Kick-off meeting

 

The kick-off meeting has taken place on the 1st of June 2018 at the Royal Belgian Institute for Space Aeronomy, Brussels. We have had fantastic speakers ! Apart from seminars from the members of the consortium (Prof. E. Artacho from CIC-nanoGUNE, Prof. J. Kohanoff from QUB, Dr. E. Botek from BISA and Dr. F. Da Pieve from BISA), seminars were given by Prof. F. Cleri from the University of Lille, Dr. Ir. Ann-Carine Vandaele (head of the Planetary Aeronomy group at BISA), Dr. J. Brown from TUDelft, and Dr. Olivier Van Hoey, expert scientist in radiation dosimetry at the Belgian Nuclear Research Center SCK-CEN. Here below you can find the Agenda of the mini-workshop. Abstracts are also available below.

 

Abstracts

Planetary Exploration

A.-C. Vandaele (1)

(1)Royal Belgian Institute for Space Aeronomy, Brussels, Belgium

I will present the Planetary Aeronomy Group and its different activities in space projects. this covers the design of space instruments, the participation to their manufacturing, testing and characterisation. The Planetary Aeronomy Group has been involved in several missions towards Venus (Venus Express with the SOIR instrument) and Mars (Mars Express, and now ExoMars with the NOMAD instrument), Jupiter (MAJIS) but also in missions looking at exoplanets (ARIEL). Our group has gained renown expertise in the analysis of remote sensing observations, and has developed its own radiative transfer code. Moreover, we are involved in modeling activities: 3D global circulation modeling of Mars, models describing radiative processes or the aerosols formation.

Towards a better understanding of Space Weather sources and effects

 E. Botek (1) , F. Da Pieve (1) and V. Pierrard (1)

(1) Royal Belgian Institute for Space Aeronomy, Brussels, Belgium

The Solar Wind group at the Space Physics division of BIRA intensively contributes to Space Weather research. Among the scientific efforts provided, models of solar wind sources and transport are developed in the group. We aim at better understanding the physical mechanisms governing the heliospheric dynamics and the high energy particles impacts on the Van Allen radiation belts, where outer space radiation is trapped at the Earth magnetic field. This radiation activity is of major concern for satellites design and operations. BIRA also participated on the development of instruments like EPT and IDEES to measure the high energy particle fluxes near earth. Presently, the Solar Wind group is in charge of analyzing and exploiting the data. This data is also provided in a Near Real Time status as one of the tools of ESA Space Situational Awareness project.

In collaboration with the group of Planetary Aeronomy, the Solar Wind group will also tackle the study of radiation effects on materials and human molecular constituents through the employment of classics and quantum mechanical tools in a challenging multiscale investigation. Some inspiring examples of material radiation shielding design are mentioning in the frame of planning future manned missions to the outer space.

 

Simulation of electron excitation processes when ions shoot through matter

 E. Artacho (1,2)

(1) CIC nanoGUNE Research Centre, San Sebastian, Spain

(2) University of Cambridge, UK

Ion projectiles shooting through condensed matter produce radiation damage of great importance for the nuclear and aerospace industries, as well as for radiation therapeutics. For projectile speeds above  0.1% of the speed of light the projectile energy is transmitted mostly to the host electrons. Various models have emerged during the last century to understand and describe the electronic stopping of the projectile, such as Lindhard's linear-response treatment of the problem or a fully non-linear theory for projectiles in an homogeneous electron liquid, well suited for simple-metal hosts. The problem is hard to treat quantitatively in general since electronic stopping represents a strongly non-equilibrium quantum problem. During the last decade, we and  others have been using time-dependent density-functional theory as follows: put a projectile in a simulation box, kick it hard, and follow the dynamics of the electrons in real time. I will present results of this direct method, which has shown to produce electronic stopping power values surprisingly similar to experimental ones in spite of the many approximations involved.

Radiation damage of biological systems from first-principles simulations

J. Kohanoff (1)

(1) Queen's University Belfast, UK

The initial stage of the irradiation process, both via energetic particles or electromagnetic radiation, consists of the ionization of the material and the consequent generation of secondary electrons, holes and radicals. These species diffuse through the sample experiencing inelastic collisions with the medium until they find an opportunity to react, and produce chemical modifications that lead to various types of damage. In the case of biological matter, damage to the genetic component (DNA) may cause the arrest of the cell cycle, mutations, and uncontrolled proliferation. This is linked to diseases like cancer and at the same time constitutes the basis for radiotherapies. But materials are subject to ionizing radiation in many other areas, such as radiation detectors, electronic devices in spacecrafts and satellites, structural components in nuclear power plants, and nuclear waste forms encapsulating disposed radioactive fuel and contaminated components. While the type of damage depends on the specific material and application, the underlying physics is similar, and is related to the fate of the reactive species generated in the irradiation process. We are studying the problem of electron and hole localization and chemical reactivity in a variety of systems using electronic structure calculations and first-principles molecular dynamics simulations.

This constitutes part of the activities of the recently created Centre for Advanced Interdisciplinary Radiation Research (CAIRR). In this talk I will present an assessment of the role of secondary electrons in the microscopic mechanisms that lead to DNA damage in a realistic environment, i.e. in the condensed phase and subject to thermal fluctuations. I will discuss the emergent picture in which a variety of protection mechanisms, which are not present in gas phase models, influence the feasibility of DNA strand breaks [1-6]. These results have been recently discussed at length in a recent review article [7]. 

References 

[1] M. Smyth and J. Kohanoff, Phys. Rev. Lett. 106, 238108 (2011) 

[2] M. Smyth and J. Kohanoff, J. Am. Chem. Soc. 134, 9122 (2012) 

[3] M. Smyth, J. Kohanoff and I. Fabrikant, J. Chem. Phys. 140, 184313 (2014) 

[4] Bin Gu, M. Smyth and J. Kohanoff, Phys. Chem. Chem. Phys. 16, 24350 (2014) 

[5] M. McAllister, M. Smyth, Bin Gu, G. Tribello, and J. Kohanoff, J. Phys. Chem. Lett. 6, 3091 (2015) [6] P.M. Dinh et al. in Nanoscale Insights into Ion-Beam Cancer Therapies, A. Solovyov (Ed.), (Springer, 2017) 

[7] J. Kohanoff, M. McAllister, G. Tribello, and Bin Gu, J. Phys. Condens. Matter 29, 383001 (2017)

 

Biophysical insights about the role of DNA strand breaks in cancer development and therapy

 F. Cleri (1)

(1) IEMN CNRS and Department of Physics, University of Lille, 59652 Villeneuve d’Ascq, France

Among the defects produced in DNA by various endogenous and external agents, single- and double-strand breaks (SSB and DSB) stand out as the most critical ones for cell survival and clonogenicity; errors in strand break repair can lead to neoplastic and EMT transformation; notably, the attempt at a controlled production of DSBs is at the heart of cancer radiotherapy. However, the detailed microscopic mechanisms of production of SSB and DSB defects in DNA and their molecular evolution are not well understood: practically, all the information is currently obtained from chemical methods, by post-processing nuclear material from cells fixed at much later stages after the time of irradiation; the biological-clinical relevance of defects is empirically deduced from "cell survival" curves, further interpreted by few-parameter phenomenological models (such as the venerable Linear-Quadratic model).

I will describe our wide-scoped biophysical program, involving biophysicists, engineers, biologists and clinicians, dedicated to the investigation of SSB and DSB production in both isolated DNA and in live cells, by photon radiation. As a key result, we demonstrated the first real-time observation of DNA degradation by a custom developed micro-electro mechanical device (MEMS), and developed a theoretical framework based on the statistical mechanics of randomly damaged bundles of elastic fibers. The model analysis with second-order kinetics allowed a peculiar interpretation of the experimental observations.

In parallel, we developed a program of in-vitro irradiation of fibroblast cells, to investigate the differential production of SSBs and DSBs as a function of various biological and physical parameters. Defect production was monitored by the fluorescence of target nuclear proteins, as well as comet assays. We developed a rich agent-based Monte Carlo simulation model, to test different hypotheses of cell population evolution under irradiation, and compare the results to the experimental observations.

In a third, very active line of research, we use molecular-scale simulations to investigate the early stages of defect formation and evolution. We performed extensive molecular dynamics simulations of DNA breaks both in the linker and nucleosomal portions of the chromatin. For the damage in the nucleosome, we performed record-length simulations up to 1.8 microseconds. The damaged structures are studied by essential dynamics, and by performing local force pulling with umbrella sampling. We use an accurate and elegant formulation of the covariant mechanical stress, to study the coupled bending and torsional stress in the nucleosome and its role in defect evolution. A recently started experimental part is carried out in this case by single-molecule force spectroscopy with optical tweezers, in collaboration with the University of Barcelona.

Monte Carlo simulation of early biological damage induced by ionising radiation at the DNA scale: overview of the Geant4-DNA project
 
J. M. C. Brown on behalf of the Geant4-DNA Collaboration

TU Delft, The Netherlands and Univ. of Wollongong, Australia

Understanding the fundamental mechanisms involved in the induction of biological damage by ionising radiation remains a major challenge of today's radiobiology research [1]. The Monte Carlo simulation of physical, physicochemical and chemical processes involved may provide a powerful tool for the simulation of early damage induction. The Geant4-DNA extension [2] of the general purpose Monte Carlo Geant4 simulation toolkit [3] aims to provide the scientific community with an open source access platform for the mechanistic simulation of such early damage. In this presentation I will give an overview of the Geant4-DNA project and discuss on-going developments.
 
References
[1] “Monte Carlo role in radiobiological modelling of radiotherapy outcomes,” Phys. Med. Biol., 57, pp. R75-R97 (2012).
[2] “Track structure modeling in liquid water: A review of the Geant4-DNA very low energy extension of the Geant4 Monte Carlo simulation toolkit,” Phys. Medica, 31, pp. 861-874 (2015).
[3] http://geant4.org

Radiation dosimetry in space with luminescent detectors and radiation transport simulations

O. Van Hoey (1)

(1) SCK•CEN, Belgian Nuclear Research Centre, Mol, Belgium

Radiation dose rates in space are typically more than two orders of magnitude higher than on earth.  Therefore, it is very important to monitor astronaut doses.  Also doses for biological experiments in space must be quantified in order to determine the possible relationship between observed biological effects and the radiation dose.  As the radiation field in space is strongly non-uniform and time dependent, this requires the use of compact passive radiation detectors. In order to cover the whole range of radiation types and energies present in space, one has to combine different types of passive detectors such as optically stimulated luminescence detectors (OSLDs), thermoluminescent detectors (TLDs) and track etch detectors (TEDs).

For many years the Belgian Nuclear Research Center SCK•CEN has been sending passive luminescent detectors for different experiments in Low Earth Orbit.  We usually send both TLDs (LiF:Mg,Ti nd LiF:Mg,Cu,P) and OSLDs (Luxel). In the framework of the international DOSIS and DOSIS 3D projects we have been sending our detectors to the ISS typically every 6 months since 2009 for mapping of the dose rates in the Columbus module.  Further, we have also regularly been sending our detectors together with biological experiments on the inside and outside of the ISS and inside the FOTON-M4 spacecraft.  In this contribution we will present our methodology and give an overview of the measurement results that were obtained.  We will also discuss the use of Monte Carlo radiation transport codes to characterize the detector response for different radiation types.

Space Radiation Environment at potential landing sites on Mars

F. Da Pieve (1), E. Botek (1) and A.C. Vandaele (1)

Royal Belgian Institute for Space Aeronomy, Brussels, Belgium

Space exploration is undergoing a rapid expansion. Several missions to Mars are already ongoing with orbiters and landers, and others are planned for the near future. Here, we present a study of the space radiation fluxes and doses at different interesting landing sites: the Gale crater, where the rover Curiosity of the Mars Science Laboratory mission has landed in 2012, the Oxia Planum region, which is in the final list of candidate sites for the ExoMars2020 rover, and the Nili Fossae region, which was on the top list of candidate sites for Curiosity. These three areas are characterized by several interesting mineralogical features, which hint at different alteration mechanisms in the geological and climate history of Mars, and which are of potential astrobiological interests. Oxia Planum and Gale Crater are rich in phyllosilicates minerals (able to trap water and organic molecules), Nili Fossae exhibits a rare carbonate exposure (which would explain a partial carbon sequestration from the past atmosphere), and both Nili Fossae and Gale crater have shown to be the source region of methane emissions. Being at mid-altitudes, such landing sites can also be considered for future manned missions, for which perspective scenarios have been already established, with short stays of about 30 days and long stays of about 600 days. We present some Monte Carlo radiation transport calculations of Galactic Cosmic Rays (GCRs) in solar quiet conditions and doses evaluated at these three landing sites, performed using the ESA’s MEREM model [1], via the interface SPENVIS [2]. The results suggest the importance of secondaries in evaluating the doses, small variation of doses when some difference of water amount in the soil is considered, and some (yet not understood) differences in the doses when diurnal variations are taken into account [see also [3]), which appear to be counterintuitive with respect to what expected in view of thermal tides of the atmosphere. Future improvements will include the study of the diurnal variation of the radiation environment when GCRs are modulated by transient events on the Sun, the use of particle transport models in a standalone mode (to improve statics and reduce errors) and possibly the inclusion of atmospheric profiles from climate models developed at our Institute, which might consider more detailed dust and water vapour condensation scenarios [4].

References

[1] S. McKenna-Lawlor et al, Icarus 218, 723 (2012)

[2] https://spenvis.oma.be

[3] J. Guo et al. J. Geophys.Res. Planets, 122, 329–341 (2017)

[4] L. Neary and F. Daerden,, Icarus 300, 458 (2017)

 

 

 

Contact: BIRA-IASB, Av. Circulaire 3, Brussels, Belgium.