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# Molecular plating: A method for the electrolytic formation of thin inorganic films

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## Abstract

A method was developed that may solve the problem of the preparations of thin films suitable for all the many different radioactive materials available for use in nuclear spectroscopy provided the thin film in question is not required as the metal. The most significant difference between the method and ordinary electrodeposition is that electrolytic dissociation does not occur to any comparable degree during the passage of current. Also, the same chemical compound, chloride or nitrate as the case may be, is deposited at the cathode as that originally dissolved in the electrolyte. Thus, the method is called molecular plating. Other differences are the use of high voltages (50-2000 v) and the use of an organic solution. The procedure and the advantages of the method are discussed. (P.C.H.)
... • a copper bulk target, with a thin layer of Ho compound deposited by means of molecular plating over it. The molecular plating is a technique consisting in an electrodeposition of metallic compounds (oxides, hydroxides, carbonates etc.) from an organic solvent by applying high voltages (100-600 V) [8]. This technique is capable of achieving yields close to 100% for many lanthanides as well as holmium (starting from holmium chloride). ...
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The HOLMES experiment aims to directly measure the ν\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\nu$$\end{document} mass studying the 163\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{163}$$\end{document}Ho electron capture decay spectrum developing arrays of TES-based microcalorimeters implanted with O(300 Bq/detector) Ho atoms. The embedding of the source inside detectors is a crucial step of the experiment. Because the 163\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{163}$$\end{document}Ho production process (neutron irradiation of a 162\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{162}$$\end{document}Er sample) is not perfectly free from impurities, Ho source must be separated from a lot of contaminants. A chemical processing removes every species other than Ho, but it is not sufficient to remove all isotope-related background sources: Indeed, 166m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{166m}$$\end{document}Ho beta decay can produce fake signal in the region of interest. For this reason, a dedicated implantation system was set up. It is designed to achieve the separation power better than 5σ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sigma$$\end{document} at 163/166 a.m.u. allowing an efficient Ho ions implantation inside microcalorimeter absorbers. Its main components are a 50 kV sputter-based ion source, a magnetic dipole and a target chamber. A specially designed co-evaporation system was designed to “grow” the gold microcalorimeter absorber during the implantation process, increasing the maximum achievable activity which can be implanted. The machine performances were evaluated by means of calibration runs using 63\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{63}$$\end{document}Cu/65\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{65}$$\end{document}Cu and Mo beams. A special care was given to the study of the more effective way to populate source plasma with Ho ions obtained from different Ho compounds by sputtering process. In this work, the machine development and commissioning are described.
... The radioactivity of 154 Dy in the sample was measured by means of α-spectroscopy. Thin and homogeneous radioactive sources, necessary to obtain high-resolution α-spectra, were prepared using the molecular plating technique-also referred to as electrodeposition 33,34 . Following the Guide to the expression of uncertainty in measurement -GUM recommendations 35,36 , a realistic and complete uncertainty budget for the measured t 1/2 is given as well. ...
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Sixty years after the discovery of 154Dy, the half-life of this pure alpha-emitter was re-measured. 154Dy was radiochemically separated from proton-irradiated tantalum samples. Sector field- and multicollector-inductively coupled plasma mass spectrometry were used to determine the amount of 154Dy retrieved. The disintegration rate of the radio-lanthanide was measured by means of α-spectrometry. The half-life value was determined as (1.40 ± 0.08)∙106 y, with an uncertainty reduced by a factor of ~ 10 compared to the currently adopted value of (3.0 ± 1.5)∙106 y. This precise half-life value is useful for the the correct testing and evaluation of p-process nucleosynthetic models using 154Dy as a seed nucleus or as a reaction product, as well as for the safe disposal of irradiated target material from accelerator driven facilities. As a first application of the half-life value determined in this work, the excitation functions for the production of 154Dy in proton-irradiated Ta, Pb, and W targets were re-evaluated, which are now in agreement with theoretical calculations.
... Many, especially of transplutonium elements, are therefore only available in minute quantities [5], which limits the applicable methods for target production. The "molecular plating" (MP) method [141] fulfills the requirements of high efficiency, target stability, the option to reprocess irradiated targets, and is applicable to actinides. The MP is based on an electrochemical deposition of dissolved material from an alcoholic solution by applying a constant current between an anode and the supporting substrate, which is biased as a cathode. ...
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Superheavy element research has been a strong pillar of the research program at GSI Darmstadt since its foundation. Six new elements were discovered along with many new isotopes. Initial results on chemical properties of the heaviest elements were obtained that allowed for comparing their behavior with that of their lighter homologs and with theoretical predictions. Main achievements of the past five decades of superheavy element research at GSI are described along with an outlook into the future of superheavy element research in Darmstadt.
... The speci c activity of 154 Dy in the sample was measured by means of αspectroscopy. Thin and homogeneous radioactive sources, necessary to obtain high-resolution α-spectra, were prepared using the molecular plating technique -also referred to as electrodeposition [34,35]. ...
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Sixty years after the discovery of ¹⁵⁴ Dy, the half-life of this pure alpha-emitter was re-measured. ¹⁵⁴ Dy was radiochemically separated from proton-irradiated tantalum samples. Sector field- and multicollector-inductively coupled plasma mass spectrometry were used to determine the amount of ¹⁵⁴ Dy retrieved. The disintegration rate of the radio-lanthanide was measured by means of α-spectrometry. The half-life value was determined as (1.33 ± 0.07)∙10 ⁶ y, with an uncertainty reduced by a factor of ~10 compared to the currently adopted value of (3.0 ± 1.5)∙10 ⁶ y. This precise half-life value is crucial for the correct estimation of p-process nucleosynthetic reactions in the lanthanide region, as well as for the safe disposal of irradiated target material from spallation facilities. As a first application of the half-life value found in this work, the excitation functions for the production of ¹⁵⁴ Dy in proton-irradiated Ta, Pb, and W targets were re-evaluated, which found to be in agreement with theoretical calculations.
... Des solvants non aqueux, tels que l'isopropanol, l'isobutanol, l'acétone ou le diméthylformamide, peuvent également être utilisés pour préparer des dépôts d'actinides par électroprécipitation. Ce procédé, appelé « Molecular Plating (MP) », est décrit pour la première fois par Parker et Falk en 1962 [103] pour décrire l'électrodépôt des actinides dans des solutions organiques. Initialement, on pensait que la forme chimique de l'élément déposé était identique à celle en solution. ...
Thesis
L’objectif de cette thèse est de comprendre les processus associés à l’électrodépôt d’uranium pour sélectionner les meilleures conditions et améliorer la qualité des cibles utilisées pour des recherches en physique nucléaire. Les couches minces d’uranium ont été préparées par électroprécipitation dans l’isobutanol, sur un substrat en aluminium. Les électrolyses ont été réalisées avec un montage à deux électrodes en imposant une tension. Une partie a été consacrée à la définition de l’électrolyte, en tenant compte de la viscosité, la densité, la conductivité électrique et des propriétés redox. Le principe de l’électroprécipitation consiste à la production d’ions OH⁻ à la cathode. Ces ions réagissent ensuite avec l’élément à déposer pour former un hydroxyde ou un oxyde hydraté qui précipite à la cathode. L’isobutanol est un solvant visqueux et peu conducteur.Lors de l’électrolyse, les ions OH⁻ se concentrent au voisinage du substrat et forment un « mur basique ». Les résultats montrent qu’il est préférable de rajouter de l’eau en fort excès par rapport à la quantité nécessaire pour atteindre le pH de début de précipitation et pour réagir avec la totalité de l’uranium initialement en solution. Une concentration de 1 mol.L⁻¹ d’eau permet d’obtenir avec de bons rendements des cibles homogènes et peu rugueuses. Pour améliorer la conductivité de la solution, il faut aussi rajouter des ions à une concentration supérieure ou égale à 2×10⁻³ mol.L⁻¹. L’uranium sous forme de sel de nitrate est soluble et totalement dissocié en cation UO₂²₊ à des pH inférieurs à 4 en solution aqueuse. L’acide nitrique a été sélectionné comme additif. Cependant, en présence de HNO₃,l’aluminium est corrodé et sa surface est dégradée. Ceci peut provoquer une mauvaise adhérence du dépôt au substrat.Pour limiter cette corrosion néfaste à la qualité de la cible, il faut limiter la teneur en acide nitrique à des concentrations inférieures à 3×10⁻³ mol.L⁻¹. Des feuilles de Al de différentes épaisseurs ont été caractérisées. Plus la feuille est mince,moins elle est rugueuse. Ceci est intéressant car les cibles pour les mesures en physique doivent être réalisées sur des feuilles les plus minces possibles. Des dépôts d’uranium ont pu être préparés avec des rendements supérieurs à 90%, mais avec des rendements faradiques faibles. La durée d’électrolyse doit être limitée car plus le temps est long, plus le dépôt d’uranium devient rugueux. Les analyses électrochimiques indiquent que la formation des ions OH⁻ est principalement réalisée par réduction de l’eau. Cette réaction s’accompagne de la formation d’hydrogène gazeux qui peut détériorer localement le dépôt. Les résultats ne permettent pas de conclure si les ions nitrate participent aussi à la formation des ions OH⁻ car ils sont 1000 fois moins concentrés que l’eau. Dans ces conditions, on ne peut pas non plus savoir si l’uranium (VI) est réduit pendant l’électrolyse. On observe la formation de deux couches, avec une couche supérieure constituée de plaques très lisses et séparées de fissures plus ou moins larges. Le traitement thermique du dépôt favorise la formation des fissures. Si le substrat est prétraité pour le rendre plus lisse, la couche déposée est plus uniforme, avec une rugosité moindre et une adhérence améliorée. Les analyses chimiques des dépôts suggèrent la formation d’un hydroxyde d’uranium (VI) hydraté et de studtite.
... 200 kBq of an 227 Ac source is introduced into 37 the vacuum and the recoiling granddaughter 223 Ra was guided by 38 electric fields to a metal surface which was placed above of the 227 Ac 39 recoil ion source. The 225 Ac source was produced via molecular plating 40 from a nitrate solution at the institute of nuclear chemistry at the 41 Johannes Gutenberg university in Mainz (Germany) [29,30]. 42 ...
Article
To study the chemical properties of the heaviest elements, a fast and efficient stopping and extraction of the highly energetic residues from heavy ion fusion reactions into the chemistry setup is essential. Currently used techniques like Recoil Transfer Chambers (RTC) relying on gas flow extraction provide high efficiencies for chemically non-reactive volatile species, but operate at extraction times textr of about 0.5 s or more. Buffer Gas Cells (BGC) with electric and Radio-Frequency (RF) fields offer much faster extraction times. Here, we demonstrate the successful coupling of a BGC to a gas chromatography setup as is used for studies of chemical properties of superheavy elements. Using ²²³Ra and ²²⁵Ac recoil ion sources providing ²¹⁹Rn and ²²¹Fr ions for off-line tests, an extraction time textr = 55(4) ms and an extraction efficiency of 35(3)% were achieved for the non-reactive ²¹⁹Rn, while ²²¹Fr was retained. The results show a BGC-based setup to be suitable for gas-phase experiments with short-lived volatile transactinide elements like Cn and Fl with half-lives substantially below 1 s.
... Different methods exist to fabricate targets or radioactive sources in many different geometries and thicknesses. A well-established method is the Molecular Plating (MP) technique [9]. This method was well characterized and enhanced by Vascon et al. to fabricate smooth crackfree large-area thin films of alpha particle emitting 147 Sm [10]. ...
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Four different techniques were applied for the production of 233 U alpha recoil ion sources, providing 229 Th ions. They were compared with respect to a minimum energy spread of the 229 Th recoil ions, using the emitted alpha particles as an indicator. The techniques of Molecular Plating, Drop-on-Demand inkjet printing, chelation from dilute nitric acid solution on chemically functionalized silicon surfaces, and self-adsorption on passivated titanium surfaces were used. All fabricated sources were characterized by using alpha spectrometry, radiographic imaging, and scanning electron microscopy. A direct validation for the estimated recoil ion rate was obtained by collecting 228 Th recoil ions from 232 U recoil ion sources prepared by self-adsorption and Molecular Plating. The chelation and the self-adsorption based approaches appear most promising for the preparation of recoil ion sources delivering monochromatic recoil ions.
Article
The formation of carbonyl complexes using atom-at-a-time quantities of short-lived transition metals from fusion and fission reactions was reported in 2012. Numerous studies focussing on this chemical system, which is also applicable for the superheavy elements followed. We report on a novel two-chamber approach for the synthesis of such complexes that allows spatial decoupling of thermalization and gas-phase carbonyl complex synthesis. Neutron induced fission on ²³⁵ U and spontaneous fission of ²⁴⁸ Cm were employed for the production of the fission products. These were stopped inside a gas volume behind the target and flushed with an inert-gas flow into a second chamber. This was flushed with carbon monoxide to allow the gas-phase synthesis of carbonyl complexes. Parameter studies of the transfer from the first into the second chamber as well as on the carbonyl complex formation and transport processes have been performed. High overall efficiencies of more than 50% were reached rendering this approach interesting for studies of superheavy elements. Our results show that carbonyl complex formation of thermalized fission products is a single-atom reaction, and not a hot-atom reaction.
Thesis
The present work deals with the production and characterization of thin inorganic layers consisting of natural isotopes and exotic radionuclides by different methods. These layers are usually deposited on thin substrates and are used, e.g., as targets in accelerator experiments and other nuclear applications for nuclear reaction studies and the synthesis of superheavy elements. With steadily increasing beam intensities of new accelerator facilities, the targets have to withstand increasing power inputs. They also have to contain more material, since the cross sections for the synthesis of the heaviest known elements are extremely small. For off-line studies of the chemical reactions of targets with low energetic electron and ion beams, a pilot experiment for “Off-line Deposit Irradiations” (ODIn) of thin layers was constructed, characterized and commissioned with lead targets. This experiment will help to develop a method to condition targets suitable for future accelerator experiments. Furthermore, the fabrication methods in this work were used for the production of thin radioactive samples, so-called recoil ion sources, which are used for the generation of particle beams of their emitted recoil ions and thus have different requirements in contrast to targets. The goal was the production of ideal recoil ions sources consisting of single atomic layers (monolayers) of alpha-decaying radionuclides. They will be used for quantum logic spectroscopy in the “Trapping And Cooling of Thorium Ions with Calcium” (TACTICa) collaboration. The aim of the TACTICa experiment is to study the isomer 229mTh trapped inside a coulomb crystal of 40Ca+ ions in a Paul trap. The 229Th is a nuclide of high interest due to its low lying isomeric state at (8.28 ± 0.17) eV. The precisely known energy and half-life of the isomeric state, which is currently studied by the nuClock collaboration, will make it usable for applications like a “nuclear clock” or quantum computing. The studies of the TACTICa collaboration are in the field of quantum logic spectroscopy and fundamental physics beyond the standard model. In addition to the production of monolayer recoil ion sources for TACTICa, a setup was developed for the electrostatic deceleration of daughter nuclei including 229mTh coming from alpha-decaying sources like 233U while maintaining their initial charge distribution and thus making them available for loading into a Paul trap.
Article
Samarium thin-films doped with a 252Cf radiotracer were used to study the effects of annealing on the release of fission fragments from electrodeposited films. An ammonium acetate molecular plating technique was utilized to perform the depositions. The fission fragment yields were measured using a unique technique involving the exposure of aluminum foils to the deposited material for a fixed time followed by gamma-ray spectroscopy to determine the rate at which the fission fragments implanted into the foils. Annealing of the electrodeposited films was found to have no effect on the release of fission fragments.
Article
Alpha-particles are easily absorbed in thin metallic layers. Consequently, the probability of deviations in the observed spectrum, originating from so-called back-scattering, may usually be considered negligible. Gamma-activities—because of their great penetration properties—can be said to be the least troublesome as far as sample technique is concerned. Three forms of sample are commonly employed: (1) metal foils or wires, (2) powdered metal or metal compounds, and (3) liquids. The drop method mostly results in poor homogeneity. The possibilities of prepreparation of material for irradiation are extensive. The technique of electrodeposition is one of the best known methods in the preparation of radioactive samples. Thin foils are of importance when photographic detection of nuclear particles is used.
Article
The initial results of an investigation dealing with the most ; appropriate methods for the preparation of radioactive materials for use in beta-; spectroscopy are reported. A short review of the methods and techniques ; developed for this type of preparation is presented, and, where possible, ; improvements are suggested. The investigation was carried out in four main ; parts, namely, thin film preparation and thickness determination, electro- and ; vacuum deposition, and miscellaneous techniques, and is reported in the same ; order. Tables designating the deposition efficiencies obtained from the ; preparation of 45 different radioactive materials by employment of the various ; methods are given. (auth);
Article
An apparatus is described for the preparation of radioactive sources by ; means of vacuum deposition for use in nuclear spectroscopy. The collimated ; crucibles described allow for smaller amounts of active material to be used in ; the preparation because of the higher yield obtained. Also the risk of ; contamination to the vacuum system is greatly reduced. Special attention is paid ; to the preparation of sources of the point of the strip variety. Total yields ; obtained from the evaporations and curves showing the distribution of active ; deposits, together with a list of sources so far prepared in this manner, are ; given. (auth);