The photochromic behaviour of a series of 2,2-diphenyl(2H)chromenes, bearing different substituents (methyl, thienyl, B(OH)
2 and nitro groups), has been investigated. The photochromism of these ...molecules is described in terms of absorption spectra, photocolouration and photobleaching quantum yields, kinetics of thermal bleaching and competition between photochemical and photophysical relaxation. The quantum yield of UV photocolouration is generally fairly high (0.7–1.0), but decreases for compounds with thienyl and nitro substituents. The ring-open coloured form thermally rearranges to the closed uncoloured form, whereas visible photobleaching is substantially negligible (≤10
−3). The thermal bleaching process is markedly affected by the substituents and, in the case of the nitro-derivatives, is characterised by a drastic decrease of activation entropy and enthalpy.
This paper describes the procurement and the production quality control system of Pseudocumene, the scintillator solvent of the solar neutrino detector Borexino at the Laboratorio Nazionale del Gran ...Sasso (Italy). This material constitutes about 99.9% of the scintillator total mass, therefore being the most critical element for the radiopurity of the detector.
In this paper we study the photophysical and photochemical behavior of two aromatic N-oxyimidosulfonate photoacid generators (PAGs), N-trifluoromethylsulfonyloxy-phthalimide (PIT) and ...N-trifluoromethylsulfonyloxy-1,8-naphthalimide (NIT), by means of absorption and emission stationary techniques and nanosecond and picosecond laser flash photolysis. Triplet states have been detected for both compounds; lifetimes of 12 μs and 43 μs (acetonitrile solution) and 2 μs and 28 μs, (benzene solution), were measured for PIT and NIT, respectively. Photoacid generation quantum yields have also been measured (Φ = 0.28 in acetonitrile, Φ = 0.21 in benzene for PIT; Φ = 0.17 in acetonitrile, Φ = 0.09 in benzene for NIT), using Rhodamine B Base as an acid sensor and 2-methyl-4,6-bis(trichloromethyl)-1,3,5-triazine as a suitable actinometer with 308-nm laser excitation. Evidence that photoacid generation occurs through an ionic mechanism from the singlet state was obtained.
The photochromism of three spiro-oxazines was investigated in a gel network (AOT/isooctane/animal gelatin/water), which is transparent to the visible and near UV light, as well as in a microemulsion ...(AOT/toluene/water) and in the hydrocarbon component of the microheterogeneous gelled system. The spectral shifts of the photomerocyanine color band, which were determined in different media, provided information on the location of the molecules in these microheterogeneous systems. By a photokinetic study of the color-forming and color-fading reactions, the photocoloration quantum yields and bleaching rate constants were determined. By comparing the results obtained in a gel network with those determined in a homogeneous solution, it was observed that for two of the compounds investigated the photocolorability markedly decreases in the gel as a consequence of hastening of the bleaching processes. For the third molecule (an anthraquinone derivative), the colorability greatly increases in a gel network. The different behaviors are explained in terms of the ground-state polarity properties of the photomerocyanines and the consequent solute/solvent interaction effects on the dynamics of thermal bleaching.
The rate of neutrino-electron elastic scattering interactions from 862 keV Be7 solar neutrinos in Borexino is determined to be 46.0±1.5(stat)-1.6+1.5(syst)counts/(day*100ton). This corresponds to a ...νe-equivalent Be7 solar neutrino flux of (3.10±0.15)×109cm-2s-1 and, under the assumption of νe transition to other active neutrino flavours, yields an electron neutrino survival probability of 0.51±0.07 at 862 keV. The no flavor change hypothesis is ruled out at 5.0σ. A global solar neutrino analysis with free fluxes determines Φpp=6.06-0.06+0.02×1010cm-2s-1 and ΦCNO<1.3×109cm-2s-1 (95% C.L.). These results significantly improve the precision with which the Mikheyev-Smirnov-Wolfenstein large mixing angle neutrino oscillation model is experimentally tested at low energy.
Jiangmen Underground Neutrino Observatory (JUNO) is a next generation liquid scintillator neutrino experiment under construction phase in South China. Thanks to the anti-neutrinos produced by the ...nearby nuclear power plants, JUNO will be able to study the neutrino mass hierarchy, one of the open key questions in neutrino physics. One key ingredient for a successful measurement is to use high speed, high resolution sampling electronics located very close to the detector signal. Linearity in the response of the electronics is another important ingredient for the success of the experiment. During the initial design phase of the electronics, a custom design with the Front-End and Read-Out electronics located very close to the detector analog signal has been developed and successfully tested. The present paper describes the electronics structure and the first tests performed on the prototypes. The electronics prototypes have been tested and they show good linearity response, with a maximum deviation of 1.3% over the full dynamic range (1-1000 p.e.), fulfilling the JUNO experiment requirements.
This paper describes the design, construction principles and operations of the distillation and stripping pilot plants tested at the Daya Bay Neutrino Laboratory, with the perspective to adapt these ...processes, system cleanliness and leak-tightness standards to the final full scale plants to be used for the purification of the liquid scintillator of the JUNO neutrino detector. The main goal of these plants is to remove radio impurities from the liquid scintillator while increasing its optical attenuation length. Purification of liquid scintillator will be performed with a system combining alumina oxide, distillation, water extraction and steam (or N2 gas) stripping. Such a combined system will aim at obtaining a total attenuation length greater than 20 m @430 nm, and a bulk radiopurity for 238U and 232Th in the 10−15÷ 10−17 g/g range. The pilot plants commissioning and operation have also provided valuable information on the degree of reliability of their main components, which will be particularly useful for the design of the final full scale purification equipment for the JUNO liquid scintillator. This paper describes two of the five pilot plants since the Alumina Column, fluorescent material mixing and the Water Extraction plants are being developed by the Chinese part of the collaboration.
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