Silicon Sensors implemented on p-type substrates for high radiation resistance applications

Silicon based micropattern detectors are essential elements of modern high energy physics experiments. Cost effectiveness and high radiation resistance are two important requirements for technologies to be used in inner tracking devices. Processes based on p-type substrates have very strong appeal for these applications. Recent results and prototype efforts under way are reviewed.Comment: 7 pages, 2 figures; invited paper at Vertex 2006, Perugia, Italy, september 200

Relativistic particle transport in extragalactic jets: I. Coupling MHD and kinetic theory

Multidimensional magneto-hydrodynamical (MHD) simulations coupled with stochastic differential equations (SDEs) adapted to test particle acceleration and transport in complex astrophysical flows are presented. The numerical scheme allows the investigation of shock acceleration, adiabatic and radiative losses as well as diffusive spatial transport in various diffusion regimes. The applicability of SDEs to astrophysics is first discussed in regards to the different regimes and the MHD code spatial resolution. The procedure is then applied to 2.5D MHD-SDE simulations of kilo-parsec scale extragalactic jets. The ability of SDE to reproduce analytical solutions of the diffusion-convection equation for electrons is tested through the incorporation of an increasing number of effects: shock acceleration, spatially dependent diffusion coefficients and synchrotron losses. The SDEs prove to be efficient in various shock configuration occurring in the inner jet during the development of the Kelvin-Helmholtz instability. The particle acceleration in snapshots of strong single and multiple shock acceleration including realistic spatial transport is treated. In chaotic magnetic diffusion regime, turbulence levels $\eta_T=/(B^2+)$ around $0.2-0.3$ are found to be the most efficient to enable particles to reach the highest energies. The spectrum, extending from 100 MeV to few TeV (or even 100 TeV for fast flows), does not exhibit a power-law shape due to transverse momentum dependent escapes. Out of this range, the confinement is not so efficient and the spectrum cut-off above few hundreds of GeV, questioning the Chandra observations of X-ray knots as being synchrotron radiation. The extension to full time dependent simulations to X-ray extragalactic jets is discussed.Comment: Astronomy & Astrophysics (in press), 18 page

On fan-shaped cold MHD winds from Keplerian accretion discs

We investigate under which conditions cold, fan-shaped winds can be steadily launched from thin (Keplerian) accretion discs. Such winds are magneto-centrifugal winds launched from a thin annulus in the disc, along open magnetic field lines that fan out above the disc. In principle, such winds could be found in two situations: (1) at the interface between an inner Jet Emitting Disc, which is itself powering magneto-centrifugally driven winds, and an outer standard accretion disc; (2) at the interface between an inner closed stellar magnetosphere and the outer standard accretion disc. We refer to Terminal or T-winds to the former kind and to Magnetospheric or M-winds to the latter. The full set of resistive and viscous steady state MHD equations are analyzed for the disc (the annulus), which allow us to derive general expressions valid for both configurations. We find that, under the framework of our analysis, the only source of energy able to power any kind of fan-shaped winds is the viscous transport of rotational energy coming below the inner radii. Using standard local $\alpha$ prescriptions for the anomalous (turbulent) transport of angular momentum and magnetic fields in the disc, we derive the strength of the transport coefficients that are needed to steadily sustain the global configuration. It turns out that, in order for these winds to be dynamically relevant and explain observed jets, the disc coefficients must be far much larger than values expected from current knowledge of turbulence occurring inside proto-stellar discs. Either the current view on MHD turbulence must be deeply reconsidered or steady-state fan-shaped winds are never realized in Nature. The latter hypothesis seems to be consistent with current numerical simulations.Comment: Among several possibilites, this paper addresses also the case of the X-wind Accepted for publication in MNRA

Lithium-Beryllium-Boron and Oxygen in the early Galaxy

Oxygen is a much better evolutionary index than iron to follow the history of Lithium-Beryllium-Boron (LiBeB) since it is the main producer of these light elements at least in the early Galaxy. The O-Fe relation is crucial to the determination of the exact physical process responsible for the LiBeB production. Calculated nucleosynthetic yields of massive stars, estimates of the energy cost of Be production, and above all recent observations reported in this meeting seem to favor a mechanism in which fast nuclei enriched into He, C and O arising from supernovae are accelerated in superbubbles and fragment on H and He in the interstellar medium.Comment: Invited Review, IAU, JD8, Manchester, August 2000, to be published in Highlights of Astronom

LiBeB Production and Associated Astrophysical Sites

The various modes of spallative LiBeB production are summarized, and classified according to their dependence or independence on the abundance of medium heavy elements (CNO) illustrated by that of oxygen in the interstellar medium. The predictions of the models are confronted to the available observational correlations (Be, B vs O). Clearly, a primary mechanism should lead to a slope one in the lg(Be/H) vs [O/H] plot and a secondary mechanism to a slope two. Due to the ambiguity of the O data, another criterion, based on energetics, can help us to select an adequate model. A purely secondary origin in the very early Galaxy is much more energy demanding than a primary one. Indeed, magnesium seems to be a possible surrogate of oxygen and iron since i) it is spectroscopically more easy to cope with and ii) its nucleosynthetic yield is independent of the mass cut and does not depend on metallicity.Comment: 10 pages, no figure, to be published in "Tle light Elements and their Evolution", IAU Symp. 198 (Natal Conf.), ASP Conf. Series, 200

INTEGRAL and Nuclear Astrophysics

We briefly review the fundamentals of nuclear gamma-ray line astronomy (radioactive astronomy), focusing on its role to decipher the intimate physics of supernovae, either immediatly (via $^{56}Co)$ or after a time delay (via $^{44}Ti$). All kinds of supernovae can be in principle tested through their radioactivities and their associated gamma-ray lines. Dedicated to the spectroscopy and imaging of celestial sources in the 15 keV to 10 MeV band, the ESA scientific observatory INTEGRAL will open a golden age of nuclear astrophysics in EuropeComment: Invited review, "Cosmic Evolution", meeting in honor of the 60th birthday of Jean Audouze and Jim Truran, to be published by World Scientific, 6 pages, 1 figur