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This document is a comment on a previous study that examined the Meissner screening properties of niobium (Nb) in a superconducting radio frequency (SRF) cavity. The authors of the comment re-analyzed the data from the original study and found no significant changes to the Meissner screening profile of Nb after mild baking. They also discovered a non-superconducting "dead layer" at the surface of the Nb sample, which may indicate spatial inhomogeneities in the screening properties. The authors recommend further high-resolution measurements to investigate this further. [Extracted from the article]

Identifying the loss mechanisms of niobium cavities enables an accurate determination of applications for future accelerator projects and points to research topics required to mitigate current limitations. For several cavities an increasing surface resistance above a threshold field, saturating at higher field has been observed. Measurements on samples give evidence that this effect is caused by the surface electric field. The measured temperature and frequency dependence is consistent with a model that accounts for these losses by interface tunnel exchange between localized states in dielectric oxides and the adjacent superconductor. [ABSTRACT FROM PUBLISHER]

Terbutryn is a widely used biocide in construction materials like paint and render to prevent the growth of microorganisms, algae and fungi. Terbutryn is released from the facades into the environment during rainfall, contaminating surface waters, soil and groundwater. Knowledge of terbutryn dissipation from the facades to aquatic ecosystems is scarce. Here, we examined in laboratory microcosms degradation half-lives, formation of transformation products and carbon and nitrogen isotope fractionation during terbutryn direct (UV light with λ = 254 nm and simulated sunlight) and indirect (simulated sunlight with nitrate) photodegradation, abiotic hydrolysis (pH = 1, 7 and 13), and aerobic biodegradation (stormwater pond sediment, soil and activated sludge). Biodegradation half-lives of terbutryn were high (>80 d). Photodegradation under simulated sunlight and hydrolysis at extreme pH values indicated slow degradability and accumulation in the environment. Photodegradation resulted in a variety of transformation products, whereas abiotic hydrolysis lead solely to terbutryn-2-hydroxy in acidic and basic conditions. Biodegradation indicates degradation to terbutryn-2-hydroxy through terbutryn-sulfoxide. Compound-specific isotope analysis (CSIA) of terbutryn holds potential to differentiate degradation pathways. Carbon isotope fractionation values (ε C) ranged from −3.4 ± 0.3‰ (hydrolysis pH 1) to +0.8 ± 0.1‰ (photodegradation under UV light), while nitrogen isotope fractionation values ranged from −1.0 ± 0.4‰ (simulated sunlight photodegradation with nitrate) to +3.4 ± 0.2‰ (hydrolysis at pH 1). In contrast, isotope fractionation during biodegradation was insignificant. ΛN/C values ranged from −1.0 ± 0.1 (hydrolysis at pH 1) to 2.8 ± 0.3 (photodegradation under UV light), allowing to differentiate degradation pathways. Combining the formation of transformation products and stable isotope fractionation enabled identifying distinct degradation pathways. Altogether, this study highlights the potential of CSIA to follow terbutryn degradation in situ and differentiate prevailing degradation pathways, which may help to monitor urban biocide remediation and mitigation strategies. [Display omitted] • The biocide terbutryn released from building facades can contaminate soil and water. • Laboratory microcosms to examine terbutryn hydrolysis, photo- and biodegradation. • Terbutryn degradation half-lives are high under environmental conditions. • Transformation products and CSIA of terbutryn to identify degradation pathways. • Differentiation of terbutryn degradation pathways based on dual-isotope values (ΛN/C). [ABSTRACT FROM AUTHOR]

We report measurements of the Meissner screening profile in a Nb (300 nm)/ Al 2 O 3 thin film using 8 Li β -detected nuclear magnetic resonance (β -NMR). The NMR probe 8 Li was ion-implanted into the Nb film at energies ≤ 20 keV, corresponding to mean stopping depths comparable to Nb 's magnetic penetration depth λ. 8 Li 's strong dipole–dipole coupling with the host 93 Nb nuclei provided a "cross-relaxation" channel that dominated in low magnetic fields, which conferred indirect sensitivity to the local magnetic field via the spin-lattice relaxation (SLR) rate 1 / T 1. From a fit of the 1 / T 1 data to a model accounting for its dependence on temperature, magnetic field, and 8 Li + implantation energy, we obtained a magnetic penetration depth λ 0 = 51.5(22) nm, consistent with a relatively short carrier mean-free-path ℓ = 18.7(29) nm typical of similarly prepared Nb films. The results presented here constitute an important step toward using 8 Li β -NMR to characterize bulk Nb samples with engineered surfaces, which are often used in the fabrication of particle accelerators. [ABSTRACT FROM AUTHOR]

Superconducting Radio-Frequency cavities are currently made out of niobium. Niobium cavities are limited by the magnetic field on the cavity walls due to the entry of vortices at the field of first vortex penetration, H vp . Low temperature baking in vacuum or low pressure gas atmosphere removes the strong decrease of the quality factor with accelerating gradient (high field Q-slope). Some cavities reach surface magnetic field above the lower critical field H c 1 . One hypothesis for this performance increase is that the outer layer affected by the treatments acts as a barrier for vortex penetration (effective bilayer). Using a vibrating sample magnetometer the field of first flux penetration (H vp ) was measured for Nb ellipsoids with various low temperature treatments. All H vp values were found to be consistent with the lower critical field, H c 1 , as predicted for clean niobium. This led to the conclusion that a metastable flux free state above H c 1 cannot be observed in DC magnetometry for low temperature baked niobium unlike for bilayers consisting of two superconductors as previously published. The effect of flux pinning differed significantly between treatments, suggesting that the high field Q-slope mitigation might be related to vortex pinning in the surface of the cavities. [ABSTRACT FROM AUTHOR]

Characterization of groundwater-surface water interactions remains challenging,especially in anthropogenically affected and geologically complex river systems. In thisstudy, groundwater inflow into the Ammer River was quantified by optimizingexfiltration rates in an implicit numerical model (FINIFLUX) to measured data ofseveral environmental tracers (e.g., sulfate (SO42−), radon (222Rn)) and organicconservative pollutants like carbamazepine and sulfamethoxazole emitted via awastewater treatment plant (WWTP). Modelling results of the selected tracers werecompared. The investigated Ammer River is strongly karstified and anthropogenically modified (millcanals, weirs, numerous artificial inputs) but representative for many small river systems inEurope. 222Rn activities in the river ranged from 500 to 3300 Bq m−3 and SO42−concentrations from 224 to 291 mg L−1. Concentrations of carbamazepine (90-130 ng L−1)and sulfamethoxazole (55-100 ng L−1) in the river water result from effluents of aWWTP. All tracers indicate major local groundwater inflows over the 6 km riverreach. Additional high peaks mainly observed in 222Rn activities indicate inputsalong geological fault lines, whereby increasing concentrations of carbamazepineand sulfamethoxazole may be attributed to inputs of groundwater contaminated byinfiltration of wastewater from a nearby WWTP. 222Rn-based calculations showed thebest optimization performance (R2=0.90) and result in a reasonable cumulativegroundwater inflow of 0.274 m3 s−1 (28.5% of total discharge) for the investigated reach.Poor optimizations for the other tracers may be due to the diurnal pattern of ionconcentrations induced by the WWTP and measurement uncertainties and the smallconcentration differences between river water and groundwater for carbamazepine andsulfamethoxazole. In our case study, 222Rn seems to be the most suitable environmental tracer despiteuncertainties in degassing and determination of the groundwater endmember concentration.However, only a multi tracer approach can account for the complexity of the investigatedriver system and may thus be indispensable for future investigations aiming to understandgroundwater-surface water interactions. [ABSTRACT FROM AUTHOR]

Measuring neutron capture cross sections of radioactive nuclei is a crucial step towards a better understanding of the origin of the elements heavier than iron. For decades, the precise measurement of direct neutron capture cross sections in the "stellar" energy range (eV up to a few MeV) was limited to stable and longer-lived nuclei that could be provided as physical samples and then irradiated with neutrons. New experimental methods are now being developed to extend these direct measurements towards shorter-lived radioactive nuclei ( t 1 / 2 < 1 y). One project in this direction is a low-energy heavy-ion storage ring coupled to the ISAC facility at TRIUMF, Canada's accelerator laboratory in Vancouver BC, which has a compact neutron source in the ring matrix. Such a pioneering facility could be built within the next 10 years and store a wide range of radioactive ions provided directly from the existing ISOL facility, allowing for the first time to carry out direct neutron capture measurements on short-lived isotopes in inverse kinematics. [ABSTRACT FROM AUTHOR]

A new high field spectrometer has been built to extend the capabilities of the β-detected nuclear magnetic resonance (β-NMR) facility at TRIUMF. This new beamline extension allows β-NMR spectroscopy to be performed with fields up to 200 mT parallel to a sample's surface (perpendicular to the ion beam), allowing depth-resolved studies of local electromagnetic fields with spin polarized probes at a much higher applied magnetic field than previously available in this configuration. The primary motivation and application is to allow studies of superconducting radio frequency (SRF) materials close to the critical fields of Nb metal, which is extensively used to fabricate SRF cavities. The details of the design considerations and implementation of the ultra-high vacuum (UHV) system, ion optics, and beam diagnostics are presented here. Commissioning of the beamline and spectrometer with radioactive ions are also reported here. Future capabilities and applications in other areas are also described. [ABSTRACT FROM AUTHOR]