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Isospin transport phenomena for the systems Kr+Ca at 35 MeV/nucleon
No full textInternational audienceExperimental data concerning isospin transport phenomena for the systems Kr80+Ca40,48 at 35 MeV/nucleon are presented. Data have been collected with four FAZIA blocks; this data set is the same analyzed in S. Piantelli , Phys. Rev. C 101, 034613 (2020)2469-998510.1103/PhysRevC.101.034613. The isotopic composition of the QuasiProjectile residue (up to Z around 25) and of its decay products in the two reactions are compared, finding a neutron enrichment when the target is Ca48. The isotopic composition of the emitted light charged particles (LCP) and intermediate mass fragments (IMF) was also investigated in different windows of velocity. The obtained results have been compared with the prediction of the transport model AMD followed by the statistical code GEMINI (used as an afterburner), with different recipes for the density dependence of the symmetry energy term in the nuclear equation of state. A weak indication in favor of a stiff symmetry energy emerges when the fragments emitted at midvelocity are examined
A Pseudo-TOF Image Reconstruction Approach for Three-Gamma Small Animal Imaging
No full textInternational audienceIn this article, we propose a novel image reconstruction technique for three-gamma (3- γ ) imaging systems that aims at reaching high image quality with a low statistics. The proposed approach is based on the utilization of a ( β+ , γ ) emitter and a liquid xenon (LXe) camera, the Xenon Medical Imaging System 2 (XEMIS2), that is currently being manufactured. The third gamma emitted is more energetic than the two 511-keV photons and interacts mostly through Compton scattering in LXE; therefore, we utilize the interactions’ position and the deposited energy to define a Compton cone that gives the direction from where the third gamma was emitted. The intersection point between the cone and the two coincidence photons’ lines of response (LOR) is the center of the probability distribution function (PDF), a resolution model similar to that of time-of-flight (TOF)-positron emission tomography (PET). The third gamma’s information is used to narrow the LOR portion employed during reconstruction. In this article, we show reconstruction results from simulation using highly realistic Geant4 Application for Emission Tomography (GATE) Monte Carlo simulation of the imaging device and a NEMA-like phantom
Radiological risk in the global burden of disease
No full textInternational audienceThe contribution of radioactivity to the overall burden of disease has rarely been put in context of overall pollution of our environment, even though it has got high public interest as standalone problem. Indeed, radioactive pollution is not even mentioned in World health statistics 2020. Is it less important for health than in public policies? There is no general accepted common frame of reference, which would allow comparing risks of none-radioactive and radioactive pollutants and sharing methods for risk management. Annually, the WHO compares the impact of chemotoxic risk with those of many other risk factors, using the global burden of diseases and the disability adjusted loss of life years (DALY), a concept that has only recently been applied to radioactive contamination by Japanese researchers. Despite some effort for risk comparison, there seems to be a silent agreement between the experts from IAEA, WHO, OECD-NEA, ICRP and many national bodies as well as antinuclear civil society groups, in the field of assessing the health impact of radiotoxicity to treat radioactivity apart. Maybe, one of the reasons is that on global level, the largest impact of radiation stems from natural radioactivity. Taking for example the public debate on potential risks from future radioactive waste disposal sites. Compared to the risk from natural radiation, the risk contribution to future generations from a radioactive waste disposal site is expected to be thousand to millon times lower. And this risk is not for the next 10000 yrs but only for the time very much beyond, close to the age of the homo sapiens. Expressed in DALY, the number of cancers cases formally attributable to a life long exposure situation by natural radiation of 1 mSv corresponds for example for the japaneze population to a reduction of life expectancy of about 1 to 1.5 month for man or woman. Hence, the impact of a radioactive waste disposal site on potential reduction of life expencency of future generations will be well below 1 day. Probably, life expectency is even increased by geological disposal, as it reduces the risk stemming from surface storage sites, which are difficult to be controlled over the time of many generations. The ICRP shall help understanding radiological risks in the overall context of other risks, the society is taking everyday
Investigation of europium retention on Callovo-Oxfordian clay rock (France) by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and percolation experiments in microcells
No full textInternational audienceClay-rock formations are under investigation in several countries as a potential host of radioactive waste repositories. In order to assess the long-term safety of these concepts, retention distribution data (Rd) are needed to describe the interaction between radionuclides and natural rock. While Rd values obtained from batch-type experiments with dispersed material are essential for the development of retention models, it is also important to generate retention data under more realistic conditions, in particular with compact samples. Specifically, the literature data on strongly retained radionuclides proves to be very scarce. The present study focuses on the retention of europium (Eu) at trace concentrations on clay samples extracted from the Callovo-Oxfordian (COx) formation in France. Rd values obtained with compact COx samples are assessed by a methodology coupling percolation experiments (in pressurized microcells), performed using submillimeter-sized samples in thickness, and Laser Ablation Inductively Coupled Plasma Mass Spectrometry measurements. The Rd found at trace concentrations under non-transient conditions are high (Rd > 104 mL g−1) and in agreement with those recorded under classical batch-type conditions or those deduced from the distribution of naturally-occurring Eu between the pore water and the clay rock. They can be described by modeling with existing sorption databases, considering an adsorption process only on the clay fraction. This was validated by solid state LA-ICP-MS analyses of one of the Eu-spiked COx samples; the added europium was found exclusively in the COx clay fraction
Carbonation Reaction Mechanisms of Portlandite Predicted from Enhanced Ab Initio Molecular Dynamics Simulations
No full textInternational audienceGeological carbon capture and sequestration (CCS) is a promising technology for curbing the global warming crisis by reduction of the overall carbon footprint. Degradation of cement wellbore casings due to carbonation reactions in the underground CO2 storage environment is one of the central issues in assessing the long-term success of the CCS operations. However, the complexity of hydrated cement coupled with extreme subsurface environmental conditions makes it difficult to understand the carbonation reaction mechanisms leading to the loss of well integrity. In this work, we use biased ab initio molecular dynamics (AIMD) simulations to explore the reactivity of supercritical CO2 with the basal and edge surfaces of a model hydrated cement phase—portlandite—in dry scCO2 and water-rich conditions. Our simulations show that in dry scCO2 conditions, the undercoordinated edge surfaces of portlandite experience a fast barrierless reaction with CO2, while the fully hydroxylated basal surfaces suppress the formation of carbonate ions, resulting in a higher reactivity barrier. We deduce that the rate-limiting step in scCO2 conditions is the formation of the surface carbonate barrier which controls the diffusion of CO2 through the layer. The presence of water hinders direct interaction of CO2 with portlandite as H2O molecules form well-structured surface layers. In the water-rich environment, CO2 undergoes a concerted reaction with H2O and surface hydroxyl groups to form bicarbonate complexes. We relate the variation of the free-energy barriers in the formation of the bicarbonate complexes to the structure of the water layer at the interface which is, in turn, dictated by the surface chemistry and the degree of nanoconfinement
Equation of state and the topology of hydrogen bonding networks in water at high temperatures and pressures
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Bremsstrahlung X-rays as a non-invasive tool for ion beam monitoring
No full textInternational audienceNon-invasive beam monitoring tools are required to guarantee the delivered dose during ion irradiation. Measuring bremsstrahlung X-rays emitted directly from the irradiated medium is a promising approach. This work presents the feasibility of the method for different incident particles with different energies. A PMMA target was bombarded with helium ions of 68 MeV and protons beams of 30, 40, and 50 MeV. The bremsstrahlung signal, measured with a SDD, was in the magnitude of 10 4 X-rays/nC, indicating the significant sensitivity of the method. A good agreement was found (<6%) between the experimental and simulation bremsstrahlung spectra. For a thick target, the bremsstrahlung yield saturates and is directly proportional to the beam energy and the deposited dose at the surface. In addition, the bremsstrahlung spectrum shape contains information about the beam energy. Therefore, the bremsstrahlung signal gives access to the deposited dose and beam energy with precision depending on the experimental uncertainties
Experimental Evidence for an Attractive p- Interaction
No full textInternational audienceThis Letter presents the first experimental evidence of the attractive strong interaction between a proton and a ϕ meson. The result is obtained from two-particle correlations of combined p-ϕ⊕ p¯-ϕ pairs measured in high-multiplicity pp collisions at s=13 TeV by the ALICE Collaboration. The spin-averaged scattering length and effective range of the p-ϕ interaction are extracted from the fully corrected correlation function employing the Lednický-Lyuboshits approach. In particular, the imaginary part of the scattering length vanishes within uncertainties, indicating that inelastic processes do not play a prominent role for the p-ϕ interaction. These data demonstrate that the interaction is dominated by elastic p-ϕ scattering. Furthermore, an analysis employing phenomenological Gaussian- and Yukawa-type potentials is conducted. Under the assumption of the latter, the N-ϕ coupling constant is found to be gN-ϕ=0.14±0.03(stat)±0.02(syst). This work provides valuable experimental input to accomplish a self-consistent description of the N-ϕ interaction, which is particularly relevant for the more fundamental studies on partial restoration of chiral symmetry in nuclear medium