We calculated the expected neutrino signal in Borexino from a typical Type II supernova at a distance of 10 kpc. A burst of around 110 events would appear in Borexino within a time interval of about 10 s. Most of these events would come from the reaction channelν e + p → e + + n, while about 30 events would be induced by the interaction of the supernova neutrino flux on 12 C in the liquid scintillator. Borexino can clearly distinguish between the neutral-current excitations 12 C(ν, ν ′ ) 12 C * (15.11 MeV) and the charged-current reactions 12 C(ν e , e − ) 12 N and 12 C(ν e , e + ) 12 B, via their distinctive event signatures. The ratio of the chargedcurrent to neutral-current neutrino event rates and their time profiles with respect to each other can provide a handle on supernova and non-standard neutrino physics (mass and flavor oscillations).
The SNO+ liquid scintillator experiment is under construction in the SNOLAB facility in Canada. The success of this experiment relies upon accurate characterization of the liquid scintillator, linear alkylbenzene (LAB). In this paper, scintillation decay times for alpha and electron excitations in LAB with 2 g/L PPO are presented for both oxygenated and deoxygenated solutions. While deoxygenation is expected to improve pulse shape discrimination in liquid scintillators, it is not commonly demonstrated in the literature. This paper shows that for linear alkylbenzene, deoxygenation improves discrimination between electron and alpha excitations in the scintillator.
The thermal, oxidative and photochemical stability of the scintillator liquid proposed for the SNO+ experiment has been tested experimentally using accelerated aging methods. The stability of the scintillator constituents was determined through fluorescence excitation emission matrix (EEM) spectroscopy and absorption spectroscopy, using parallel factor analysis (PARAFAC) as an multivariate analysis tool. By exposing the scintillator liquid to a well-known photon flux at 365 nm and by measuring the decay rate of the fluorescence shifters and the formation rate of their photochemical degradation products, we can place an upper limit on the acceptable photon flux as 1.38 ± 0.09 × 10 photon mol L. Similarly, the oxidative stability of the scintillator liquid was determined by exposure to air at several elevated temperatures. Through measurement of the corresponding activation energy it was determined that the average oxygen concentration would have to be kept below 4.3-7.1 ppb (headspace partial pressure below 24 ppm). On the other hand, the thermal stability of the scintillator cocktail in the absence of light and oxygen was remarkable and poses no concern to the SNO+ experiment.
The Sudbury Neutrino Observatory completed taking data in its third phase on November 28, 2006. In this phase ^He proportional counters deployed in the heavy water served as the detectors for the neutrons produced by neutral-current interactions from ^B solar neutrinos. With this ability to distinguish neutral current events the goal is to bring the total uncertainty for the neutral current signal below 5%. Several improvements in the analysis have sharpened the energy resolution. Improvements in SNO water systems have also lowered background levels during the third phase. These improvements allow for a lower analysis threshold and SNO is working on this also. After the heavy water is removed from the SNO detector, the plan is to fill the detector with a liquid scintillator. SNO+, as this is called, will be able to detect lower energy neutrinos such as the pep solar neutrinos, geoneutrinos and reactor antineutrinos. By loading the SNO+ scintillator with neodymium, a competitive neutrinoless double beta decay search is also possible.
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