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A prototype array of modular sensors for online monitoring of radioactive waste was developed at INFN-LNS. We implemented a new kind of gamma mini-sensor, based on Silicon PhotoMultipliers and scintillating fibers, that behaves like a cheap scintillating Geiger-Muller counter. It can be placed in shape of a fine grid around each single waste drum in a repository. After simulating the counting response of thin scintillating fibers to gamma radiation, we verified our simulation results with measurements using radioactive sources. Front-end electronics and an FPGA-based counting system were developed to handle the field data, also implementing data transmission, a graphical user interface and a data storage system. A test of four sensors in a real radwaste storage site was performed with promising results.

In this paper we present the results of the first electrical and optical characterization performed on 1 mm2 total area Silicon Photomultipliers (SiPM) fabricated in standard silicon planar technology at the STMicroelectronics Catania R&D clean room facility. The device consists of 289 microcells and has a geometrical fill factor of 48%. Breakdown voltage, gain, dark noise rate, crosstalk, photon detection efficiency and linearity have been measured in our laboratories. The optical characterization has been performed by varying the temperature applied to the device. The results shown in the manuscript demonstrate that the device already exhibits relevant features in terms of low dark noise rate and inter-pixel crosstalk probability, high photon detection efficiency, good linearity and single photoelectron resolution. These characteristics can be considered really promising in view of the final application of the photodetector in the Positron Emission Tomography (PET).

The fabrication of silicon shallow junction photodiodes is a relevant topic for the detection of blue and near ultraviolet weak photon fluxes. In this paper we present a simple model to calculate the quantum detection efficiency (QDE) of a Geiger mode avalanche photodiode (GMAP) as a function of the dead layer thickness above the junction depletion layer. A comparison between calculated and experimental data is also presented. Moreover, by using the same model, an analysis of the QDE at 420 nm wavelength of conventional GMAPs based on shallow N+-P and P+-N junctions is given.

We outline the possible applications of newly developed single photon avalanche detectors (SPAD) operating at low voltage and fabricated in silicon planar technology, reporting on tests done with scintillators. We envisage the integration of large arrays of identical sensors, employing a common read-out mode in order to achieve a high resolution and high sensitivity solid state photomultiplier. The applications of such a device would be many, particularly if we consider that we are also working on the production of microoptical components, perfectly suited for the lossless coupling of these photosensors to several light sources (lasers, ordinary and scintillating fibers, scintillators, optical devices), by exploiting the promising deep lithography with ions (DLI) technology. Crossed time-of-flight and charge measurements between SPADs and usual photomultipliers, coupled to scintillators, have allowed to compare their relative performance. Specific issues regarding the SPAD and the scintillating fiber readout are presented, also in view of possible applications in the field of particle/radiation tracking systems.

We have developed two techniques for microscopic particle beam imaging and dose measurement, both based on scintillators. One employs a scintillating fiberoptic plate to display the two-dimensional beam transversal profile, the other makes use of a small scintillator optically coupled to a compact photomultiplier. We have proved the possibility of detection from single beam particles up to several nanoampere currents. Both the devices are successfully being exploited for on-line control of low and very low intensity proton beams, down to a beam size of

In the framework of the HADES (High Acceptance DiElectron Spectrometer) collaboration we are developing the Time Of Flight (TOF) wall subdetector. In order to efficiently select events with e/sup +/e/sup -/ pairs produced in the nuclear matter, the TOF wall must be able to resolve electrons from pions up to 0.5 GeV/c and from protons up to 2 GeV/c. Because the short flight path of about 2 m requires a 100-150 ps time resolution, we are building a granular system made of scintillator rods readout on both ends by means of photomultipliers, capable of such performance.

In the framework of the EXCYT radioactive ion beam facility, now under development at LNS Catania, we have developed several devices for beam monitoring. These devices are mainly based on scintillator detectors and photosensors, since they should allow to reconstruct beam informations even when operating at very low intensity, where conventional electrical devices are no longer sensitive. This new class of devices promises to give a good reliability and robustness at a cheap price, and in some case it will also allow counting the beam particles one by one.

The data acquisition system for the 4 pi multidetector Crystal Ball of the LNS (Laboratorio Nazionale del Sud) is described. This system is built around a modular multiprocessor architecture. VMEbus-based, using a one-broadcasting/many receivers data-passing scheme, in order to allow different functions to be performed asynchronously and concurrently on separate receiver stations. A well-tested software architecture is used, to keep simple the interaction of the user with the whole system. >

A modular multiprocess software architecture for off-line experimental nuclear data handling has been developed. It is mainly based on a circular queueing network with server processes, and data buffers as service requests. A general controller process implements a user friendly interface, communicating in a transparent way with the related server to control the whole system. The efficiency of this architecture has been already tested with the realization of a package of programs, running on a VAX computer under VAX/VMS operating system, to be used for off-line analysis. This architecture, with some modifications, has been translated into a VMEbus multiprocessor environment, to be used as acquisition software for the Crystal Ball data acquisition system. >

A trigger and preanalysis system for the 4 pi multidetector Crystal Ball of the LNS is (Laboratorio Nazionale del Sud) is under development. This electronic trigger, set up using about sixty CAMAC modules connected by a fast auxiliary bus in ECL (emitter coupled logic), has been designed to handle the data coming from the ADC (analog-to-digital converter) and TDC (time-to-digital converter) systems and reorganize them on a detector-by-detector basis, in order to broadcast them via a distribution bus to the attached computer system. >