Over the course of several decades, organic liquid scintillators have formed the basis for successful neutrino detectors. Gadolinium-loaded liquid scintillators provide efficient background suppression for electron antineutrino detection at nuclear reactor plants. In the Double Chooz reactor antineutrino experiment, a newly developed beta-diketonate gadolinium-loaded scintillator is utilized for the first time. Its large scale production and characterization are described. A new, light yield matched metal-free companion scintillator is presented. Both organic liquids comprise the target and "Gamma Catcher" of the Double Chooz detectors. In the Double Chooz (DC) experiment [3] two new types of Gd-LS have been studied and further tested. These are Gd-BDK TM (for Gd beta-diketonate) and Gd-CBX TM (for Gd carboxylate) [4,5]. These two systems meet the basic requirements for the DC scintillator: chemical stability of the Gd molecules and the other LS components, compatibility with detector materials, transparency, intrinsic light yield, radiopurity, Gd solubility and the stability of these properties over several years of data taking. Optimization of the optical properties includes the need to tune the light yield while maintaining a constant density and matching the light emission to the spectral response of the photomultiplier tubes (PMTs).The Gd-LS that is currently loaded in the DC Far Detector is based on beta-diketone chemistry, the first use in a large scale antineutrino detector. The chemistry of this new Gd-BDK scintillator [6] is based in part on knowledge obtained from studies of the similar Indium (In-BDK) system [7] developed at MPIK, Heidelberg and used in the LENS (Low Energy Neutrino Spectroscopy) Prototype at Gran Sasso [8]. The specific Gd organic scintillator candidate, that we initially considered, was based on the use of the simplest five carbon BDK anion -ACAC (acetylacetonate). We found this BDK compound difficult to sublime and thus it lacked a potential productive route to achieving the level of optical and radiochemical purity needed in the DC experiment. Consequently, in the final version, the BDK was selected to be THD (2,2,6,6-tetramethyl-heptane-3,5-dionate) based on extensive research experience in producing solid, liquid and gaseous Gd-THD for testing in the Ho-163 neutrino mass experiments [9]. The more effective shielding of the metal ions by the

A: The S experiment is a very short baseline reactor antineutrino experiment aiming at testing the hypothesis of light sterile neutrinos as an explanation of the deficit of the observed neutrino interaction rate with respect to the predicted rate, known as the Reactor Antineutrino Anomaly. The detector center is located 10 m away from the compact, highly 235 U enriched core of the research nuclear reactor of the Institut Laue Langevin in Grenoble, France. This paper describes the S site, the detector components and associated shielding designed to suppress the external sources of background which were characterized on site. It reports the performances in terms of detector response and energy reconstruction.

For the simulation of the scintillation and Cherenkov light propagation in large liquid scintillator detectors a detailed knowledge about the absorption and emission spectra of the scintillator molecules is mandatory. Furthermore reemission probabilities and quantum yields of the scintillator components influence the light propagation inside the liquid. Absorption and emission properties are presented for liquid scintillators using 2,5-Diphenyloxazole (PPO) and 4-bis-(2-Methylstyryl)benzene (bis-MSB) as primary and secondary wavelength shifter. New measurements of the quantum yields for various aromatic molecules are shown.

The electron antineutrino spectrum in the S reactor experiment (ILL Grenoble) is measured via the inverse beta decay signals in an organic liquid scintillator. The six target cells of the S detector are filled with about 1800 litres of Gd-loaded liquid scintillator optimised for the requirements of the experiment. These target cells are surrounded by similar cells containing liquid scintillator without the Gd-loading. The development and characteristics of these scintillators are reported. In particular, the transparency, light production and pulse shape discrimination capabilities of the organic liquids are discussed.