Protactinium (Pa) is an actinide with chemical properties that are unique among the actinide elements. While the properties of other actinides are to a large extent understood, much of the chemistry of Pa remains a mystery. This thesis aims to illuminate new understanding of Pa chemistry through behavioral analysis using analytical techniques including liquid-liquid extraction (LL); extraction chromatography (ExC); and spectroscopic studies. Applications of radioanalytical chemistry and Pa: Through the research presented in this dissertation, we have developed a new way to separate uranium (U), thorium (Th), and Pa from complex environmental samples. The approach has been demonstrated for U-series dating of materials by alpha spectrometry. The method can be applied to geochronology, as well as to nuclear-forensic analysis of uranium-containing materials. In studies presented here, samples from a Paleolithic lake (Lake Bonneville, Utah USA) were analyzed for the radioactivity concentration of 230Th, 231Pa, 234U, 235U, and 238U by isotope dilution alpha spectrometry. Radioactivities were used to estimate of the time period of formation of the deposit from which the samples were collected. Ages were determined from the isotopics ratios; i.e., 231Pa/235U (40 ka); and 230Th/238U (39.5 ka) we found to be concordant with radiocarbon-14 dates (37 ka) obtained by collaborators at Brigham Young University. These studies inspired the development of a novel ExC resin to facilitate preparation of highly pure tracer isotope (233Pa) from a neptunium-237 (237Np) source. The material used for this development comprised 1-octanol adsorbed to a semi-porous resin material. The new approach greatly improved the yield and purity of 233Pa used for these chronometric analyses Developing an understanding of the chemistry of Pa at trace concentrations: The new-improved analytical described above led to the hypothesis that analytical separations approaches could be used to develop a more detailed understanding of Pa chemistry. Toward this goal, experiments were conducted to understand how the extraction of Pa is impacted by solution acidity [H+], anion concentration [A-; Cl-, NO3-], and extractant concentration ([2,6-dimethyl-4-heptanol, DIBC]). A full-factorial experimental design was employed to create a model that would allow for predictions in Pa behavior, as well as describe the nature of the observations. This model generated a multivariate equation that relates the distribution coefficient ([Pa] organic phase/ [Pa] aqueous phase) to each of the parameters ([H+], [A-], and [DIBC]). Further studies expanded to other alcohols (ROH) used as extractants (1-octanol, (2,6)-dimthyl-4-heptanol, and 2-ethyl-hexanol); and the results were analyzed using the slope analysis and comparative extraction studies using the model and compared to other actinide elements (Th, U, Np, americium (Am)) by both LL and ExC systems. These experiments revealed unique chemical behavior of Pa with respect to the other actinides. For example, it was found that Pa was the only actinide element to be extracted into the organic phase under acidic conditions (HCl and HNO3). Slope analysis experiments elucidated the stoichiometric identity of Pa species, with respect to the anion and extractant. Future studies will aim to identify the oxygen stoichiometry and species by X-ray absorption techniques. Investigations of the organic phase: In the final sections of this thesis, experiments are presented that are intended to determine if aggregation plays a key role in the extraction of Pa in systems containing 1-octanol and 2-ethyl-hexanol. This work is done in the absence of metal ions to control the dynamics of the organic phase, and are analyzed by tensiometry and Karl Fisher titrations with small angle X-ray scattering and molecular dynamic simulations. A key novel finding of these studies in that ROH molecules arrange in nanoscale aggregates that decrease the interfacial tension between the phases and extract a significant amount of water into the aggregates stabilized by a network of H-bonding. These studies lead to the hypothesis for future studies that Pa extraction is likely facilitated by solvation into the organic phase via ROH aggregates. The sum of the findings and observations of this dissertation provide insight into the chemical nature of Pa: (1) Novel extraction methods to obtain radiochemically pure fractions show that Pa can be efficiently extracted and separated from complex matrices to aid in chronometric analysis for geochronology or nuclear forensics; (2) Statistical modeling to develop a better understanding of the main effects of solvent extraction parameters; (3) Equilibrium analysis to improve our understanding of chemistry of Pa and how it is unique to the actinides; (4) Aggregation analysis to demonstrate a solvent centric understanding of extraction studies, these results lead to future experiments to investigate how organic phase aggregation can influence solvent extraction selectivity.

The ocean is both a repository and reactor for chemicals at the Earth’s surface. As chemicals enter the ocean they are taken up by organisms, transported by currents, reacted with particle surfaces, and eventually buried at the seafloor. This dynamic set of chemical processes and exchanges are encapsulated by the term biogeochemistry. Marine biogeochemistry can be broadly deconstructed into two parts: ocean interfaces and internal cycling. Ocean interfaces are where chemical constituents enter and leave the ocean, including the air-sea boundary, mid-ocean ridges, continental margins, and rivers. Internal cycling is how chemical constituents are reacted, transported, taken up by organisms, and redistributed within the ocean. For a complete understanding of marine biogeochemical cycles, the input, output, and internal cycling rates of major and trace elements must be quantified. However, this rate information is difficult to infer from the observational snapshots of chemical concentrations typically collected on oceanographic expeditions. The long-lived radioisotopes of thorium (Th) and protactinium (Pa) provide an opportunity to quantify these elusive biogeochemical rates. The radiogenic isotopes 230Th and 231Pa are produced at a uniform rate throughout the water column by uranium decay. A third isotope, 232Th, is primordial and brought to the ocean by the dissolution of lithogenic matter. While uranium is highly soluble, Th and Pa are highly insoluble, and are rapidly removed from solution by adsorption onto settling particle matter. Due to their insolubility and known input rates, 230Th and 231Pa have well-constrained 1-d mass budgets between radiogenic production and scavenging removal. This thesis explores new ways Th and Pa isotopes can be used to understand and quantify rates of biogeochemical processes in the South Pacific Ocean, and to assess how measurements of sedimentary Th and Pa isotopes can be used to study these processes in the geologic past. In chapter 1, I characterize the effects of submarine hydrothermal activity on the distributions of 230Th and 231Pa, finding strong removal due to adsorption by Fe and Mn oxide particles. In chapter two, I utilize the radioactive disequilibria of two additional radiogenic thorium isotopes with much shorter half-lives, 234Th and 228Th, to constrain the kinetics of Th scavenging by hydrothermal particles. Chapter three switches gears towards quantifying the internal cycling of particulate organic carbon in the subtropical South Pacific. Using a new method based on measurements of particulate 230Th, I generated high-resolution water column profiles of particulate organic carbon flux to constrain carbon regeneration lengthscales in both oligotrophic and oxygen minimum zone settings. In chapter 4, I demonstrate the importance of isopycnal mixing in transporting 230Th, 231Pa, and 232Th into the Pacific Southern Ocean, showing the first high-resolution dissolved Th and Pa data from the region. Chapter 5 provides estimates of dust input spanning the South Pacific using two methods based on paired 230Th-232Th, evaluates the flux of dust-borne iron, and discusses the impacts on measured and modeled nitrogen fixation rates in the South Pacific gyre. Finally, in chapter 6 I present enigmatic profiles of Th and Pa isotopes from the semi-enclosed Peru and Bauer Basins, with anomalous Th and Pa removal extending 1-2km above the seafloor. I hypothesize that these depletions are related to the extent of water mass contact the seafloor, allowing for scavenging removal of Th and Pa by resuspended sediments.

Made available in DSpace on 2014-10-09T12:29:21Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:44Z (GMT). No. of bitstreams: 1 01240.pdf: 3735807 bytes, checksum: 0e9709821f36bbfb1be6ca3ed86a7d0f (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:29:21Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:44Z (GMT). No. of bitstreams: 1 01240.pdf: 3735807 bytes, checksum: 0e9709821f36bbfb1be6ca3ed86a7d0f (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

The naturally occurring isotopes 231Pa and 230Th are used as tracers of marine biogeochemical processes. They are both produced from the radioactive decay of their uniformly distributed uranium parents (235U and 234U) in seawater. After production, 231Pa and 230Th are removed by adsorption onto settling particles (scavenging) and subsequently buried in marine sediments. 230Th is more particle reactive compared to 231Pa. Consequently, 230Th will be removed from the open ocean by adsorption onto settling particles, while 231Pa tend to be laterally transported by currents and removed by scavenging in areas of high particle flux (e.g. ocean margins). The primordial 232Th indicates lithogenic supply via rivers and resuspension of sediments, which provides additional information about processes involved in the cycling of particle reactive elements in the ocean. The preferential deposition of particle reactive elements at ocean margins (boundary scavenging) has important implications for our understanding of the distribution and dispersion of micronutrients (e.g. iron) and pollutants in the ocean. It is therefore valuable to understand the nature of boundary scavenging processes in order to evaluate the relative contribution of circulation and scavenging behaviors.The major characteristics of thermohaline circulation in the Mediterranean are well known and have been studied for decades. This sea is an almost land-locked area, where limited water-exchange with the Atlantic Ocean only occurs through the Strait of Gibraltar. Therefore, this marginal sea is often referred to as a “miniature ocean” suitable as a “laboratory” for marine environmental research. In this licentiate thesis, distributions of 231Pa, 230Th and 232Th in seawater and marine particles collected during the GEOTRACES MedSeA-GA04-S cruise in 2013 are presented. Observed nuclide distributions indicate the impact of deep water formation processes, where observed differences can be linked to the type of deep water formation process that occurs in respective basin. Essentially all in-situ produced 230Th is buried in Mediterranean Sea sediments. Despite lower affinity of 231Pa for marine particles, most 231Pa is also scavenged and deposited in Mediterranean Sea sediments. The efficient scavenging of 231Pa produces a relatively low fractionation between 231Pa and 230Th in terms of the fractionation factor FTh/Pa. This licentiate thesis presents a summary of the methods used for the analysis of 231Pa and Th-isotopes with details on the exchange chromatography method and the treatment of mass spectrometric data. The study of 231Pa, 230Th and 232Th in the Mediterranean Sea has important implications for our understanding of processes that control their water column distributions and how their behavior can be utilized to trace chemical flux in modern and past ocean environments. / GEOTRACES / MeDSeA

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1981. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaves 262-273. / by Robert Frederick Anderson. / Ph.D.

Kasimir Fajans und Oswald Göhring entdeckten 1913 das von ihnen Brevium (Bv) genannte Element 91 als kurzlebiges Protactiniumisotop 234mPa in unmittelbarer Folge des von Alexander S. Russell, Frederick Soddy und Fajans entdeckten radioaktiven Verschiebungsgesetzes, nachdem das als UX bezeichnete thoriumähnliche Tochterprodukt des Urans noch ein entsprechend der Voraussage von Dimitri Mendeleev tantalähnliches unbekanntes Radioelement enthalten muss. Auf der Suche nach dem langlebigen Mutterkörper des Actiniums fanden Otto Hahn und Lise Meitner 1918 das langlebige Isotop des Breviums (231Pa), das sie Protactinium nannten. Obgleich sie es als Isotop des Breviums bezeichneten, wurden sie in der Folgezeit nicht nur als Namensgeber; sondern meist auch als Entdecker des Elementes Nr. 91 genannt. / In 1913 Kasimir Fajans and Oswald Göhring discovered the element number 91as its short-lived isotope 234mPa. They named it brevium (Bv). The discovery was the result of the displacement law discovered by Alexander Smith Russell, Frederick Soddy and Fajans. According to this law and the periodic system of Dimitri Mendeleev the daughter of uranium UX must contain an unknown radioelement chemical similar to tantalum. In 1918 during the search of the mother of actinium Otto Hahn and Lise Meitner found the long-lived Isotope of Brevium (231Pa), which they designated as protactinium. Later often is written, that Hahn and Meitner have non-only given the name but also discovered the element number 91

Kasimir Fajans und Oswald Göhring entdeckten 1913 das von ihnen Brevium (Bv) genannte Element 91 als kurzlebiges Protactiniumisotop 234mPa in unmittelbarer Folge des von Alexander S. Russell, Frederick Soddy und Fajans entdeckten radioaktiven Verschiebungsgesetzes, nachdem das als UX bezeichnete thoriumähnliche Tochterprodukt des Urans noch ein entsprechend der Voraussage von Dimitri Mendeleev tantalähnliches unbekanntes Radioelement enthalten muss. Auf der Suche nach dem langlebigen Mutterkörper des Actiniums fanden Otto Hahn und Lise Meitner 1918 das langlebige Isotop des Breviums (231Pa), das sie Protactinium nannten. Obgleich sie es als Isotop des Breviums bezeichneten, wurden sie in der Folgezeit nicht nur als Namensgeber; sondern meist auch als Entdecker des Elementes Nr. 91 genannt. / In 1913 Kasimir Fajans and Oswald Göhring discovered the element number 91as its short-lived isotope 234mPa. They named it brevium (Bv). The discovery was the result of the displacement law discovered by Alexander Smith Russell, Frederick Soddy and Fajans. According to this law and the periodic system of Dimitri Mendeleev the daughter of uranium UX must contain an unknown radioelement chemical similar to tantalum. In 1918 during the search of the mother of actinium Otto Hahn and Lise Meitner found the long-lived Isotope of Brevium (231Pa), which they designated as protactinium. Later often is written, that Hahn and Meitner have non-only given the name but also discovered the element number 91

Fuel comprised of thorium has been explored since the early development of nuclear energy in the 1960s. In the last decade, there has been a renewed interest in thorium fuel and it has now become a primary focus in studies and proposed in next-generation nuclear reactors. This has been prompted by a limited supply of uranium in the foreseeable future and an abundance of thorium resources. Additionally, when compared to natural uranium (NU), thoria (ThO$_2$) produces substantially less long-lived radioactive waste and the fissile content can be reprocessed for additional fuel cycles. The CANDU 6 reactor has a unique ability to harvest thorium fuels because of its superior neutron economy. Thorium requires a driving isotope to sustain neutron fission until the long absorption chain produces viable amounts of U-233. Previous studies have investigated many different practical fissile isotopes and core modeling techniques that would make thorium feasible in a CANDU 6 reactor. This thesis focuses on a safety evaluation of thorium fuel compared to NU fuel in a lattice cell and full core configuration. \\ DRAGON 3.06 and SERPENT 2 are used to examine the infinite lattice cell containing NU and homogeneous thorium fuel enriched with 2.0\% U-235, emphasizing the relationship between multiple nuclear libraries. This configuration is used to determine the enrichment concentration, temperature coefficient, coolant void reactivity, and the power relationship. Thorium fuel exhibits a higher negative temperature coefficient, a lower coolant void reactivity, and a greater reactivity change when simulated at different powers. If the lattice cell is simulated at 75\% nominal power there is an 11 mk adjustment for thorium fuel, whereas the adjustment is only three mk for NU fuel. This is related to the extensive cross section of Th-232 and the long fertile absorption chain results in a sizeable inventory of the intermediate isotope Pa-233. The fissile content of the fuel bundle after exiting the reactor will continue to accumulate U-233 and should be monitored and properly stored. \\ A full core evaluation in a CANDU 6 reactor is performed in DONJON 4. Thorium fuel has an inferior reactivity worth for the control mechanism than does NU fuel in an operating CANDU 6 reactor. The reactivity worth of leakage and absorption in the reactor is estimated to be slightly lower for the thorium fuel. \\ This thesis presents a new computational model for analyzing full core power transients built upon previous results. The approximation model utilizes many assumptions to develop an expeditious code for analyzing the infinite square lattice retaining the isotopic densities. This model has demonstrated the ability to accurately emulate the reactivity of a lattice cell at different powers and power transients formed in DRAGON. The model is coupled with a point kinetic code to perform power transients in a CANDU 6 reactor. \\ Load following operations are performed in cycles of 24 hours examined at 80\%, 60\%, and 40\% full power. Power adjustments are performed in increments of 10 minutes, two hour, or four hour periods with a constant reactivity input. The power adjustment time has minimal effect on the reactivity perturbations and only influences the rate of reactivity. Thorium fuel has enhanced load following capabilities compared to conventional NU fuel.\\ The long-lasting effects of Pa-233 introduces safety concern when reducing power or reactor shutdown scenarios. Reactivity transformation within the first two days of immediate power reduction will yield similar results for both fuels. Excess reactivity in the thorium fuel will continue to accumulate and eventually double the reactivity peak of NU fuel in the following 90 to 120 days. A shutdown simulation is performed in incremental power reduction steps of 20\% for a range of different days. It is found that NU fuel can adequately control the additional reactivity in this simulation. Thorium fuel maintains a disconcerting amount of excess reactivity that will need to be addressed accordingly. The protactinium transient highlights the need to adequately monitor the buildup of Pa-233 for thorium-based fuels in a reactor. / Thesis / Master of Applied Science (MASc)

L’acquisition de données structurales et thermodynamiques relatives à des systèmes actinides (An(III), Pu(IV) Pa(V))–acides organiques polyfonctionnels (citrique, NTA, DTPA), en solution aqueuse, vise à une meilleure compréhension des interactions actinides-ligands essentielle à l’optimisation de procédés de séparation, de décorporation, et également à l’évaluation de la sûreté des sites de stockage de déchets radioactifs. Le comportement du protactinium pentavalent à l’échelle des traces en présence des anions citrates et NTA a fait l’objet d’études systématiques par extraction liquide-liquide dans le système TTA/Toluène/HClO₄/NaClO₄/Pa(V)/ligands. Après avoir déterminé l’ordre limite des complexes (3 pour Pa(V)-Cit et 2 pour Pa(V)-NTA), les constantes de formation associées à chaque espèce ont pu être calculées. L’étude multi-technique (électrophorèse capillaire et spectrofluométrie laser) sur la complexation des An(III) par le DTPA, réalisée à plusieurs pH, a permis de mettre en évidence la coexistence des complexes mono-protoné (AnHDTPA–) et déprotoné. (AnDTPA²–) pour des solutions acides et faiblement acides. Une réinterprétation des données de la littérature, en considérant les deux complexes, a permis de faire converger les valeurs des constantes de complexation des espèces qui étaient jusqu’à maintenant dispersées. L’étude thermodynamique a ensuite été complétée par une étude théorique (calculs DFT). La structure des complexes protoné et non protoné et le mode de coordination du Curium ont ainsi été établis. L’étude exploratoire sur la complexation du Pu(IV) par le DTPA dans des conditions de pH proches du milieu biologique a nécessité le développement d’un protocole expérimental en trois étapes : protection de Pu(IV) contre l’hydrolyse avec NTA (pH faible), augmentation du pH vers des conditions neutres, compétition entre la complexation de Pu(IV) par le NTA et le DTPA. Les expériences préliminaires réalisées entre pH 1,5 et 3,5 par électrophorèse capillaire (EC-ICP-MS), semblent indiquer l’existence d’effet cinétique ou/et l’existence d’un complexe mixte. Les interprétations faites lors de cette étude exploratoire sont à confirmer. / A thorough knowledge of the chemical properties of actinides is now required in a wide variety of fields: extraction processes involved in spent fuel reprocessing, groundwater in the vicinity of radioactive waste packages, environmental and biological media in the case of accidental release of radionuclides. In this context, the present work has been focused on the complexation of Am(III), Cm(III), Cf(III), Pu(IV) and Pa(V) with organic ligands: DTPA, NTA and citric acid. The complexation of pentavalent protactinium with citric and nitrilotriacetic acids was studied using liquid-liquid extraction with the element at tracer scale (CPa < 10-10M). The order and the mean charge of each complex were determined from the analysis of the systematic variations of the distribution coefficient of Pa(V) as function of ligand and proton concentration. Then, the apparent formation constants related of the so-identified complexes were calculated. The complexation of trivalent actinides with DTPA was studied by fluorescence spectroscopy (TRLFS) and capillary electrophoresis (CE-ICP-MS). The coexistence of the mono-protonated and non-protonated complexes (AnHDTPA– and AnDTPA²–) in acidic media (1.5 ≤ pH ≤ 3.5) was shown unambiguously. Literature data have been reinterpreted by taking into account both complexes and a consistent set of formation constants of An(III)-DTPA has been obtained. The experimental study was completed by theoretical calculations (DFT) on Cm-DTPA system. The coordination geometry of Cm in CmDTPA²- and CmHDTPA- including water molecules in the first coordination sphere has been determined as well as interatomic distances. Finally, a study on the complexation of Pu(IV) with DTPA was initiated in order to more closely mimic physiological conditions. A three-step approach was proposed to avoid plutonium hydrolysis: i/ complexation of Pu(IV) with (NTA) in order to protect Pu(IV) from hydrolysis (at low pH) ii/ increase of pH toward neutral conditions and iii/ competition between the complexation of Pu with NTA and with DTPA. The preliminary experiments performed with CE-ICP-MS in the pH range 1.5 - 3.5 tend to indicate kinetic effect or/and the presence of mixed complex.