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D. Dauvergne

Publications and source records attributed to D. Dauvergne.

11 recordsLinked to original sources

Random Sums of Weighted Orthogonal Polynomials in ${\mathbb C}^d$

We consider random polynomials of the form $G_n(z):= \sum_{|α|\leq n} ξ^{(n)}_αp_{n,α}(z)$ where $\{ξ^{(n)}_α\}_{|α|\leq n}$ are i.i.d. (complex) random variables and $\{p_{n,α}\}_{|α|\leq n}$ form a basis for $\mathcal P_n$, the holomorphic polynomials of degree at most $n$ in ${\mathbb C}^d$. In particular, this includes the setting where $\{p_{n,α}\}$ are orthonormal in a space $L^2(e^{-2n Q} τ)$, where $τ$ is a compactly supported Bernstein-Markov measure and $Q$ is a continuous weight function. Under an optimal moment condition on the random variables $\{ξ^{(n)}_α\}$, in dimension $d=1$ we prove convergence in probability of the zero measure to the weighted equilibrium measure, and in dimension $d \ge 2$ we prove convergence of zero currents.

math.PR

RF pulse amplifier for CVD-diamond particle detectors

This article introduces a design of a Low Noise Amplifier (LNA), for the field of diamond particle detectors. This amplifier is described from simulation to measurements, which include pulses from α particles detection. In hadron therapy, with high-frequency pulsed particle beams, the diamond detector is a promising candidate for beam monitoring and time-stamping, with prerequisite of fast electronics. The LNA is designed with surface mounted components and RF layout techniques to control costs and to allow timing performance suitable for sub-nanosecond edges of pulses. Also this amplifier offers the possibility of high voltage biasing, a characteristic essential for driving diamond detectors. Finally the greatest asset of this study is certainly the minimization of the power consumption, which allows us to consider designs with multiple amplifiers, in limited space, for striped diamond detectors.

physics.ins-det

Characterization of a beam-tagging hodoscope for hadrontherapy monitoring

A beam tagging hodoscope prototype made of squared 1 mm$^2$ fibers arranged in two perpendicular planes and coupled to multi-anode photomultipliers has been studied using 65 MeV proton as well as 95 MeV/u $^{12}$C beams at various intensities. This hodoscope successfully provided 2D images of proton beams with a detection efficiency larger than 98 % with logical OR condition between the two fiber planes. The detection efficiency with a coincidence between the two planes is close to 75 % for beam intensities up to $\sim1$ MHz. Moreover, the timing resolution is around 1.8 ns FWHM. Overall, the performances show that such a technology is viable for beam monitoring during hadrontherapy.

physics.ins-det

Ultra-fast prompt gamma detection in single proton counting regime for range monitoring in particle therapy

In order to fully exploit the ballistic potential of particle therapy, we propose an online range monitoring concept based on high-resolution Time-Of-Flight (TOF)-resolved Prompt Gamma (PG) detection in a single proton counting regime. In a proof of principle experiment, different types of monolithic scintillating gamma detectors are read in time coincidence with a diamond-based beam hodoscope, in order to build TOF spectra of PG generated in a heterogeneous target presenting an air cavity of variable thickness. Since the measurement was carried out at low beam currents ($<$ 1 proton/bunch) it was possible to reach excellent coincidence time resolutions, of the order of 100 ps ($σ$). Our goal is to detect possible deviations of the proton range with respect to treatment planning within a few intense irradiation spots at the beginning of the session and then carry on the treatment at standard beam currents. The measurements were limited to 10 mm proton range shift. A Monte Carlo simulation study reproducing the experiment has shown that a 3 mm shift can be detected at 2$σ$ by a single detector of $\sim 1.4 \times 10^{-3}$ absolute detection efficiency within a single irradiation spot ($\sim$10$^{8}$ protons) and an optimised experimental set-up.

physics.med-ph

Recent Results from Polycrystalline CVD Diamond Detectors

Diamond is a material in use at many nuclear and high energy facilities due to its inherent radiation tolerance and ease of use. We have characterized detectors based on chemical vapor deposition (CVD) diamond before and after proton irradiation. We present preliminary results of the spatial resolution of unirradiated and irradiated CVD diamond strip sensors. In addition, we measured the pulse height versus particle rate of unirradiated and irradiated polycrystalline CVD (pCVD) diamond pad detectors up to a particle flux of $20\,\mathrm{MHz/cm^2}$ and a fluence up to $4 \times 10^{15}\,n/\mathrm{cm^2}$.

physics.ins-det

Statistical effects of dose deposition in track-structure modelling of radiobiology efficiency

Ion-induced cell killing has been reported to depend on the irradiation dose but also on the projectile parameters. In this paper we focus on two approaches developed and extensively used to predict cell survival in response to ion irradiation: the Local Effect Model and the Katz Model. These models are based on a track-structure description summarized in the concept of radial dose. This latter is sensitive to ion characteristics parameters and gives to both models the ability to predict some important radiobiological features for ion irradiations. Radial dose is however an average quantity, which does not include stochastic effects. These radiation-intrinsic effects are investigated by means of a Monte-Carlo simulation of dose deposition. We show that both models are not fully consistent with the nanometric and microscopic dose deposition statistics.

physics.bio-ph

Monitoring the Bragg peak location of 73 MeV/u carbon ions by means of prompt $γ$-ray measurements

By means of a time-of-flight technique, we measured the longitudinal profile of prompt $γ$-rays emitted by 73 MeV/u $^{13}$C ions irradiating a PMMA target. This technique allowed us to minimize the shielding against neutrons and scattered $γ$-rays, and to correlate prompt gamma emission to the ion path. This correlation, together with a high counting rate, paves the way toward real-time monitoring of the longitudinal dose profile during ion therapy treatments. Moreover, the time correlation between the prompt gamma detection and the transverse position of the incident ions measured by a beam monitor can provide real-time 3D control of the irradiation.

physics.atom-ph

Swift Highly Charged Ion Channelling

We review recent experimental and theoretical progress made in the scope of swift highly charged ion channelling in crystals. The usefulness of such studies is their ability to yield impact parameter information on charge transfer processes, and also on some time related problems. We discuss the cooling and heating phenomena at MeV/u energies, results obtained with decelerated H-like ion beams at GSI and with ions having an excess of electrons at GANIL, the superdensity effect along atomic strings and Resonant Coherent Excitation.

physics.atom-ph

Electron gas polarization effect induced by heavy H-like ions of moderate velocities channeled in a silicon crystal

We report on the observation of a strong perturbation of the electron gas induced by 20 MeV/u U$^{91+}$ ions and 13 MeV/u Pb$^{81+}$ ions channeled in silicon crystals. This collective response (wake effect) in-duces a shift of the continuum energy level by more than 100 eV, which is observed by means of Radiative Electron Capture into the K and L-shells of the projectiles. We also observe an increase of the REC probability by 20-50% relative to the probability in a non-perturbed electron gas. The energy shift is in agreement with calculations using the linear response theory, whereas the local electron density enhancement is much smaller than predicted by the same model. This shows that, for the small values of the adiabaticity parameter achieved in our experiments, the density fluctuations are not strongly localized at the vicinity of the heavy ions.

physics.atom-ph

Summary of experimental studies at CERN on a positron source using crystal effects

New kind of positron sources for future linear colliders, where the converter is a tungsten crystal oriented on the <111> axis, has been studied at CERN in the WA103 experiment. In such sources the photons which create the $e^+ e^-$ pairs result from channeling radiation and coherent bremsstrahlung. In this experiment electron beams of 6 and 10 GeV were sent on different kinds of targets: a 4 mm thick crystal, a 8 mm thick crystal and a compound taraget (4 mm crystal + 4 mm amorphous disk). An amorphous tungsten target 20 mm thick was also used for comparison with the 8 mm crystal. Tracks of outgoing charged particles were detected and analyzed by a drift chamber in a magnetic field. The energy and angle spectra of the positrons were obtained for energies up to 150 MeV and angles up to 30 degrees. The measured positron distribution in momentum space (longitudinal versus transverse) is also presented, giving a full momentum space description of the source. Results on outgoing photons are also presented. A significant enhancement of both photon and positron production is clearly observed. At 10 GeV incident energy, the positron enhancement factor is 4 for the 4 mm crystal, about 2 for the 8 mm crystal. Besides, the simulation code for the crystal processes is validated by a quite good agreement between the simulated and experimental spectra, both for positrons and photons.

physics.ins-det

Experimental Determination of the Characteristics of a Positron Source Using Channeling

Numerical simulations and `proof of principle' experiments showed clearly the interest of using crystals as photon generators dedicated to intense positron sources for linear colliders. An experimental investigation, using a 10 GeV secondary electron beam, of the SPS-CERN, impinging on an axially oriented thick tungsten crystal, has been prepared and operated between May and August 2000. After a short recall on the main features of positron sources using channeling in oriented crystals, the experimental set-up is described. A particular emphasis is put on the positron detector made of a drift chamber, partially immersed in a magnetic field. The enhancement in photon and positron production in the aligned crystal have been observed in the energy range 5 to 40 GeV, for the incident electrons, in crystals of 4 and 8 mm as in an hybrid target. The first results concerning this experiment are presented hereafter.

physics.acc-ph