The ANTARES Optical Beacon System

ANTARES is a neutrino telescope being deployed in the Mediterranean Sea. It consists of a three dimensional array of photomultiplier tubes that can detect the Cherenkov light induced by charged particles produced in the interactions of neutrinos with the surrounding medium. High angular resolution can be achieved, in particular when a muon is produced, provided that the Cherenkov photons are detected with sufficient timing precision. Considerations of the intrinsic time uncertainties stemming from the transit time spread in the photomultiplier tubes and the mechanism of transmission of light in sea water lead to the conclusion that a relative time accuracy of the order of 0.5 ns is desirable. Accordingly, different time calibration systems have been developed for the ANTARES telescope. In this article, a system based on Optical Beacons, a set of external and well-controlled pulsed light sources located throughout the detector, is described. This calibration system takes into account the optical properties of sea water, which is used as the detection volume of the ANTARES telescope. The design, tests, construction and first results of the two types of beacons, LED and laser-based, are presented.Comment: 21 pages, 18 figures, submitted to Nucl. Instr. and Meth. Phys. Res.

First results of the Instrumentation Line for the deep-sea ANTARES neutrino telescope

In 2005, the ANTARES Collaboration deployed and operated at a depth of 2500 m a so-called Mini Instrumentation Line equipped with Optical Modules (MILOM) at the ANTARES site. The various data acquired during the continuous operation from April to December 2005 of the MILOM confirm the satisfactory performance of the Optical Modules, their front-end electronics and readout system. as well as the calibration devices of the detector. The in situ measurement of the Optical Module time response yields a resolution better than 0.5 ns. The performance of the acoustic positioning system, which enables the spatial reconstruction of the ANTARES detector with a precision of about 10 cm, is verified. These results demonstrate that with the full ANTARES neutrino telescope the design angular resolution of better than 0.3 degrees can be realistically achieved

Study of large hemispherical photomultiplier tubes for the ANTARES neutrino telescope

The ANTARES neutrino telescope, to be immersed depth in the Mediterranean Sea, will consist of a 3 dimensional matrix of 900 large area photomultiplier tubes housed in pressure resistant glass spheres. The selection of the optimal photomultiplier was a critical step for the project and required an intensive phase of tests and developments carried out in close collaboration with the main manufacturers worldwide. This paper provides an overview of the tests performed by the collaboration and describes in detail the features of the PMT chosen for ANTARES

The data acquisition system for the ANTARES neutrino telescope

The ANTARES neutrino telescope is being constructed in the Mediterranean Sea. It consists of a large three-dimensional array of photo-multiplier tubes. The data acquisition system of the detector takes care of the digitisation of the photo-multiplier tube signals, data transport, data filtering, and data storage. The detector is operated using a control program interfaced with all elements. The design and the implementation of the data acquisition system are described.Comment: 20 pages, 6 figures, accepted for publication in Nucl. Instrum. Meth.

The effects of thyroidectomy on the extraocular muscles of the rat: A histochemical study

The effects of thyroidectomy on the metabolic properties of the rat extraocular muscles have been studied using histochemical techniques. Six months after removal of the thyroid gland a significant increase in the proportion of Type 1 fibres was found in the central zone of the superior rectus (SR) and in the levator palpebrae superioris muscles, but not in the medial rectus (MR) or superior oblique (SO) muscles. Other changes included an increased proportion of Type 2a fibres and reduced proportions of Type 2a and 2b fibres in the central zone of the SR, and an increased proportion of type 2a, and a reduced proportion of Type 2a' fibres in the peripheral zone of the SR, MR and SO. In addition, there was a mild hypertrophy of Type 1 fibres in the MR, and a mild atrophy of Type 2 fibres in each of the muscles studied. The physiological significance of these findings is discussed

A histochemical study of fibre types in rat extraocular muscles

The histochemical fibre type composition of the rat superior and medial rectus (SR and MR), superior oblique (SO) and levator palpebrae superioris (LPS) muscles was studied using the myofibrillar ATPase and NADH-tetrazo-lium reductase (NADH-TR) techniques. In the SR, MR and SO a peripheral zone containing small fibres and a central zone containing both small and large fibres could be identified. Four fibre types were present in the central zone of these muscles and were categorised as Type 1, Type 2a, Type 2a', and Type 2b. Four fibre types were also identified in the peripheral zone–Type 1, Type 2a, Type 2a' and Type 2c. In the LPS Type 1, Type 2, Type 2a', Type 2b and Type 2c fibres were evenly intermixed without a zonal arrangement. The Type 1, Type 2a, Type 2b and Type 2c fibres correspond to accepted fibre types in the rat limb muscles. The Type 2a' and Type 2a' fibres were differentiated from the Type 2a fibres on the basis of size and pattern and intensity of staining with the NADH-TR technique. The Type 2c fibres, which possess both acid-stable and alkali-stable myofibrillar ATPase, are considered to represent intermediate fibres in the process of transformation from Type 2 to Type 1, rather than fibres with a dual innervation as has been suggested in the past. The implications of these histochemical findings are considered in relationship to the physiology of individual motor units and to the function of the extraocular muscles