Shape staggering of midshell mercury isotopes from in-source laser spectroscopy compared with density-functional-theory and Monte Carlo shell-model calculations

Neutron-deficient 177−185Hg isotopes were studied using in-source laser resonance-ionization spectroscopy at the CERN-ISOLDE radioactive ion-beam facility in an experiment combining different detection methods tailored to the studied isotopes. These include either α-decay tagging or multireflection time-of-flight gating for isotope identification. The endpoint of the odd-even nuclear shape staggering in mercury was observed directly by measuring for the first time the isotope shifts and hyperfine structures of 177−180Hg. Changes in the mean-square charge radii for all mentioned isotopes, magnetic dipole, and electric quadrupole moments of the odd-A isotopes and arguments in favor of I=7/2 spin assignment for 177,179Hg were deduced. Experimental results are compared with density functional theory (DFT) and Monte Carlo shell model (MCSM) calculations. DFT calculations using Skyrme parametrizations predict a jump in the charge radius around the neutron N=104 midshell, with an odd-even staggering pattern related to the coexistence of nearly degenerate oblate and prolate minima. This near-degeneracy is highly sensitive to many aspects of the effective interaction, a fact that renders perfect agreement with experiments out of reach for current functionals. Despite this inherent difficulty, the SLy5s1 and a modified UNEDF1SO parametrization predict a qualitatively correct staggering that is off by two neutron numbers. MCSM calculations of states with the experimental spins and parities show good agreement for both electromagnetic moments and the observed charge radii. A clear mechanism for the origin of shape staggering within this context is identified: a substantial change in occupancy of the proton πh9/2 and neutron νi13/2 orbitals

Rare Earth Elements in Agriculture with Emphasis on Animal Husbandry

Calculations performed in consideration of a continuously increasing world population have revealed that animal production needs to be enhanced worldwide by at least 2 % each year so as to provide sufficient feed. Yet, effective growth promoting agents, in terms of in-feed antibiotics, have been completely banned throughout Europe due to the possible development and spread of multiresistance in bacteria. New efficient, safe and inexpensive feed additives are therefore needed in order to maintain or even further improve performance levels in animal husbandry. Based upon this information, rare earth elements have been considered as promising natural feed additive. Thus, this study was designed to bring together the current research on rare earths in order to analyze the data obtained and to facilitate the discussion of its relevance to agricultural utilization. The term rare earth elements comprises the elements scandium (21), yttrium (39), lanthanum (57) and the 14 chemical elements following lanthanum (58 -71) called lanthanoids. Favoring the tripositive oxidation state, rare earths present a high affinity for ionic bonding, thus a large number of both organic and inorganic rare earth salts may be formed. Nevertheless, rare earths may also form complexes especially with chelating oxygen ligands. In nature, rare earths occur in multiple minerals, such as bastnaesite and monazite which are mainly used for industrial production. Today, rare earths are part of several daily used devices such as lighters, television sets and computers. Additionally they are found in medical technology, nuclear engineering, automobile industry, military devices and even in spacecraft. Furthermore, rare earth-containing drugs are used for the treatment of hyperphosphatemia in chronic renal failure patients and for burn treatment. Based upon their paramagnetic properties, rare earths, especially gadolinium, have also been arranged as contrast agents in magnetic resonance imaging and computer tomography. In the future, among other uses, rare earths might be involved in cancer therapy, treatment and prevention of osteoporosis and atherosclerosis as well as organ transplantation. In China, rare earths have been successfully used at low concentrations as feed additives and fertilizers for decades. Yet, careful interpretation of Chinese data is recommended due to the fact that Chinese papers are often only available in native language and furthermore not up to standard with Western scientific research reports, hence lacking statistical treatment of data and details of experimental methods. However, in China, both yield increases and quality improvements were achieved in multiple plant species including cereals, fruits and vegetables after rare earth application. Recommended application rates vary with the crop species, the application technique (soil, foliar or seed dressing) as well as the timing. As feed additives, rare earths were shown to improve body weight gain and feed conversion in nearly all categories of farming animals (chickens, pigs, ducks, cattle). Additionally, improvements in milk production in dairy cows, in egg production in laying hens and in output and survival rate of fish and egg hatching of shrimps were noticed. Feed additives used thereby predominantly contain light rare earths (La, Ce, Pr, Nd) but even though both organic (nitrates, chlorides etc.) and inorganic (ascorbates, citrates etc.) rare earth feed additives are commercially available, organic ones are claimed to provide better results. Based on the effects reported in Chinese studies, experiments were initiated under Western conditions in order to investigate the action of rare earths on both plant and animal growth. Several Western feeding trials conducted on animals have been able to demonstrate significant performance enhancing effects after dietary rare earth application, while results obtained from experiments on the effects of rare earths on plant growth have been controversial. In pigs, improvements in body weight gain of up to 19 % and in feed conversion rate of 10 % were observed after their diets were supplemented with low-dosed rare earth chlorides. Even better effects were however noticed after rare earth citrates were added to the feed of pigs. Furthermore, under field conditions, rare earths were shown to increase body weight gain by up to 10 % and improve feed conversion by up to 9 % in pigs. Following these results, rare earth containing feed additives in terms of Lancer® have entered the market in Switzerland, where a temporary permission has been granted for their use in pig production. In addition, in broilers, rare earths were also shown to increase final weights by 7 % and improve feed conversion by up to 3 %. Very recent studies also confirmed performance enhancing effects in broilers with increased body weight gain and feed intake of up to 6.6 % and 6.9 %, respectively. In rats, which were used as a small animal model, improvements in body weight gain and feed conversion of 4 -7 % and 3 -11 %, respectively, followed the application of rare earths. Thus, clear performance enhancing effects were achieved in Western studies on rats, pigs and poultry due to dietary rare earth supplementation. However, there are also studies in which positive effects of rare earths on animal performance were not as obvious or not observed at all. A comparison between the results of these feeding experiments as to the mixture of rare earths, the concentration as well as the compound applied showed that these parameters are involved in the magnitude of performance enhancing effects of rare earths. At present, no definitive statement on optimum composition can be made. However, a dose-dependency was observed in several trials and better effects have been achieved when the mixture of rare earths was applied instead of single lanthanum. Additionally, it seems that organic rare earth compounds have a higher impact on animal performance than inorganic ones. This is probable ascribable to different chemical characteristics, which lead to variations in both absorption and bioavailability. Generally, absorption of orally applied rare earths is very low, with more than 95 % being recovered in the feces of animals. According to minute gastrointestinal absorption of rare earths, oral toxicity is very low and comparable to usual table salt. LD50 values determined in various animal experiments rang from 830 mg/kg to 10 g/kg body weight. None of the feeding trials performed reported any effects on the state of health of the animals, which coincides with low oral toxicity and additionally supports the safe application of rare earth feed additives to animals. In addition, no effects on either meat or carcass quality were observed. Likewise, rare earth concentrations determined in organ samples were very low and similar or even lower than in control animals. This is attributed to the ubiquitous occurrence of rare earths, thus also in plants and soils. As a result they also appear in commercial diets and subsequently in animal and human tissue. It has also been shown that rare earth contents in usual vegetable foodstuff are still higher than those in meat obtained from animals additionally fed with rare earths. Therefore, the application of rare earths as feed additive is also considered to be safe for humans. Furthermore, as to current knowledge, no damage is to be expected on the environment as a consequence of rare earth application to agriculture. In fact, as rare earths can improve feed conversion, they may support the efficient use of natural resources, while additionally reducing environmental loads in terms of animal excrements. Hence, with respect to animal, human and environmental safety, rare earths meet legal recommendations of the European Union for their registration as feed additive. Although the mechanism underlying performance enhancing effects of rare earths is not completely understood, several proposals have been made. According to current research, rare earths might exert their action locally within the gastrointestinal tract, including effects on the bacterial micro-flora as well as on nutrient uptake, digestibility and utilization. Likewise, anti-inflammatory and anti-oxidative effects may also contribute to positive effects. Additionally, actions on the intermediate metabolism in terms of effects on cellular functions, growth-and digestibility-related hormones and enzymes or the immune system have also been considered. It might also be possible that rare earths are not yet identified essential elements. Based on the information gained in this study, it has been concluded that rare earths are of high interest as possibly new, safe, inexpensive feed additive in Europe, especially in pig and poultry production

Hydrogeochemistry of a Heterogeneous Aquifer Located in Unaweep Canyon, Mesa County, Western Colorado

The intersection of an increasing population, climate change, pollution, and over allocation of water continue to place additional strain on groundwater resources in arid regions. Groundwater in arid environments is particularly susceptible to overuse, and therefore a thorough understanding of groundwater sources and its contribution to sensitive ecosystems is vital. Unaweep Canyon, in the arid region of Colorado’s western slope, is a geologically unique site that harbors a buried paleovalley. The modern valley contains up to ~500 m of sediment fill comprising unconsolidated lacustrine, fluvial, and mass-wasting deposits, as well as possible lithified sedimentary rocks. We hypothesize that the unconsolidated layers in Unaweep Canyon aquifer are not hydro-geochemically linked and represent different, unique sources of groundwater. Our study focused on integrating published geologic information, geophysical data, and seasonal geochemical properties of groundwater and surface water to delineate multiple sources of water for both human and ecosystem needs. Several streams, seeps, Precambrian bedrock spring aquifers, and several domestic wells were sampled for metals, anions, and stable isotopes (18O and 2H) during spring, summer, and fall 2020 to identify seasonal effects. Piper plots also revealed that the Precambrian bedrock spring aquifers may be a sodium chloride or mixed type water, the spring is a sodium chloride type water, and the surface and groundwaters are magnesium-bicarbonate type waters. Furthermore, the isotopic composition of the seeps, West Creek, domestic well and Precambrian bedrock samples range from -14.06 to -15.16‰ δ18O and -103.5 to -109.46‰ δ2H, -12.89‰ to -14.7‰ δ18O and -99.3 to -106.68‰ δ2H, -13.64 to -14.77‰ δ18O and -102.4 to -105.94‰ δ2H, -14.27 to -15.39‰ δ18O and -108.7 to -112.78‰ δ2H respectively. Principal Component Analysis coupled with Spearman Correlation supported the existence of seasonal variation and multiple groundwater sources from all the sampling locations. Seasonal variability amongst in-situ water chemistry, metal and stable isotope results were attenuated, likely attributable to the drought conditions of 2020. Our results suggest the presence of multiple sources of groundwater within Unaweep Canyon, leading for the potential to utilize each source in a sustainable fashion. The findings and methodology used in our study may have applicability in similar hydrogeologic settings where alternate water sources

Modélisation des effets d'historique dans un réacteur à eau pressurisée

Les codes de physique des réacteurs DRAGON4 et DONJON4, respectivement dédié à l'étude neutronique des réseaux et des cours entiers, ont été conçus par l'Institut de Génie Nucléaire (IGN) pour simuler des CANDU et des Advanced CANDU Reactor. Le code DRAGON4 peut, en théorie, s'appliquer aux Réacteurs à Eau légère Pressurisée (REP) mais le code DONJON4 requiert un réacteur de type CANDU et doit être adapté pour traité les REP. La physique des REP est differente de celle des réacteurs CANDU. La présence d'eau légère, la géométrie, le type de combustible ainsi que le type de rechargement affectent le comportement du réacteur lorsque certains de ses paramètres sont modifiés. Électricité de France (EDF), dont le parc nucléaire est consititué de REPs, a sollicité la création d'une simulation avec "effets d'historique", à l'aide des codes de l'IGN, sur une campagne de production représentative d'un réacteur de sa flotte. Le premier objectif de la maîtrise a été la mise à niveau d'un calcul DRAGON3/DONJON3 vers DRAGON4/DONJON4 afin de le comparer avec un calcul DRAGON4/COCAGNE d'EDF. Cette comparaison inédite (des modifications ont été apportées aux codes de l'IGN afin de les adapter aux particularités des REPs) a d'une part, permis la validation de DONJON4, et d'autre part, aboutit à une réflexion sur la modélisation des mécanismes de contre-réaction dans les codes de coeur concernés. Le deuxième objectif a été la mise en place d'un schéma de calcul avec "effets d'historique". EDF a fourni du temps sur un cluster de calcul pour la simulation, et DONJON4 a été parallèlisé pour tirer parti de ces ressources. Une simulation de l'exploitation d'un REP a été effectuée en utilisant un scénario pré-établi, correspondant à une campagne de production représentative d'un réacteur de la flotte EDF. Celle-ci a été comparée au schéma de calcul de la première partie et les écarts ont été analysés.----------Abstract The neutronic codes DRAGON4 and DONJON4, respectively dedicated to lattices and cores calculations, have been designed by the Institute of Nuclear Engineering (IGN) to simulate CANDU and Advanced CANDU reactors. DRAGON4 code can theoretically be applied to pressurized water reactors (PWRs) but DONJON4 code is more oriented towards CANDU reactors and requires some adaptation to be applied to PWR. PWR physics is different from that of a CANDU reactor. The presence of light water, the geometry, the fuel type and the refuelling type affect the behavior of the reactor when some of these parameters are changed. Électricité de France (EDF), which has a reactor fleet of PWRs, solicited the creation of a "history-based" simulation over a campaign length of a typical reactor of theirs, using IGN's codes. The first objective of this work was to update a PWR calculation from DRAGON3 /DONJON3 to DRAGON4 / DONJON4 and to compare it with a DRAGON4 / COCAGNE calculation - COCAGNE being a core code made by EDF. This new and unique comparison (changes were made to IGN's codes to fit the specificities of PWRs) has enabled the validation of DONJON4, and has also led to a reflection on counter-reaction mechanisms in core calculations. The second objective was to establish a "history based" calculation scheme. EDF has provided some calcultation on its cluster Clamart2, and DONJON4 has been parallelized to take advantage of these resources. A campaign length simulation of a PWR was conducted using a pre-established scenario. It was compared with the calculation scheme of the first part and differences have been analyzed

A contribution to the development of sensitive and isotope-selective analytical methods based on sector-field ICP-MS : for supporting the development of Gen IV nuclear reactors

Ondanks zijn bijzonder omstreden reputatie, zeker in de nasleep van de kernramp bij Fukushima, voorziet nucleaire energie momenteel nog in een groot deel van de globale elektriciteitsbehoefte. Zodoende is het zeer waarschijnlijk dat nucleaire energie, althans in de nabije toekomst, een belangrijke rol zal blijven spelen. Desalniettemin is het essentieel dat er een nieuwe generatie van nucleaire reactoren ontwikkeld wordt, die er voor zal zorgen dat de duurzaamheid van nucleaire energie in de toekomst verbetert. De inspanningen die het Studiecentrum voor Kernenergie (SCK●CEN) levert met betrekking tot de ontwikkeling van zulke vernieuwende systemen zijn samengebracht in het MYRRHA project. Van zodra hij operationeel is, zal de MYRRHA onderzoeksreactor dienst doen als bron van protonen en neutronen voor verscheidene toepassingen, onder andere bij het onderzoek naar brandstoffen en structurele materialen voor geavanceerde nucleaire systemen. Daarnaast zal deze reactor onder meer aangewend worden bij het onderzoek naar de transmutatie van zowel bestaand als toekomstig hoogradioactief afval, waardoor de vereiste opslagtijd voor dit type afval in de toekomst drastisch zou kunnen ingeperkt worden. Het innovatieve karakter van de MYRRHA onderzoeksreactor zorgt er wel voor dat er nog een aantal belangrijke uitdagingen bestaan die dienen overwonnen te worden, onder andere met betrekking tot de performantie van de structurele materialen (d.i. hooggelegeerde stalen) die in direct contact staan met het beoogde koelmiddel, een eutectisch mengsel van lood en bismut (LBE). Dit koelmiddel bezit een aantal gunstige thermofysische en neutronische eigenschappen, maar is tegelijk ook uiterst corrosief bij de beoogde werktemperaturen. In deze context is de multi-element sporenanalyse van LBE en hooggelegeerde stalen van groot belang, bijvoorbeeld voor de bepaling van spoorelementen die bepalend zijn voor de mechanische eigenschappen van staallegeringen, of om de opname van corrosieproducten door het koelmiddel te monitoren. In beide gevallen zullen de spoorelementen in kwestie echter slechts op μg/g niveau, of lager, aanwezig zijn, waardoor het gebruik van een uiterst gevoelige analytische techniek essentieel is. Daarbovenop zal er op het SCK●CEN in de toekomst ook een blijvende nood zijn aan isotoop-selectieve analytische methoden, onder andere in het kader van de ontwikkeling van nieuwe nucleaire brandstoffen en bij het onderzoek naar de transmutatie van actiniden in hoogradioactief nucleair afval. Dubbel-focusserende sector-veld inductief gekoppeld plasma-massaspectrometrie (ICP-SFMS) is de analytische techniek bij uitstek voor de multi-element en isotoop-selectieve analyse van een grote verscheidenheid aan monsters, zoals LBE en hooggelegeerde stalen. Door zulk type instrument aan een handschoenkast te koppelen, wordt de analyse van radioactieve monsters, zoals bestraalde kernbrandstoffen, eveneens mogelijk. Ondanks het feit dat ICP-SFMS uiterst geschikt is voor de multi-element ultra-sporenanalyse van LBE en hooggelegeerde stalen, wordt de accurate bepaling van spoorelementen in kwestie vaak gehinderd door het voorkomen van niet-spectrale interferenties (d.i. matrixeffecten). De meest eenvoudige en elegante manier om deze matrixeffecten te elimineren bestaat uit het selectief afscheiden van de matrix, na het oplossen van de monsters in kwestie, alvorens de spoorelementen te bepalen aan de hand van ICP-SFMS. Om dit te bewerkstelligen werd in dit werk gebruik gemaakt van kolomchromatografie, omwille van zijn eenvoud en gebruiksgemak. Hierbij werden zeer selectieve harsen geselecteerd, die in staat waren om de matrixelementen te weerhouden, terwijl ze slechts een beperkte affiniteit vertoonden voor de spoorelementen. De methoden die hiertoe ontwikkeld werden, werden vervolgens gevalideerd en uiteindelijk ook toegepast op echte monsters van LBE en hooggelegeerde stalen, afkomstig van onderzoeksprojecten die verband houden met de ontwikkeling van de MYRRHA onderzoeksreactor. In een laatste fase werd een verkennende studie uitgevoerd, om het gebruik van ICP-SFMS voor de bepaling van isotopenratio’s te evalueren. Hierbij werden onder meer enkele van de belangrijkste aspecten, die gepaard gaan met de bepaling van isotopenratio’s a.d.h.v. ICP-SFMS, zoals de verwezenlijkbare optimale interne precisie, bestudeerd