Sensitivity Analysis in Coupled Radiation Transport Simulations.

Purpose In radiation physics, Monte Carlo radiation transport simulations are powerful tools to evaluate the cellular responses after irradiation. When investigating such radiation-induced biological effects, it is essential to perform track structure simulations by explicitly considering each atomic interaction in liquid water at the sub-cellular and DNA scales. The Particle and Heavy-Ion Transport code System (PHITS) is a Monte Carlo code which enables to calculate track structure at DNA scale by employing the track-structure modes for electrons, protons and carbon ions. In this paper, we review the recent development status and future prospects of the track-structure modes in the PHITS code. Conclusions To date, the physical features of these modes have been verified using the available experimental data and Monte Carlo simulation results reported in literature. These track-structure modes can be used for calculating microdosimetric distributions to estimate cell survival and for estimating initial DNA damage yields. The use of PHITS track-structure mode is expected not only to clarify the underlying mechanisms of radiation effects but also to predict curative effects in radiation therapy. The results of PHITS simulations coupled with biophysical models will contribute to the radiobiological studies by precisely predicting radiation-induced biological effects based on the Monte Carlo approach.

The increasing availability of SPECT/CT devices with advanced technology offers the opportunity for the accurate assessment of the radiation dose to the biological target volume during radionuclide therapy. Voxel dosimetry can be performed employing direct Monte Carlo radiation transport simulations, based on both morphological and functional images of the patient. On the other hand, for voxel dosimetry calculations the voxel S value method can be considered an easier approach than patient-specific Monte Carlo simulations, ensuring a good dosimetric accuracy at least for anatomic regions which are characterized by uniform density tissue. However, this approach has been limited because of the lack of tabulated S values for different voxel dimensions and radionuclides. The aim of this work is to provide a free dataset of values which can be used for voxel dosimetry in targeted radionuclide studies. Seven different radionuclides (89Sr, 90Y, 131I, 153Sm, 177Lu, 186Re, 188Re), and 13 different voxel sizes (2.21, 2.33, 2.4, 3, 3.59, 3.9, 4, 4.42, 4.8, 5, 6, 6.8 and 9.28 mm) are considered. Voxel S values are calculated performing simulations of monochromatic photon and electron sources in two different homogeneous tissues (soft tissue and bone) with DOSXYZnrc code, and weighting the contributions on the basis of the radionuclide emission spectra. The outcomes are validated by comparison with Monte Carlo simulations obtained with other codes (PENELOPE and MCNP4c) performing direct simulation of the radionuclide emission spectra. The differences among the different Monte Carlo codes are of the order of a few per cent when considering the source voxel and the bremsstrahlung tail, whereas the highest differences are observed at a distance close to the maximum continuous slowing down approximation range of electrons. These discrepancies would negligibly affect dosimetric assessments. The dataset of voxel S values can be freely downloaded from the website www.medphys.it.

Use of MCAM in creating 3D neutronics model for ITER building

Monte Carlo volume integration of dose point kernels was used for calculating voxel S values of beta emissions of radionuclides of interest for internal radiotherapy. The method was verified by comparing our results with others derived from Monte Carlo radiation transport simulation. The algorithm has been implemented in a C++ program that can be used by any laboratory to calculate voxel S values of beta emissions from tabulated dose point kernels and for any combination of pixel edges and the thickness of SPECT and PET images without the complexity and expertise needed for direct Monte Carlo radiation transport simulations.

Pulsed beams of energetic x-rays and neutrons from intense laser interactions with solid foils are promising for applications where bright, small emission area sources, capable of multi-modal delivery are ideal. Possible end users of laser-driven multi-modal sources are those requiring advanced non-destructive inspection techniques in industry sectors of high value commerce such as aerospace, nuclear and advanced manufacturing. We report on experimental work that demonstrates multi-modal operation of high power laser-solid interactions for neutron and x-ray beam generation. Measurements and Monte Carlo radiation transport simulations show that neutron yield is increased by a factor ~2 when a 1 mm copper foil is placed behind a 2 mm lithium foil, compared to using a 2 cm block of lithium only. We explore x-ray generation with a 10 picosecond drive pulse in order to tailor the spectral content for radiography with medium density alloy metals. The impact of using >1 ps pulse duration on laser-accelerated electron beam generation and transport is discussed alongside the optimisation of subsequent bremsstrahlung emission in thin, high atomic number target foils. X-ray spectra are deconvolved from spectrometer measurements and simulation data generated using the GEANT4 Monte Carlo code. We also demonstrate the unique capability of laser-driven x-rays in being able to deliver single pulse high spatial resolution projection imaging of thick metallic objects. Active detector radiographic imaging of industrially relevant sample objects with a 10 ps drive pulse is presented for the first time, demonstrating that features of 200 μm size are resolved when projected at high magnification.

The FLUKA general purpose radiation transport Monte Carlo code being developed and maintained by CERN (https://fluka.cern) has adopted modern software development standards including a formal quality assurance process. This includes the FLUKAVAL testing framework that takes into account the specific needs of testing a Monte Carlo radiation transport simulation code. FLUKAVAL allows to submit, process and validate a large number of test cases for a new FLUKA version and compare the results against previous versions and reference data. It produces a quantitative and qualitative comparison and compiles a summary report over all selected test cases, which is reviewed before the new FLUKA version is released. The overall validation requires only few manual steps and makes use of large computing clusters to run simulations in parallel.

Kernel Density Estimators (KDEs) are a non-parametric density estimation technique that has recently been applied to Monte Carlo radiation transport simulations. Kernel density estimators are an alternative to histogram tallies for obtaining global solutions in Monte Carlo tallies. With KDEs, a single event, either a collision or particle track, can contribute to the score at multiple tally points with the uncertainty at those points being independent of the desired resolution of the solution. Thus, KDEs show potential for obtaining estimates of a global solution with reduced variance when compared to a histogram. Previously, KDEs have been applied to neutronics for one-group reactor physics problems and fixed source shielding applications. However, little work was done to obtain reaction rates using KDEs. This paper introduces a new form of the MFP KDE that is capable of handling general geometries. Furthermore, extending the MFP KDE to 2-D problems in continuous energy introduces inaccuracies to the solution. An ad-hoc solution to these inaccuracies is introduced that produces errors smaller than 4% at material interfaces.

In this paper, observer based synchronization of chaotic Lorenz system is presented. The virtual system concept is used for synchronization of observer states to actual system states. First, synchronization is presented without any uncertainty in system parameters and further synchronization is achieved for the case with uncertainty in system parameters. Adaptation law for uncertain parameters are developed as a consequence of stability analysis. Convergences of uncertain parameters are also analyzed. Simulation results are presented in the end to verify the synchronization of observer states to actual system states.

Uncertainty quantification in a resonant nonlinear MEMS structure

Feasibility analysis and techno-economic design of grid-isolated hybrid renewable energy system for electrification of agriculture and irrigation area: A case study in Dongola, Sudan

The goals of this project are to develop Monte Carlo radiation transport methods and simulation software for engineering analysis that are robust, efficient and easy to use; and provide computational resources to assess and improve the predictive capability of radiation transport methods and nuclear data.

In the paper, based on a combination of the robust control approach and an adaptive control technique, a design procedure of a new robust adaptive controller is proposed for power system load-frequency control with system parametric uncertainties. The system parametric uncertainties are obtained by changing parameters by 30% to 50% simultaneously from their typical values. In the design of the proposed controller, only the bounds of system parameters are required. The motivation of combining the robust control with an adaptive control is to use the robust control approach to deal with the small parametric uncertainties and to use the adaptive control for large parametric uncertainties so that stability of the overall system and good performance can both be achieved for all admissible uncertainties. The simulation results demonstrate that for the example system the proposed load-frequency controller can achieve good performance even in the presence of the generation rate constraint (GRC).

Purpose: The biological response of tissue exposed to radiations emitted by internal radioactivity is often correlated with the mean absorbed dose to a tissue element. However, experimental studies show that even when the mean absorbed dose to the tissue element is constant, the response of the cell population within the tissue element can vary significantly depending on the distribution of radioactivity at the cellular and multicellular levels. The present work develops theoretical models to simulate these observations.Materials and methods: Two theoretical models were created to simulate experimental three-dimensional cell culture models with homogeneous and inhomogeneous tissue environments. The cells were assigned activities according to lognormal distributions of an alpha particle emitter or a monoenergetic electron emitter. Absorbed doses to the cell nuclei were assessed with point-kernel geometric-factor and Electron Gamma Shower version nrc (EGSnrc) Monte Carlo radiation transport simulations, respectively. The self- and cross-dose to individual cell nuclei were calculated and a Monte Carlo method was used to determine their fate. Survival curves were produced after tallying the live and dead cells.Results: Both percent cells labeled and breadth of lognormal distribution affected the dose distribution at the cellular level, which in turn, influenced the shape of the cell survival curves.Conclusions: Multicellular Monte Carlo dosimetry-models offer improved capacity to predict response to radiopharmaceuticals compared to approaches based on mean absorbed dose to the tissue.

\nMayo Clinic Scottsdale (Scottsdale, Arizona) is building a cyclotron vault containing a cyclotron with adjacent targets and a beam line leading to an external target. The targets are irradiated by high energy (15 to 16.5 MeV) protons for the production of radioisotopes. We performed Monte Carlo radiation transport simulations to calculate the radiation dose outside of the vault during irradiation of the cyclotron and external targets. We present the Monte Carlo model including the geometry, sources, and variance reduction methods. Mesh tallies surrounding the vault show the external dose rate is within acceptable limits.\n

Study of the response of a lithium yttrium borate scintillator based neutron rem counter by Monte Carlo radiation transport simulations