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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on SnHg2(SBr)2 by Materials Project

Hg2Sn(SBr)2 crystallizes in the monoclinic P2_1/c space group. The structure is two-dimensional and consists of one Hg2Sn(SBr)2 sheet oriented in the (1, 0, 2) direction. there are two inequivalent Hg2+ sites. In the first Hg2+ site, Hg2+ is bonded in a distorted linear geometry to two S2- atoms. There are one shorter (2.36 Å) and one longer (2.38 Å) Hg–S bond lengths. In the second Hg2+ site, Hg2+ is bonded in a distorted linear geometry to two S2- atoms. There are one shorter (2.36 Å) and one longer (2.38 Å) Hg–S bond lengths. Sn2+ is bonded in a distorted rectangular see-saw-like geometry to one S2- and three Br1- atoms. The Sn–S bond length is 2.91 Å. There are a spread of Sn–Br bond distances ranging from 2.67–3.11 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted water-like geometry to two Hg2+ atoms. In the second S2- site, S2- is bonded in a 3-coordinate geometry to two Hg2+ and one Sn2+ atom. There are two inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a single-bond geometry to one Sn2+ atom. In the second Br1- site, Br1- is bonded in a distorted L-shaped geometry to two equivalent Sn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb(SBr)2 by Materials Project

Nb(SBr)2 crystallizes in the triclinic P-1 space group. The structure is two-dimensional and consists of one Nb(SBr)2 sheet oriented in the (0, 0, 1) direction. Nb5+ is bonded in a 8-coordinate geometry to four S+1.50- and four Br1- atoms. There are two shorter (2.50 Å) and two longer (2.51 Å) Nb–S bond lengths. There are a spread of Nb–Br bond distances ranging from 2.75–2.81 Å. There are two inequivalent S+1.50- sites. In the first S+1.50- site, S+1.50- is bonded in a 10-coordinate geometry to two equivalent Nb5+ and one S+1.50- atom. The S–S bond length is 2.02 Å. In the second S+1.50- site, S+1.50- is bonded in a 9-coordinate geometry to two equivalent Nb5+ and one S+1.50- atom. There are two inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a distorted water-like geometry to two equivalent Nb5+ atoms. In the second Br1- site, Br1- is bonded in a distorted water-like geometry to two equivalent Nb5+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb(SBr)2 by Materials Project

Nb(SBr)2 crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of one Nb(SBr)2 sheet oriented in the (0, 0, 1) direction. Nb5+ is bonded in a 8-coordinate geometry to four S+1.50- and four equivalent Br1- atoms. There are two shorter (2.50 Å) and two longer (2.51 Å) Nb–S bond lengths. There are two shorter (2.75 Å) and two longer (2.79 Å) Nb–Br bond lengths. There are two inequivalent S+1.50- sites. In the first S+1.50- site, S+1.50- is bonded in a 2-coordinate geometry to two equivalent Nb5+ and one S+1.50- atom. The S–S bond length is 2.01 Å. In the second S+1.50- site, S+1.50- is bonded in a 10-coordinate geometry to two equivalent Nb5+ and one S+1.50- atom. Br1- is bonded in a distorted water-like geometry to two equivalent Nb5+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Langmuir adsorption model to assess the impact of silane coupling on nano-dispersion of silica in SBR

Surface active agents are often used to improve dispersion of nanoparticles. Quantitative correlation between these surface-active molecules and nanoscale dispersion is absent from the literature partly because a quantitative measure of nanoscale dispersion does not exist. Recently, we have developed the Virial-van der Waals method to quantify dispersion in nanocomposites using virial coefficients. In this paper, the Langmuir adsorption model is used to quantify the influence of surface-active agents on nano-scale dispersion in terms of the effective second virial coefficient B 2 *. The impact of silane coupling agent on the nano-dispersion and silica aggregate structure in precipitated silica/SBR nanocomposites is demonstrated. It is shown that the higher viscosity SBR matrix led to a greater silica aggregate structural breakup, while lower viscosity matrix improved surface silanization. The isomeric content of the SBR, which impacts the dielectric behavior, impacted whether the system could be modeled through a mean-field or specific interactions. We earlier showed that larger aggregates improve dispersion, and this is reaffirmed in these results. After account is made for aggregate size, nano-scale dispersion improves with the addition of silane coupling agent. The behavior is well modeled using Langmuir monolayer adsorption.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

On the direct ink write (DIW) 3D printing of styrene-butadiene rubber (SBR)-based adhesive sealant

Direct Ink Writing (DIW) utilizes a wide range of ink formulations to produce desirable 3D-printed structures and properties. Styrene-butadiene rubber (SBR) is an attractive candidate for 3D printing owing to its commercial availability, rheology, excellent mechanical properties, good impact resilience, and chemical stability. The SBR-based sealant was 3D printed in a DIW process, even in an ambient environment. The rheological behavior was assessed and correlated with optimized printing parameters. Important physico-chemical properties of the 3D-printed material were reported showing excellent properties as an elastomer. Finally, this work should expand the potential applications of existing rubber-based materials in additive manufacturing.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SBr by Materials Project

SBr crystallizes in the orthorhombic Aea2 space group. The structure is zero-dimensional and consists of four disulphur dibromide molecules. S is bonded in a water-like geometry to one S and one Br atom. The S–S bond length is 1.93 Å. The S–Br bond length is 2.29 Å. Br is bonded in a single-bond geometry to one S atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hg3(SBr)2 by Materials Project

Hg3(SBr)2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are four inequivalent Hg2+ sites. In the first Hg2+ site, Hg2+ is bonded in a 5-coordinate geometry to two S2- and three Br1- atoms. Both Hg–S bond lengths are 2.46 Å. There are a spread of Hg–Br bond distances ranging from 2.94–3.58 Å. In the second Hg2+ site, Hg2+ is bonded to two S2- and four Br1- atoms to form distorted HgS2Br4 octahedra that share corners with four equivalent HgS2Br4 octahedra, a cornercorner with one HgS2Br3 square pyramid, edges with four equivalent HgS2Br4 octahedra, and an edgeedge with one HgS2Br3 square pyramid. The corner-sharing octahedra tilt angles range from 0–4°. There are one shorter (2.43 Å) and one longer (2.44 Å) Hg–S bond lengths. There are a spread of Hg–Br bond distances ranging from 3.21–3.48 Å. In the third Hg2+ site, Hg2+ is bonded to two equivalent S2- and three Br1- atoms to form a mixture of distorted edge and corner-sharing HgS2Br3 square pyramids. The corner-sharing octahedral tilt angles are 64°. Both Hg–S bond lengths are 2.46 Å. There are a spread of Hg–Br bond distances ranging from 2.94–3.38 Å. In the fourth Hg2+ site, Hg2+ is bonded in a 5-coordinate geometry to two equivalent S2- and three Br1- atoms. Both Hg–S bond lengths are 2.45 Å. There are a spread of Hg–Br bond distances ranging from 3.01–3.31 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 3-coordinate geometry to three Hg2+ atoms. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three Hg2+ atoms. There are five inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a 6-coordinate geometry to six Hg2+ atoms. In the second Br1- site, Br1- is bonded in a 5-coordinate geometry to five Hg2+ atoms. In the third Br1- site, Br1- is bonded in a distorted square co-planar geometry to four equivalent Hg2+ atoms. In the fourth Br1- site, Br1- is bonded in a distorted body-centered cubic geometry to eight Hg2+ atoms. In the fifth Br1- site, Br1- is bonded in a distorted trigonal non-coplanar geometry to three Hg2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SnHg2(SBr)2 by Materials Project

Hg2Sn(SBr)2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Hg2+ sites. In the first Hg2+ site, Hg2+ is bonded in a distorted T-shaped geometry to two S2- and one Br1- atom. There are one shorter (2.36 Å) and one longer (2.38 Å) Hg–S bond lengths. The Hg–Br bond length is 3.38 Å. In the second Hg2+ site, Hg2+ is bonded in a distorted rectangular see-saw-like geometry to three S2- and one Br1- atom. There are a spread of Hg–S bond distances ranging from 2.38–3.25 Å. The Hg–Br bond length is 3.43 Å. Sn2+ is bonded to one S2- and three Br1- atoms to form distorted edge-sharing SnSBr3 trigonal pyramids. The Sn–S bond length is 2.91 Å. There are a spread of Sn–Br bond distances ranging from 2.68–3.03 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 3-coordinate geometry to two Hg2+ and one Sn2+ atom. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three Hg2+ atoms. There are two inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a 1-coordinate geometry to two Hg2+ and one Sn2+ atom. In the second Br1- site, Br1- is bonded in a distorted L-shaped geometry to two equivalent Sn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hg3(SBr)2 by Materials Project

Hg3(SBr)2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are five inequivalent Hg2+ sites. In the first Hg2+ site, Hg2+ is bonded to two S2- and three Br1- atoms to form distorted HgS2Br3 trigonal bipyramids that share corners with three HgS2Br4 octahedra, a cornercorner with one HgS2Br3 trigonal bipyramid, edges with three HgS2Br4 octahedra, and an edgeedge with one HgS2Br3 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 58–65°. There are one shorter (2.48 Å) and one longer (2.49 Å) Hg–S bond lengths. There are one shorter (2.83 Å) and two longer (3.30 Å) Hg–Br bond lengths. In the second Hg2+ site, Hg2+ is bonded to two equivalent S2- and four Br1- atoms to form distorted HgS2Br4 octahedra that share corners with four equivalent HgS2Br4 octahedra, corners with two equivalent HgS2Br3 trigonal bipyramids, edges with four HgS2Br4 octahedra, edges with two equivalent HgS2Br3 trigonal bipyramids, and faces with two equivalent HgS2Br4 octahedra. The corner-sharing octahedra tilt angles range from 2–11°. Both Hg–S bond lengths are 2.43 Å. There are two shorter (3.26 Å) and two longer (3.44 Å) Hg–Br bond lengths. In the third Hg2+ site, Hg2+ is bonded in a 5-coordinate geometry to two equivalent S2- and three Br1- atoms. Both Hg–S bond lengths are 2.43 Å. There are a spread of Hg–Br bond distances ranging from 3.08–3.51 Å. In the fourth Hg2+ site, Hg2+ is bonded to two equivalent S2- and four Br1- atoms to form distorted HgS2Br4 octahedra that share corners with four equivalent HgS2Br4 octahedra, corners with two equivalent HgS2Br3 trigonal bipyramids, edges with two equivalent HgS2Br4 octahedra, edges with two equivalent HgS2Br3 trigonal bipyramids, and faces with two equivalent HgS2Br4 octahedra. The corner-sharing octahedra tilt angles range from 61–66°. Both Hg–S bond lengths are 2.45 Å. There are a spread of Hg–Br bond distances ranging from 3.13–3.54 Å. In the fifth Hg2+ site, Hg2+ is bonded to two equivalent S2- and four Br1- atoms to form HgS2Br4 octahedra that share corners with eight HgS2Br4 octahedra, corners with two equivalent HgS2Br3 trigonal bipyramids, edges with four HgS2Br4 octahedra, and edges with two equivalent HgS2Br3 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 2–66°. Both Hg–S bond lengths are 2.44 Å. There are two shorter (3.32 Å) and two longer (3.36 Å) Hg–Br bond lengths. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 3-coordinate geometry to three Hg2+ atoms. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three Hg2+ atoms. There are four inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a 3-coordinate geometry to three Hg2+ atoms. In the second Br1- site, Br1- is bonded in a 6-coordinate geometry to six Hg2+ atoms. In the third Br1- site, Br1- is bonded in a 5-coordinate geometry to five Hg2+ atoms. In the fourth Br1- site, Br1- is bonded in a 7-coordinate geometry to seven Hg2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hg2Pb(SBr)2 by Materials Project

Hg2Pb(SBr)2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Hg2+ sites. In the first Hg2+ site, Hg2+ is bonded in a distorted linear geometry to two S2- atoms. There are one shorter (2.37 Å) and one longer (2.38 Å) Hg–S bond lengths. In the second Hg2+ site, Hg2+ is bonded in a 2-coordinate geometry to two S2- and two equivalent Br1- atoms. There are one shorter (2.36 Å) and one longer (2.38 Å) Hg–S bond lengths. There are one shorter (3.55 Å) and one longer (3.62 Å) Hg–Br bond lengths. Pb2+ is bonded to one S2- and three Br1- atoms to form distorted edge-sharing PbSBr3 trigonal pyramids. The Pb–S bond length is 3.06 Å. There are a spread of Pb–Br bond distances ranging from 2.75–3.01 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted water-like geometry to two Hg2+ and one Br1- atom. The S–Br bond length is 3.96 Å. In the second S2- site, S2- is bonded in a 2-coordinate geometry to two Hg2+, one Pb2+, and one Br1- atom. The S–Br bond length is 4.05 Å. There are two inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a 2-coordinate geometry to two equivalent Pb2+ and two S2- atoms. In the second Br1- site, Br1- is bonded in a 1-coordinate geometry to two equivalent Hg2+ and one Pb2+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SnHg2(SBr)2 by Materials Project

Hg2Sn(SBr)2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Hg2+ sites. In the first Hg2+ site, Hg2+ is bonded in a 2-coordinate geometry to two S2- and three Br1- atoms. Both Hg–S bond lengths are 2.40 Å. There are two shorter (3.38 Å) and one longer (3.43 Å) Hg–Br bond lengths. In the second Hg2+ site, Hg2+ is bonded in a 2-coordinate geometry to three S2- and two equivalent Br1- atoms. There are a spread of Hg–S bond distances ranging from 2.40–3.08 Å. There are one shorter (3.46 Å) and one longer (3.56 Å) Hg–Br bond lengths. Sn2+ is bonded to two S2- and three Br1- atoms to form distorted edge-sharing SnS2Br3 square pyramids. There are one shorter (3.01 Å) and one longer (3.08 Å) Sn–S bond lengths. There are a spread of Sn–Br bond distances ranging from 2.84–2.96 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 3-coordinate geometry to two Hg2+ and one Sn2+ atom. In the second S2- site, S2- is bonded in a 4-coordinate geometry to three Hg2+ and one Sn2+ atom. There are two inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a 1-coordinate geometry to four Hg2+ and one Sn2+ atom. In the second Br1- site, Br1- is bonded in a 3-coordinate geometry to one Hg2+ and two equivalent Sn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba2Cu(SBr)2 by Materials Project

Ba2Cu(SBr)2 is (La,Ba)CuO4-derived structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ba2+ is bonded in a 9-coordinate geometry to four equivalent S2- and five equivalent Br1- atoms. All Ba–S bond lengths are 3.19 Å. There are four shorter (3.50 Å) and one longer (3.53 Å) Ba–Br bond lengths. Cu2+ is bonded to four equivalent S2- and two equivalent Br1- atoms to form distorted corner-sharing CuS4Br2 octahedra. The corner-sharing octahedral tilt angles are 0°. All Cu–S bond lengths are 2.35 Å. Both Cu–Br bond lengths are 3.29 Å. S2- is bonded to four equivalent Ba2+ and two equivalent Cu2+ atoms to form a mixture of edge, face, and corner-sharing SBa4Cu2 octahedra. The corner-sharing octahedral tilt angles are 0°. Br1- is bonded in a 6-coordinate geometry to five equivalent Ba2+ and one Cu2+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

BioGeoChemistry of Actinides (LLNL SFA OBER - SBR FY20 Program Management and Performance Report)

The focus of the BioGeoChemistry of Actinides SFA is to identify and quantify the biogeochemical processes and the underlying mechanisms that control actinide mobility in an effort to reliably predict and control the cycling and migration of actinides in the environment. The research approach includes: (1) Field Studies (Research Thrust 1) that capture actinide behavior on the timescale of decades and (2) Fundamental Laboratory Studies (Research Thrust 2) that isolate specific biogeochemical processes observed in the field. These research thrusts are underpinned by the unique capabilities and staff expertise at Lawrence Livermore National Laboratory (LLNL), allowing the BioGeoChemistry of Actinides SFA to advance our understanding of actinide migration behavior in the environment, and serve as an international resource for environmental radiochemistry research (Figure 1). Research Thrusts 1 and 2 are guided by broad central hypotheses: Thrust 1 Hypothesis: Biogeochemical processes occurring on the timescale of years to decades lead to greater actinide recalcitrance in sediments and limit their migration in surface and groundwater. Thrust 2 Hypothesis: Long-term biogeochemical processes include mineral and surface alteration, which leads to stabilization of actinide surface associations or incorporation into mineral precipitates. Our strategic goal is to use the knowledge gained from our Science Plan to advance our understanding of the behavior of actinides, providing DOE with the scientific basis for remediation and long-term stewardship of DOE’s legacy sites and, more broadly, increasing our understanding of transport phenomena in environmental systems sciences with a particular emphasis on environmentally relevant (long-term) timescales. Although our focus is on actinide biogeochemistry, the increased focus on biogeochemistry at unique Test Bed locations associated with this SFA is providing fundamental information on redox processes and associated microbiological processes that control the cycling of redox sensitive metals under dynamic and transient biogeochemical conditions.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Styrene-Based Elastomer Composites with Functionalized Graphene Oxide and Silica Nanofiber Fillers: Mechanical and Thermal Conductivity Properties

The mechanical and thermal conductivity properties of two composite elastomers were studied. Styrene–butadiene rubber (SBR) filled with functionalized graphene oxide (GO) and silica nanofibers, and styrene–butadiene–styrene (SBS) block copolymers filled with graphene oxide. For the SBR composites, GO fillers with two different surface functionalities were synthesized (cysteamine and dodecylamine) and dispersed in the SBR using mechanical and liquid mixing techniques. The hydrophilic cysteamine-based GO fillers were dispersed in the SBR by mechanical mixing, whereas the hydrophobic dodecylamine-based GO fillers were dispersed in the SBR by liquid mixing. Silica nanofibers (SnFs) were fabricated by electrospinning a sol–gel precursor solution. The surface chemistry of the functionalized fillers was studied in detail. The properties of the composites and the synergistic improvements between the GO and SnFs are presented. For the SBS composites, GO fillers were dispersed in the SBS elastomer at several weight percent loadings using liquid mixing. Characterization of the filler material and the composite elastomers was performed using x-ray photoelectron spectroscopy, x-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, dynamic mechanical analysis, tensile testing, nanoindentation, thermal conductivity and abrasion testing.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Long-term effects of cycle time and volume exchange ratio on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production from food waste digestate by Haloferax mediterranei cultivated in sequencing batch reactors for 450 days

Food waste digestate was fed into a sequencing batch reactor (SBR) for Haloferax mediterranei (HM) to produce poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). This SBR was operated uninterruptedly for 450 days to test its stability, during which the cycle time and volume exchange ratio were varied to understand their impacts on the PHBV fermentation performance under ranged organic loading rates (OLR). Results showed that 1) PHBV productivity was proportional to OLR of food waste digestate; 2) substrate and product inhibitions were two limiting factors constraining substrate utilization and PHBV yields; 3) PHBV titer was dependent on the hydraulic retention time of the SBR while a volume exchange ratio lower than 0.5 is unfavorable due to the product inhibitor accumulation. Furthermore, this study for the first time demonstrated that the long-term stability of food waste-fed PHBV production by HM and revealed that inhibition effects could be barriers in SBR limiting the full-scale application of the technology.

09 BIOMASS FUELS↗
DOE OSTI2021

Mechanical Characterization of Low Modulus Polymer-Modified Calcium-Silicate-Hydrate (C-S-H) Binder

Calcium-silicate-hydrate (C-S-H) represents a key microstructural phase that governs the mechanical properties of concrete at a large scale. Defects in the C-S-H phase are also responsible for the poor ductility and low tensile strength of concrete. Manipulating the microstructure of C-S-H can lead to new cementitious materials with improved structural performance. This paper presents an experimental investigation aiming to characterize a new synthetic polymer-modified synthetic calcium-silicate-hydrate (C-S-H)/styrene-butadiene rubber (SBR) binder. The new C-S-H/SBR binder is produced by calcining calcium carbonate and mixing this with fumed silica (SiO 2 ), deionized water and SBR. Mechanical, physical, chemical and microstructural characterization was conducted to measure the properties of new hardened C-S-H binder. Results from the experimental investigation demonstrate the ability to engineer a new C-S-H binder with low elastic modulus and improved toughness and bond strength by controlling the SBR content and method of C-S-H synthesis. The new binder suggests the possible development of a new family of low-modulus silica-polymer binders that might fit many engineering applications such as cementing oil and gas wells.

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

Analytical characterization of laser induced plasmas towards uranium isotopic analysis in gaseous uranium hexafluoride

To perform direct enrichment assay on gaseous uranium hexafluoride (UF 6 ) with laser induced breakdown spectroscopy (LIBS), the dominant spectral-line features, evolution of the signal and background of the U II 424.437 nm line, and its Stark width and shift, were studied as a function of UF 6 gas pressure and pulse energy of a nanosecond Nd:YAG laser. In this work, vapor pressure of UF 6 was found to be the most important parameter for LIBS analysis of gaseous UF 6 . Spectral congestion with numerous U lines of high excitation potential was observed and signal-to-background ratio (SBR) was low for measurements with 80 Torr UF 6 . Only when both UF 6 vapor pressure and laser pulse energy were low, for example, less than 20 Torr pressure and 30 mJ pulse energy, the resultant LIBS spectra from gaseous UF 6 resembled those obtained from solid U samples. The experimental data also suggest that U and F atoms recombine back to UF 6 after the laser pulse. The U emission was found to decay fast with a persistent background signal, degrading SBR with delay time. Systematic positive biases were found for UF 6 enrichment assays performed with the 235 U– 238 U line pair at 424.412–424.437 nm, which was confirmed to be caused by self-absorption. Even with optimization of experimental parameters and incorporation of a self-absorption term into the spectral-fitting algorithm, to reduce and compensate for self-absorption, self-absorption is still a main factor limiting accurate UF 6 enrichment assay. The use of another spectral window which contains no resonance lines is a prospective solution for the self-absorption issue.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗