction independent of the flow pattern of a gas-liquid two-phase flow was estimated with a mean relative error less than 1.17%. Although the error obtained in this study is almost close to those obtained in other similar works, only one detector was used, while in the previous studies at least two detectors were employed. Advantages of using fewer detectors are: cost reduction and system simplification.
    Źródło:
    Metrology and Measurement Systems; 2018, 25, 2; 347-358
    0860-8229
    Pojawia się w:
    Metrology and Measurement Systems
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Gamma-ray beam attenuation to assess the influence of soil texture on structure deformation
    Autorzy:
    Pires, L.
    Bacchi, O.
    Dias, N.
    Powiązania:
    https://bibliotekanauki.pl/articles/147480.pdf
    Data publikacji:
    2006
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    gamma-ray attenuation
    soil physical properties
    soil structure deformation
    soil sampling
    soil porosity
    Opis:
    Gamma-ray beam attenuation is a non-invasive technique that permits analysis of soil porosity without disturbing the region of interest of the core sample. The technique has as additional advantage to allow measurements point by point on a millimetric scale in contrast to other methodologies that are invasive and analyze the soil properties in the bulk sample volume. Soil porosity can be used as an important parameter to quantify soil structural damages, which affect soil aeration, water movement and retention. In this study, porosities of three soils different in texture were measured at various positions in order to analyze the impact of the sampling procedure on the structure of each particular soil texture. The gamma-ray attenuation system consisted of an 241Am radioactive source having an activity of 3.7 GBq, collimated with cylindrical lead collimators of 2 mm diameter. The results obtained show the presence of dense regions near the edges of samples and that different soil textures can suffer distinct deformations at sampling.
    Źródło:
    Nukleonika; 2006, 51, 2; 125-129
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Gamma-ray computed tomography as a tool to evaluate porosity changes along depth for surface crusted soils
    Autorzy:
    Pires, L. F.
    Bacchi, O. O. S.
    Reichardt, K.
    Dias, N. M. P.
    Powiązania:
    https://bibliotekanauki.pl/articles/146838.pdf
    Data publikacji:
    2007
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    gamma-ray attenuation
    soil density
    soil structure
    soil surface sealing
    241 Am
    applied nuclear physics
    gamma tomography
    Opis:
    Assessment of changes in porosity (ö) along depth for soils with surface crusting is difficult because conventional soil physical investigation tools are destructive and usually require a long period of time for preparation and analysis of the samples. Computed tomography (CT) has frequently been used as a method to evaluate soil structure in a nondestructive, sensitive, and rapid manner. CT data can be used for measuring at a millimetric scale changes in ö along depth for soils with surface crusting. The main objective of this work was to investigate the sensibility of the gamma-ray CT to assess soil structural changes along depth in samples presenting structural crust. CT images were taken with a first generation scanner of 1.14 mm resolution along eight different soil layers within the 0 28 mm depth. Porosity increased along depth up to the 14 17.5 mm layer. Through the analysis of the ö distribution of each layer it was possible to show that the sealed surface layer presented ö values of approximately 30%, while the other layers were greater than 30% up to 60% (macropore regions). The sealing crust thickness was estimated to be in the range of 2.3 3.5 mm.
    Źródło:
    Nukleonika; 2007, 52, 3; 125-131
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Self-absorption correction in gamma-ray spectrometry of environmental samples - an overview of methods and correction values obtained for the selected geometries
    Autorzy:
    Jodłowski, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/148531.pdf
    Data publikacji:
    2006
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    gamma-ray spectrometry
    self-attenuation
    self-absorption
    correction factor
    Opis:
    Of major concern are the self-absorption correction factors Cs in precise gamma-ray spectrometry of environmental samples. The overview of Cs determination methods (experimental, Monte Carlo calculations, analytical function application) is presented. Among several available methods, the author chose the one proposed by Debertin where the uncertainty level of Cs correction factor is 1÷2%. The point-like detector model is assumed whilst its efficiency is taken to be proportional to the weighted sum (integral) of the number of photons coming from sample volume elements. Computer program was developed to support the computation of Cs by the Debertin's method for samples in cylindrical geometries and Marinelli beakers. The input data are sample dimensions, density and the mass attenuation coefficient. The Cs uncertainty due to an arbitrarily chosen position of a point-like detector would not exceed 1% for the considered photon energies and the sample density range. Utilising this computer program, the relationships Cs(E,ń) were obtained for the applied geometries and a SiO2 matrix to support routine measurements. The SiO2 matrix is widely encountered in environmental spectrometry. This relationship was derived by fitting the computed data with the function Cs(E,ń) in the form proposed by Bolivar. It was shown that while handling this function to samples with the H2O matrix, the error involved in estimations would not exceed 3%.
    Źródło:
    Nukleonika; 2006, 51,suppl.2; 21-25
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-7 z 7

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