The heterogeneous reactivity of gaseous nitrogen dioxide on mineral oxide particles was investigated. In particular, spectroscopic and kinetic measurements have been made to investigate surface reactions of NO2 on Al2O3, Fe2O3, and TiO2 at 298 K. Both gas-phase and surface-bound products are formed from the reaction of NO2 with these mineral oxide particles. At low coverages, FT-IR spectra of the mineral oxide surface exposed to gaseous NO2 show absorptions due to surface nitrite, specifically a chelating nitrito species. As the coverage increases, the surface becomes populated with surface nitrate bonded in several different bonding coordinations (monodentate, bidentate, and bridging). The predominant gas-phase product is NO, although there is a small amount (<1%) of detectable N2O. A Knudsen cell reactor coupled to a quadrupole mass spectrometer was used to measure the uptake coefficient, γ, for NO2 on these oxide particles and to characterize gas-phase product formation. The Knudsen cell data showed NO to be the major gas-phase product with a delay in the onset of NO production. There was little production of N2O and no gas-phase HONO or HNO3 was detected. By monitoring the reaction until completion, the ratio of NO2 reacted to NO produced was determined to be ∼2:1. These results complement the FT-IR data and suggest a two-step mechanism in which NO2(g) is initially adsorbed as a nitrite species which subsequently reacts with additional NO2 to form surface nitrate and gas-phase NO. Finally, the initial uptake coefficient was determined from the Knudsen cell data for NO2 on Al2O3, Fe2O3, and TiO2. Because NO2 can diffuse into the underlying layers of these oxide particles, the use of a geometric area does not give accurate values of the uptake coefficient. Gas diffusion must be taken into account to more accurately determine the uptake coefficient.

In this Technical Design Report (TDR) we describe the NEXT-100 detector that will search for neutrinoless double beta decay (β β 0ν) in 136 Xe at the Laboratorio Subterráneo de Canfranc (LSC), in Spain. The document formalizes the design presented in our Conceptual Design Report (CDR): an electroluminescence time projection chamber, with separate readout planes for calorimetry and tracking, located, respectively, behind cathode and anode. The detector is designed to hold a maximum of about 150 kg of xenon at 15 bar, or 100 kg at 10 bar. This option builds in the capability to increase the total isotope mass by 50% while keeping the operating pressure at a manageable level. The readout plane performing the energy measurement is composed of Hamamatsu R11410-10 photomultipliers, specially designed for operation in low-background, xenon-based detectors. Each individual PMT will be isolated from the gas by an individual, pressure resistant enclosure and will be coupled to the sensitive volume through a sapphire window. The tracking plane consists in an array of Hamamatsu S10362-11-050P MPPCs used as tracking pixels. They will be arranged in square boards holding 64 sensors (8 × 8) with a 1-cm pitch. The inner walls of the TPC, the sapphire windows and the boards holding the MPPCs will be coated with tetraphenyl butadiene (TPB), a wavelength shifter, to improve the light collection.

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NEXT-DEMO is a high-pressure xenon gas TPC which acts as a technological testbed and demonstrator for the NEXT-100 neutrinoless double beta decay experiment. In its current configuration the apparatus fully implements the NEXT-100 design concept. This is an asymmetric TPC, with an energy plane made of photomultipliers and a tracking plane made of silicon photomultipliers (SiPM) coated with TPB. The detector in this new configuration has been used to reconstruct the characteristic signature of electrons in dense gas. Demonstrating the ability to identify the MIP and "blob" regions. Moreover, the SiPM tracking plane allows for the definition of a large fiducial region in which an excellent energy resolution of 1.82% FWHM at 511 keV has been measured (a value which extrapolates to 0.83% at the xenon Q β β ).

In this study, heterogeneous reactions of NO2 on NaCl and Al2O3 particles, two different types of particles present in the Earth’s atmosphere, are compared. Transmission Fourier-transform infrared spectroscopy and diffuse reflectance UV/Vis spectroscopy are used to characterize gas-phase and adsorbed products following reaction with NO2. For Al2O3 particles, two adsorbed species have been identified. At low NO2 pressures, adsorbed nitrite is formed whereas at higher NO2 pressures, nitrate is present on the surface of the aluminum oxide particles. For NaCl particles, adsorbed nitrate forms at all NO2 pressures. Kinetic measurements show that nitrate formation on sodium chloride is second order in NO2 pressure, in agreement with previous studies, whereas nitrate formation on aluminum oxide is first order in NO2 pressure. The potential importance of heterogeneous reactions of NO2 with these particles in the atmosphere is discussed.