Natural uranium isotopes determination in 24h-urine samples from exposed workers to enriched uranium

peer reviewedIndividual monitoring of occupationally exposed workers to enriched uranium is mandatory, due to its radiotoxicity. The aim of this work is to determine if the use of Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and an estimation method for 234U activity, could supply the information obtained by Alpha Spectrometry (AS), which is the analytical technique commonly employed in this scenario. A total of 105 samples of 24 h-urine from exposed workers were analyzed by both techniques and the obtained results were compared. 235U activity results were only quantifiable in 7 samples by AS (0.07–0.30 mBq/d) while ICP-MS quantified it in most of the cases.238U activity was measurable in 88 samples by AS and ICP-MS with wide range of results (0.11–2.4 mBq/d). For these isotopes no significant dosimetry differences were found between both techniques. However, 234U activities results obtained by AS ranged from 0.15 to 7.6 mBq/d and the isotopic ratio of 234U/238U were highly variable. 234U estimation was done with the average of these isotopic ratios and 235U and 238U ICP-MS results. Significant differences between estimated results and the ones obtained by AS were observed. Therefore, ICP-MS cannot supply the information given by AS, although can complement it. New studies must be started in order to obtain better and faster results applying radiochemical separation and ICP-MS measurement and studying the real contribution of diet in final uranium dose assessment

Radiopurity assessment of the tracking readout for the NEXT double beta decay experiment

The Neutrino Experiment with a Xenon Time-Projection Chamber (NEXT) is intended to investigate the neutrinoless double beta decay of 136Xe, which requires a severe suppression of potential backgrounds; therefore, an extensive screening and selection process is underway to control the radio-purity levels of the materials to be used in the experimental set-up of NEXT. The detector design combines the measurement of the topological signature of the event for background discrimination with the energy resolution optimization. Separate energy and tracking readout planes are based on different sensors: photomultiplier tubes for calorimetry and silicon multi-pixel photon counters for tracking. The design of a radio pure tracking plane, in direct contact with the gas detector medium, was a challenge since the needed components have typically activities too large for experiments requiring ultra-low background conditions. Here, the radiopurity assessment of tracking readout components based on gamma-ray spectroscopy using ultra-low background germanium detectors at the Laboratorio Subterráneo de Canfranc (Spain) is described. According to the obtained results, radiopure enough printed circuit boards made of kapton and copper and silicon photomultipliers.We deeply acknowledge John Murphy and Carl Jackson from SensL Technologies Ltd for their efficient collaboration in the analysis of SiPMs. We very much thank also Vicenzo Mancini from SOMACIS company for the care in the development of radiopure kapton PCBs. Special thanks are due to LSC directorate and staff for their strong support for performing the measurements at the LSC Radiopurity Service. The NEXT Collaboration acknowledges funding support from the following agencies and institutions: the European Research Council under the Advanced Grant 339787-NEXT and the T-REX Starting Grant ref. ERC-2009-StG-240054 of the IDEAS program of the 7th EU Framework Program; the Spanish Ministerio de Economia y Competitividad under grants CONSOLIDER-Ingenio 2010 CSD2008-0037 (CUP), FPA2009-13697-C04-04, and FIS2012-37947-C04; the Director, Office of Science, Office of Basic Energy Sciences of the US DoE under Contract no. DE-AC02-05CH11231; and the Portuguese FCT and FEDER through the program COMPETE, Projects PTDC/FIS/103860/2008 and PTDC/FIS/112272/2009.Cebrian, S.; Perez, J.; Bandac, I.; Labarga, L.; Alvarez, V.; Barrado, AI.; Bettini, A.... (2015). Radiopurity assessment of the tracking readout for the NEXT double beta decay experiment. Journal of Instrumentation. 10:1-14. https://doi.org/10.1088/1748-0221/10/05/P05006S1141

Influence of the ligand concentration and pH on the complexation of Cu(II) by a soil fulvic acid

Anodic Stripping Voltammetry has been tested in a non-traditional, pH-variable procedure, to study the interaction between Cu(II) with a soil fulvic acid. The study was performed at 25 °C and I = 1.0 M, and covered wide ranges of fulvic acid concentration ($5 - 20~{\rm mg}~{\rm L}^{-1}$), Cu(II) concentration ($2.10^{-5}-4.10^{-6}$ M), and pH (3.5 – ca 8). Mean complexation equivalent weights (between 800 and 5000 g mol$^{-1}$, depending of experimental conditions) and apparent equilibrium constants (between ca. 3 and 0.02 for pH-independent constants), and their variations with pH and fulvic acid concentration were calculated through an iterative procedure. The results obtained are consistent with those published before for the implementation of the pH-variable procedure with Cu(II) ion selective electrode potentiometry, and show that Anodic Stripping Voltammetry at pH-variable conditions is suitable for the study of Cu(II) - fulvic acid interactions