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Radiochronometry provides the model age of nuclear materials, which is useful for understanding the production history of materials found outside of regulatory control. Certified reference materials (CRMs) are important for radiochronometry to increase confidence in measurement quality; however, the absence of 231Pa/235U CRMs necessitates that nuclear forensic laboratories measure the 231Pa/235U model ages of preexisting uranium reference materials. Here, new consensus 231Pa/235U model ages are reported from three nuclear forensic laboratories for three reference materials using current analytical methods. These updated consensus values can be used for quality control of 231Pa/235U model age measurements. [ABSTRACT FROM AUTHOR]

This study explores the distinctive behavior of protactinium (Z=91) within the actinide series. In contrast to neighboring elements like uranium or plutonium, protactinium in the pentavalent state diverges by not forming the typical dioxo protactinyl moiety PaO2+ in aqueous phase. Instead, it manifests as a monooxo PaO3+ cation or a Pa5+. Employing first‐principle calculations with implicit and explicit solvation, we investigate two stoichiometrically equivalent neutral complexes: PaO(OH)2(X)(H2O) and Pa(OH)4(X), where X represents various monodentate and bidentate ligands. Calculating the Gibbs free energy for the reaction PaO(OH)2(X)(H2O)→Pa(OH)4(X), we find that the PaO(OH)2(X)(H2O) complex is stabilized with Cl−, Br−, I−, NCS−, NO3−, and SO42− ligands, while it is not favored with OH−, F−, and C2O42− ligands. Quantum Theory of Atoms in Molecules (QTAIM) and Natural Bond Orbital (NBO) methods reveal the Pa mono‐oxo bond as a triple bond, with significant contributions from the 5f and 6d shells. Covalency of the Pa mono‐oxo bond increases with certain ligands, such as Cl−, Br−, I−, NCS−, and NO3−. These findings elucidate protactinium's unique chemical attributes and provide insights into the conditions supporting the stability of relevant complexes. [ABSTRACT FROM AUTHOR]

The isolation and purification of protactinium from uranium materials is essential for 231Pa–235U radiochronometry, but separating Pa from uranium-niobium alloys, a common material in the nuclear fuel cycle, is challenging due to the chemical similarity of Pa and Nb. Here we present three resin chromatography separation techniques for isolating Pa from U and Nb which were independently developed by three different laboratories through ad hoc adaptations of standard operating procedures. Our results underscore the need for and value of purification methods suitable for a diversity of uranium-based materials to ensure the operational readiness of nuclear forensics laboratories. [ABSTRACT FROM AUTHOR]

The α -decay half-lives for odd Z Pa isotopes were estimated by using the modified generalized liquid drop model (MGLDM) in the neutron number range 1 2 0 ≤ N ≤ 1 5 0. These half-lives are found to be an excellent match with available experimental data certified by the least root mean-square error when compared with the other recently proposed empirical formulas. The applicability of MGLDM is proved on the odd Z -odd N (even N) nuclei in a successful manner in describing their α -decay half-lives which are employed to predict half-lives of few unknown Pa isotopes. Our results are expected to provide more extensive and precise information of half-lives for the upcoming experiments eyeing on the boundaries of the trans-led nuclei. [ABSTRACT FROM AUTHOR]

The accurate interpretation of uranium metal 230Th/234U and 231Pa/235U radiochronometry model ages requires an understanding of how uranium parent nuclides and decay progeny (230Th and 231Pa) behave during uranium metal casting. In order to directly measure the spatial distribution of 230Th and 231Pa in uranium metal before and after vacuum induction melting (VIM), Los Alamos National Laboratory identified uranium metal feedstock, characterized the metal feedstock, conducted a controlled casting experiment of an approximately 120 kg uranium metal rod, and characterized the cast metal. This study presents radiochronometry results and quantified 230Th and 231Pa VIM separation factors from bulk uranium. [ABSTRACT FROM AUTHOR]

We present a chromatography chemistry for purifying protactinium from uranium metal alloys containing weight-percent concentrations of niobium. Niobium is precipitated in 9 M HCl without the co-precipitation of Pa as demonstrated by gamma-ray spectrometry. Protactinium is further purified using Bio-Rad™ anion resin AG® 1-X8 and 9 M HCl + 0.0128 M HF. A Pa/Nb separation factor of 85,000 and a 90% Pa recovery is demonstrated, which is amenable to 231Pa concentration determination by isotope dilution and 231Pa/235U model age calculation for nuclear forensics. [ABSTRACT FROM AUTHOR]

The sorption of uranium and thorium fluorides by activated carbon from the eutectic was studied. The sorption isotherms of both fluorides at a temperature of 650°C have a pronounced convex character and are described by the Langmuir equation. Experiments were carried out on the sorption of protactinium by activated carbon AG-3 at 650°С from a melt of alkali metal fluorides LiF–NaF–KF containing thorium and neodymium fluorides. It was found that with an increase in the concentrations of neodymium or thorium fluorides, the value of protactinium sorption diminishes, and in the case of thorium fluoride, the decrease occurs to a greater extent. When protactinium is sorbed by activated carbon with metallic sodium, the sorption enhances by a factor of 20 at the 30% sodium content in the carbon. The separation factors of protactinium from other actinides rise with increasing sodium content in the carbon. [ABSTRACT FROM AUTHOR]

Improved methods employed at Los Alamos National Laboratory for 231Pa/235U radiochronometry are outlined. We present elution curves obtained during 233Pa tracer preparation from 237Np. Additionally, we report model ages for uranium certified reference materials (CRMs) exhibiting a range of 235U enrichments including the first 231Pa/235U model ages for CRMs U200 and U900. Our results enable these CRMs to be used, with increased confidence, as quality control materials during nuclear forensics investigations. [ABSTRACT FROM AUTHOR]

Nuclear Power Plants (NPP) is one of alternative energy that can be used to replace fossil energy. NPP is a clean energy that doesn't emit CO2 as a residue from the power plant. Pressurized Water Reactor (PWR) is the most widely used commercial reactor to date. This reactor usually uses UO2 as fuel with enrich U-235 and produce plutonium as a waste nuclear. In this study, the fuel uses natural uranium and the addition of plutonium from the spent fuel of PWR, calling it Uranium-Plutonium Nitride (UN-PuN) fuel. Plutonium from spent fuel PWR (U-fueled) consists of Pu-238, Pu-239, Pu-240, Pu-241 and Pu-242, which Pu-239 and Pu-241 are fissile material. The aim of using plutonium is to reduce the amount of nuclear waste and prevent the use of plutonium as a nuclear weapon. The addition of neptunium and protactinium is also carried out in the fuel. Neptunium is one of the minor actinide materials which have high toxicity, so add Np-237 it is very useful to reduce the amount of neptunium in the world. And also, the addition of Np-237 and Pa-231 aims to decrease the keff value both in the Beginning of Life (BOL) and End of Life (EOL) in the reactor. This research calculates the neutronic calculations for PWR use SRAC2006 with COREBN Code and Japanese Evaluated Nuclear Data Library 4.0 (JENDL-4.0) for the nuclear data library. The COREBN code is a calculation method based on interpolation of macroscopic cross-section and finite-difference diffusion theory. The optimum design reached the maximum k-eff value 1.017077 and the maximum power density was 58.47 W/cc. The results obtained are the excess reactivity value of 1.68 % smaller than previous study which produces an excess reactivity value of 11.94 %. So this design has the potential to be applied in the PWR design. [ABSTRACT FROM AUTHOR]

A multi-target recoil chamber technique was applied to study online chemical properties of protactinium in chlorinating and brominating gas media using 226Pa (T1/2 = 1.8 min) decaying by alpha emission (74%) and β+/EC decay (26%). A 58 MeV proton beam passing 15 × 50 μg/cm2 thick 232Th targets enabled production of 226Pa formed in the reaction 232Th(p,7n). Isothermal gas chromatography in quartz columns allowed for the determination of adsorption enthalpies of oxohalides and pure halides of Pa5+ compounds. On the basis of empirical correlations, these adsorption enthalpies (ΔH0ads) could be converted to sublimation enthalpies (ΔH0subl). Resulting values for the assumed compounds PaCl5, PaOCl3, PaBr5, and PaOBr3 were 113 ± 15, 329 ± 16, 165 ± 5 and 235 ± 17 kJ/mol, respectively. These values are rather similar to known ΔH0subl data for group-5 elements Nb, Ta and Db in support of the assumption that Pa is a pseudo-group 5 element. [ABSTRACT FROM AUTHOR]

This review concerns the speciation of protactinium in aqueous solution under its both oxidation states +IV and +V. Emphasis is placed on experimental data obtained at trace level but also in macroscopic amount leading to the determination of thermodynamic and structural data. Thus, the complexation of Pa(V) with mineral acids and organic acids, mainly polyaminocarboxylic acids (iminodiacetic acid [IDA], nitrilotriacetic acid [NTA], ethylenediaminetetraacetic acid [EDTA] and diethylenetriaminepentaacetic acid [DTPA]) are highlighted and compared. The review also includes the actual knowledge about the Pa(IV) aqueous chemistry pinpointing its spectroscopic features. [ABSTRACT FROM AUTHOR]

An in-house radiochemical procedure for the separation of 231Pa from siliceous cake - a waste stream of monazite processing plant, followed by its determination using gamma ray spectrometry, has been developed in our laboratory. Evaluation of reliability of analytical results of the radiochemical procedure is important for validating the fitness of purpose of an analytical method. The present paper describes the statistical evaluation of the analytical results obtained, by estimating the overall uncertainty in the measurement process. The bottom-up approach, also called as ISO approach (ISO/IEC guide 98-3:2008), was adopted to evaluate the overall uncertainty in which the individual sources were identified, evaluated and propagated. The major contribution to the combined uncertainty in measurement of 231Pa was from efficiency calibration. Besides this, counting statistics in the sample and chemical yield of the process incorporated significant contribution to combined uncertainty. The precision of the results obtained was found to be acceptable, as ascertained by the Horwitz Ratio, for the performance of a single laboratory. [ABSTRACT FROM AUTHOR]

Protactinium contamination is a mayor issue in the thorium fuel cycle. We investigate, in this work, the consequences of Pa incorporation in vacancy defects and interstitials in Th, ThC and ThN. We calculate charge transfers and lattice distortions due to these incorporations as well as migration paths and energies involved in the diffusion of Pa.

231Pa and 230Th are two crucial isotopes in the ongoing GEOTRACES Project. However, the controversy on 231Pa/230Th proxy pertaining to archiving ocean circulation or recording paleoproductivity, is still unresolved, partly owing to the unclear understanding of fractionation between 231Pa and 230Th during adsorption. In this study, controlled experiments were conducted to examine the adsorption of 234Th and 233Pa onto biogenic particles (SiO2 and CaCO3), authigenic minerals (MnO2 and Fe2O3), and lithogenic minerals (kaolinite, attapulgite, montmorillonite, and aluminum oxyhydroxides), and the role of organic compounds in regulating the adsorption of 234Th and 233Pa in natural seawater was evaluated. The distribution coefficients (Kd, presented as logKd) varied from 3.56 to 6.05 and from 3.27 to 5.82 for 234Th and 233Pa, respectively. Fe2O3 is the strongest sorbent for both 234Th and 233Pa. Most of the particles showed comparable logKd values for either 234Th (∼4.8) or 233Pa (∼3.9) in the presence of dextran, indicating that the adsorption of Th and Pa is likely controlled by organic coating on particle surfaces. The fractionation factors (FTh/Pa) of SiO2 (3±1) and CaCO3 (33±1) suggest in situ observed preferential scavenging of 230Th to 231Pa in the surface water of low- to mid-latitude regions and the nearly equal removal in the Antarctic Ocean where biogenic silica dominates the particle regime. The FTh/Pa values of the lithogenic and biogenic particles indicate that 230Th is scavenged prior to 231Pa in the particle-scarce ocean interior. The equal scavenging of 230Th and 231Pa at the ocean margins and the ridge crests is dominated by high particle fluxes instead of particle composition control. These results imply that 230Th/231Pa can be used as different proxies in different oceanic settings. [ABSTRACT FROM AUTHOR]

CL resin (TrisKem International) was characterized for separations of radium, actinium, thorium and protactinium. Batch studies are presented for radium, actinium and thorium in HCl and HNO3 as well as for radium, thorium and protactinium in HF. The uptake of thorium from dilute HNO3 (≤ 10−4 M) and dilute HCl (≤ 10−4 M) was found to be very high (Dw > 100 in HNO3 and > 1000 in HCl). Kinetics studies on thorium were performed in HCl and HNO3 to determine suitably for column separations. Six column separation studies are presented including the separation of trace thorium from radium and actinium in dilute HCl and HNO3, the separation of radium from 1 mg 232Th in dilute HCl, the separation of thorium and radium in the presence of HCl and excess Cl−, the separation of radium, protactinium and thorium by retention of protactinium and the separation of protactinium and thorium by retention of thorium. [ABSTRACT FROM AUTHOR]

Initial excess protactinium (231Pa) is a frequently suspected source of discordance in baddeleyite (ZrO2) geochronology, which limits accurate U/Pb dating, but such excesses have never been directly demonstrated. In this study, Pa incorporation in late Holocene baddeleyite from Somma-Vesuvius (Campanian Volcanic Province, central Italy) and Laacher See (East Eifel Volcanic Field, western Germany) was quantified by U-Th-Pa measurements using a large-geometry ion microprobe. Bad-deleyite crystals isolated from subvolcanic syenites have average U concentrations of ~200 ppm and are largely stoichiometric with minor abundances of Nb, Hf, Ti, and Fe up to a few weight percent. Measured (231Pa)/(235U) activity ratios are significantly above the secular equilibrium value of unity and range from 3.4(8) to 14.9(2.6) in Vesuvius baddeleyite and from 3.6(9) to 8.9(1.4) in Laacher See baddeleyite (values within parentheses represent uncertainties in the last significant figures reported as 1σ throughout the text). Crystallization ages of 5.12(56) ka (Vesuvius; MSWD = 0.96, n = 12) and 15.6(2.0) ka (Laacher See; MSWD = 0.91, n = 10) were obtained from (230Th)/(238U) disequilibria for the same crystals, which are close to the respective eruption ages. Applying a corresponding age correction indicates average initial (231Pa)/(235U)0 of 8.8(1.0) (Vesuvius) and 7.9(5) (Laacher See). For reasonable melt activities, model baddeleyite-melt distribution coefficients of DPa/DU = 5.8(2) and 4.1(2) are obtained for Vesuvius and Laacher See, respectively. Speciation-dependent (Pa4+ vs. Pa5+) partitioning coefficients (D values) from crystal lattice strain models for tetra- and pentavalent proxy ions significantly exceed DPa/DU inferred from direct analysis of 231Pa for Pa5+. This is consistent with predominantly reduced Pa4+ in the melt, for which D values similar to U4+ are expected. Contrary to common assumptions, baddeleyite-crystallizing melts from Vesuvius and Laacher See appear to be dominated by Pa4+ rather than Pa5+. An initial disequilibrium correction for baddeleyite geochronology using DPa/DU = 5 ± 1 is recommended for oxidized phonolitic melt compositions. [ABSTRACT FROM AUTHOR]

The Southern Ocean hosts complex connections between ocean physics, chemistry, and biology. Changes in these connections are hypothesized to be responsible for significant alterations of ocean biogeochemistry and carbon storage both on glacial‐interglacial timescales and in the future due to anthropogenic forcing. Isotopes of thorium (230Th and 232Th) and protactinium (231Pa) have been widely applied as tools to study paleoceanographic conditions in the Southern Ocean. However, understanding of the chemical behavior of these isotopes in the modern Southern Ocean has been limited by a paucity of high‐resolution observations. In this study, we present measurements of dissolved 230Th, 231Pa, and 232Th on a meridional transect along 170°W from 67°S to 54°S in the Pacific sector of the Southern Ocean, with high vertical and meridional sampling resolution. We find Th/Pa fractionation factors below 1, highlighting the preferential removal of Pa relative to Th in a region with low lithogenic inputs where the particle flux is dominated by biogenic opal. We also find steep gradients in all three of these isotopes along neutral density surfaces from north to south, demonstrating the importance of isopycnal mixing in transporting these nuclides to the Southern Ocean. Our results suggest that 231Pa and 230Th in the Southern Ocean are highly sensitive tracers of physical transport that may find use in studies of Southern Ocean biogeochemical‐physical connections in the past, present, and future. Key Points: Large gradients in dissolved 230Th, 231Pa, and 232Th are found along upwelling isopycnals in the Pacific Southern OceanZonal variations in Th/Pa fractionation across the Southern Ocean are driven by particle compositionIsopycnal mixing is of primary importance for transporting 231Pa to the Southern Ocean [ABSTRACT FROM AUTHOR]

During 2017–2018 Los Alamos National Laboratory, Lawrence Livermore National Laboratory and the China Institute of Atomic Energy collaborated in an interlaboratory 231Pa/235U radiochronometry exercise. The laboratories used different analytical methods to obtain a consensus model purification date for CRM U010 of December 28, 1958 ± 198 days and for CRM U850 of May 20, 1958 ± 363 days. These results agree with previously reported model dates using the 230Th/234U radiochronometer as well as the production histories of these materials. The concordance of interlaboratory data confirms the ability of laboratories to make reproducible radiochronometry measurements using distinct analytical approaches. [ABSTRACT FROM AUTHOR]

Application of the 231Pa/235U radiochronometer for nuclear forensic investigations is challenged by a lack of certified reference materials with 231Pa/235U model purification dates. The Japan Atomic Energy Agency, Los Alamos National Laboratory, and Lawrence Livermore National Laboratory completed an interlaboratory study measuring 231Pa/235U model ages of New Brunswick Laboratory CRM U100. Results from independent laboratories were combined to calculate a consensus 231Pa/235U model purification date for CRM U100 of March 26, 1959 ± 237 days. This 231Pa/235U consensus date for CRM U100 may be used by the nuclear forensic community for quality control of 231Pa/235U radiochronometry measurements of unknown materials. [ABSTRACT FROM AUTHOR]

In this study we report about the aromaticity of the prototypical [(HtAc)3(μ2-H)6], [(HtTh)3(μ2-H)6]+, and [(HtPa)3(μ2-H)6] clusters via two magnetic criteria: nucleus-independent chemical shifts (NICS) and the magnetically induced current density. All-electron density functional theory calculations were carried out using the two-component zeroth-order regular approach and the four-component Dirac-Coulomb Hamiltonian, including scalar and spin-orbit relativistic effects. Four-component current density maps and the integration of induced ring-current susceptibilities clearly show that the clusters [(HtAc)3(μ2-H)6] and [(HtTh)3(μ2-H)6]+ are non-aromatic whereas [(HtPa)3(μ2-H)6] is anti-aromatic. However, for the thorium cluster we find a discrepancy between the current density plots and the classification through the NICS index. Our results also demonstrate the increasing influence of f orbitals, on bonding and magnetic properties, with increasing atomic number in these clusters. We think that the enhanced electron mobility in [(HtPa)3(μ2-H)6] is due the significant 5f character of its valence shell. Also the participation of f orbitals in bonding is the reason why the protactinium cluster has the shortest bond lengths of the three clusters. This study provides another example showing that the magnetically induced current density approach can give more reliable results than the NICS index. [ABSTRACT FROM AUTHOR]

Environmental detection of trace isotopes 233U and 236U are important forensic signatures for identifying uranium ore materials or tracking anthropogenic releases from weapons fallout or nuclear reprocessing. Currently, Accelerator Mass Spectrometry (AMS) is the only method sensitive enough to detect signatures of 233U/U and 236U/U at the natural level due to the molecular interferences of 232ThH and 235UH, respectively, often present in conventional mass spectrometry. In this work, we detail the AMS capabilities of actinides developed at the University of Notre Dame's Nuclear Science Laboratory (NSL). For the first time in our laboratory, we have measured isotopic ratios of 236U/U and explored additional signatures of 233U and decay chain products 231Pa and 230Th in both natural ore material and two National Bureau of Standards samples. In this work we estimate a system sensitivity for 236U/U of 1.4 × 10 - 11 and characterize the simultaneous detection of 233U, 231Pa, and 230Th. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the structure, Curie temperature and magnetostriction of protactinium compound alloys using optical microscopy and x-ray diffraction. Experimental procedure; Results and discussion.

Sorption study of Nb(V) and Pa(V) was carried out on silica in the pH range of 1–12. Presence of humic acids has positive effects on sorption in acidic pH and has negative effects in basic pH which is more severe. The sorption mechanism was evaluated using classical as well as spectroscopic techniques. Ionic strength study reveals outer sphere complexation in acidic region, whereas strong possibility of inner sphere surface complexation in neutral and basic regions. Thermodynamic data further reinforce the findings of salinity studies. Extended X-ray Absorption Fine Structure (EXAFS) analysis of Nb(V) sorbed silica at different pH clearly showed that in acidic medium, Nb is not coordinated with any Si atom, whole coordination number is satisfied by O atom and water molecules whereas in neutral and basic medium, Nb is coordinated with 1–2 Si atoms at 3.44 Å and 3.5 Å via O bridge. The spectroscopic analysis endorses the claim by salinity and thermodynamic data, and concludes the physisorption in acidic medium and chemisorption in neutral as well as basic region. [ABSTRACT FROM AUTHOR]

Radiochronometric data, a key signature in evaluating the provenance and process history of nuclear material out of regulatory control, are conventionally acquired via multi-collector mass spectrometry. Here we explore the potential of age-dating by single-collector mass spectrometry. To evaluate model age accuracy/precision across different instrument designs, we performed 230Th–234U and 231Pa–235U radiochronometry of CRM 125-A using two single-collector and one multi-collector plasma source mass spectrometers. Single-collector instruments produce accurate model ages for this uranium standard and thus hold promise for nuclear forensics radiochronometry. Increased acquisition of age information via multiple instrument designs will bolster the global response to nuclear interdictions. [ABSTRACT FROM AUTHOR]

This review highlights recent data on the complexation of Pa(V) with inorganic (fluoride and sulphate) and organic (oxalate, nitrilotriacetate, diethylenetriaminepentaacetate) ligands in solution. New thermodynamic parameters relative to the complexation of Pa(V) with sulphate are presented. The review also includes gas phase and theoretical studies focused on the interaction of Pa(V) in the dioxo and oxo forms with water. [ABSTRACT FROM AUTHOR]

The redetermination of the crystal structure of trigonal UCl6, which is the eponym for the UCl6 structure type, showed that certain atomic coordinates had been incorrectly reported. This led to noticeably different U−Cl distances within the octahedral UCl6 molecule (2.41 and 2.51 Å). Within the revised structure model presented here, which is based on single crystal data as well as quantum chemical calculations, all U−Cl distances are essentially equal within standard uncertainty (2.431(5), 2.437(5), and 2.439(6) Å). This room temperature modification, called rt‐UCl6, crystallizes in the trigonal space group P3‾m1, No. 164, hP21, with a=10.907(2), c=5.9883(12) Å, V=616.9(2) Å3, Z=3 at T=253 K. A new low‐temperature (lt) modification of UCl6 is also presented that was obtained by cooling a single crystal of rt‐UCl6. The phase change occurs between 150 and 175 K. lt‐UCl6 crystallizes isotypic to a low‐temperature modification of SF6 in the monoclinic crystal system, space group C2/m, No. 12, mS42, with a=17.847(4), b=10.8347(18), c=6.2670(17) Å, β=96.68(2)°, V=1203.6(5) Å3, Z=6 at 100 K. The Cl anions form a close‐packed structure corresponding to the α‐Sm type with uranium atoms in the octahedral voids. During the synthesis of UBr5 a new modification was obtained that crystallizes in the triclinic crystal system, space group P1‾ , No. 2, aP36, with a=10.4021(6), b=11.1620(6), c=12.2942(7) Å, α=68.3340(10)°, β=69.6410(10)° and γ=89.5290(10)°, V=1231.84(12) Å3, Z=3 at T=100 K. In this structure the UBr5 units are dimerized to U2Br10 molecules. The Br anions also form a close‐packed structure of the α‐Sm type with adjacent uranium atoms in the octahedral voids. Comparisons of the crystal structures of the compounds MX5 (M=Pa, U; X=Cl, Br) show that the crystal structure of monoclinic α‐PaBr5 is probably not correct. [ABSTRACT FROM AUTHOR]

The 5f1→6d1 absorption spectrum of 231Pa4+ diluted in a single crystal of Cs2ZrCl6 has been measured at 4.2 K. Three bands corresponding to the 6d(Γ8g, Γ7g, and Γ’8g ) levels are assigned. Extensive vibronic structure has been observed for the lowest 5f→6d transition and this structure is compared to that recently reported for the 6d1→5f1 emission spectra in the same system. [ABSTRACT FROM AUTHOR]

Emission spectra from the parity-allowed electronic transitions between the lowest crystal field level of the 6d1 configuration to all the electronic levels of the 5f1 configuration of Pa4+ diluted into single crystals of Cs2ZrCl6 at 4.2 K show highly structured vibronic sidebands. Vibronic progressions are seen along the 310 cm-1 totally symmetric stretch of the PaCl2-6 complex. Most vibronic peaks correspond to even parity vibrations of the PaCl2-6 complex or the host lattice. Additionally, electronic Raman scattering was observed between the two lowest crystal field levels of the 5f1 configuration by exciting with an argon ion laser in near resonance with the lowest level of the 6d1 configuration. [ABSTRACT FROM AUTHOR]

Reprocessing of spent nuclear fuel usually employs the solvent extraction technique to recover fissile material, isolate other valuable radionuclides, recover precious metals, and remove contaminants. Efficient recovery of these species from highly radioactive solutions requires a detailed understanding of reaction conditions and metal speciation that leads to their isolation in pure forms. Due to the complex nature of these systems, identification of ideal reaction conditions for the efficient extraction of specific metals can be challenging. Thus, the development of experimental approaches that have the potential to reduce the number of experiments required to identify ideal conditions are desirable. In this study, a full-factorial experimental design was used to identify the main effects and variable interactions of three chemical parameters on the extraction of protactinium (Pa). Specifically we investigated the main effects of the anion concentration (NO3-, Cl-) extractant concentration, and solution acidity on the overall extraction of protactinium by 2,6-dimethyl-4-heptanol (diisobutylcarbinol; DIBC) from both HCl and HNO3 solutions. Our results indicate that in HCl, the extraction of protactinium was dominated by the solution acidity, while in nitric acid the extraction was strongly effected by the [DIBC]. Based on our results, a mathematical model was derived, that describes the relationship between concentrations of anions, extractant, and solution acidity and the expected values of Pa distribution coefficients in both HCl and HNO3. This study demonstrates the potential to predict the distribution coefficient values, based upon a mathematical model generated by a full-factorial experimental design.

Abstract Limited information exists on the movement and partitioning of 235U series radionuclides following their release to the environment from activities associated with the nuclear fuel cycle. Only three isotopes in the series, 235U, 231Pa and 227Ac, have half-lives greater than a month. The extent to which the radiologically-significant isotopes of the 235U series differentiate and fractionate in the environment, and then accumulate in biota, is largely controlled by the chemical properties of these three elements and by their biological uptake. This is particularly the case for biota with life cycles in the order of years. There is therefore potential for changes in the radiation dose received by humans and the environment during, for example, the operational and post-remediation phases of uranium mining practices, particularly where mine sites revert to traditional land uses such as hunting, fishing and camping. Natural activity concentrations of 235U are ∼20 times lower than for 238U. In an environmental context, however, the radiation dose that arises from subsequent members of the 235U decay chain will be determined by their abundance distribution and can exceed that from the 238U series. The half-lives of the protactinium isotopes allow only 231Pa to accumulate independently of its parent radionuclide along the transport pathways and/or through preferential uptake by biota. In particular, 231Pa could make a disproportionately high contribution to the dose if it is preferentially transported and/or taken up. The AMS technique is capable of assessing accumulation of 231Pa in natural environmental samples. We report on a new, safer radiochemical extraction method to prepare the 233Pa isotopic tracer (one that does not use hydrofluoric acid), and on the development of 231Pa AMS measurements at the Australian National University. [ABSTRACT FROM AUTHOR]

The application of multiple radiochronometers in a forensic investigation of bulk uranium provides increased confidence for interpreting age-dating results. We have developed a streamlined method for the purification of Pa and Th from bulk uranium and have applied this method in analyzing uranium certified reference materials (CRMs) IRMM-1000 and CRM U100, using the 231Pa-235U and 230Th-234U radiochronometers. Our improved 233Pa spike calibration technique has replaced the time-intensive, conventional calibration using geologic rock standards. Paired Pa-U and Th-U age-dating analyses of CRM U100 produce concordant results. In contrast, analyses of IRMM-1000 demonstrate reproducibly-discordant Th-U and Pa-U age-dates. [ABSTRACT FROM AUTHOR]

Protactinium-233 (233Pa) is used as a tracer for radiochemical analysis and is of particular interest as an isotope dilution mass spectrometry (IDMS) spike for 231Pa/235U radio-chronometry. To this end, we present massic activity determinations by two methods for a 233Pa solution, which was prepared at Lawrence Livermore National Laboratory (LLNL) and is being characterized at multiple labs as part of a 231Pa reference material production project. One activity determination method was 4πβ-γ anti-coincidence counting in a multi-dimensional extrapolation model, with Monte Carlo corrections. An independent massic activity determination was completed by γ-ray spectrometry using 5 high purity germanium (HPGe) detectors using 5 γ-ray lines. The anti-coincidence and γ-ray spectrometry results agree and have combined standard uncertainties of about 0.33% and 1.0% respectively. In addition, the two methods were combined to derive γ-ray emission probabilities from 233Pa decay. [ABSTRACT FROM AUTHOR]