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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Fast and efficient charge breeding of the Californium rare isotope breeder upgrade electron beam ion source

The Electron Beam Ion Source (EBIS), developed to breed Californium Rare Isotope Breeder Upgrade (CARIBU) radioactive beams at Argonne Tandem Linac Accelerator System (ATLAS), is being tested off-line. A unique property of the EBIS is a combination of short breeding times, high repetition rates, and a large acceptance. Overall, we have implemented many innovative features during the design and construction of the CARIBU EBIS as compared to the existing EBIS breeders. The off-line charge breeding tests are being performed using a surface ionization source that produces singly charged cesium ions. The main goal of the off-line commissioning is to demonstrate stable operation of the EBIS at a 10 Hz repetition rate and a breeding efficiency into single charge state higher than 15%. These goals have been successfully achieved and exceeded. We have measured (20% ± 0.7%) breeding efficiency into the single charge state of 28+ cesium ions with the breeding time of 28 ms. In general, the current CARIBU EBIS operational parameters can provide charge breeding of any ions in the full mass range of periodic table with high efficiency, short breeding times, and sufficiently low charge-to-mass ratio, 1/6.3 for the heaviest masses, for further acceleration in ATLAS. In this study, we discuss the parameters of the EBIS and the charge breeding results in a pulsed injection mode with repetition rates up to 10 Hz.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Development of electron beam ion source charge breeder for rare isotopes at Californium Rare Isotope Breeder Upgrade

Recently, the Californium Rare Isotope Breeder Upgrade (CARIBU) to the Argonne Tandem Linac Accelerator System (ATLAS) was commissioned and became available for production of rare isotopes. Currently, an electron cyclotron resonance ion source is used as a charge breeder for CARIBU beams. To further increase the intensity and improve the purity of neutron-rich ion beams accelerated by ATLAS, we are developing a high-efficiency charge breeder for CARIBU based on an electron beam ion source (EBIS). The CARIBU EBIS charge breeder will utilize the state-of-the-art EBIS technology recently developed at Brookhaven National Laboratory (BNL). The electron beam current density in the CARIBU EBIS trap will be significantly higher than that in existing operational charge-state breeders based on the EBIS concept. The design of the CARIBU EBIS charge breeder is nearly complete. Long-lead components of the EBIS such as a 6-T superconducting solenoid and an electron gun have been ordered with the delivery schedule in the fall of 2011. Measurements of expected breeding efficiency using the BNL Test EBIS have been performed using a Cs{sup +} surface ionization ion source for external injection in pulsed mode. In these experiments we have achieved {approx}70% injection/extraction efficiency and breeding efficiency into the most abundant charge state of {approx}17%.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Design of the injection beamline for the Californium Rare Isotope Breeder Upgrade electron beam ion source charge breeder

The design of the ion injection line connecting the electron beam ion source (EBIS) charge breeder and the Californium Rare Isotope Breeder Upgrade radio frequency quadrupole cooler-buncher at the Argonne Tandem Linear Accelerator System was investigated with particle tracking simulations. The injection line was configured to accommodate several differential pumping sections, individual optical components were optimized to minimize emittance growth, and the ion beam parameters were matched with the EBIS electron beam acceptance to minimize losses upon injection.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Unusual structure, bonding and properties in a californium borate

The participation of the valence orbitals of actinides in bonding has been debated for decades. Recent experimental and computational investigations demonstrated the involvement of 6p, 6d and/or 5f orbitals in bonding. However, structural and spectroscopic data, as well as theory, indicate a decrease in covalency across the actinide series, and the evidence points to highly ionic, lanthanide-like bonding for late actinides. Here we show that chemical differentiation between californium and lanthanides can be achieved by using ligands that are both highly polarizable and substantially rearrange on complexation. A ligand that suits both of these desired properties is polyborate. Here, we demonstrate that the 5f, 6d and 7p orbitals are all involved in bonding in a Cf(III) borate, and that large crystal-field effects are present. Synthetic, structural and spectroscopic data are complemented by quantum mechanical calculations to support these observations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Pressure-Induced Spectroscopic Changes in a Californium 1D Material Are Twice as Large as Found in the Holmium Analog

Here, in this study, the synthesis, characterization, and pressure response of a 1D californium mellitate (mellitate = 1,2,3,4,5,6-benzenehexacarboxylate) coordination polymer, Cf 2 (mell)(H 2 O) 10 ·4H 2 O (Cf-1), are reported. The Cf–O lengths within the crystal structure are compared to its gadolinium (Gd-1) and holmium (Ho-1) analogs as well. These data show that the average Cf–O bond distance is slightly longer than the average Gd–O bond, consistent with trends in effective ionic radii. UV–vis-NIR absorption spectra as a function of pressure were collected using diamond-anvil techniques for both Cf-1 and Ho-1. These experiments show that the Cf(III) f → f transitions have a stronger dependence on pressure than that of the holmium analog. In the former case, the shift is nearly linear with applied pressure and averages 6.6 cm –1 /GPa, whereas in the latter, it is <3 cm –1 /GPa.

absorption spectroscopy↗
DOE OSTI2015

Metastable charge-transfer state of californium( iii ) compounds

Among a series of anomalous physical and chemical properties of Cf(III) compounds revealed by recent investigations, the present work addresses the characteristics of the optical spectra of An(HDPA) 3 ·H 2 O (An = Am, Cm, and Cf), especially the broadband photoluminescence from Cf(HDPA) 3 ·H 2 O induced by ligand-to-metal charge transfer (CT). As a result of strong ion–ligand interactions and the relative ease of reducing Cf(III) to Cf(II), a CT transition occurs at low energy (<3 eV) via the formation of a metastable Cf(II) state. It is shown that the systematic trend in CT transitions of the lanthanide series is not paralleled by actinide elements lighter than Cf(III), and californium represents a turning point in the periodicity of the actinide series. Analyses and modeling of the temperature-dependent luminescence dynamics indicate that the metastable Cf(II) charge-transfer state undergoes radiative and non-radiative relaxations. Broadening of the CT transition arises from strong vibronic coupling and hole–charge interactions in the valence band. As a result, the non-radiative relaxation of the metastable CT state results from a competition between phonon-relaxation and thermal tunneling that populates the excited states of Cf(III).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Electrochemical Studies of Selected Lanthanide and Californium Cryptates

Efforts to quantitatively reduce Cf III → Cf II in solution as well as studies of its cyclic voltammetry have been hindered by its scarcity, significant challenges associated with manipulating an unusually intense γ emitter, small reaction scales, the need for nonaqueous solvents, and its radiolytic effects on ligands and solvents. In an effort to overcome these impediments, we report on the stabilization of Cf II by encapsulation in 2.2.2-cryptand and comparisons with the readily reducible lanthanides, Sm 3+ , Eu 3+ , and Yb 3+ . Cyclic voltammetry measurements suggest that Cf III/II displays electrochemical behavior with characteristics of both Sm III/II and Yb III/II . The °E 1/2 values of −1.525 and −1.660 V (vs Fc/Fc + in tetrahydrofuran (THF)) for [Cf(2.2.2-crypt)] 3+/2+ and [Sm(2.2.2-crypt)] 3+/2+ , respectively, are similar. However, the ΔE values upon complexation by 2.2.2-cryptand for Cf III/II more closely parallels Yb III/II with postencapsulation shifts of 705 and 715 mV, respectively, whereas the shift of Sm III/II (520 mV) mirrors that of Eu III/II (524 mV). This suggests more structural similarities between Cf II and Yb II in solution than with Sm II that likely originates from more similar ionic radii and local coordination environments, a supposition that is corroborated by crystallographic and extended X-ray absorption fine structure measurements from other systems. Competitive-ion binding experiments between Eu III/II , Sm III/II , and Yb III/II were also performed and show less favorable binding by Yb III/II . Connectivity structures of [Ln(2.2.2-cryptand)(THF)][BPh 4 ] 2 (Ln = Eu II , Sm II ) are reported to show the important role that THF plays in these redox reactions.

ethers↗
DOE OSTI2015

Californium Electrodepositions at Oak Ridge National Laboratory

Electrodepositions of californium isotopes were successfully performed at Oak Ridge National Laboratory (ORNL) during the past year involving two different types of deposition solutions, ammonium acetate (NH 4 C 2 H 3 O 2 ) and isobutanol ((CH 3 ) 2 CHCH 2 OH). A californium product that was decay enriched in 251 Cf was recovered for use in super-heavy element (SHE) research. This neutron-rich isotope, 251 Cf, provides target material for SHE research for the potential discovery of heavier isotopes of Z=118. The californium material was recovered from aged 252 Cf neutron sources in storage at ORNL. These sources have decayed for over 30 years, thus providing material with a very high 251 Cf-to- 252 Cf ratio. After the source capsules were opened, the californium was purified and then electrodeposited using the isobutanol method onto thin titanium foils for use in an accelerator at the Joint Institute for Nuclear Research in Dubna, Russia. Another deposition method, ammonium acetate, was used to produce a deposition containing 1.7 0.1 Ci of 252 Cf onto a stainless steel substrate. This was the largest single electrodeposition of 252 Cf ever prepared. The 252 Cf material was initially purified using traditional ion exchange media, such as AG50-AHIB and AG50-HCl, and further purified using a TEVA-NH 4 SCN system to remove any lanthanides, resulting in the recovery of 3.6 0.1 mg of purified 252 Cf. The ammonium acetate deposition was run with a current of 1.0 amp, resulting in a 91.5% deposition yield. Purification and handling of the highly radioactive californium material created additional challenges in the production of these sources.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2019

Contemporary Chemistry of Berkelium and Californium

The merging of small-scale syntheses and rapid crystallization methods have provided access to crystalline samples of berkelium (Z=97) and californium (Z=98) coordination complexes and compounds that can be interrogated with a suite of spectroscopic tools and structural elucidation approaches that have come online over the last 20 years. The combination of this experimental data with relativistic theoretical methods that capture the effects of spin-orbit coupling and scalar relativistic effects have allowed us to understand the electronic structure of berkelium and californium compounds at a level of detail that was not previously possible. The harbinger of this new era of post-curium chemistry was the synthesis and characterization of [Cf{B 6 O 8 (OH) 5 }]. This compound possesses a structure type that is distinct from earlier actinide borates, a reduction in coordination number for californium, contracted Cf-O bond lengths, a substantially reduced magnetic moment with respect to the calculated free-ion moment and, most importantly, vibronically coupled broadband photoluminescence. Ligand-field analysis also showed that the splitting of the ground state was larger than typically found in the f-block elements, and when taken together places its overall electronic structure as a hybrid of d- and f-block components. The discovery of the unusual properties of this compound has led to the development of large families of 4f and 5f coordination complexes, in an effort to uncover the underlying origin of the electronic structure oddities, and whether there really is a sharp onset of these changes at californium. This in turn pushed the development of far more challenging berkelium chemistry (from a radiologic standpoint) because the half-life of the isotopes decreases from 351 years for 249 Cf to 330 days for 249 Bk. This short review details some of the chemistry that has been reported over the last 15 years, and its consequences for understanding the periodic table.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Emergence of californium as the second transitional element in the actinide series

Abstract A break in periodicity occurs in the actinide series between plutonium and americium as the result of the localization of 5 f electrons. The subsequent chemistry of later actinides is thought to closely parallel lanthanides in that bonding is expected to be ionic and complexation should not substantially alter the electronic structure of the metal ions. Here we demonstrate that ligation of californium(III) by a pyridine derivative results in significant deviations in the properties of the resultant complex with respect to that predicted for the free ion. We expand on this by characterizing the americium and curium analogues for comparison, and show that these pronounced effects result from a second transition in periodicity in the actinide series that occurs, in part, because of the stabilization of the divalent oxidation state. The metastability of californium(II) is responsible for many of the unusual properties of californium including the green photoluminescence.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Probing electronic structure in berkelium and californium via an electron microscopy nanosampling approach

Due to their rarity and radioactive nature, comparatively little is known about the actinides, particularly those with atomic numbers higher than that of plutonium, and their compounds. In this work, we describe how transmission electron microscopy can provide comprehensive, safe, and cost-effective characterization using only single nanogram amounts of highly-radioactive, solid compounds. Chlorides of the rare elements berkelium and californium are dropcast and then converted in situ to oxides using the electron beam. The f-band occupancies are probed using electron energy loss spectroscopy and an unexpectedly weak spin-orbit-coupling is identified for berkelium. In contrast, californium follows a jj coupling scheme. These results have important implications for the chemistries of these elements and solidify the status of californium as a transitional element in the actinide series.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Electrodeposition method development for Californium Rare Isotope Breeder Upgrade (CARIBU) Source

Electrodeposition is one of the most widely utilized techniques for thin-film production with high yields. Although it is used extensively, this technique still presents several issues limiting its usefulness, including excess thickness and frequent cracking of deposited films. Efforts to improve thin-film production recently undertaken at Oak Ridge Laboratory by the authors have included studying operating conditions and applied electrolytes. Samarium was used as a surrogate material for californium, and yield was compared with different deposition condition. The final procedure from the optimized condition will be applied during production of the californium-252 source for the Californium Rare Isotope Breeder Upgrade (CARIBU) project, and the fission fragment will be analyzed.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2019

Radiation Induced Redox Chemistry of Californium-249

A complete understanding of californium chemistry necessitates knowledge of its radiation induced redox behavior, owing to its inherent nuclear instability propagating self-radiolysis. Only a handful of studies have investigated californium radiation chemistry, due to lack of availability and difficulty associated with handling highly radioactive material. To date, reaction rate coefficients have only been experimentally determined for the reduction of Cf(III) by the hydrated electron (e¯aq, k > 3 × 109 M–1 s–1), and subsequent decay of the corresponding transient Cf(II) (k = (7 ± 1) × 105 s–1)[1]. However, there are a number of other important transient radiolysis products radiolytically generated in solutions pertinent to Cf manipulations, e.g. the hydrogen atom (H•, Eo = 2.31 V), hydroxyl radical (•OH, Eo = –2.73 V), and nitrate radical (NO3•, Eo = –2.3 – –2.6 V). These species are more than capable of influencing the redox behavior of Cf, and have been shown to do so with a number of actinides, e.g. neptunium and americium. Here we present a time-resolved picosecond pulsed electron irradiation study for californium-249.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2011

Californium-252 Brachytherapy Combined With External-Beam Radiotherapy for Cervical Cancer: Long-Term Treatment Results

Purpose: To observe, by retrospective analysis, the curative effects and complications due to californium-252 ({sup 252}Cf) neutron intracavitary brachytherapy (ICBT) combined with external-beam radiotherapy (EBRT) in the treatment of cervical cancer. Methods and Materials: From February 1999 to December 2007, 696 patients with cervical cancer (Stages IB to IIIB) were treated with {sup 252}Cf-ICBT in combination of EBRT. Of all, 31 patients were at Stage IB, 104 at IIA, 363 at IIB, 64 at IIIA, and 134 at IIIB. Californium-252 ICBT was delivered at 7-12 Gy per insertion per week, with a total dose of 29-45 Gy to reference point A in three to five insertions. The whole pelvic cavity was treated with 8-MV X-ray external irradiation at 2 Gy per fraction, four times per week. After 16-38 Gy of external irradiation, the center of the whole pelvic field was blocked with a 4-cm-wide lead shield, with a total external irradiation dose of 44-56 Gy. The total treatment course was 5 to 6 weeks. Results: Overall survival rate at 3 and 5 years for all patients was 76.0% and 64.9%, respectively. Disease-free 3- and 5-year survival rates of patients were 71.2% and 58.4%, respectively. Late complications included vaginal contracture and adhesion, radiation proctitis, radiation cystitis, and inflammatory bowel, which accounted for 5.8%, 7.1%, 6.2%, and 4.9%, respectively. Univariate analysis results showed significant correlation of stage, age, histopathologic grade, and lymph node status with overall survival. Cox multiple regression analysis showed that the independent variables were stage, histopathologic grade, tumor size, and lymphatic metastasis in all patients. Conclusion: Results of this series suggest that the combined use of {sup 252}Cf-ICBT with EBRT is an effective method for treatment of cervical cancer.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Divalent and trivalent gas-phase coordination complexes of californium: evaluating the stability of Cf( II )

The divalent oxidation state is increasingly stable relative to the trivalent state for the later actinide elements, with californium the first actinide to exhibit divalent chemistry under moderate conditions. Although there is evidence for divalent Cf in solution and solid compounds, there are no reports of discrete complexes in which Cf II is coordinated by anionic ligands. Described here is the divalent Cf methanesulfinate coordination complex, Cf II (CH 3 SO 2 ) 3 -, prepared in the gas phase by reductive elimination of CH 3 SO 2 from Cf III (CH 3 SO 2 ) 4 -. Comparison with synthesis of the corresponding Sm and Cm complexes reveals reduction of CfIII and SmIII, and no evidence for reduction of Cm III . This reflects the comparative 3+/2+ reduction potentials: Cf 3+ (-1.60 V) ≈ Sm 3+ (-1.55 V) >> Cm 3+ (-3.7 V). Association of O 2 to the divalent complexes is attributed to formation of superoxides, with recovery of the trivalent oxidation state. Lastly, the new gas-phase chemistry of californium, now the heaviest element to have been studied in this manner, provides evidence for Cf II coordination complexes and similar chemistry of Cf and Sm.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Actinide complexes with Wells–Dawson polyoxometalates (part 2): californium

We report the first example of a polyoxometalate (POM) compound containing californium. Using a Wells–Dawson POM ligand, K 17 Cf(P 2 W 17 O 61 ) 2 ·2H 2 O was synthesized and characterized. Californium is the heaviest element ever crystalized with a POM. Significant solubility differences among the POM's f-element complexes were observed, enabling selective precipitation with separation factors rivaling liquid–liquid extraction.

and nuclear chemistry↗
DOE OSTI2020

Understanding Materials Characteristics of Palladium Lanthanide Cermet Wires as a Mimic of Californium Wire Production

Californium-252 (Cf-252) has been synthesized on a large scale (mg) since the 1970s for use as a portable neutron source. With a half-life of 2.645 years and a spontaneous fission fraction of 3.09%, Cf-252 emits 2.31 × 10 12 neutrons/gram second. Today most of the Cf-252 produced in the world is made at Oak Ridge National Laboratory (ORNL) using the High Flux Isotope Reactor (HFIR) and the Radiochemical Engineering Development Center (REDC). Because of its highly radioactive nature, all manipulations of Cf-252 need to be performed in hot cell facilities by highly trained personnel. The Cf-252 produced at ORNL is done at the REDC, which is conveniently located next to the HFIR. Cf-252 is sold as bulk wire, which has been described as palladium (Pd) metal incasing californium oxide (Cf 2 O 3 ). The process was developed by Mosley et al. at Savannah River Laboratory (SRL) where it was modeled after the thorium work done by Fuschillo et al. This process has been used since the 1970s to synthesize this unique wire, but its fundamental chemistry and materials characteristics were never openly reported. Here we aim to better understand the chemistry and the materials characteristics of Cf-252 wire production for process improvements and to better our fundamental understanding of the mid-late actinides. Though there are many challenges in working with radioactive elements such as Cf, the isotope Cf-252 is even more complicated due to its neutron emission. One challenge with neutron emission is the ability of neutrons to penetrate much deeper through materials, causing radiation damage. This makes using instrumentation to characterize the chemistry and materials properties of this process difficult. For this reason, this study will first focus on terbium (Tb) as a surrogate for Cf. Currently Tb is used as a carrier or filler in Cf production when small amounts of Cf are being processed. This, along with their similar size and charge, makes Tb a reasonable surrogate for this study.

36 MATERIALS SCIENCE↗