A. Colavita

Measurement of the positron to electron ratio in the cosmic rays above 5-GeV

As part of a series of experiments to search for antimatter in cosmic rays, the New Mexico State University balloon-borne magnet spectrometer was configured for a flight to study positrons. Two completely new instruments, a transition radiation detector and a silicon-tungsten imaging calorimeter, were added to the magnet spectrometer. These two detectors provided a proton rejection factor better than 3 × 104. This instrument was flown from Fort Sumner, New Mexico, at an average depth of 4.5 g cm-2 of residual atmosphere for a period of 25 hr. We report here the measured fraction of positrons e+/(e+ + e-) from ~5 to 60 GeV at the top of the atmosphere. Our measurements do not show any compelling evidence for an increase in this ratio with energy, and our results are consistent with a constant fraction of 0.078 ± 0.016 over the entire energy region.

The mirror system of COMPASS RICH-1

The architecture and the properties of the mirror system of the COMPASS RICH-1 detector, composed by 116 spherical VUV reflecting units supported by a lightweight mechanical structure, are described.

The radiator gas and the gas system of COMPASS RICH-1

The design of the COMPASS RICH-1 gas system, its operational modes, the cleaning setups for the preparation of the radiator gas and transmission measurement installations are described. The gas system in presently fully operational and satisfactory transmission of VUV light through the radiator gas has been reached.

COMPASS RICH-1

RICH-1, one of the key detectors of the COMPASS experiment at CERN SPS, is described. Photon detectors are MWPCs equipped with CsI photo-cathodes.

The COMPASS RICH project

The set-up of the COMPASS experiment (NA58 at CERN SPS) consists of two spectrometers (a large-angle one followed by a small-angle spectrometer) both equipped with a gas RICH (RICH 1 and RICH 2) for hadron identification. RICH 1 is currently under construction, while RICH 2 will be added at a second stage. RICH 1 design parameters and technological choices are discussed

Chaotic instability of currents in a reverse biased multilayered structure

A new principle to generate chaotic signals using the phenomenon of charge avalanche multiplication and internal feedback in multilayered semiconductor structures is suggested. Linear and nonlinear theories for the self-oscillations are developed and existence of the chaotic regime with fast decay of correlations is proven.

Current oscillations in avalanche particle detectors with p-n-i-p-n-structure

We describe the model of an avalanche high energy particle detector consisting of two p-n-junctions, connected through an intrinsic semiconductor with a reverse biased voltage applied. We show that this detector is able to generate the oscillatory response on the single particle passage through the structure. The possibility of oscillations leading to chaotic behavior is pointed out.

The COMPASS RICH-1 read-out system

This paper describes the reconfigurable read-out system for the 82944 RICH-1 channels of the COMPASS experiment (NA58) at CERN. The system is based on 192 identical large front-end boards (BORA board). BORA was designed for acquiring, digitizing, threshold subtracting and transmitting event data. The overall operation of the board is controlled and supervised by a DSP tightly interacting with an FPGA that acts as a parallel co-processor. The DSP allows characterizing each analog channel by locally calculating noise and pedestal. Each BORA communicates with the outside world through two optical fibers and through a dedicated DSP network. One optical fiber is used to receive event triggers, and the other one is used to transmit event data to subsequent processing stages of the acquisition system. The DSP network allows reconfiguring and reprogramming the DSPs and FPGAs as well as acquiring sample events to visualize the overall operation of the system. The whole RICH has eight DSP networks working in parallel. These networks are handled by DOLINA, a PC resident multiprocessor board containing eight DSPs. Each network is formed by 24 BORA DSPs and 1 DOLINA DSP. The read-out system can steadily work up to a trigger rate of 75 kHz with maximum pixel occupancy of 20%, reaching a transmission data rate of 5.13 Gbytes/s.

MAXIMUM ENTROPY IMPROVEMENT OF X-RAY DIGITAL MAMMOGRAMS

Our approach to X-ray digital image enhancement was based on entropy maximization, which allows distributions to be estimated in cases when incomplete or corrupt information is only available. In data analysis, maximum entropy (ME) techniques are generally used to reconstruct positive distributions, such as images and spectra, from blurred or noisy data. Within this framework, positive distributions ought to be assigned probabilities which are based on the entropy of these distributions. If we consider a complete collection of images corresponding to all possible intensity distributions, then measurements act as a filter over the collection by restricting our attention to the images that satisfy the data with noise. Among these, a natural choice may be the one that could have arisen in the maximum number of ways, depending on our counting rule.

MEDUSA-32: A low noise, low power silicon strip detector front-end electronics, for space applications

Abstract In this report we describe a mixed analog-digital integrated circuit (IC) designed as the front-end electronics for silicon strip-detectors for space applications. In space power consumption, compactness and robustness become critical constraints for a pre-amplifier design. The IC is a prototype with 32 complete channels, and it is intended for a large area particle tracker of a new generation of gamma ray telescopes. Each channel contains a charge sensitive amplifier, a pulse shaper, a discriminator and two digital buffers. The reference trip point of the discriminator is adjustable. This chip also has a custom PMOSFET transistor per channel, included in order to provide the high dynamic resistance needed to reverse-bias the strip diode. The digital part of the chip is used to store and serially shift out the state of the channels. There is also a storage buffer that allows the disabling of non-functioning channels if it is required by the data acquisition system. An input capacitance of 30 pF introduced at the input of the front-end produces less than 1000 electrons of RMS equivalent noise charge (ENC), for a total power dissipation of only 60 μW per channel. The chip was made using Orbits 1.2 μm double poly, double metal n-well low noise CMOS process. The dimensions of the IC are 2400 μm × 8840 μm.