Kiel Holliday

A new incorporation mechanism for trivalent actinides into bioapatite : a TRLFS and EXAFS study

One of the most toxic byproducts of nuclear power and weapons production is the transuranics, which have a high radiotoxicity and long biological half-life due to their tendency to accumulate in the skeletal system. This accumulation is inhomogeneous and has been associated with the chemical properties and structure of the bone material rather than its location or function. This suggests a chemical driving force to incorporation and requires an atomic scale mechanistic understanding of the incorporation process. Here we propose a new incorporation mechanism for trivalent actinides and lanthanides into synthetic and biologically produced hydroxyapatite. Time-resolved laser fluorescence spectroscopy and extended X-ray absorption fine structure have been used to demonstrate that trivalent actinides and lanthanides incorporate into the amorphous grain boundaries of apatite. This incorporation site can be used to explain patterns in uptake and distribution of radionuclides in the mammalian skeletal system.

Site-selective time resolved laser fluorescence spectroscopy of Eu and Cm doped LaPO4

Abstract Samples of LaPO4 doped with Eu3+ or Cm3+ were synthesized by a hydrothermal process which resulted in a solid solution at temperatures less than conventional processing. Time resolved laser fluorescence spectroscopy was used to probe the incorporated Eu3+ or Cm3+ in order to gain structural information on its local environment. This revealed that Eu3+ and Cm3+ incorporate on the La site as expected. The emission spectrum of Eu3+ resolves the fully degenerate 5-fold splitting of the peaks in the F2 transition due to the low symmetry of the site, confirming previous calculations. A minor site in the Eu3+ doped sample is identified as coordinated with hydroxide contamination. Direct excitation of Cm3+ doped samples show the presence of “satellite” species. Although these spectral features have been observed in Cm3+ doped LuPO4 and YPO4, this is the first time that these satellites are resolved into their individual species. These are hypothesized to be due to a disturbance in the ideal structure which creates a break in the equivalence of the four lanthanum sites within a unit cell. The 4-fold ground state splitting of all species is identical, although slightly shifted, indicating similar environments. The fluorescence lifetimes were long (1.2 ms for Cm and 3.6 ms for Eu) indicating an absence of water in the immediate coordination sphere due to the incorporation of the doping ion.

The incorporation of europium into apatite: anew explanation

Abstract Time resolved laser fluorescence spectroscopy (TRLFS) and X-ray absorption fine structure (XAFS) are used as complimentary techniques to show that the hetero-valent incorporation of europium into apatite at temperatures relevant to environmental and biological processes occurs at grain boundaries and not the crystallographic calcium sites as previously presumed. For this study, we focus on mechanisms at the solid solution interface and therefore define this temperature regime as the range in which liquid water exists (0–100 ºC). Site-selective TRLFS show that the local Eu3+ symmetry does not match the presumed crystallographic site of incorporation. This is confirmed by XAFS results that show a deviation from the local environment in apatite. The transition of this amorphous europium to acrystallographic calcium site upon heating is then explained by grain growth and followed through a transition species by TRLFS.

Physical characterization of uranium oxide pellets and powder applied in the Nuclear Forensics International Technical Working Group Collaborative Materials Exercise 4

Physical characterization is one of the most broad and important categories of techniques to apply in a nuclear forensic examination. Physical characterization techniques vary from simple weighing and dimensional measurements to complex sample preparation and scanning electron microscopy-electron backscatter diffraction analysis. This paper reports on the physical characterization conducted by several international laboratories participating in the fourth Collaborative Materials Exercise, organized by the Nuclear Forensics International Technical Working Group. Methods include a range of physical measurements, microscopy-based observations, and profilometry. The value of these results for addressing key investigative questions concerning two uranium dioxide pellets and a uranium dioxide powder is discussed.

Comparing results of X-ray diffraction, µ-Raman spectroscopy and neutron diffraction when identifying chemical phases in seized nuclear material, during a comparative nuclear forensics exercise

This work presents the results for identification of chemical phases obtained by several laboratories as a part of an international nuclear forensic round-robin exercise. In this work powder X-ray diffraction (p-XRD) is regarded as the reference technique. Neutron diffraction produced a superior high-angle diffraction pattern relative to p-XRD. Requiring only small amounts of sample, µ-Raman spectroscopy was used for the first time in this context as a potentially complementary technique to p-XRD. The chemical phases were identified as pure UO2 in two materials, and as a mixture of UO2, U3O8 and an intermediate species U3O7 in the third material.