VELO Module Production: Vacuum Tank Tests

This document describes the procedure for the burn-in of the completed module in the vacuum tank

Studies of the radiation hardness of oxygen-enriched silicon detectors

Detectors of high-energy particles sustain substantial structural defects induced by the particles during the operation period. Some of the defects have been found to be electrically active, degrading the detector's performance. Understanding the mechanisms of the electrical activities and learning to suppress their influence are essential if long 'lifetime' detectors are required. This work report s about radiation hardness of silicon P-I-N devices fabricated from oxygen-enriched, high-resistivity material. The high and nearly uniform concentration of oxygen in float-zone silicon has been achie ved by diffusion of oxygen from SiO2 layers

Study of the evolution ot the active volume in irradiated silicon detectors

Red (670 nm) LED light was used to study the charge collection properties of non-irradiated and irradiated n-type silicon detectors. The advantages of red LED, compared to low-range alpha particles, are the availability of an external trigger, and a very shallow distribution of the created electron-hole pairs (< 10 µm). These features, combined with the use of a fast current amplifier and a 2.5 G s/s sampling oscilloscope, allow the electric field evolution in irradiated detectors to be studied. Evidence of a sensitive region on both sides of the detector was observed. The model of the diode d epletion volume from the n+ junction side after conduction-type inversion is discussed, and the electric field distribution in the inverted detector is presented. A first evaluation of the strength of the electric field in the undepleted bulk of the detector is proposed

Experimental results on radiation-induced bulk damage effects in float-zone and epitaxial silicon detectors

A comparative study of the radiation hardness of silicon pad detectors, manufactured from Float-Zone and Epitaxial n-type monocrystals and irradiated with protons and neutrons up to a fluence of 3.5 1014 cm-2 is presented. The results are compared in terms of their reverse current, depletion voltage, and charge collection as a function of fluence during irradiation and as a function of time after irradiation

Charge Transport in Non-Irradiated and Irradiated Silicon Diodes

A model describing the transport of charge carriers generated in silicon detectors (standard planar float zone and MESA diodes) by ionizing particles is presented. The current pulse response induced by $\alpha$ and $\beta$ particles in non-irradiated detectors and detectors irradiated up to fluences $\Phi \approx 3 \cdot 10^{14}$ particles/cm$^2$ is reproduced through this model: i) by adding a small n-type region 15 $\mu$m deep on the $p^+$ side for the standard planar float zone detectors at fluences beyond the n to p-type inversion and ii) for the MESA detectors, by considering one dead layer 14 $\mu$m deep (observed experimentally) on each side, and introducing a second (delayed) component. For both types of detectors, the model gives mobilities decreasing linearily up to fluences of about $5 \cdot 10^{13}$ particles/cm$^2$ and converging, beyond, to saturation values of about 1000 cm$^2$/Vs and 455 cm$^2$/Vs for electrons and holes, respectively. At a fluence $\Phi \approx 10^{14}$ particles/cm$^2$, charge collection deficits of about 13\% for $\beta$ particles, 25\% for $\alpha$ particles incident on the front and 35\% for $\alpha$ particles incident on the back of the detector are found for both type of diodes

Study of charge Transport in Silicon Detectors: Non-Irradiated and Irradiated

The electrical characteristics of silicon detectors (standard planar float zone and MESA detectors) as a function of the particle fluence can be extracted by the application of a model describing the transport of charge carriers generated in the detectors by ionizing particles. The current pulse response induced by $\alpha$ and $\beta$ particles in non-irradiated detectors and detectors irradiated up to fluences $\Phi \approx 3 \cdot 10^{14}$ particles/cm$^2$ is reproduced via this model: i) by adding a small n-type region 15 $\mu$m deep on the $p^+$ side for the detectors at fluences beyond the n to p-type inversion and ii) for the MESA detectors, by considering one additional dead layer of 14 $\mu$m (observed experimentally) on each side of the detector, and introducing a second (delayed) component to the current pulse response. For both types of detectors, the model gives mobilities decreasing linearily up to fluences of about $5 \cdot 10^{13}$ particles/cm$^2$ and converging, beyond, to saturation values of about 1050 cm$^2$/Vs and 450 cm$^2$/Vs for electrons and holes, respectively. At a fluence $\Phi \approx 10^{14}$ particles/cm$^2$ (corresponding to about ten years of operation at the CERN-LHC), charge collection deficits of about 14\% for $\beta$ particles, 25\% for $\alpha$ particles incident on the front and 35\% for $\alpha$ particles incident on the back of the detector are found for both type of detectors

Comparison of radiation damage in silicon induced by proton and neutron irradiation

The subject of radiation damage to Si detectors induced by 24-GeV/c protons and nuclear reactor neutrons has been studied. Detectors fabricated on single-crystal silicon enriched with various impurities have been tested. Significant differences in electrically active defects have been found between the various types of material. The results of the study suggest for the first time that the widely used nonionizing energy loss (NIEL) factors are insufficient for normalization of the electrically active damage in case of oxygen- and carbon-enriched silicon detectors. It has been found that a deliberate introduction of impurities into the semiconductor can affect the radiation hardness of silicon detectors. (16 refs)

Charge Transport in Non-Irradiated and Irradiated Silicon Detectors

A model describing the transport of the carriers of the charge deposited in n-type silicon detectors by ionizing particles is presented. In order to reproduce the experimental current pulse responses induced by alpha and beta particles in non-irradiated and irradiated detectors up to fluences ($\Phi$) much beyond the n to p-type inversion, a n-type region 15 microns deep is introduced on the p$^+$ side of the diode. This model also gives mobilities decreasing linearily up to fluences of around $5 \cdot 10^{13}$ particles/cm$^2$, and beyond, converging to saturation values of about 1000 cm$^2$/Vs and 450 cm$^2$/Vs for electrons and holes, respectively. The charge carrier lifetime degradation, due to trapping with increased fluence, is responsible for a charge collection deficit for $\beta$ particles and for $\alpha$ particles found in agreement with direct CCE measurements

Study of charge transport in non-irradiated and irradiated silicon detectors

The electrical characteristics of non-irradiated and irradiated n-type silicon detectors (p -n -n diode) are extracted by fitting a charge transport model to a set of experimental data obtained from the measurememt of the current pulse response induced by a and b particles. . The detectors were irradiated with either \@1 MeV neutrons up to a fluence of 9.92 x 10 n/cm or with 24 GeV/c protons up to a fluence if 10.6 x 10 p/cm . After n- to p- type inversion, a small junction on the p side of the detector is introduced to fit the experimental data and to account for the evolution fo the electr ical characteris

Transport of Cosmic Rays in Chaotic Magnetic Fields

The transport of charged particles in disorganised magnetic fields is an important issue which concerns the propagation of cosmic rays of all energies in a variety of astrophysical environments, such as the interplanetary, interstellar and even extra-galactic media, as well as the efficiency of Fermi acceleration processes. We have performed detailed numerical experiments using Monte-Carlo simulations of particle propagation in stochastic magnetic fields in order to measure the parallel and transverse spatial diffusion coefficients and the pitch angle scattering time as a function of rigidity and strength of the turbulent magnetic component. We confirm the extrapolation to high turbulence levels of the scaling predicted by the quasi-linear approximation for the scattering frequency and parallel diffusion coefficient at low rigidity. We show that the widely used Bohm diffusion coefficient does not provide a satisfactory approximation to diffusion even in the extreme case where the mean field vanishes. We find that diffusion also takes place for particles with Larmor radii larger than the coherence length of the turbulence. We argue that transverse diffusion is much more effective than predicted by the quasi-linear approximation, and appears compatible with chaotic magnetic diffusion of the field lines. We provide numerical estimates of the Kolmogorov length and magnetic line diffusion coefficient as a function of the level of turbulence. Finally we comment on applications of our results to astrophysical turbulence and the acceleration of high energy cosmic rays in supernovae remnants, in super-bubbles, and in jets and hot spots of powerful radio-galaxies.Comment: To be published in Physical Review D, 20 pages 9 figure