arXiv subjects

M. Dupont

Publications and source records attributed to M. Dupont.

7 recordsLinked to original sources

arXiv2026

TIARA: a fast gamma-ray detector for range monitoring in Proton Therapy

We developed a novel gamma-ray detection system (TIARA) for range monitoring in Particle Therapy. The system employs Cherenkov-based gamma-ray detection modules arranged around the target or patient, operated in time coincidence with a fast plastic beam monitor (described in a separate paper). This work focuses on the design and comprehensive characterization of the gamma-ray detection module. It consists of a monolithic PbF$_2$ crystal (2 $\times$ 1.5 $\times$ 1.5 cm$^{3}$) coupled to a 2 $\times$ 2 SiPM matrix from Hamamatsu. A series of beam tests at different clinical facilities (MEDICYC and ProteusOne in France, CNAO in Italy) enabled the determination of the detector time resolution under various conditions, with values ranging from 222 to 283 ps FWHM (Full Width Half Maximum). Monte Carlo simulations including the optical response of PbF$_2$ allowed for the determination of the detection efficiency as a function of particle type and energy. For the final TIARA prototype, which will be composed of 30 modules, an overall detection efficiency of 0.45% is expected. Comparison with experimental data confirmed that the modules are effectively insensitive to neutrons, yielding an excellent signal-to-noise ratio (SNR), with an estimated SNR of 17 for a module placed at 25 cm from the 148 MeV proton beam axis. These features translate into high range accuracy: while the performance varies with beam energy and irradiation conditions, a range accuracy of 3.3 mm at 2$\sigma$ significance level was achieved at low intensity with 63 MeV protons at MEDICYC, for a small irradiation spot of $\mathbf{\sim}$10$\mathbf{^{7}}$ protons.

physics.ins-det↗

arXiv2026

Magnetic field-induced phases in a model S=1 Haldane chain system

An $S=1$ Haldane chain is a one-dimensional (1D) quantum magnet where strong fluctuations result in quantum disordered singlet ground state with a gapped excitation spectrum. The gap magnitude is primarily set by the dominant intrachain interaction ($J_\text{1D}$). An applied magnetic field closes the gap at $B_\text{c1}$ and drives the system into a gapless Tomonaga-Luttinger liquid (TLL) regime, followed by, at lower temperatures, a Bose-Einstein condensate (BEC) ground state, persisting up to $B_\text{c2} \propto 4 J_\text{1D}/g\mu_B$. Almost all previously studied experimental realizations of such systems were based on transition-metal complexes which typically suffer from intrinsic anisotropies or large $J_\text{1D}$ values, limiting the access to the full theoretical phase diagram. We report a comprehensive study of TLL and BEC phases in the organic Haldane chain system 3,5-bis(N-tert-butylaminoxyl)-3'-nitrobiphenyl (BoNO). The absence of anisotropy and a moderate $J_\text{1D}$ enable exploration of the complete $B-T$ phase diagram. Through $^1$H nuclear magnetic resonance, combined with theoretical analysis, we characterize the TLL properties, map the BEC phase boundary $T_c (B)$, determine the associated critical exponent $\nu \approx 0.66$ at $B_\text{c2}$, and demonstrate universal quasiparticle scaling in the quantum-critical regime. These results provide full experimental validation of theoretical predictions for field-induced phases in an $S=1$ Haldane chain, made over two decades ago.

cond-mat.str-el↗

arXiv2023

First ClearMind gamma detector prototype for TOF-PET imaging

The ClearMind project aims to develop a TOF-PET position-sensitive detection module optimized for time and spatial resolutions and detection efficiency. For this, we use a 59 mm $\times$ 59 mm $\times$ 5 mm monolithic PbWO$_4$ (PWO) crystal, which is encapsulated within a commercial Micro-Channel Plate Photomultiplier tube MAPMT253 with a bialkali photocathode directly deposited on the crystal. We report the proof of concept of the directly deposited of a bialkali photocathode on a PWO crystal and its stability over time. The full calibration of the ClearMind photodetector module in the single-photoelectron regime is described. We measured a time resolution of 70 ps FWHM using a 20 ps pulsed laser. We present the performance of the prototype used in coincidence with a 3 $\times$ 3 $\times$ 3 mm$^3$ LYSO:Ca,Ce crystal readout by a SiPM. We obtained a coincidence time resolution of 350 ps FWHM, a spatial resolution of 4 to 5 mm, and a detection efficiency of 28 %, consistent with Monte Carlo simulations of the ClearMind detector module.

physics.ins-det↗

arXiv2021

Witnessing quantum criticality and entanglement in the triangular antiferromagnet KYbSe$_2$

The Heisenberg triangular lattice quantum spin liquid and the phase transitions to nearby magnetic orders have received much theoretical attention, but clear experimental manifestations of these states are rare. This work investigates a new spin-half Yb$^{3+}$ delafossite material, KYbSe$_2$, whose inelastic neutron scattering spectra reveal a diffuse continuum with a sharp lower bound. Applying entanglement witnesses to the data reveals significant multipartite entanglement spread between its neighbors, and analysis of its magnetic exchange couplings shows close proximity to the triangular lattice Heisenberg quantum spin liquid. Key features of the data are reproduced by Schwinger-boson theory and tensor network calculations with a significant second-neighbor coupling $J_2$. The strength of the dynamical structure factor at the $K$ point shows a scaling collapse in $\hbar\omega/k_\mathrm{B}T$ down to 0.3 K, indicating a second-order quantum phase transition. Comparing this to previous theoretical work suggests that the proximate phase at larger $J_2$ is a gapped $\mathbb{Z}_2$ spin liquid, resolving a long-debated issue. We thus show that KYbSe$_2$ is close to a spin liquid phase, which in turn sheds light on the theoretical phase diagram itself.

cond-mat.str-el↗

arXiv2020

Detection of Kardar-Parisi-Zhang hydrodynamics in a quantum Heisenberg spin-$1/2$ chain

Classical hydrodynamics is a remarkably versatile description of the coarse-grained behavior of many-particle systems once local equilibrium has been established. The form of the hydrodynamical equations is determined primarily by the conserved quantities present in a system. Some quantum spin chains are known to possess, even in the simplest cases, a greatly expanded set of conservation laws, and recent work suggests that these laws strongly modify collective spin dynamics even at high temperature. Here, by probing the dynamical exponent of the one-dimensional Heisenberg antiferromagnet KCuF$_3$ with neutron scattering, we find evidence that the spin dynamics are well described by the dynamical exponent $z=3/2$, which is consistent with the recent theoretical conjecture that the dynamics of this quantum system are described by the Kardar-Parisi-Zhang universality class. This observation shows that low-energy inelastic neutron scattering at moderate temperatures can reveal the details of emergent quantum fluid properties like those arising in non-Fermi liquids in higher dimensions.

cond-mat.str-el↗

arXiv2018

Detection of a Disorder-Induced Bose-Einstein Condensate in a Quantum Spin Material at High Magnetic Fields

The coupled spin-1 chains material NiCl$_2$-4SC(NH$_2$)$_2$ (DTN) doped with Br impurities is expected to be a perfect candidate for observing many-body localization at high magnetic field: the so-called "Bose glass", a zero-temperature bosonic fluid, compressible, gapless, incoherent, and short-range correlated. Using nuclear magnetic resonance (NMR), we critically address the stability of the Bose glass in doped DTN, and find that it hosts a novel disorder-induced ordered state of matter, where many-body physics leads to an unexpected resurgence of quantum coherence emerging from localized impurity states. An experimental phase diagram of this new "order-from-disorder" phase, established from NMR $T_1^{-1}$ relaxation rate data in the (13 $\pm$ 1)% Br-doped DTN, is found to be in excellent agreement with the theoretical prediction from large-scale quantum Monte Carlo simulations.

cond-mat.str-el↗

arXiv2011

The First 1 1/2 Years of TOTEM Roman Pot Operation at LHC

Since the LHC running season 2010, the TOTEM Roman Pots (RPs) are fully operational and serve for collecting elastic and diffractive proton-proton scattering data. Like for other moveable devices approaching the high intensity LHC beams, a reliable and precise control of the RP position is critical to machine protection. After a review of the RP movement control and position interlock system, the crucial task of alignment will be discussed.

physics.ins-det↗