Electrochemical properties of titanium electrodes under alpha irradiation

Bombardment of the back face of thin titanium foil electrodes with alpha particles causes important modifications of their electrochemical properties in aqueous solution at room temperature. We have observed two electrochemical regimes depending on the energy spectrum of the a particles attaining the Ti/solution interface : regime I corresponding to the [0, 1.6 MeV] range for which α-radiation reactivates the Ti surface in 1 M H2SO4, regime II corresponding to the [0, 3 MeV] range for which α-radiation passivates the Ti surface in otherwise identical experimental conditions. By changing the nature, concentration and pH of the solution, by using a scavenger of primary radicals (H, OH), it is suggested that water radiolysis plays a role in the electrochemical behaviour reported in regime I. The importance of the native oxide at the Ti electrode surface á-irradiated prior to immersion in solution is also emphasized. A mechanism in two steps involving reduction of the surface cations by H radicals followed by further oxidation during anodic polarisation of the electrode was inferred, solely applicable in regime I

Sorption of selenium anionic species on apatites and iron oxides from aqueous solutions

The sorption of selenite and selenate ions from aqueous solutions was investigated on hydroxyapatite, fluorapatite, goethite and hematite, in order to simulate the behavior of radioactive selenium in natural or artificial sorbing media. Correlation studies with acido-basic properties and solubility of the solids were also performed. The sorption is pH dependant, but these solids are very efficient for retaining selenite at pH values generally encountered in natural waters, with however higher K-d values for oxides than apatites. Selenate ions are much less sorbed than selenite. Several methods such as electron microscopy and spectroscopic techniques were used to identify the sorption mechanisms. In the case of hydroxyapatite, sorption proceeds by substitution of phosphate groups in the lattice of the apatite crystal in the superficial layers of the solid. In the case of goethite and hematite, sorption can be interpreted and modeled by a surface complexation process, but there is a discrepancy between sorption site densities for selenite and for protons. (C) 2003 Elsevier Science Ltd. All rights reserved.International Workshop on the Mobility of Iodine, Technetium, Selenium and Uranium in the Biosphere, Apr 03-05, 2002, Nancy, Franc

Cerebral perfusion using ASL in patients with COVID-19 and neurological manifestations: A retrospective multicenter observational study

Background and purpose: Cerebral hypoperfusion has been reported in patients with COVID-19 and neurological manifestations in small cohorts. We aimed to systematically assess changes in cerebral perfusion in a cohort of 59 of these patients, with or without abnormalities on morphological MRI sequences. Methods: Patients with biologically-confirmed COVID-19 and neurological manifestations undergoing a brain MRI with technically adequate arterial spin labeling (ASL) perfusion were included in this retrospective multicenter study. ASL maps were jointly reviewed by two readers blinded to clinical data. They assessed abnormal perfusion in four regions of interest in each brain hemisphere: frontal lobe, parietal lobe, posterior temporal lobe, and temporal pole extended to the amygdalo-hippocampal complex. Results: Fifty-nine patients (44 men (75%), mean age 61.2 years) were included. Most patients had a severe COVID-19, 57 (97%) needed oxygen therapy and 43 (73%) were hospitalized in intensive care unit at the time of MRI. Morphological brain MRI was abnormal in 44 (75%) patients. ASL perfusion was abnormal in 53 (90%) patients, and particularly in all patients with normal morphological MRI. Hypoperfusion occurred in 48 (81%) patients, mostly in temporal poles (52 (44%)) and frontal lobes (40 (34%)). Hyperperfusion occurred in 9 (15%) patients and was closely associated with post-contrast FLAIR leptomeningeal enhancement (100% [66.4%-100%] of hyperperfusion with enhancement versus 28.6% [16.6%-43.2%] without, p = 0.002). Studied clinical parameters (especially sedation) and other morphological MRI anomalies had no significant impact on perfusion anomalies. Conclusion: Brain ASL perfusion showed hypoperfusion in more than 80% of patients with severe COVID-19, with or without visible lesion on conventional MRI abnormalities