[en] We apply a perturbation method to quantify the impact of space charge accumulation on the output current of ionization chambers. We then obtain the formulae of the saturation curves delivered by these detectors under the form of series for which we calculate the first coefficients. The spatial variations of the primary charge density are taken into account in the calculations. For uniform ionization rates, we demonstrate that the amplitude of the space charge perturbations depends only on the values of the electronic and ionic Langevin factors of the filling fluid. We show that the influence of space charges can be neglected when the Langevin factor, λ, is small. These results were confirmed using numerical resolutions of the charge propagation equations. Finally, we evaluate the voltage that delimits the transition between the recombination regime and the saturation plateau when the space charges are taken into account.

[en] We solve the electric charge transport equations in the recombination and saturation regimes using an iterative perturbation method. We then calculate the charge collection efficiencies of ionization chambers. The formulae obtained are presented in the form of series for which we calculate the first coefficients. Our approach allows to account for the spatial as well as the temporal variations of the primary charge density N(r,t) in the calculations. Finally, we apply our method to study different density patterns, N, including the textbook case N=N₀δ(t) and the charge clusters and columns.

[en] We developed a perturbation method to predict the behaviour of ionization chambers functioning in current mode when the space charges are neglected. This method allowed us to go for the first time beyond the Thomson problem by taking into account, in the output current calculation, the spatial variations of the primary charge density induced by the incident ionizing particles. The results obtained are presented under the form of series for which we studied the convergence radius and quality in a simple case. Additionally, we solved the Thomson problem when the space charges are neglected and established for the first time the explicit relationship linking the input voltage to the output current. Finally, we calculated the voltage that delimits the transition between the recombination regime and the saturation plateau

[en] We report the formulation of the number of elastic scatterings required to slow down a neutron. By establishing its analytical expression, we show that this number displays a discontinuity and an oscillatory transient that progressively dampens when the neutron energy decreases. This result does not apply to neutrons with energies lower than a few eV, as we restrict our study to scatterings on free stationary nuclei.

[en] In this paper, we study the fraction of electric charges that escape recombination in homogeneous clusters and columns. In high electric fields, when the Coulomb interactions and diffusion processes can be neglected, we show that Boag's box model reproduces the theoretical predictions resulting from the solution of the charge propagation equations. Starting from this comparison, we improve Boag's formula by introducing an angular dependence required for a better description of columnar recombination.

[en] We present the detailed formulae of the saturation currents for the four main categories of fission chambers operating in current mode. The results obtained are function of simple parameters: number of fission reactions within the chamber deposits, geometric characteristics of the electrodes and filling gas properties. A direct relation between the saturation current values and the ambient neutron flux is thus established. These results should reduce the number, the duration and the cost of the calibration procedures required to operate the fission chambers.

[en] The Grenoble Subatomic Physics and Cosmology Laboratory - LPSC aims to improve our knowledge about the most elementary particles and about the forces that govern their interactions. It helps to broaden our understanding of the universe, its structure and its evolution. The LPSC is a Mixed Teaching and Research Unit, affiliated to the National Nuclear and Particle Physics Institute (IN2P3), the National Institute of Universe Sciences (INSU) and the National Institute of Engineering Sciences and Systems (INSIS) from the National Centre for Scientific Research (CNRS), as well as to the Joseph Fourier University and the Grenoble National Polytechnique Institute. The LPSC also plays a significant role at the national level and is involved in several international scientific and technical projects. Fundamental research is the driving force of LPSC activities. Among the themes studied at the LPSC, some are focused on the greatest unsolved mysteries of the universe, e.g. the unification of forces, the origin of the mass of particles, the origin of the matter-antimatter asymmetry in the universe and the search for dark matter and energy. Research starts at the scales of the nuclei of atoms and even much smaller, where quantum and relativistic physics laws prevail. The goal here is to understand the characteristics of the most elementary building blocks of matter and their interactions, to study the limits of existence of atoms and to discover new states of nuclear matter, such as the quark-gluon plasma. Research also extends towards the infinitely large; the goal here is to understand the origin of the structures of the universe and the cosmic phenomena that take place, and to understand the characteristics of the very first stages of the universe, just after the Big Bang. The branches of physics at these two extremes are actually closely linked. Infinitely small-scale physics plays an essential role in the first moments of the universe. Particle physics and cosmology both seek answers to the existence of dark matter and dark energy in the universe. The locations of the experiments are very diverse: ground-based, underground-based or even satellite-based. LPSC also studies artificially created short-lived particles (created by accelerators which our laboratory helps to design) or cosmic particles that were produced at different epochs of the history of the universe. These activities require the development of sophisticated, state-of-the-art instrumentation. A close collaboration between physicists, engineers and technicians is required to achieve the required performance. In addition, a strong theoretical research activity supports the experiments during the preparatory stages and during the data analysis. This report presents the activities of the laboratory during the years 2012-2013: 1 - Forewords, Presentation of the laboratory; 2 - Highlights and awards; 3 - Quarks, leptons and FUNDAMENTAL INTERACTIONS (STEREO experiment, Ultra-cold Neutrons (UCN), DΦ experiment at Tevatron, ATLAS experiment at LHC, International Linear Collider (ILC) project; 4 - Astro-particles and Cosmology (ultra-high energy cosmic radiation, ultra-high energy cosmic rays, LSST Large Synoptic Survey Telescope and theoretical cosmology, Directional detection of dark matter with MIMAC (MIcro-tpc Matrix of Chambers), NIKA project, fossil radiation study with PLANCK); 5 - Hadrons and nuclei (ALICE experiment at LHC, Hadrons structure, Nuclear structure); 6 - Reactor physics: nuclear data, ADS subcritical reactors (GUINEVERE/FREYA project), Molten Salt Fast Reactor (MSFR) concept development, Thorium cycle with water reactors: full Monte-Carlo analysis; 7 - Theoretical physics: QCD, Beyond-the-Standard-Model; 8 - Interdisciplinary research (Medical profiler, Research centre on plasmas-materials-nano-structures - CRPMN); 9 - Accelerators and ion sources (SPIRAL2 Project, GENEPI-2 accelerator, GENEPI-3C accelerator for the ADS GUINEVERE program, 60 GHz ECR ion source prototype, EMILIE collaboration (Enhanced Multi-Ionization of short-Lived Isotopes at EURISOL), Low Energy Beam Transport line (LEBT) of the MYRRHA project, contract for the production and test of the pole face windings, Other projects and activities); 10 - Technological and teaching platforms: International Platform for Advanced Plasma Processing (IAP3), Nuclear Physics Platform, Molten Fluorides platform, IN2P3-LPSC grid node calculation platform; 11 - Support to research activities: detectors and Instrumentation, Mechanics, Electronics and Computers departments, Documentation and Communication department, Administration, Health and safety, radiation protection, Heritage and infrastructures; 12 - Valorisation and technology transfer (low-level counting facility, electronics department, Ion sources department, Accelerators department, Astro-particles group, Medical developments and applications, Research centre on plasmas-materials-nano-structures - CRPMN, Training, Communication and dissemination of scientific knowledge, Seminars, Publications, PhDs, accreditations to supervise research, Prices and awards, Staff

[en] A comprehensive theoretical model is proposed to explain the functioning of fission chambers operated in current mode, even in very high neutron fluxes. The calibration curves are calculated as a function of basic physical parameters as fission rate, gas pressure and geometry of the chambers. The output current at saturation is precisely calculated, as well as the maximum voltage to be applied in order to avoid avalanche phenomena. The electric field distortion due to the space charge phenomena is also estimated. Within this model, the characteristic responses of fission chambers are correctly reproduced, in agreement with the experience feedback obtained at the ILL/Grenoble High-Flux Reactor

[en] The neutronic performances of the MEGAPIE target will be studied using fission micro-chambers specially designed to stand the severe irradiation conditions of flux and temperature. The absolute neutron flux will be monitored on-line at different positions inside the target in order to studied its spatial and temporal variations. Together with the flux characterisation, actinide incineration potential of such target will be study through ²⁴¹Am and ²³⁷Np isotopes. Prototype fission detectors and electronics have been successfully tested during the past three years at the High Flux Reactor of Laue Langevin Institute. The results of these tests are presented

[en] This publication gathers 51 contributions made by PhD students and session coordinators on traditional topics (astro-particles, cosmology, standard model) and on instrumentation, neutrinos, nuclear physics and hadronics. As far as astro-particles are concerned, the subjects were: Life and work of astro-particles; Alpha Magnetic Spectrometer 02, a particle sensor on the International Space Station; Anisotropy of cosmic radiation between 10 GeV and 100 TeV; H.E.S.S. and the cosmic accelerators called blazars; Ultra-high energy neutrinos at the Pierre Auger Laboratory; Autonomous radio-detection of high-energy cosmic rays with Codalema. The second theme was 'Beyond the standard model': Physics beyond the standard model; Probing the photon helicity: from BABAR to LHCb; The search for a new physics in the t t invariant mass spectrum with the CMS experiment; To connect supersymmetry and dark matter; Fine tuning in the NMSSM according to the results at 1fb"-"1 of the LHC; Search for new physics in events with 4 top quarks in the ATLAS experiment. For cosmology: Cosmological context; Physical properties of type Ia supernovae, the contribution of SNLS and SNFactory experiments; Reconstruction and analysis of the Sungaev-Zel'dovich effect with Planck; Local host galaxy properties of type Ia supernovae from the Nearby SuperNovae Factory; Observational cosmology with the Planck satellite: the re-ionization. For instrumentation: Introduction to instrumentation; ALFA, Absolute Luminosity For Atlas; Development of the mirrors for the second generation gravitational waves detector Advanced Virgo; EASIER, a radio detector at the Pierre Auger Laboratory; Spectral analysis algorithms in on-board gamma spectrometry; For the Standard Model: Introduction to the session; Triggering optimisation on electrons in CMS; The search for the Higgs boson in the process of vector boson fusion production and study of photon trigger with ATLAS at the LHC; Analysis of the Charmless decay B"0 → ρπ in the LHCb experiment; Correction of radiations in the final state in H → ZZ"* → 4I; Towards a measurement of the γ angle of the CKM theory via the B"0 → D"0K"+"0 disintegration with the LHCb detector; Measurement of the photon pair production cross section in the LHC with the ATLAS detector; The search for the Higgs in the 4-electron channel in ATLAS; Search for the Higgs boson in the H → γγ decay channel with the ATLAS detector. For neutrinos: Neutrino physics; The search for the double β disintegration without neutrino emission in the NEMO experiments; Coincident searches between gravitational waves and high-energy neutrinos with the ANTARES and LIGO/Virgo detectors; Use of the NA61-SHINE data to improve the prediction of the neutrino beam at T2K. For hadronic physics: A phenomenological study of helicity amplitudes of high energy exclusive lepto-production of the ρ-meson; Proton antiproton annihilation into heavy leptons at PANDA experiment; Study of the density of particles charged in collisions of heavy ions in the ALICE experiment at the LHC; Photon + heavy-flavor jet production at Tevatron and LHC; Quarkonium production in ultra-relativistic heavy-ion collisions with the ALICE experiment at the LHC; Loop calculations in gage theories. The last theme was nuclear physics and applications: Introduction to the session; Measurement of mass yields of the reaction "2"4"1Am(2n,f) at the Lohengrin spectrometer; Xenon mobility in uranium dioxide; Ga-Ni coating obtained by electrodeposition in chloride environment