Statistical analysis and modeling of the local ionospheric critical frequency: a mid-latitude single-station model for use in forecasting

The hourly values of the F-layer critical frequency from the ionospheric sounder in Dourbes (50.1°N, 4.6°E) during the time interval from 1957 to 2010, comprising five solar cycles, were analyzed for the effects of the solar activity. The hourly time series were reduced to hourly monthly medians which in turn were used for fitting a single station foF2 monthly median model. Two functional approaches have been investigated: a statistical approach and a spectral approach. The solar flux F10.7 is used to model the dependence of foF2 on the solar activity and is incorporated into both models by a polynomial expression. The statistical model employs polynomial functions to fit the F-layer critical frequency while the spectral model is based on spectral decomposition of the measured data and offers a better physical interpretation of the fitting parameters. The daytime and nighttime foF2 values calculated by both approaches are compared during high and low solar activity. In general, the statistical model has a slightly lower uncertainty at the expense of the larger number of fitting parameters. However, the spectral approach is superior for modeling the periodic effects and performs better when comparing the results for high and low solar activity. Comparison with the International Reference Ionosphere (IRI 2012) shows that both local models are better at describing the local values of the F-layer critical frequency

NMDB@Home: 1st virtual symposium on cosmic ray studies with neutron detectors

An overview on the presentations at the first virtual symposium on cosmic ray studies with neutron detectors is given. The meeting was held online in July 2020. Neutron detectors on ground are shown to provide significant contributions to research on interactions of galactic cosmic rays with magnetic fields in the Heliosphere and on the acceleration of energetic particles, as well as to a growing range of applications, including geophysics and space weather. The advent of easily accessible databases makes original data easily available to a large user community. The present overview outlines and introduces the more detailed articles contained in the proceedings

NMDB@Athens: Hybrid symposium on cosmic ray studies with neutron detectors

A brief overview is given regarding the presentations delivered at the NMDB@Athens meeting which was held, in a hybrid fashion, in September 2022. Participants joined both remotely but also physically at the National and Kapodistrian University of Athens, Greece. Unlike traditional cosmic ray meetings and conferences where the focus is mainly on the science related to neutron monitor measurements, the ›NMDB@Athens‹ meeting uniquely also addresses hardware issues related to these instruments and, importantly, also databases where different data products can be accessed by a growing and increasingly diverse user base. The present overview outlines and introduces the more detailed articles contained in the proceedings

Preparation of 6LiF deposits and characterisation via Monte Carlo simulations and Neutron Depth Profiling

The Institute for Reference Materials and Measurements (IRMM) is measuring the 6Li(n,t)4He cross section aiming at extending its status of standard over the MeV energy range. We developed a protocol to stretch-mount 0.75 micronmeter, 1.5 micronmeter, 8 micronmeter, and 20 micronmeter thick aluminium foils onto 0.5 mm thick tantalum rings. 6LiF samples were produced by depositing, by vacuum evaporation onto the aluminium backings, a layer of lithium fluoride 95.5% enriched in 6Li. We engineered dedicated tools and containers to handle and transport the resulting samples. These were characterised first at IRMM by differential weighing, then by Neutron Depth Profiling (NDP) at the TU Delft. These two measurements were found to be consistent for a selected sample, probed by a thermal neutron beam in three different regions to measure the 6LiF layer thickness and uniformity (defined as variation of the thickness relative to its average). The latter was found to be 0.8%, and the 6Li thickness to be 7.30 +/- 0.12, 7.35 +/- 0.12, and 7.29 +/- 0.12 micronmeter/cm2 in the three regions. We performed Monte Carlo simulations to estimate the uniformity of the 6LiF layer, and benchmarked the calculation against the NDP measurements. They were consistent with respect to the deposit uniformity although the simulations were found to overestimate the thickness of the layer.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Liquid metal corrosion of T91 and A316L materials in Pb-Bi eutectic at temperatures 400-600 °C

The corrosion resistance of T91 and A316L materials was tested in stagnant liquid lead-bismuth eutectic (LBE). The materials were exposed for 175, 500, 1250, 2300 and 3000 11 at temperatures front 425 to 600 °C under 5%H-2+Ar cover gas atmosphere. Severe corrosion occurred at temperatures above 500 °C where three corrosion modes were distinguished: stable oxide film mode, transition mode, and final dissolution mode featuring Cr and Ni leaching and material loss. The principle corrosion mechanisms were uniform penetration and dissolution of the penetrated volumes. At these temperatures (>500 °C) T91 had a better corrosion resistance (corrosion rate similar to ∼≤137 µm/year) compared to A316L (≤250 µm/year). The transition corrosion mode continued 2-3 times longer for T91 material due to residual oxides found even after 3000 h of exposure. At low temperatures (<450 °C) both materials showed good corrosion resistance but A316L performed better than T91 with corrosion rates 2-5 times lower.status: publishe

Physical vapour deposition of metallic lithium

The preparation of thin films of LiF restarted a few years ago at the Institute for Reference Materials and Measurements (IRMM). Deposits of 6LiF and 7LiF with an areal density up to approximately 500 µg·cm-2 are prepared by physical vapour deposition for neutron production (Li(p,n)) in the Van de Graaff accelerator at IRMM. In order to reach higher neutron yields, a larger number of Lithium nuclei per unit of surface is requested. In a proton beam however, high-energetic gamma rays are produced by interaction with Fluorine and disturb experiments making use of gamma spectrometry. In this regard, the deposition of metallic Lithium by means of physical vapour deposition up to an areal density of 300 µg·cm-2 was examined. Yet, metallic Li is known to diffuse into certain materials and react with atmospheric air by forming several reaction products. In this regard, the effect of protective covers of Au or LiF (sandwiches), deposited by means of a multi-crucible evaporation system, was investigated and the stability of the layers in the proton beam was measured.JRC.D.2-Standards for Innovation and sustainable Developmen

New insight into UO2F2 particulate structure by micro-Raman spectroscopy

Uranyl fluoride particles produced via controlled hydrolysis of uranium hexafluoride have been deposited on different substrates: polished graphite disks, silver foil, stainless steel and gold-coated silicon wafer, and measured with micro-Raman spectroscopy (MRS). All three metallic substrates enhanced the Raman signal delivered by UO2F2 in comparison to the graphite one. The fundamental stretching of the U-O band appeared at 867cm-1 in case of the graphite substrate, while in case of the others it was shifted to lower frequencies (847-839 cm-1). All applied metallic substrates showed the expected effect of Raman signal enhancement with respect to Uranyl stretching vibration; however the gold layer appeared most effective. Application of this improved method for MRS analysis of uranyl fluoride particles could be found in the field of nuclear safeguards and environmental analysis.JRC.D.2-Standards for Innovation and sustainable Developmen

Preparation and Characterization of Thin Film Nuclear Targets by Vacuum Evaporation

Among the many different techniques to prepare thin uniform deposits for nuclear experiments, physical vacuum deposition is the most widely applied. After several years of standstill, the preparation of thin deposited layers restarted in the Target Preparation Laboratory at IRMM. At present the laboratory is producing thin layers of 6LiF, Au, 10B and 35UF4. Knowing that the nuclear experimental results depend among other things on the uniformity and areal characteristics of the deposited layer, the deposition parameters have been optimized and investigation started to improve the characterization. Besides photospectrometry for thickness monitoring, other techniques are presented and compared. Experiments on the deposition of pure lithium are under investigation. This article reviews the available equipment and methods on the preparation of thin uniform deposits and reports on the progress in the characterization of thin layers produced by physical vapour deposition.JRC.DG.D.2-Reference material

Preparation and characterisation of thin film nuclear targets for neutron physical measurements

In the target preparation laboratory of the Insitute for Reference Materials and Measurements, lithium fluoride, 10B, gold and tristearin thin films are produced by physical vapour deposition for neutron spectroscopy experiments and for neutron cross section measurements. In all of these applications the accuracy of the obtained measurements greatly depends on the properties of the deposited films and the characterisation of the surface density. In this work we describe the production of various nuclear targets. The characterisation methods depend on the nature of the particular film/substrate system. Different characterisation techniques and the uncertainties in the determined areal densities necessary for neutron physical calculations are presented and compared.JRC.D.2-Reference material