Etude et impact du bruit de fond corrélé pour la mesure de l'angle ...

3.1 The Double Chooz detector 47
its associated error are crucial parameters for the experiment. The error on
the proton number is minimised by using a well defined and pure chemicals
in combination with a precise knowledge of the weights of each chemical
added in the scintillator production. The amount of scintillator in the target
has been determined upon liquid thermalisation by weight measurement,
with a precision of 0.04 %. The H fraction in the target scintillator is known
with a 0.3 % precision [21].
3.1.2 Gamma Catcher
tel-00821629, version 1 - 11 May 2013
The gamma catcher volume (GC) surrounds the target with the function to
collect gammas from IBD and n-Gd capture increasing the energy containment
e ciency of the detector. It consists in a 12 mm thick acrylic vessel
filled with 22.3 m 3 of liquid scintillator.
The GC liquid scintillator composition consists of 30 % dodecane, 66 %
mineral oil, 4 % PXE, 2 g/l of PPO and 20 mg/l of bis-MSB. Liquid composition
is tuned to match target liquid density and light yield to assure the
safety of the acrylics vessel and increase uniformity of the detector response.
3.1.3 Bu↵er
The bu↵er optically isolates the ID from the IV and serves as support for the
390 ID photomultiplier tubes. The bu↵er is another main improvement with
respect to CHOOZ design, its main function is to shield the T and the GC
volumes from gammas radioactivity (mainly from PMTs photocathode) and
neutrons created by muon interacting in the rock surrounding the detector.
It consists in a 105 cm thick volume of 114 m 3 filled with non scintillating
oil.
Oil composition consists of 47.2 % CobersolC70 and 52.8 % Ondina917 oils
and has been chosen to ensure material compatibility with the GC acrylics
vessel and PMTs and high transparency in the scintillator emission wavelengths.
3.1.4 Inner Veto
The IV is an active liquid scintillator detector surrounding the ID. Its main
purpose is to shield the ID against low energy radioactive background and
to detect with high e ciency cosmic muons and spallation neutrons crossing
its volume.
The IV consists of a cylinder of 90 m 3 filled with liquid scintillator, ⇠50 %
n-alkanes and ⇠50 % LAB (linear alkyl benzene) with 2 g/l of PPO and 20
mg/l of bis-MSB as wavelength shifters.
The IV is equipped with 78 PMTs fixed on the bottom, on the lateral surface
of the 10 mm thick inner veto tank and on the upper bu↵er lid. The PMTs