45 research outputs found
Monte Carlo analysis of dosimetric issues in space exploration
No full textThe Radiation protection is of paramount importance in the planning of human exploration activities in space. The related risks must be considered with respect to two aspects: devising a proper shielding and providing answers to the requirement of an effective dosimetry evaluation in astronaut’s activities. Both aspects have been considered using the Monte Carlo (MC) code MCNP 6.2 as the reference tool. As case study an application devised for the National Aeronautics and Space Administration (NASA) Artemis program has been chosen. The project aims to establish a sustainable human presence on the Moon, envisioning the realization of an outpost that will serve as a steppingstone for space exploration endeavors. A Class III shelter, in situ resource utilization (ISRU) built habitat for the Moon, has been designed through computational methods and topology optimization techniques, and analyzed in terms of radiation shielding performances and the strictly related structural behavior. The outpost must be able to withstand temperature variations, micrometeorite impacts, and the absence of a substantial atmosphere. Any solution studied to respect the constraints must devise robust and innovative materials and techniques to create habitats that have as goal the shielding from the Galactic Cosmic Rays (GCR) and from the solar flares to provide a safe and habitable environment at the time scales scheduled for the missions. Moreover, the outpost design must incorporate strategies for extracting and utilizing local re- sources. Overcoming such challenges will pave the way for the establishment of a sustainable human presence on the Moon and serve as a crucial leap for future space exploration missions
Monte Carlo Analysis of dosimetric issues in space exploration
No full textIntroduction
The radiation protection is of paramount importance in the planning of human exploration activities in space.
The related risks must be considered with respect two aspects: devising a proper shielding and answer to the requirement of an effective dosimetry evaluation during astronaut activities.
Both aspects have been considered using as reference tool the Monte Carlo code MCNP 6.2. As case study a possible application to the NASA Artemis program has been chosen.
The project aims to establish a sustainable human presence on the Moon, envisioning the realization of an outpost that will serve as a steppingstone for space exploration endeavors.
Methods
A Class III shelter, ISRU derived habitat with local resources available on the Moon, has been designed through computational methods and topology optimization techniques, and analyzed in terms of radiation shielding performances and structural behavior.
Results
The outpost must be able to withstand temperature variations, micrometeorite impacts, and the absence of a substantial atmosphere.
Any solution studied to respect the constraints must devise robust and innovative materials and techniques to create habitats that have as goal the shielding from the Galactic Cosmic Rays and from the solar flares to provide a safe and habitable environment at the time scales scheduled for the mission.
Resource utilization is crucial for sustaining long-duration missions on the Moon as envisaged in the ARTEMIS program.
This implies the outpost design must incorporate strategies for extracting and utilizing local resources.
Conclusions
The design of a lunar outpost for the NASA Artemis program is a complex undertaking that involves addressing challenges related to lunar environment, resource utilization, power generation, logistics, and crew well-being.
Overcoming such challenges will pave the way for the establishment of a sustainable human presence on the Moon and serve as a crucial leap for future space exploration missions
Shape, Structure and Material Compliance with Radiation Protection Requirements for Extraplanetary Modules
No full textThis research aims to explore a design solution for an innovative extraplanetary module that combines architectural design, structure and radiation protection for sustaining human life on Mars.
The WATER (Water shielded Architectural Tree for Extraplanetary Resiliency) module is designed in order to increment the use of local resources (In Situ Resources Utilization) and robotic fabrication techniques for remote construction before human arrival on Mars.
The key element of the design is the water that can be extracted from the substrate of the Martian regolith. Water plays an essential role in both in supporting life and protecting humans inside the habitat. Because of the reduced gravity and the fine atmosphere, the major load that a structure has to withstand on Mars is the internal pressurization. To balance that load and have a more efficient foundation system, the structure needs to be covered by a thick layer of water that is also extremely important for shielding against the harmful cosmic radiation.
In fact, it is well known that a major threat to extraplanetary exploration is given by high energy cosmic particles and gamma fluxes. This work deals with the radiation protection constraints that should be considered for the WATER module, designed as an optimized possible long term habitat for Mars. The main materials considered for the module are the Martian regolith and, with respect to radiation shielding, the water that will be driven to fill the layer between the external and internal surfaces that will sustain the exposed external structures.
The simulations, carried out with a standard Monte Carlo code like MCNPX and MCNP6, that is able to directly analyze the mesh geometries coming from the WATER module structural Finite Element model, define the optimal conditions in terms of shielding thickness and layer’s material composition.
As output of the analysis, expositions and doses, that the inhabitants of these future architecture should bear, have been obtained.
The final shielding configuration is integrated in the Finite Element model of the project for the structural analysis. The results prove that the water content, subjected to the Martian gravity, helps reducing the tensile stresses inside the structure due to the internal pressurization
Monte Carlo benchmark of the experimental evaluation of the activation processes in an electron linear accelerator for radiotherapy applications
No full textSeveral kinds of isotopes are generated during radiotherapy treatments with high-energy electron sources due to the onset of many nuclear reactions. These isotopes are often unstable, can appear both in the device and in the treatment chamber materials and, as a consequence of the decay process, involving also gamma-ray emissions, some additional dose is given to the patient and to the radiotherapy unit staff. These effects have been experimentally monitored with a LaBr detector for gamma spectrometry. Then the measurement setup and data have been benchmarked through Monte Carlo (MC) simulations, with the MCNPX code, aiming to evaluate all kinds of activation, due to both photons and photoneutrons. All the MC activation estimates have been parameterized with respect to the 187W produced in the primary collimator of the accelerator. The simulation results obtained with MCNPX have shown a good agreement with the experimental measurements. The results suggest a possible general approach to perform the activation analysis by coupling the experimental spectrometric measurements with MC calculations to properly identify photopeaks and source components
A Monte Carlo model for photoneutron generation by a medical LINAC
No full textFor an optimal tuning of the radiation protection planning, a Monte Carlo model using the MCNPX code has been built, allowing an accurate estimate of the spectrometric and geometrical characteristics of photoneutrons generated by a Varian TrueBeam Stx © medical linear accelerator. We considered in our study a device working at the reference energy for clinical applications of 15. MV, stemmed from a Varian Clinac©2100 modeled starting from data collected thanks to several papers available in the literature. The model results were compared with neutron and photon dose measurements inside and outside the bunker hosting the accelerator obtaining a complete dose map. Normalized neutron fluences were tallied in different positions at the patient plane and at different depths. A sensitivity analysis with respect to the flattening filter material were performed to enlighten aspects that could influence the photoneutron production
Compact and very high dose-rate plasma focus radiation sources for medical applications
No full textA Dense Plasma Focus (DPF) is a pulsed device able to produce a hot and dense short-lived plasma that could become a fast radiation source for diagnostic applications, external radiotherapy, or intra-operative radiation therapy. The plasma confinement phase, identified as “pinch”, lasts few tens of nanoseconds, during which thermonuclear temperatures and densities could be reached. When the DPF vacuum chamber is filled with gases such as nitrogen, the only significant output are self-collimated charged particle beams (electrons and ions in opposite direction). Using that electron beam, it is possible to devise an ultra-high dose-rate source, with applications for direct irradiation of a tumor bed or for photon conversion after the interaction with a suitable target. The ultra-high dose rate could have potential benefits in mitigating the intrinsic or acquired malignant cell radio-resistance, which can be considered the main obstacle to the long-term survival of a patient, also sparing healthy tissues. This is due as the faster the dose deposition, the more relevant is the radiobiological efficacy (as the tumor cells do not have the time to activate the sub-lethal damage repair mechanisms responsible of the radio-resistance). Due to the novelty of the fast source, the usual models cannot easily describe the biological outcomes, therefore new numerical approaches are needed for predicting the RBE outlined in these regimens.
A parametric investigation through the Monte Carlo Damage Simulation Software (MCDS), coupled with the Monte Carlo N-Particle (MCNP) code, has been performed for supporting the experimental results previously obtained by irradiating melanoma cell lines with the Plasma Focus Device for Medical Applications #3 (PFMA-3) as UHDR source and a conventional XRT as standard of comparison.
The experimental data were benchmarked with MCNP-MCDS, properly fitting the XRT curves. The validation of the MCDS-MCNP coupling was performed by comparing literature data for conventional XRT, with less than 4% of differences. Next, the experimentally evaluated RBE highlighted that for high doses the RBE calculated on the basis of the surviving fraction (RBE(SF)), is the same of the one from double strand break damages (RBE(DSB)), making coherent the application of the Repair Misrepair Fixation theory (RMF) and providing a basis for a reliable comparison between the two devices. The DPF irradiation outcome has been numerically investigated correlating the experimental experiences with a wide range of code parameter variations to find numerical conditions able to reproduce the data. A recipe based on a combination of more than one SF curves to fit the clonogenic assay in UHDR regimen has also been proposed.
The results suggested that the UHDR regimen obtained from the DPF source could change the environmental conditions (e.g., oxygen concentration) while cumulating the dose. This implies that a combination of data and MCDS-MCNP analysis could be applied as a strategy for quantifying biological effects
Monte Carlo estimation and measurement of the activation products due to an electron linear accelerator for medical applications
No full textDuring radiotherapy treatments with high energy electron sources some nuclear reactions take place. This means that several kinds of radioisotopes are generated both in the device and then in the treatment chamber walls and some additional dose is given to the patient and to the staff of the radiotherapy unit, due to the decay processes, often implying gamma-ray emissions. To show these effects a portable NaI(Tl) monitor is used for gamma spectrometry
A monte carlo calibration approach for a dual-energy ct system
No full textThis work shows the effectiveness of Monte Carlo methods for calibrating a dual-energy CT (DECT) system on a heterogeneous phantom for radiotherapy. The reference phantom comprising 20 inserts of different materials and densities representing human tissues inserted in a plastic water cylinder has been considered. The reliability of the model, built with the Penelope code, has been verified by comparing the results of the simulations at 80kVp and 140kVp with the experimental data acquired from the CT scans and dosimetry measurements. The effective atomic number from the various materials is also considered a control parameter. Tests for calibration and dose calculation are also based on a homogeneous phantom in PMMA and measurements in air with an ionization chamber. The Monte Carlo simulations coupled with dose evaluations allowed the calibration of the dose deposition effects on the considered tissue models
A digital twin for (64)Cu production with cyclotron and solid target system
No full textOne method for finding reliable and cost-effective solutions for designing radioisotope production systems is represented by the “digital twin” philosophy of design. Looking at cyclotron solid targets, uncertainties of the particle beam, material composition and geometry play a crucial role in determining the results. The difference between what has been designed and what can be effectively manufactured, where processes such as electroplating are poorly controllable and generate large non-uniformities in deposition, must also be considered. A digital twin, where the target geometry is 3D scanned from real models, can represent a good compromise for connecting “ideal” and “real” worlds. Looking at the (64)Ni(p,n)(64)Cu reaction, different Unstructured-Mesh MCNP6 models have been built starting from the 3D solid target system designed and put into operation by COMECER. A characterization has been performed considering the designed ideal target and a 3D scan of a real manufactured target measured with a ZEISS contact probe. Libraries and physics models have been also tested due to limited cross-section data. Proton spectra in the target volume, 3D proton-neutron-photon flux maps, average energies, power to be dissipated, shut-down dose-rate, (64)Cu yield compared with various sources of experimental data and beam axial shifting impact, have been estimated. A digital twin of the (64)Ni(p,n)(64)Cu production device has been characterized, considering the real measured target geometry, paving the way for a fully integrated model suitable also for thermal, structural or fluid-dynamic analyses
