JUNO is a massive liquid scintillator detector with a primary scientific goal of determining the neutrino mass ordering by studying the oscillated anti-neutrino flux coming from two nuclear power plants at 53 km distance. The expected signal anti-neutrino interaction rate is only 60 counts per day (cpd), therefore a careful control of the background sources due to radioactivity is critical. In particular, natural radioactivity present in all materials and in the environment represents a serious issue that could impair the sensitivity of the experiment if appropriate countermeasures were not foreseen. In this paper we discuss the background reduction strategies undertaken by the JUNO collaboration to reduce at minimum the impact of natural radioactivity. We describe our efforts for an optimized experimental design, a careful material screening and accurate detector production handling, and a constant control of the expected results through a meticulous Monte Carlo simulation program. We show that all these actions should allow us to keep the background count rate safely below the target value of 10 Hz (i.e. ∼1 cpd accidental background) in the default fiducial volume, above an energy threshold of 0.7 MeV.
A novel advanced oxidation process
(AOP) using ultraviolet/sodium
chlorite (UV/NaClO2) is developed for simultaneous removal
of SO2 and NO. NH4OH, as an additive, was used
to inhibit the generation of ClO2 and NO2. The
removal efficiencies of SO2 and NO reached 98.7 and 99.1%.
NO removal was enhanced by greater UV light intensity and shorter
wavelengths but was insensitive to changes in pH and temperature.
SO2 at 500–1000 mg/m3 improved NO removal,
especially in the absence of UV. The coexistence of SO2 and O2 facilitated the removal of NO by ClO2
–. HCO3
–, Cl–, and Br– enhanced NO removal, but their roles
were negligible when UV was added. The generation of ClO2 and ClO•/HO• was verified by
an UV–vis spectrometer, electron spin resonance (ESR), and
radical-quenching tests. The mechanisms responsible for the removal
of SO2 and NO were attributed to the synergism between
acid–base neutralization and radical-induced oxidation. The
ClO2
– evolution and product composition
were demonstrated by UV–vis and X-ray photoelectron spectroscopy
(XPS). Kinetics analyses showed that the Hatta numbers were 329–798
and 747–1000 without and with UV. Thus, the gas–film
resistance mainly controlled the mass-transfer process.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.