HAL-IN2P3
Not a member yet
78719 research outputs found
Sort by
Long-duration in situ monitoring of H2O and CH4 in the equatorial tropopause with the Pico-STRAT Bi Gaz balloon borne laser diode spectrometer during the Strateole 2 campaign
No full textInternational audienceThe Pico-STRAT Bi Gaz spectrometer provides in situ mixing ratio measurements of H2O and CH4 (or CO2 ) under balloon. The instrument was flown in the tropical upper troposphere and lower stratosphere in 2019/2020 and 2021/2022 during the Strateole 2 campaigns for a total of five flights of 20 to 80 days between 18 and 20 km altitude. In this frame, in situ measurements of water vapor and methane were performed every 4 to 12 minutes in the equatorial tropopause layer. On several occasions, water vapor measurements of Pico-STRAT Bi Gaz have been compared with localized measurements from the FLASH-B Lyman-α hygrometer and vertical profiles of the NOAA Global Monitoring Laboratory (GML) frost point hygrometer over Hilo, Hawaii. Pico-STRAT Bi Gaz measurements agreed with the FLASH-B hygrometer to within 2.2 ± 5.3 % between 18.2 and 18.7 km in 2021 and to within 1.3 ± 5.3 % near 19 km in December 2019. Pico-STRAT Bi Gaz agreed with NOAA’s FPH hygrometer to within 1.2 ± 4.1% between 18 and 19 km on four occasions during the two campaigns. These are within both instruments’ uncertainties. Methane measurements from Pico-STRAT Bi Gaz have been compared with in situ measurements from the Whole Air Sampler instrument (WAS), flown aboard the NASA WB-57 aircraft during the ACCLIP 2022 campaign over South Korea, eight months after the Pico-STRAT Bi Gaz overpass. The relative difference between both instruments is found to be of (−0.1 ± 0.9) % within the altitude range from 17 to 19 km and within the Pico-STRAT measurement uncertainty
Diffusion studies in UO2 with an improved tight-binding potential: SMTB-QB
No full textInternational audienceThe theoretical modeling of metal oxides represents a fundamental challenge in materials science due to their complex iono-covalent bonding, multiple valence states, and the crucial role of defects in determining their physical properties. Among these materials, uranium dioxide (UO₂) stands as both a technologically important compound and a model system for studying actinide oxides. We present here an improved tight-binding potential, SMTB-QB, which introduces variable charges ensuring local electroneutrality at the bond level. This key feature enables an accurate description of charged defects, the emergence of an electronic gap, and the ability to handle multiple valence states of the same cation (e.g. U³⁺, U⁴⁺, U⁵⁺, etc.). The model extends the capabilities of previous potentials while maintaining computational efficiency applicable to various oxide systems. Its accuracy is validated through extensive comparisons with DFT calculations and experimental data properties of UO₂. Using molecular dynamics simulations, we investigate oxygen and uranium diffusion mechanisms across different temperature ranges and stoichiometries (UO₂±ₓ). Our results reveal three distinct diffusion regimes for oxygen, with migration energies of 0.47 ± 0.03 eV in UO₂₋ₓ and 0.79 ± 0.03 eV in UO₂₊ₓ below 2400 K, converging to an activation energy of 3.67 ± 0.14 eV above 2500 K regardless of stoichiometry. For uranium diffusion, we demonstrate a vacancy-mediated mechanism with a migration energy of 4.07 ± 0.76 eV in stoichiometric UO₂, which shows agreement with experimental data. The SMTB-QB potential thus provides a robust framework for studying nuclear fuel materials and potentially other complex oxide systems
Cosmological neutrino mass: a frequentist overview in light of DESI
No full textInternational audienceWe derive constraints on the neutrino mass using a variety of recent cosmological datasets, including DESI BAO, the full-shape analysis of the DESI matter power spectrum and the one-dimensional power spectrum of the Lyman- forest (P1D) from eBOSS quasars as well as the cosmic microwave background (CMB). The constraints are obtained in the frequentist formalism by constructing profile likelihoods and applying the Feldman-Cousins prescription to compute confidence intervals. This method avoids potential prior and volume effects that may arise in a comparable Bayesian analysis. Parabolic fits to the profiles allow one to distinguish changes in the upper limits from variations in the constraining power of the different data combinations. We find that all profiles in the CDM model are cut off by the bound, meaning that the corresponding parabolas reach their minimum in the unphysical sector. The most stringent 95% C.L. upper limit is obtained by the combination of DESI DR2 BAO, Planck PR4 and CMB lensing at 53 meV, below the minimum of 59 meV set by the normal ordering. Extending CDM to non-zero curvature and CDM relaxes the constraints past 59 meV again, but only CDM exhibits profiles with a minimum at a positive value. Using a combination of DESI DR1 full-shape, BBN and eBOSS Lyman- P1D, we successfully constrain the neutrino mass independently of the CMB. This combination yields meV (95% C.L.). The addition of DESI full-shape or Lyman- P1D to CMB and DESI BAO results in small but noticeable improvement of the constraining power of the data. Lyman- free-streaming measurements especially improve the constraint. Since they are based on eBOSS data, this sets a promising precedent for upcoming DESI data
Measuring short-range correlations and quasi-elastic cross sections in A(e,e') at x>1 and modest Q
No full textInternational audienceWe present results from the Jefferson Lab E08-014 experiment, investigating short-range correlations (SRC) through measurements of absolute inclusive quasi-elastic cross sections and their ratios. This study utilized 3.356 GeV electrons scattered off targets including H, He, He, C, Ca, and Ca, at modest momentum transfers () did not yield a clear plateau; instead, the data diverged from the predicted 3N-SRC behavior as momentum transfer increased. However, when analyzed in terms of the struck nucleon's light-cone momentum, the data exhibited the opposite trend, progressively approaching the predicted 3N-SRC plateau. These observations suggest that future measurements at higher energies may facilitate a definitive isolation and identification of 3N-SRCs
Operational experience and performance of the Silicon Vertex Detector after the first long shutdown of Belle II
No full textInternational audienceIn 2024, the Belle II experiment resumed data taking after the Long Shutdown 1, which was required to install a two-layer pixel detector and upgrade accelerator components. We describe the challenges of this shutdown and the operational experience thereafter. With new data, the silicon-strip vertex detector (SVD) confirmed the high hit efficiency, the large signal-to-noise ratio, and the excellent cluster position resolution. In the coming years, the SuperKEKB peak luminosity is expected to increase to its target value, resulting in a larger SVD occupancy caused by beam background. Considerable efforts have been made to improve SVD reconstruction software by exploiting the excellent SVD hit-time resolution to determine the collision time and reject off-time particle hits. A novel procedure to group SVD hits event-by-event, based on their time, has been developed using the grouping information during reconstruction, significantly reducing the fake rate while preserving the tracking efficiency. The front-end chip (APV25) is operated in the multi-peak mode, which reads six samples. A 3/6-mixed acquisition mode, based on the timing precision of the trigger, reduces background occupancy, trigger dead-time, and data size. Studies of the radiation damage show that the SVD performance will not seriously degrade during the lifetime of the detector, despite moderate radiation-induced increases in sensor current and strip noise
Next Generation Multi-element monolithic Germanium detectors for Spectroscopy: First integration at ESRF facility
No full textInternational audienceThe XAFS-DET work package of the European LEAPS-INNOV project is developing a high-purity Germanium detectors for synchrotron applications requiring spectroscopic-grade response. The detectors integrate three key features: (1) newly designed monolithic Germanium sensors optimised to mitigate charge-sharing events, (2) an improved cooling and mechanical design structure supported by thermal simulations, and (3) complete electronic chain featuring a low-noise CMOS technology-based preamplifier. enabling high X-ray count rate capability over a broad energy range (5-100 keV). This paper discusses the first integration and characterization of one of the two multi-element Ge detectors at the European Synchrotron Radiation Facility (ESRF). The integration phase included validating high-throughput front-End electronics, integrating them with the Ge sensor, and operating them at liquid nitrogen temperature, in addition to the experimental characterization, which consists of electronics noise study and spectroscopic performance evaluation
Precision cross-sections for advancing cosmic-ray physics and other applications: a comprehensive programme for the next decade
No full textInternational audienceCosmic-ray physics in the GeV-to-TeV energy range has entered a precision era thanks to recent data from space-based experiments. However, the poor knowledge of nuclear reactions, in particular for the production of antimatter and secondary nuclei, limits the information that can be extracted from these data, such as source properties, transport in the Galaxy and indirect searches for particle dark matter. The Cross-Section for Cosmic Rays at CERN workshop series has addressed the challenges encountered in the interpretation of high-precision cosmic-ray data, with the goal of strengthening emergent synergies and taking advantage of the complementarity and know-how in different communities, from theoretical and experimental astroparticle physics to high-energy and nuclear physics. In this paper, we present the outcomes of the third edition of the workshop that took place in 2024. We present the current state of cosmic-ray experiments and their perspectives, and provide a detailed road map to close the most urgent gaps in cross-section data, in order to efficiently progress on many open physics cases, which are motivated in the paper. Finally, with the aim of being as exhaustive as possible, this report touches several other fields -- such as cosmogenic studies, space radiation protection and hadrontherapy -- where overlapping and specific new cross-section measurements, as well as nuclear code improvement and benchmarking efforts, are also needed. We also briefly highlight further synergies between astroparticle and high-energy physics on the question of cross-sections
Quantum vs. semiclassical description of in-QGP quarkonia in the quantum Brownian regime
No full textInternational audienceIn this work, we explore the range of validity of the semiclassical approximation of a quantum master equation designed to describe the dynamics in a quark gluon plasma at various temperatures, in the quantum Brownian regime. We perform a comparative study of various properties, e.g. the charmonia yield, of the Wigner density obtained with the Lindblad equation and with the associated semiclassical Fokker-Planck equation. The semiclassical description is found to reproduce with a remarkable accuracy the results obtained through the full quantum description. We show that, to a large extent, this can be attributed to the non-unitary components of the dynamics that result from the contact of the subsystem with the thermal bath, leading to a rapid classicalization of the subsystem
Deuteron-induced nuclear reactions to produce Lu: Extension of cross-sections data up to 33 MeV and impact on purity
No full textInternational audienceActivation cross-sections of lutetium and ytterbium radionuclides have been measured by deuteron-induced nuclear reaction on natYb(d,x) at the GIP ARRONAX (Saint-Herblain, France) cyclotron facility with a beam energy up to 33 MeV using the stacked-foil activation technique combined with high resolution γ-ray spectrometry. The measured experimental values enable the extension of the cross-section to higher energies. As a primary objective, we have focused on the cumulative measurement of the direct and indirect production routes of the therapeutic radioisotope 177gLu, via 176Yb(d,n) 177g,mLu and 176Yb(d,p) 177Yb →177gLu respectively. Post-irradiation gamma analysis, including a long gamma counting period, was performed to calculate the yield of the undesirable metastable isotopic impurity 177mLu. The results showed that it was found to be lower than our detection limit i.e. <0.0005% of 177gLu yield. Thick target yields for all detected radionuclides are also calculated in this paper. These measurements enabled the estimation of the production yield and isotopic purity of 177Lu obtained via deuteron-induced nuclear reactions for large production batches using highly enriched 176Yb2O3 samples (>99.5%). •Cross-section measurement of the theranostic radioisotope 177Lu induced by deuterons up to 33 MeV.•Metastable impurity 177mLu below the detection limit (<0.0005% of 177gLu yield).•Production yields and isotopic purities estimated from enriched 176Yb2O3 samples (>99.5%)
Fusion of C+Si at deep sub-barrier energies
No full textInternational audienceThe existence of fusion hindrance is not well established in light heavy-ion systems. Studying slightly heavier cases allows extrapolating the trend to light systems of astrophysical interest. Fusion of 12C + 28Si has been measured down to deep sub-barrier energies, using 28Si beams from the XTU Tandem accelerator of LNL on thin 12C targets. The fusion-evaporation residues were detected by a detector telescope following an electrostatic beam separator, and coincidences between the gamma-ray array AGATA and segmented silicon detectors DSSD were performed, where the evaporated light charged particles were identified by pulse shape analysis. Fusion cross sections have been obtained in the wide range 150 mb-42 nb. Coupled-channel (CC) calculations using a Woods-Saxon potential reproduce the data above 0.1 mb. Below that, hindrance shows up and the CC results overestimate the cross sections which get close to the one-dimensional potential tunnelling limit. This suggests that the coupling strengths gradually vanish, as predicted by the adiabatic model. The hindrance threshold follows a recently updated phenomenological systematics