Sedimentation and fouling of optical surfaces at the ANTARES site

Abstract

ANTARES is a project leading towards the construction and deployment of a neutrino telescope in the deep Mediterranean Sea. The telescope will use an array of photomultiplier tubes to detect the Cherenkov light emitted by muons resulting from the interaction with matter of high energy neutrinos. In the vicinity of the deployment site the ANTARES collaboration has performed a series of in-situ measurements to study the change in light transmission through glass surfaces during immersions of several months. The average loss of light transmission is estimated to be only ∼ 2% at the equator of a glass sphere one year after deployment. It decreases with increasing zenith angle, and tends to saturate with time. The transmission loss, therefore, is expected to remain small for the several year lifetime of the ANTARES detector whose optical modules are oriented downwards. The measurements were complemented by the analysis of the 210 Pb activity profile in sediment cores and the study of biofouling on glass plates. Despite a significant sedimentation rate at the site, in the 0.02 -0.05 cm · yr −1 range, the sediments adhere loosely to the glass surfaces and can be washed off by water currents. Further, fouling by deposits of light-absorbing particulates is only significant for surfaces facing upwards.

Hunting for cosmic neutrinos under the deep sea: the ANTARES experiment

“…Sometimes sudden, short bursts which may reach up to several MHz are also detected, presumably due to living macro-organisms. The fraction of time in which bursts occur (Burst Fraction or BF) ranges between a few percent and 50 percent, with an average value of about 4 ÷ 5% [21,22,23].…”

High-energy astrophysics with neutrino telescopes

“…From 1996 to 1999 an extensive R&D program has been successfully performed to prove the feasibility of the detector concept. Site properties have been studied such as: optical properties of the surrounding water [216]; biofouling on optical surfaces [217]; optical backgrounds due to bioluminescence and to the decay of the radioactive salts present in seawater [218]; geological characteristics of its ground. These studies lead to the selection of the current site, 40 km off La Seyne-sur-Mer (France) at a 2475 m depth.…”

The ANTARES Neutrino Telescope

“…The ANTARES neutrino telescope is located in the Mediterranean Sea, about 40 km from the coast of Toulon, France, at 42°48'N, 6°10'E, and at a depth of 2475 m [9] [10]. A schematic view of the detector is shown in Fig.…”