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

46 3. The Double Chooz experiment
tel-00821629, version 1 - 11 May 2013
Figure 3.4: View of the Inner Detector. From inside to outside, the target,
gamma-catcher and bu↵er volume equipped with 390 PMTs.
3.1.1 Target
The target volume (T) is the e↵ective fiducial volume for ¯⌫ e interaction. It
consists in a 8 mm thick acrylic vessel filled with 10.3 m 3 of organic liquid
scintillator.
The liquid scintillator in the target is composed of 80 % dodecane (C 12 H 26 ),
20 % PXE (C 6 H 18 ), 7 g/l of PPO, 20 g/l of bis-MSB and 1 g/l of Gd. PXE
and dodecane are aromatic molecules which get easily excited or ionised by
energy deposition. The energy is transferred non-radiatively to a PPO and
bis-MSB molecule which shift the scintillating light frequency to match the
PMT quantum e ciency range.
To ensure time stability of the Gd-doped liquid, the Gd atoms are encapsulated
in a Gd(dpm) 3 molecule, for an e cient dissolving in the scintillator
and a durable transparency. The optical stability of the liquid scintillator is
granted by the stability of the energy peak of neutron capture on Gd, which
has been found stable within 1 % over about one year [20]. This is one of
the main improvement with respect to the CHOOZ experiment, which was
limited in sensitivity because the optical instability of its liquid scintillator.
The proton number in the target (i.e. the absolute number of H nuclei) and