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Design of innovative diamond detectors for beam monitoring in highly radiative environment for applications in nuclear and medical physics
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Développements théoriques pour les jets dans les collisions d’ions lourds
No full textThe quark-gluon plasma (QGP) is an exotic phase of matter, composed of deconfined quarks and gluons and is briefly created in heavy-ion collisions (HIC) at the LHC and at the RHIC. High-energy, self-collimated structures of final-state particles also created in HIC, called jets, probe the QGP, piercing through it on their way to the particle detector. In particular, as the jet propagates, it is quenched, shedding its energy through its interaction with the QGP. Quantum field theory at finite temperature – thermal field theory, is then an extremely powerful tool, capable of analytically quantifying how such a high-energy object interacts with a weakly coupled thermal bath. In this thesis, we work towards the computation of corrections (in the expansion of the strong coupling constant) to two quantities, which dictate how jets are quenched by the QGP. The first being the transverse momentum broadening coefficient, which describes how the jet diffuses in transverse momentum space through its interaction with the medium. We focus on the computation of logarithmically enhanced corrections, carefully showing how the thermal scale affects the logarithmic phase space. The second is the asymptotic mass, which can be thought of as a shift in the jet’s dispersion relation as it undergoes forward scattering with the medium’s constituents. We complete a matching calculation, which rids the mass’ classical corrections of any unphysical divergences, while also beginning the completion of its full two-loop, quantum correctionsLe plasma de quarks et de gluons (QGP) est une phase exotique de la matière composée de quarks et de gluons déconfinés. Il se forme brièvement lors des collisions d’ion lourds (HIC) au LHC et RHIC. Dans le cadre de ces collisions, des structures hautement énergétiques d'états finaux, connues sous le nom de jets, servent de sondes idéales. Ces jets pénètrent le QGP en chemin vers les détecteurs de particules. Lorsque le jet se propage il est éteint, perdant son énergie par son interaction avec le QGP. La théorie quantique des champs à température finale – la théorie des champs théoriques, est un outil extrêmement puissant qui est capable de quantifier analytiquement la façon dont un objet de si haute énergie interagit avec un bain thermique faiblement couplé. Dans cette thèse, notre travaille se concentre sur le calcul des corrections (dans l'expansion de la constante de couplage fort) de deux quantités, qui déterminent la manière dont les jets sont éteints par le QGP. Le premier est le coefficient d'élargissement du moment transverse, qui décrit comment le jet se diffuse dans l'espace du moment transverse par son interaction avec le milieu. Notre attention se porte sur le calcul des corrections logarithmiques associées à cette quantité. La seconde est la masse asymptotique, qui peut être considérée comme un changement dans la relation de dispersion du jet lorsqu'il subit une diffusion vers l'avant avec les constituants du milieu. Nous effectuons un calcul correspondant, en nous basant sur certains résultats de la littérature pour débarrasser les corrections classiques de la masse de toute divergence non physique, tout en commençant à compléter ses corrections complètes à une boucl
Photoproduction of J/ and dileptons in Pb-Pb collisions with nuclear overlap
No full textInternational audiencePhoton-photon reactions and the production of J/ meson through photonuclear reactions have been extensively studied in ultra-peripheral heavy-ion collisions, in which the impact parameter is larger than twice the nuclear radius. In recent years, coherently photoproduced J/ and dilepton production via photon-photon interactions have also been observed in nucleus-nucleus (A-A) collisions with nuclear overlap. The former can help to constrain the nuclear gluon distributions at low Bjorken- and high energy, while the latter could be used to further map the electromagnetic fields produced in heavy-ion collisions. In addition, these measurements can shed light on the theory behind photon-induced reactions in A-A collisions with nuclear overlap, including possible interactions of the measured probes with the formed and fast expanding quark-gluon plasma. Since the produced quarkonium is expected to keep the polarization of the incoming photon due to -channel helicity conservation, the photoproduction origin of the J/ yield excess at very low transverse momentum, , can be confirmed by the measurement of the J/ polarization. The ALICE detector can perform quarkonium production measurements at both mid () and forward () rapidities down to . In the following, the new ALICE measurements of the J/-differential cross section and the first polarization results of coherently photoproduced J/ via the dimuon decay channel at forward rapidity in Pb-Pb collisions at 5.02 TeV are reported. Additionally, the measurement of an excess with respect to expectations from hadronic production in the dielectron yield, at low mass and , at midrapidity in Pb-Pb collisions at 5.02~TeV, is presented. The results are compared with available theoretical models
Effect of Curing Time and Water to Binder Ratio on Magnesium Potassium Phosphate Cement Exposed to Gamma Irradiation
No full textInternational audienceAbstract Metallic Waste (MW) is one type of low and intermediate radioactive waste. It is estimated that the current fleet of civil nuclear power reactors throughout the world would produce about 500 000 tons of this kind of waste in the near future due to their advancing age. MW comes mainly from spent fuel reprocessing facility, storage ponds and reactor primary circuit systems. MW typically consists of stainless steels or nickel alloys, which are the primary components of nuclear installations. Aluminum and beryllium belong to this waste category and are also called Reactive Metallic Waste (RMW). The major risk involved in trying to encapsulate RMW is corrosion, resulting in hydrogen release. In a specific pH range, MW forms a stable protective oxide coating. It is therefore important to employ matrices that provide a favorable environment, reducing the reactivity of MW and thus the production of hydrogen gas. Ordinary Portland Cement (OPC) is not recommended for RMW encapsulation due to its extremely alkaline pore solution which favors corrosion. Moreover, the high content of free water may further contribute to H2 production due to water radiolysis. One of the potential matrices being considered for the encapsulation of RMW is Magnesium Potassium Phosphate Cement (MKPC), produced from the acid-base reaction between magnesium oxide (MgO) and dihydrogen potassium phosphate salt (KH2PO4). The lower pH ensures RMW remains inside the passivation range, while maintaining high performance characteristics, such as compressive strength and stability towards leaching. To assess the applicability of MKPC as a containment matrix for radioactive RMW, it is important to evaluate its resistance to radiation, thus ascertaining the radiolytic production of H2, as well as its durability. In this study, a Cs-137 gamma source has been used to irradiate: i. at 200 kGy samples with different curing ages, ranging from few days to 28 days, to shed light on the effects of irradiation during the curing period, ii. at different doses samples with the same 28 days curing time (reference) to better understand the effect of the total absorbed dose, iii. at 200 kGy samples with slightly different water to binder ratio to investigate the impact on radiolytic production of H2. To evaluate possible radiation-induced modification of the structure and morphology of the MKPC, XRD and SEM-EDX have been used. Micro-gas chromatography analyses have been performed to determine the amount of radiolytic H2 released. The water immersion resistance of irradiated MKPC is also evaluated by a standard leaching protocol. Non irradiated MKPC samples have been tested as reference. The encouraging results obtained in this work further promote the use of MKPC for the encapsulation of RMW.</jats:p
Core-corona effect in hadron collisions and muon production in air showers
No full textInternational audienceIt is very well known that the fraction of energy in a hadron collision going into electromagnetic particles (electrons and photons, including those from decays) has a large impact on the number of muons produced in air shower cascades. Recent measurements at the LHC confirm features that can be linked to a mixture of different underlying particle production mechanisms such as a collective statistical hadronization (core) in addition to the expected string fragmentation (corona). Since the two mechanisms have a different electromagnetic energy fraction, we present a possible connection between statistical hadronization in hadron collisions and muon production in air showers. Using a novel approach, we demonstrate that the core-corona effect as observed at the LHC could be part of the solution for the lack of muon production in simulations of high energy cosmic rays. To probe this hypothesis, we study hadronization in high energy hadron collisions using calorimetric information over a large range of pseudorapidity in combination with the multiplicity of central tracks. As an experimental observable, we propose the production of energy in electromagnetic particles versus hadrons, as a function of pseudorapidity and central charged particle multiplicity
Measurement of inclusive J/ pair production cross section in pp collisions at TeV
No full textInternational audienceThe production cross section of inclusive J/ pairs in pp collisions at a centre-of-mass energy TeV is measured with ALICE. The measurement is performed for J/ in the rapidity interval . The production cross section of inclusive J/ pairs is reported to be nb in this kinematic interval. The contribution from non-prompt J/ (i.e. originated from beauty-hadron decays) to the inclusive sample is evaluated. The results are discussed and compared with data
Dynamical mechanisms for deuteron production at mid-rapidity in relativistic heavy-ion collisions from SIS to RHIC energies
No full textInternational audienceThe understanding of the mechanisms for the production of weakly bound clusters, such as a deuteron , in heavy-ion reactions at mid-rapidity is presently one of the challenging problems which is also known as the "ice in a fire" puzzle. In this study we investigate the dynamical formation of deuterons within the Parton-Hadron-Quantum-Molecular Dynamics (PHQMD) microscopic transport approach and advance two microscopic production mechanisms to describe deuterons in heavy-ion collisions from SIS to RHIC energies: kinetic production by hadronic reactions and potential production by the attractive potential between nucleons. Differently to other studies, for the "kinetic" deuterons we employ the full isospin decomposition of the various , channels and take into account the finite size properties of the deuteron by means of an excluded volume condition in coordinate space and by the projection onto the deuteron wave function in momentum space. We find that considering the quantum nature of the deuteron in coordinate and momentum space reduces substantially the kinetic deuteron production in a dense medium as encountered in heavy-ion collisions. If we add the "potential" deuterons by applying an advanced Minimum Spanning Tree (aMST) procedure, we obtain good agreement with the available experimental data from SIS energies up to the top RHIC energy
Diatom DNA metabarcoding to assess the effect of natural radioactivity in mineral springs on ASV of benthic diatom communities
No full textInternational audienceLittle is still known about the low dose effects of radiation on the microbial communities in the environment. Mineral springs are ecosystems than can be affected by natural radioactivity. These extreme environments are, therefore, observatories for studying the influence of chronic radioactivity on the natural biota. In these ecosystems we find diatoms, unicellular microalgae, playing an essential role in the food chain. The present study aimed to investigate, using DNA metabarcoding, the effect of natural radioactivity in two environmental compartments (i.e. spring sediments and water) on the genetic richness, diversity and structure of diatom communities in 16 mineral springs in the Massif Central, France. Diatom biofilms were collected during October 2019, and a 312 bp region of the chloroplast gene rbcL (coding for the Ribulose Bisphosphate Carboxylase) used as a barcode for taxonomic assignation. A total of 565 amplicon sequence variants (ASV) were found. The dominant ASV were associated wit
Effects of vapor hydration and radiation on the leaching behavior of nuclear glass
No full textInternational audience•Chemical durability of nuclear glass was studied by considering combined effects of vapor hydration and radiation.•No significant impact of ionizing effect was observed on the leaching behavior of hydrated glass.•The presence of pre-hydrated layer, especially the secondary phases, showed major impacts on glass chemical durability. During the long-term disposal of high-level nuclear waste glass in the geological disposal facility, the nuclear glass could be exposed to an unsaturated vapor environment prior to the direct contact with groundwater. Additionally, glass will experience damages due to self-irradiation. In this study, experiments were performed to investigate the chemical durability of glass after being hydrated and irradiated. This study proposes an attempt to investigate the impact of ionizing effect by applying alpha or gamma radiations to the pre-hydrated glass. The impact on chemical durability is evaluated by leaching the hydrated and irradiated glass samples. With the studied doses, 8 Giga Gy of alpha radiation or 100 kGy of gamma radiation, no significant modification of chemical durability is observed upon irradiation. On the other hand, leaching of pre-hydrated glass shows the increase of the initial release of Si, which is considered to be related to the dissolution of secondary phases. Furthermore, the total dissolution of hydrated layer is observed, which would result in the release of radionuclides at the same rate as Si does and thus needs further investigation
