J.R. Peterson

Determination of the first ionization potential of nine actinide elements by resonance ionization mass spectroscopy (RIMS)

The high sensitivity of RIMS enables the precise determination of the first ionization potential of actinide elements with a sample size of ≤1012 atoms. By multiple resonant laser excitation, the actinide atoms under investigation are ionized in the presence of an electric field, and the ions are mass-selectively detected in a time-of-flight spectrometer. The first ionization potential is obtained by scanning the wavelength of the laser used for the last excitation step across the ionization threshold Wth—indicated by a sudden increase of the ion count rate—at various electric field strengths. Extrapolation of Wth to electric field strength zero leads directly to the first ionization potential. The first ionization potentials (IP) of Am, Cm, Bk, Cf and Es were determined for the first time as IPAm=5.9736(3) eV, IPCm=5.9914(2) eV, IPBk=6.1979(2) eV, IPCf=6.2817(2) eV, IPEs=6.3676(5) eV with samples of 1012 atoms. Furthermore, the ionization potentials of Th, U, Np and Pu were remeasured.

Effect of curing temperature on green light emission from Er3+-doped sol-gel silica glass

Abstract Green and less intense red emissions from Er3+ (4f11)-doped sol-gel silica samples (prepared from tetraethylorthosilicate at room temperature and dried at 70°C) under 488 nm excitation were monitored as a function of sample curing temperature. These green and red emission bands, centered at 550 and 660 nm, are the 4 S 3 2 → 4 I 15 2 and 4 F 9 2 → 4 I 15 2 transitions in Er3+ ions, respectively. The emission intensities were found to increase with increasing sample curing temperature ranging from 200 to 1000°C. Green upconversion emission from Er3+ ions in the same samples was also recorded under 647.1 nm light excitation. Its efficiency was enhanced with increased sample curing temperature. This enhancement is attributed to the Er3+-coordination environment produced by different sample curing temperatures. Increasing curing temperatures produces increasing degrees of dehydration and de-alcoholation around the Er3+ ions, thus resulting in a decrease in the non-radiative emission rate.

Study of the phase behavior of Eu2O3 under pressure via luminescence of Eu3

Abstract We have investigated the phase transition of Eu 2 O 3 under pressure from a C-type b.c.c. structure to a B-type monoclinic structure by the luminescence spectra of the Eu 3+ ion. It is suggested that the luminescence from f—f transitions in Eu 3+ is very sensitive to the Eu 3+ ion environment and can be used as a spectral probe to identify the crystal structure. The C-to-B transition occurs at about 8.0 GPa and the B-type structure was retained after the pressure had been released. The transition thermodynamics and kinetics are discussed, and the entropy for the C-to-B transformation was estimated. It was concluded that the C type is the room temperature and pressure stable structure, whereas the B type is metastable at room temperature.

SPECTROPHOTOMETRIC STUDIES OF TRANSCURIUM ELEMENT HALIDES AND OXYHALIDES IN THE SOLID STATE

The present state of a microscale spectrophotometric technique is described. The unique advantages of applying both spectrophotometric and X-ray powder diffraction methods on the sample, in order to identify and characterize newly synthesized compounds, are also discussed.

Raman spectra of some actinide dioxides and of EuF2

Abstract Raman spectra have been obtained for the first time from polycrystalline samples of NpO2, PuO2 and EuF2. Raman spectra were also obtained from polycrystalline samples of ThO2, UO2 and CeO2 for comparison with published results. Each of these compounds exhibits the CaF2 (fluorite)-type cubic crystal structure. The observed Raman active phonon (T2g) frequencies were used in conjunction with reported optically active IR phonon (T1u) frequencies to calculate the force constants for both the cation-anion stretching (K) and anion-anion repulsion (F).

Aqueous leachability of lanthanide and plutonium titanates

Abstract The leachabilities of titanate and zircono-titanate solid solutions, Ce 2 Ti 2 O 7 , Er 1.78 Ce 0.22 Ti 2 O 7 , Er 1.78 Pu 0.22 Ti 2 O 7 (9.5 wt% Pu) Er 1.78 Ce 0.22 Ti 0.5 Zr 1.5 O 7 , SrCe 2 Ti 4 O 12 , SrPu 2 Ti 4 O 12 (50.7 wt% Pu) and Sr 2 Ce 2 Ti 5 O 16 , have been investigated in WIPP ‘A’ brine, 0.1 M NaCl, and 0.1 M HCl solutions using a modified MCC-3 procedure with a duration of 60 days. The concentrations of plutonium leached by the brine were less than 1 ppm. Where cerium was used as a surrogate for plutonium, its concentration in WIPP brine was below the limit of detection (10 ppm) established for the inductively coupled plasma (ICP) atomic emission spectrometer used. Concentrations of strontium leached by WIPP brine from stable strontium-containing titanate compounds, considered as possible immobilizers of both 90 Sr and actinide elements, were on the order of 30–60 ppm.

X-ray diffraction of berkelium metal under pressure to 57 GPa

Abstract An investigation of the structural behavior of berkelium metal under pressure has been carried out up to 57 GPa. Evidence for a sudden decrease in volume (“collapse”) of the berkelium metal with increasing pressure up to 22 GPa was not observed. Instead, three different metal phases were observed over the range of applied pressure. The initial double-hexagonal close-packed structure of the berkelium metal first transformed to an f.c.c. structure at 8 GPa, which above 22 GPa converted to a third phase. Diffraction data obtained from this latter phase can be indexed on the basis of the α-U-type (orthorhombic) structure. A bulk modulus of 30(10) GPa was estimated from the relative volume V V 0 and pressure data for berkelium metal below 22 GPa. (The error is given in parentheses.)

Stabilization of divalent neodymium (Nd2+) in strontium tetraborate

Luminescence and absorption spectra from SrB4O7:Nd2+ samples prepared from Nd,O, (1 mol% based on Sr2+ ion mass) in air at high temperatures have been recorded at room temperature. A broad emission band centered in the vicinity of 560 nm has been observed from the samples upon excitation at 514.5 nm. We suggest that it is due to emission from the 5d band in Nd2+ ion into its ground state 4f level (5I4). Analysis of absorption spectra recorded from the same samples support this conclusion. SrB4O7:Nd2+ samples prepared in Ar/H2(4%) atmosphere exhibited more strongly the optical characteristics of Nd2+ ion compared to samples prepared in air. Several conditions promoting the stabilization of Nd2+ ion in this matrix are discussed. The range of f-element reducibility and stabilization in SrB4O7 has been extended from Tm2+ to Nd2+ in the present work; however, the limit of this facile reduction process has not yet been determined.

A luminescence study of single-crystal EuPO4 at high pressure

The pressure dependence of the luminescence from the 5D0 → 7F0–2 transitions in the Eu3+ ion in singlecrystal EuP04 has been investigated to about 20 GPa using a diamond anvil cell. Based on the level energies derived from the luminescence spectra recorded from the same crystal specimen, the parameterization of the free ion and crystal field effects was carried out with good results, as indicated by the low RMS deviations obtained. The lifetime of the 5D0 level was also measured as a function of pressure via monitoring a peak in the 5D0 → 7F1 transition manifold. Abrupt changes in the Eu3+ ion luminescence spectra and lifetime were observed between 6 and 8 GPa, while the general spectral pattern remained the same over the entire pressure range investigated. Calculated crystal field parameters also displayed a discontinuity between 6 and 8 GPa. These facts indicate that the site symmetry of the Eu3+ ion in EuPO4 is not changed by the application of pressure to about 20 GPa, but the strength of the crystal field probably changes significantly between 6 and 8 GPa. These observations are consistent with the crystal undergoing an isostructural volume collapse between 6 and 8 GPa. The ambient-pressure phase, which exhibits the monazitetype monoclinic structure, is retained to at least 20 GPa.

X-ray diffraction of curium-248 metal under pressures of up to 52 GPa

Abstract An investigation of the structural behavior of curium-248 metal under pressures of up to 52 GPa has been carried out. Three different metal phases were observed over the range of applied pressure. The initial double hexagonal close-packed structure (Cm I) of the curium metal first transformed at 23 GPa to an f.c.c. structure (Cm II), which then converted to an orthorhombic structure (Cm III). A bulk modulus of 33(5) GPa was derived from the relative volume V V 0 and pressure data for curium metal below 40 GPa.