MOPAC and LAMMPS molecular dynamics codes and reaction kinetics code based on
multi-ionic continuum-based model are used to analyze the impact of gamma
radiation on concrete hydration. The ...experimental studies showed that while
cured with the low gamma dose concrete shows a statistically significant
increase in its strength compared to conventionally cured concrete. The
potential reason is the interactions of gamma rays with water causing
concrete faster hydration. The question then to ask is would the higher gamma
dose enhance the concrete curing further producing its higher strength. This
paper provides in-depth numerical analyses of the high-dose gamma radiation
effect on concrete based on molecular dynamics and reaction kinetics models.
Under these conditions, it is assumed that gamma radiation interacting with
water within the concrete induces water radiolysis. These numerical
simulations show that the reactivity is generally increased in the presence
of electrophiles. However, the early hydration models of tricalcium silicate
(alite) and dicalcium silicate (belite) with H+, OH-, and H3O+ show that the
hydration process is slowed down leading to a lower concrete strength.
Additionally, the reaction kinetics model used to estimate the effect of
OH- on tricalcium silicate hydration shows that an increase or decrease of
OH- during tricalcium silicate hydration can respectively slow down or
enhance its rate of hydration. The dose necessary to produce the water
radiolysis resulting in varying OH- during tricalcium silicate hydration is
required to be extremely high and therefore, will damage the concrete
structure itself. This leads to the conclusion that increasing the gamma dose
to concrete above that used in the experimental studies in order to induce
water radiolysis will not improve concrete strength, therefore water
radiolysis is not the required condition for improving concrete strength when
cured under gamma radiation.
nema
Accurate dosimetry and determination of the biological effectiveness of boron neutron capture therapy (BNCT) is challenging because of the mix of different types and energies of radiation at the ...cellular and subcellular levels. In this paper, we present a computational, multiscale system of models to better assess the relative biological effectiveness (RBE) and compound biological effectiveness (CBE) of several neutron sources as applied to BNCT using boronophenylalanine (BPA) and a potential monoclonal antibody (mAb) that targets HER-2-positive cells with Trastuzumab. The multiscale model is tested against published in vitro and in vivo measurements of cell survival with and without boron. The combined dosimetric and radiobiological model includes an analytical formulation that accounts for the type of neutron source, the tissue- or cancer-specific dose-response characteristics, and the microdistribution of boron. Tests of the model against results from published experiments with and without boron show good agreement between modeled and experimentally determined cell survival for neutrons alone and in combination with boron. The system of models developed in this work is potentially useful as an aid for the optimization and individualization of BNCT for HER-2-positive cancers, as well as other cancers, that can be targeted with mAb or a conventional BPA compound.
The subject of this paper is the special legal regime for administrative contracts under the recently enacted Serbian Law on General Administrative Procedure of 2016. We offer a comprehensive ...analysis of the new statutory rules, and examine their relationship to the general rules and principles of Serbian contract law. In addition, we identify the main shortcomings of the new regime, especially in the context of the lack of any statutory, scholarly and judicial typology of administrative contracts in Serbia. Furthermore, we highlight the lack of references to the notions of public interest, public purpose or public needs in the statutory definition of administrative contracts. This is cause for concern, since only the need to protect the public interest could justify the new statutory provisions, which significantly improve the contractual position of a public body as a contracting party in relation to the position of a private entity as the other party in administrative contracts. There is as yet no case law pertaining to administrative contracts in Serbia. This is why we turn to practical experience in the Croatian legal system, which is sufficiently similar and historically connected to Serbia via a shared Yugoslav heritage. We also consider German and French legal models, since they traditionally serve as comparative points of reference for Serbian legal scholars, judges and law makers.
A novel hybrid approach for analysis of complex gamma-ray spectra of various origins is described and the test results using spectra obtained from a sodium iodide detector (NaI) are presented. This ...novel approach exploits the synergism of two artificial intelligence tools; fuzzy logic and genetic algorithms, where the two are merged to identify isotopes and their respective contribution in a given spectrum. The fuzzy logic module focuses on identifying isotopes in the spectrum, while the genetic algorithm (GA) fits and subsequently computes the fractional abundances of the identified isotopes. The fitting of the spectrum is controlled by an assessment procedure based on the test for significance of abundance coefficients, and on the computation of Theil coefficients. This unique synergism between fuzzy logic and GA presents a novel mechanism for automated selection of isotopes for use in spectrum fitting, and as a result eliminates manually-based fitting and/or user intervention. A variety of test cases-including NaI real measured spectra-are used to benchmark this new approach. In addition, the performance of the hybrid method is compared to the multiple linear regression (MLR) fitting approach, along with the combination of fuzzy logic with MLR. This comparison demonstrates a slight superiority of this novel approach regarding accuracy, precision and number of reported false detections.
In this paper, we present a new algorithm that improves muon-based generated
tomography images with increased precision and reduced image noise applicable
to the detection of nuclear materials. ...Cosmic muon tomography is an
interrogation-based imaging technique that, over the last decade, has been
frequently employed for the detection of high-Z materials. This technique
exploits a magnitude of cosmic muon scattering angles in order to construct
an image. The scattering angles of the muons striking the geometry of
interest are non-uniform, as cosmic muons vary in energy. The randomness of
the scattering angles leads to significant noise in the muon tomography
image. GEANT4 is used to numerically create data on the momenta and positions
of scattered muons in a predefined geometry that includes high-Z materials.
The numerically generated information is then processed with the point of
closest approach reconstruction method to construct a muon tomography image;
statistical filters are then developed to refine the point of closest
approach reconstructed images. The filtered images exhibit reduced noise and
enhanced precision when attempting to identify the presence of high-Z
materials. The average precision from the point of closest approach
reconstruction method is 13 %; for the integrated method, 88 %. The filtered
image, therefore, results in a seven-fold improvement in precision compared
to the point of closest approach reconstructed image.
nema
Control rod reactivity (worths) for the three control rods and fuel rod power
peaking factors in the University of Utah research reactor (100 kW TRIGA Mark
I) are characterized using the AGENT code ...system and the results described in
this paper. These values are compared to the MCNP6 and existing experimental
measurements. In addition, the eigenvalue, neutron spatial flux distributions
and reaction rates are analyzed and discussed. The AGENT code system is
widely benchmarked for various reactor types and complexities in their
geometric arrangements of the assemblies and reactor core material
distributions. Thus, it is used as a base methodology to evaluate neutronics
variables of the research reactor at the University of Utah. With its much
shorter computation time than MCNP6, AGENT provides agreement with the MCNP6
within a 0.5 % difference for the eigenvalue and a maximum difference of 10%
in the power peaking factor values. Differential and integral control rod
worths obtained by AGENT show well agreement with MCNP6 and the theoretical
model. However, regulating the control rod worth is somewhat overestimated by
both MCNP6 and AGENT models when compared to the experimental/theoretical
values. In comparison to MCNP6, the total control rod worths and shutdown
margin obtained with AGENT show better agreement to the experimental values.
nema
A significant challenge to current and future manned and/or unmanned space missions is due to deep space radiation. An improvement in more realistic (more accurate) simulation models in predicting ...the effects of radiation within the spacecraft is required, especially to better predict dose to astronauts, energy deposition within sensitive electronics, and effectiveness of radiation shielding for long-term space missions. The International Space Station provides an invaluable resource for long-term measurements of the radiation environment in Low Earth Orbit (LEO); however, the only manned missions with dosimetry data available beyond LEO are the Apollo missions. Thus the physiological effects and dosimetry for deep space missions are not well understood in planning extended missions. GEANT4, a Monte Carlo method, represents a powerful physics simulation tool to assess the effects of radiation transport through spacecraft. The newest version of GEANT4 supports multithreading and Message Passing Interface (MPI) allowing for much faster distributive processing of simulations, using a high-performance computing environment. This paper introduces a new simulation model and application using GEANT4 that greatly reduces computational time to hours instead of weeks without any post simulation processing based on high-performance computing. This paper also introduces a new set of GEANT4 computational detectors for calculating dose distribution, besides the historically used International Commission of Radiation Units simulation spheres. The computational detectors include a thermoluminescent detector, tissue equivalent proportional counter, and human phantom, along with additional new scorers to calculate dose equivalence based on the International Commission of Radiation Protection standards. This study presents GEANT4 simulations of the dose deposition for the International Space Station and the Apollo 11 and 14 missions, which replicate well the dose measurements during these missions. The simulations of both Apollo missions show consistent doses from galactic cosmic rays and radiation belts with a small variation in dose distribution across the Apollo capsule. The greatest contributor to radiation dose for both Apollo missions in the simulations came from galactic cosmic rays. Simulations of historical solar particle events during an Apollo missions show a solar particle event would not be fatal and below mission limits. These GEANT4 models also provides the values of the dose deposition and dose equivalent for various organs within a human phantom in the International Space Station and Apollo command module, which are developed for the first time using this GEANT4 based application.
•A new application simulated radiation through full-sized spacecraft.•Application implemented new computational detectors including human phantom.•Simulations of dose for ISS and Apollo 11 matched well experimental measurements.•Greatest contributor to radiation dose for Apollo missions was from GCR.•Simulations of Apollo 14 showed higher measured dose most likely due to SPE.
BRITTS (Burnup of Reactor Isotopes, Tracking in Time and Space) is a newly developed burnup module based on the Runge-Kutta 4th order method supplementing the well-known AGENT neutronics code. Unlike ...other burnup codes that are limited to 2D models, cumulative-only calculations, or one specific fuel type, BRITTS provides detailed spatial distributions of actinides in 2D and approximate 3D (through a 2D/1D coupled characteristic solution provided by the AGENT code) at user-specified points in a burn cycle. Using two simple MOX fuel pins, BRITTS is compared with SCALE6.2. BRITTS is also compared against a well-known OECD/NEA benchmark of UO2 fuel pin with 16 participants. These comparisons show that BRITTS provides reliable calculations for concentrations of nuclear fuel actinides and fission products in both 2D and approximate 3D and can be uniquely used to analyze the spatial distributions of the actinides during the burn-cycles. This paper presents the mathematical and numerical methods employed in BRITTS and a series of benchmark examples showing the code capabilities for reactor fuel analyses.
Estimating the health effects of radon exposure is of great interest because radon is considered the second leading cause of lung cancer after smoking. The dose-response curve is not well understood ...at low-dose levels where radon exposure is estimated. Therefore, the health mechanisms of radiation due to radon progeny at the cellular and molecular levels are of interest for providing an indication of a possible threshold value above which the exposure may indicate cancer formation. In this paper we present a macroscopic and cellular level numerical analysis of the radon-induced dose estimates based on the Geant4 code system. Macroscopic estimates are assessed based on patient-specific computer tomography scans that provide geometries easily applicable to modeling radiation effects of the radon progeny sources. A small tissue volumes analysis based on the Geant4 code system is developed so as to provide information about the interactions and particle track structures at the microscopic (cellular) levels producing the dosimetric effects of radon short-lived progenies. The results presented in this paper also call attention to the capabilities of Geant4 to provide radon-related dosimetric parameters of large and small-scale biological systems.
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