Heures thésards

Animé par Johannès Jahan

jeudi 18 juin 2020 à 14:00

En visio

High energy PIXE: new K-shell ionization cross-section measurements

Quantin Mouchard

Subatech (équipe Prisma)

Q. Mouchard(1), C. Koumeir(2,1), N. Servagent(1) and V. Métivier(1)

(1) SUBATECH, IMT Atlantique, Univerité de Nantes, CNRS/IN2P3, Nantes, France
(2) GIP ARRONAX, Saint-Herblain, France

A high-energy ion beam analysis platform is set up at ARRONAX cyclotron. One of the non-destructive techniques available uses X-ray emissions induced by the high-energy particle beam (HE-PIXE) [1]. This technique has already made it possible to analyze geological samples, but also thick objects such as old paintings and archaeological pieces [2].
HE-PIXE technique optimizes the X-ray production cross-section induced by protons for medium and heavy elements, compared to lower energies. Their identifications are facilitated by the more energetics K-shell X-ray emissions. This feature combined with the fact that the stopping power decreases with protons energies, makes the HE-PIXE technique well suited for the analysis of thick objects and potentially limiting the risk of damage. This technique is especially interesting for objects whose composition is different between the surface and the depth.
The knowledge of the ionization cross-section is imperative to allow a quantitative analysis with the PIXE technique. The experimental data available in the literature are scarce. Based on this observation, a campaign of K-shell X-ray production cross-section measurement was carried out at ARRONAX cyclotron, for different elements in the energy range of 30MeV to 68 MeV. The parameters of the experimental devices such as the detector efficiency, the beam intensity and the targets thicknesses, have been characterized accurately in order to obtain precise measurements.
Special care has been made to select the most accurate K-shell fluorescence yields from the literature data, in order to convert the K X-ray production cross sections to the K shell ionization cross section. We will present, a review of the theoretical model RECPSSR[3], followed by a description of our experiment (beam, detector, and target). The outcomes of the experiment will be compared with the existing data and the theoretical predictions of the model.

[1] C. Koumeir, et al., Proceedings of the 14th European Conference on X-Ray Spectromectry, 2010, 23-33.
[2] A. Denker, et al., Nuclear Instrument and Methods B239, 2005, 65-70.
[3] S.J. Cipolla, et al., Computer Physics Communications, 182 (11), 2011, 2439-2440

Dynamical Thermalization in Heavy-Ion Collisions


Subatech (équipe Théorie)

The development of the merged EPOS+PHSD approach is one way to study the influence of the initial non-equilibrium stage of the heavy-ion reactions on the final observables. The microscopic understanding of the initial phase of heavy-ion collisions is a intricate problem, in this respect the EPOS and PHSD approaches provide a unique possibility to address this problem. We employ the EPOS to do the initial stage of Heavy-Ion Collisions based on a multiple Pomeron exchange in Gribov Reggeon Field Theory formalism. EPOS is a particularly successful event generator and universal model for all collisions. PHSD is a microscopic covariant dynamical approach for strongly interacting systems formulated based on Kadanoff-Baym equations. Following injecting particles from EPOS to PHSD, we investigated about the “flow behavior”. The easiest way to study was to look at the particle production. Once there are sufficient interactions, the magnitude of the flow increases, indicating that we are close to Thermalization. I am going to present our results concerning various observables like “elliptical flow” and "pt spectra" in EPOS+PHSD and make compare with EPOS+hydro, EPOS-hydro and pure PHSD.