E. Fiandrini

The L3 silicon microvertex detector

Abstract The design and construction of the silicon strip microvertex detector (SMD) of the L3 experiment at LEP are described. We present the sensors, readout electronics, data acquisition system, mechanical assembly and support, displacement monitoring systems and radiation monitoring system of the recently installed double-sided, double-layered SMD. This detector utilizes novel and sophisticated techniques for its readout.

Leptons with E > 200 MeV trapped in the Earth's radiation belts

Accurate measurements of under cutoff electron and positron fluxes, in the energy range 0.2÷10 GeV, have been performed with the Alpha Magnetic Spectrometer (AMS) in low Earth Orbit. For the first time a clear transition is observed from a Stably-Trapped population, detected on the boundaries of the South Atlantic Anomaly, to a Quasi Trapped population, revealed outside the South Atlantic Anomaly. The radial profiles, energy spectra and magnetic asymmetries of these populations are presented. 1. Introduction The study of the radiation environment in the Earth’s proximity is relevant to determine the radiation dose for satellite and manned spacecrafts and to evaluate backgrounds in space and ground based experiments. However, a complete model of the sources and losses, which can reproduce and predict the energy spectra and the spatial distribution of the different particle components does not yet exists. This is particulary true in the region of the South Atlantic Anomaly (SAA), where the Inner Van Allen Belts (IVAB) approach the Earth’s atmosphere. There, a relevant contribution to the high energy belt population could come from particles generated in the interaction of cosmic rays with the Earth’s atmosphere. These particles can be injected to closed shells after scattering within the residual atmosphere. In this contribution, we use the high statistics data sample collected by the AMS experiment [1] for a detailed study of the high energy (O(1) GeV) e ± fluxes on the boundaries of the SAA. Results on the e ± fluxes observed outside the SAA have been presented in the 27 th ICRC and published in [2].[1] For the first time, accurate measurements of electron and positron fluxes in the energy range 0.2-10 GeV have been performed with the Alpha Magnetic Spectrometer (AMS) at altitudes of 370-390 km in the geographic latitude interval ±51.7°. We describe the observed under-cutoff lepton fluxes outside the region of the South Atlantic Anomaly. The separation in quasi-trapped, long-lifetime (O(10 s)), and albedo, short-lifetime (O(100 ms)), components is explained in terms of the drift shell populations observed by AMS. A significantly higher relative abundance of positrons with respect to electrons is seen in the quasi-trapped population. The flux maps as a function of the canonical adiabatic variables L, α 0 are presented for the interval 0.95 < L < 3, 0° < α 0 < 90° for electrons (E < 10 GeV) and positrons (E < 3 GeV). The results are compared to existing data at lower energies. The properties of the observed under-cutoff particles are also investigated in terms of their residence times and geographical origin.

TCAD-based analysis of radiation-hardness in silicon detectors

The application of a general-purpose device-simulator to the analysis of silicon microstrip radiation detector is described. Physical models include charge-collection dynamics, as well as radiation-induced deep-level recombination centers. Realistic description of multiple-strip devices can be accounted for. To allow for validation of the analysis tool, actual detectors have been measured, before and-after being irradiated with neutrons. Simulation predictions agree well with experiments. Limitations of the adopted model are discussed, with reference to simulation-based comparison with higher-order models.

The L3 Silicon Microvertex Detector: installation and results on 1993 performance

Abstract The status of the Silicon Microvertex Detector (SMD) and its installation into the LEP-L3 experiment are presented, highlighting novel features and sophisticated techniques. Preliminary results based on 1993 data are given and compared with Monte Carlo predictions, to understand the detector performances and its tracking capabilities.

Comprehensive modeling of silicon microstrip detectors

In this work, the application of numerical device simulation to the analysis of high resistivity silicon microstrip detectors is illustrated. The analysis of DC, AC and transient responses of a single-sided, DC-coupled detector has been carried out, providing results in good agreement with experimental data. In particular, transient-mode simulation has been exploited to investigate the collection of charges generated by ionizing particles. To this purpose, an additional generation term has been incorporated into the transport equations; the motion of impact-generated carriers under the combined action of ohmic and diffusive forces is hence accounted for. Application to radiation tolerance studies is also introduced.

Innovative carbon nanotube-silicon large area photodetector

We report on a new photodetector fabricated using carbon nanostructures grown on a silicon substrate. This device exhibits low noise, a good conversion efficiency of photons into electrical current and a good signal linearity in a wide range of radiation wavelengths ranging from ultraviolet to infrared at room temperature. The maximum quantum efficiency of 37% at 880 nm has been measured without signal amplification. Such innovative devices can be easily produced on large scales by Chemical Vapour Deposition (CVD) through a relatively inexpensive chemical process, which allows large sensitive areas from a few mm2 up to hundreds of cm2 to be covered.

The design of the L3 silicon muvertex detector

Abstract An upgrade of the L3 central tracking system, a silicon muvertex detector (SMD), is described. The detector consists of two layers of silicon, each equipped for rφ and z readout with resolution ≈ 6 μ m and ≈ 20 μ m respectively. The SMD will provide full azimuthal coverage over the polar angular range 22°≤ θ ≤158°. The total thickness is ≈0.9% of one radiation length.

Observation of a photoinduced, resonant tunneling effect in a carbon nanotube–silicon heterojunction

Summary A significant resonant tunneling effect has been observed under the 2.4 V junction threshold in a large area, carbon nanotube–silicon (CNT–Si) heterojunction obtained by growing a continuous layer of multiwall carbon nanotubes on an n-doped silicon substrate. The multiwall carbon nanostructures were grown by a chemical vapor deposition (CVD) technique on a 60 nm thick, silicon nitride layer, deposited on an n-type Si substrate. The heterojunction characteristics were intensively studied on different substrates, resulting in high photoresponsivity with a large reverse photocurrent plateau. In this paper, we report on the photoresponsivity characteristics of the device, the heterojunction threshold and the tunnel-like effect observed as a function of applied voltage and excitation wavelength. The experiments are performed in the near-ultraviolet to near-infrared wavelength range. The high conversion efficiency of light radiation into photoelectrons observed with the presented layout allows the device to be used as a large area photodetector with very low, intrinsic dark current and noise.

A silicon microstrip tracker in space: Experience with the AMS silicon tracker on STS-91

SummaryThe Alpha Magnetic Spectrometer (AMS) is designed as an independent module for installation on the International Space Station (ISS) in the year 2003 for an operational period of three years. The principal scientific objectives include the searches for antimatter and dark matter in cosmic rays. The AMS tracker uses silicon microstrip sensors to reconstruct charged-particle trajectories. A first version of the AMS, equipped with 2.1 m2 of silicon sensors and a permanent magnet, was flown on the NASA space shuttle Discovery duringJune 2–12, 1998. In this contribution, we describe the detector and present results of the tracker performance duringthe flight.

Status of the L3 silicon microvertex detector

Abstract A report on the status of the construction of the L3 Silicon Microvertex Detector is presented here. The detector will consist of two double sided AC coupled silicon layers equipped with rφ and z readout with an expected intrinsic resolution of ≈ 6 μ m and ≈ 25 μ m respectively. A description of the detector with its mechanical support, alignment system and readout electronics is presented.