2nd quarter 1999 The Actinide Research Los Alamos National

12 Pages·1999·0.79 MB·English

2nd quarter 1999
The Actinide Research
Los Alamos National Laboratory
N u c l e a r M aQ t e ru i a al s rR e ts e ea r cr h l a ny d T e c h n o l o g y
a U.S. Department of Energy Laboratory
Experiments Aim to Extend the Limits
of Magnetic Separation
In This Issue
Magnetic separation has received much
attention recently from industrial, medical,
1 and governmental researchers interested in
Experiments Aim to selective separation technologies. Currently,
Extend the Limits of we are developing technologies for single-
Magnetic Separation particle capture of submicron actinide
particles from forensic samples of interest.
4
The retrieval and concentration of transu-
XANES Reveals
ranic and fission products from the local
Oxidation State of
environment or sample sources can also be
Plutonium
used to learn about the environment around
6 nuclear facilities.
Fruitful Research High-gradient magnetic separation
Collaboration (HGMS) utilizes large magnetic field gradi-
Follows Common ents to effectively separate micron-sized
Guidelines paramagnetic par-
ticles of actinide
8
compounds. HGMS
Researchers Evaluate
can extract and con-
Isotope Ratio Tech-
centrate micron-
niques for Actinide
sized actinides and
Analysis
actinide-containing
10 particulates with no Figures. Scanning
NMT Completes sample destruction. electron micro-
Annual Division Most host materials graphs of ex-
Review such as air, water, truded stainless
and organic matter steel matrix
12 are diamagnetic, which will allow for a material (see
Publications and physical separation of the paramagnetic pages 2 and 3).
Invited Talks
actinides from these materials. Typically,
HGMS separators consist of a high-field
solenoid magnet, the bore of which contains
a fine-structured ferromagnetic matrix mate-
rial. The matrix fibers locally distort the mag-
netic field, generating high-field gradients at the surface of the
filaments. These areas then become trapping sites for paramagnetic
particles and are the basis for the magnetic separation.
Using commercially available 45-micron-diameter stainless steel
wool, the kaolin clay industry and soil remediation and water treat-
ment processes have demonstrated HGMS of micron-sized materials.
continued on page 2
1
Nuclear Materials Research and Technology/Los Alamos National Laboratory
Actinide Research Quarterly
Experiments Aim to Extend the Limits of
Magnetic Separation (continued)
The magnetic capture of smaller particles with the analytical model, which was devel-
(submicron) can be obtained by increasing oped previously with a systematic series of
This article was the magnetic force between the fibers and the soil remediation tests.
contributed by paramagnetic particles. One approach towards
Laura A. Worl. increasing the magnetic force and improving Single-Particle Collection
Other researchers separator efficiency is to reduce the size of the Assuming a spherical particle with a
on the project are matrix. Others have examined submicron-sized known density, we can calculate the concen-
David Devlin, spheres for the collection of nanometer-sized tration of a specific-diameter particle. For a
Dallas Hill, and particles. In addition, fractionation methods for concentration of 4 parts per billion (ppb) of a
Dennis Padilla, HGMS of nanometer particles are under devel- 0.8-micron particle, there would be approxi-
all of NMT-6, opment. We are investigating dendritic growth mately 1300 plutonium oxide particles in 1 ml
and F. Coyne on surfaces and controlled corrosion of stain- of solution. In the initial feed concentrations
Prenger, less steel wool in an effort to reduce the effec- for our experiments, we typically use starting
(ESA-EPE). tive matrix capture diameter. plutonium concentrations in the range of 2–15
The matrix materials currently used for ppb and an initial volume of 100 ml. This
HGMS are inhomogeneous and have a com- would translate to approximately 6500 par-
plex cross section. In addition, the paramag- ticles with a 0.8-micron diameter in the feed
netic particles are nonspherical and include a solution. In these applications, we attempt to
range of particle sizes. All of these factors dis- extract all the 6500 particles to get below the
courage precise analytical treatment. There- single-particle threshold.
fore, our approach is semiempirical, combining To obtain a concentration of less than 3 x
a mechanistic analytical model with empirical 10-11 M (~3 ppt) (parts per trillion) of pluto-
input from controlled experiments. nium oxide, the small but finite solubility of
Previously we derived a rate model from a PuO in water demanded that we examine al-
force balance on individual paramagnetic par- terna2te carrier fluids. Though the PuO solu-
ticles in the immediate vicinity of a matrix fi- bility constant is very low, in slightly b2asic
ber. The model assumes that if the magnetic conditions plutonium (IV) in water solutions
10 microns capture forces are greater than the competing at pH 8 can be found at concentrations up to
viscous drag and gravity forces, the particle is 10-7M. Preliminary HGMS tests conducted in
captured and removed from the flow stream. pH 8 water failed to remove plutonium from
Figure 1. Scanning The rate model depends on the magnitude of the feed samples. For the remaining HGMS
electron micro- the capture cross section (separation coeffi- tests, we have examined dodecane as a carrier
graph of extruded cient) as determined by the force balance on fluid to enhance the insolubility of the pluto-
stainless steel the particle. In this work we have expanded nium. Plutonium oxide particles sized from
matrix material. the model to include the loading behavior of 0.2–0.8 microns were removed below 6 ppt.
Results of experi- particles on the matrix fibers using the continu- The separation efficiencies for these tests were
ments show that ity equation, and we utilize capture-rate data over 99%. This value is the detection limit of
maximum separa- from the experimental results. The resulting the current analytical method (liquid scintilla-
tion effectiveness analytical model predicts the critical separation tion counting) without a preconcentration step
is obtained when parameters for submicron, single-particle col- in the sample preparation. The data are in
the matrix fiber lection presented in this article. It thus pro- general agreement with the analytical model.
diameter ap- vides a predictive tool for HGMS tests
proaches the conducted here and can be used for designing Matrix Material
diameter of the both prototype and full-scale units for specific
The experiments discussed here used a
particles to be applications.
matrix material based on extruded stainless
captured. We have conducted a series of HGMS ex-
steel fibers. Figure 1 shows a scanning electron
periments using particulate oxides of copper,
micrograph of the extruded material. The mul-
praseodymium, or plutonium suspended in a
tiple ridges in the material form a continuum
liquid. The experimental data were correlated
2 Nuclear Materials Research and Technology/Los Alamos National Laboratory
2nd quarter 1999
of sharp axial edges that generate large mag- diameter of the wool
netic field gradients and serve as trapping sites fiber substrate,
for the submicron particles. The extruded shown in Figure 2.
sample developed for this program contains a The resulting matrix
much higher density of edge locations com- material has a very
pared with traditional HGMS shaved stainless high surface area con-
steel wool materials. The extrusions produce taining fine points
small matrix fiber diameters and high matrix that may greatly en-
loading capacities. hance the high field
The effect of matrix diameter was exam- gradients. In addition
ined experimentally by determining HGMS to magnetic charac-
effectiveness for four different matrix materials terization of the ma- 60 microns 6 microns
with different cross-sectional areas. The results terial, HGMS testing
indicate that for selective small-particle cap- on these materials is planned in the future. Figure 2. Scanning
ture, very fine matrix fibers are required. For This material has the potential to advance electron micro-
particles below 0.2 m m, HGMS separation is HGMS towards subnanometer particle collec- graph of extruded
much more effective with smaller wire diam- tion. We are currently evaluating the HGMS stainless steel
eters (5 m m). performance of the new materials. matrix material
The effect of changing the applied mag- with nickel den-
netic field for the same matrix size from 7 T to Summary drites grown on
2.5 T is not nearly as significant as the effect of We have derived a model from a continu- the surface of the
reducing the matrix size. At 2.5 T the matrix material. This is
ity equation that uses empirically determined
material is nearly saturated magnetically, and one approach in
capture cross-section values. The model allows
any further increase in the applied field has a the development
us to predict high-gradient magnetic separator
small effect on the separation. Increasing the of new matrices
performance for a variety of materials and
matrix residence time will also increase the with submicron-
applications. The model can be used to opti-
separation effectiveness, but at extremely low sized fiber diam-
mize the capture cross-section values and thus
superficial velocities the resulting particle set- eters. The other is
increase the capture efficiency. Results show
tling can be a significant problem. controlled corro-
that maximum separation effectiveness is
To greatly enhance performance and to sion studies on
obtained when the matrix fiber diameter
achieve a single-particle collection threshold, 25-m m-sized
approaches the diameter of the particles to
it has become apparent through model predic- drawn stainless
be captured.
tions and experimental data that the matrix steel wool
Experimentally, we obtained a single-par-
fiber diameter is a crucial separation variable. ticle capture limit with 0.8-m m PuO particles material.
Tests have been initiated to develop new ma- 2
with dodecane as a carrier fluid. The finite
trices with submicron-sized fiber diameters.
solubility of plutoniumin water prevented the
Two different approaches are being studied to
complete removal of the contaminants when
generate these materials. One approach is con-
using water as the carrier fluid.
trolled corrosion studies on 25-m m-sized
The development of new matrix materials
drawn stainless steel wool material, and the
is being pursued through the controlled corro-
second approach is the growth of micron-sized
sion of stainless steel wool and the deposition
nickel dendrites on stainless steel wool fibers
of nickel dendrites on the existing stainless
by chemical vapor deposition.
steel matrix material. The new materials are
Nickel dendrites were deposited on the
promising for the submicron collection of
stainless steel matrix material using a hot-wall
paramagnetic particles. HGMS experiments
reactor. Nickel dendrite structures were uni-
on the new materials are planned.
formly deposited on the surface throughout
the wool structure. The length of the dendrites
is 1–2 orders of magnitude smaller than the
3
Nuclear Materials Research and Technology/Los Alamos National Laboratory
Actinide Research Quarterly
XANES Reveals Oxidation State of Plutonium
Oxidation state and chemical speciation Our work on the aquo ions of plutonium
define the chemistry of plutonium and other represented our first effort to study the effect
actinides. These properties underlie the behav- of oxidation state on the x-ray near edge struc-
This article was
ior of plutonium in a wide range of systems, ture (XANES) spectrum. It was found that the
contributed by
from separation processes to transport proper- edge energy of XANES spectra increases by
D. Kirk Veirs
ties in the environment. Predicting the fate of about 1.7 eV per oxidation state in going from
(NMT-11). Other
plutonium in the environment, designing Pu(III) to Pu(VI). Still to be determined was the
researchers on
remediation processes for plutonium-contain- influence of the speciation and the physical
the project in-
ing residues, and evaluating stabilization tech- state (liquid or solid) on the XANES spectrum.
clude S. D.
nologies for unstable residues all rely to some In order to sort out these effects, we studied a
Conradson
extent on knowledge of the oxidation state and large number of well-characterized plutonium
(MST-8), D. L.
speciation. samples. The goal of our work is to develop a
Clark (NMT-
In all of these systems the plutonium con- methodology to determine oxidation states
DO), D. W.
tent can be low, and determination of these from the XANES spectrum of actinides in
Keogh, M. P.
fundamental chemical properties can be prob- any matrix. The work includes understanding
Neu, and S. D.
lematic. Standard methods for elemental the instrumental and data reduction limita-
Reilly (CST-18),
analysis yield no information on oxidation tions on determining precise energies of the
W. Runde and
state or speciation. X-ray absorption spectros- XANES features.
P. D. Palmer
copy (XAS) is an established technique for de- In the XANES spectrum the L absorption
(EM-ET), and III
termination of oxidation states and speciation edge of plutonium occurs at about 18050 eV.
J.B. Tracy
in transition metals and is beginning to be It arises from allowed optical transitions be-
(NMT-11).
used to study actinides. XAS is sensitive, re- tween the 2p core state to the unoccupied
3/2
quires no sample preparation, is applicable to 6d states and/or to the continuum. The un-
3/2
liquids and to solids, whether or not the solids certainty of the final state arises from different
are amorphous or crystalline, and can be ap- interpretations of the “white line” feature of
plied to complex and opaque matrices. In this actinide XANES spectra. The XANES spectra
work we are concerned with the oxidation of Pu(III) and Pu(VI) aquo ions illustrate char-
state; however, it is recognized that speciation acteristic features of actinide XANES spectra
information can be acquired at the same time and the types of changes in those features that
Figure 1. XANES
by extending the energy range over which the allow oxidation state determination, as shown
spectra of Pu(III)
data are collected. in Figure 1. The XANES spectra of the III and
(black) and Pu(VI)
IV oxidation states of plutonium share similar
(gray) aquo ions. 2.0 features—a strong, narrow “white line” fol-
The absorption b lowed by deep EXAFS oscillations. In contrast,
edge (a) and
the dioxo species typically found in the V and
“white line” maxi-
VI oxidation states have a much weaker
mum (b) generally 1.5 c
“white line” feature, a shoulder rather than the
shift to higher
deep oscillation, and a somewhat flat transi-
energy for higher e
c tion to the EXAFS (extended x-ray fine absorp-
n
oxidation states. ba 1.0 tion structure) region. These features are typi-
Dioxo cations r
o cal of all actinide L XANES spectra.
have a character- Abs Theoretical calcIIuI lations of the XANES
istic shoulder (c)
edges of actinides using multiple scattering
and reduced 0.5
theory quantitatively accounts for all observed
“white line” inten- a
features. It attributes the “white line” mainly
sity. XAS spectra
to multiple scattering, either atomic XAFS or
are normalized to
0 electron scattering of the low-energy electrons
an edge jump
18000 18050 18100 from the neighbors, with a small contribution
absorbance of 1.
X-ray energy (eV) from the atomic transition. Theoreticians also
4 Nuclear Materials Research and Technology/Los Alamos National Laboratory
2nd quarter 1999
Polychromatic
conclude that the Fermi level is not necessarily beam from Monochromatic Fluorescent Zr calibration foil
the midpoint of the edge jump in the XANES. storage ring beam IF detectors
XANES spectra can be fit using an arc tan-
gent function for the edge jump and any num- IO II IC
ber of line shapes for the “white line.” The
Sample
dioxo species require additional peaks in the fit
LN2 Cryostat Beam
in order to obtain an adequate fit. The position Si (220) double stop
crystal
of the arc tangent is generally reported as the
monochromator Ionization
absorption edge. The “white line” peak posi- detectors
tion reported here is obtained by determining
Sample absorbance = log(I/I ) Transmission
the energy of the peak maximum from the first Sample absorbance = log(II/IO) Fluorescence
F I
derivative with respect to energy. The peak Zr calibration absorbance = log(IC/II) Transmission
maximum obtained using the derivative is not
dependent upon choices of peak line shape or halogens such as chloride. The XANES spectra Figure 2.
Schematic of data
initial parameters from a fit of the data; thus, it varied considerably in the intensity of the
collection at the
is more closely tied to the observed data. “white line” feature and the overall width of
Stanford
XAS data are collected in both transmis- the transition as measured by the difference
Synchrotron
sion and fluorescence in most cases (Figure 2). between the edge position and the peak posi-
Radiation
Synchrotron emission passes through a double tion. However, there was remarkably little
Laboratory. XAS
Si-crystal monochromator, and the intensity is variation in the energy of the peak position.
data are usually
measured with an ionization chamber. This The range of the peak positions is – 2.4s based
collected in both
monochromatic beam impinges upon the on the resin data; thus, it does not appear that
transmission and
sample, and fluorescence is detected using an the peak position changes. In two cases pluto-
fluorescence. The
array of germanium energy-dispersive detec- nium surrounded by the same ligands was
synchrotron
tors. The remaining beam passes through a sec- prepared in both the solid state and in solu-
emission passes
ond ionization chamber, a zirconium calibra- tion, which allowed direct measurement of the through a double
tion foil with a K absorption edge energy of effect of physical state on the XANES spectra. Si-crystal
17999.35 eV, and a third ionization chamber The solid state XANES spectra is always more monochromator,
before termination. The transmission data are broad, and the “white line” are always of and the intensity is
more reliable for XANES measurements and lower intensity than in the XANES spectra measured with an
are used here. Data for solid samples are col- of the same species in solution. ionization
lected at near liquid-nitrogen temperature to Uranium, neptunium, and americium chamber. This
minimize Debye-Waller motion. Data for liq- were examined in addition to plutonium, and monochromatic
uid samples are collected at room temperature. trends were observed. The general rules de- beam impinges
The reproducibility of the XANES spec- scribed below apply to these four actinides upon the sample,
trum was evaluated using fifteen scans of ten and can be used to determine their oxidation and fluorescence
different proprietary resin samples with state in many matrices. The dioxo cations V is detected using
an array of
adsorbed Pu(IV). The adsorbed species are and VI are distinguished from III and IV by
germanium
identical so any observed changes in the the characteristic dioxo shoulder about 10 eV
energy-dispersive
XANES spectra are due to limitations in the higher in energy than the “white line.” The
detectors. The
data. Reproducibility of the edge energies, s = peak maximum of III is 3 to 4 eV lower in en-
remaining beam
0.31 eV, and the “white line” peak maximum, s ergy than the peak maximum of IV. The peak
passes through a
= 0.20 eV, was found to be adequate for distin- maximum of V is lower in energy by 2 eV
second ionization
guishing between oxidation states based on the from the peak maximum of VI and is lower in
chamber, a
1.7 eV separation observed for aquo ions. energy by about 1 eV from the peak maximum
zirconium
Thirty well-characterized plutonium of IV. The energy of the peak maxima alone
calibration foil, and
samples of varying speciation and physical cannot distinguish the dioxo cations from IV.
a third ionization
state were examined. The range of speciation
chamber before
spanned weak oxo ligands such as nitrate to termination.
5
Nuclear Materials Research and Technology/Los Alamos National Laboratory
Actinide Research Quarterly
Editorial
Fruitful Research Collaboration
Follows Common Guidelines
The Nuclear Materials Technology (NMT) needed for the research and programmatic ac-
Division has a wide range of research collabo- tivities carried out in the national laboratories.
rations with universities, national laboratories, These are, therefore, the key elements to our
industrial companies, and several interna- future progress.
tional organizations. The division presently NMT Division, as a science and technol-
carries out active research collaborations with ogy organization, has generally encouraged all
about three dozen external entities. The nature forms of individual and institutional collabo-
This article was
of these collaborations ranges from individual- rations, internal and external, within the
contributed by researcher-initiated research projects with ex- bounds of our institutional mission. The suc-
Kyu C. Kim, ternal collaborators to institutionally backed cess of these external collaborations has been
projects. If one includes the co-authorship in outstanding. That said, any collaboration
NMT Chief
research papers published in scientific jour- should meet some of the basic premises of re-
Scientist.
nals, this number becomes even larger. search collaboration in NMT Division and, on
University collaborations typically take the larger scale, in the Laboratory. Some of
the form of conducting joint research on cam- these premises are stated in the following:
puses or at Los Alamos with students partici-
pating as part of their academic degree 1. The area of the collaboration has to be
programs. These collaborations can be particu- defined by the collaborators. The research ar-
larly helpful for students as they make the eas within NMT Division are very broad, and
transition from their formal training to career- these are documented in division science and
oriented research. NMT provides a unique technology strategic plans. The division strives
environment where nuclear materials can be to maintain four core technical capabilities:
handled safely for those interested in nuclear
materials research. The nation’s universities
typically lack resources in this area because
of the specialized facilities involved and the
safety and oversight requirements that must
be met.
International collaborations are being
developed in many research areas aimed at
reducing the global nuclear danger—safe-
guarding nuclear materials through detection
and instrumentation, safe storage and disposi-
tion of fissile materials, development of waste
treatment technologies, etc. Industrial partner-
ships have been forged through CRADAs
(cooperative research and development agree-
ments) for a number of new or advanced
process engineering projects.
The goals of these collaborations vary
widely. However, one common objective
among all these collaborations is to enrich and
to advance the science and technology in the
specific areas of each collaboration. In some
cases, we are also able to recruit unique scien-
tific resources and talents through our univer-
sity interactions. Traditionally, these
interactions with universities have provided a
significant portion of the human resources
6 Nuclear Materials Research and Technology/Los Alamos National Laboratory
2nd quarter 1999
plutonium metallurgy, actinide process chem- 3. The scope of the collaboration has to be
istry, actinide materials science including ac- defined and agreed upon. Once the proposed
tinide ceramics, and nuclear facility operation. work is realistically sized, there have to be suf-
In each of these core capabilities, there may be ficient resources in terms of budget, personnel,
specific capabilities needed to enhance science and facility. Additionally, one has to consider
and technology activities. When a collabora- the right mix of talents, steady funding sources
tive work is proposed, it is therefore desirable to carry the work to conclusion, and a suite of
and necessary to conduct a relevance check of required research equipment.
the proposed work against the division’s core 4. The need for the collaboration has to
capabilities. be justifiable with relatively high priority. In
2. Technical merits of the proposed work the real world of limited science and technol- The opinions in
should be evaluated and reviewed by compe- ogy budgets, we have to prioritize our work so this editorial are
tent independent reviewers. As we strive to that we get maximum benefits for the dollars mine; they do not
achieve excellence in our research work, this spent. We recognize that not all scientific en- necessarily repre-
is perhaps one of the most important criteria. deavors lead to immediately useful results or sent the opinions
If the proposed work has some outstanding applications. With limited resources, however, of Los Alamos
technical merits or potential payoffs, there it is essential to prioritize our tasks and to plan National Labora-
may be alternative ways of supporting such within the agreed upon scope for long-term tory, the Univer-
work in this Laboratory besides the Division. stability of our research activities. sity of California,
We do not wish to miss out on the opportuni- 5. Finally, it is important to recognize the Department of
ties. The Laboratory Directed Research and that NMT Division is not a funding organiza- Energy, or the U.S.
Development program is just tion for a variety of internal and external col- Government
such a mechanism. laborations. Unlike government or private
grant awarding organizations, the Laboratory’s
operating funds are allocated for specific mis-
sions. It is safe to say that all funds in this
Laboratory are associated with our mission-
oriented programs, small and large, and re-
source allocation is performed by the program
offices throughout the Laboratory. This means
that the program offices should be made to see
the benefits of the proposed collaborations and
to support the work as an essential part of the
program planning and execution. There is no
excess in today’s Laboratory operating budget,
and we must use our resources sparingly.
Aside from the formalized collaborations
described above, there are examples of numer-
ous informal collaborations in the scientific
community. Collaboration has become nearly
synonymous with any scientific work in
today’s world, and it is expected to be more
so in the future. It’s a necessity as well as a
driving force for scientific progress.
7
Nuclear Materials Research and Technology/Los Alamos National Laboratory
Actinide Research Quarterly
Researchers Evaluate Isotope Ratio Techniques
for Actinide Analysis
Isotope ratio and isotope dilution analyses need for strictly matrix-matched standards.
play a key role in the characterization of The GD ion source is highly efficient and is
nuclear materials for both defense and energy capable of measuring ~99% of the elements in
applications. In many cases we use thermal the periodic table. Its chief limitation is that
ionization mass spectrometry (TIMS), which samples must conduct electricity. For ceramics,
This article was
offers optimum accuracy and precision: soils, and other insulating materials, bulk
submitted by
<0.001% relative standard deviation (RSD). analyses are performed by mixing a powdered
David M. Wayne
However, in cases where less-precise and less- sample with a conducting metal binder, or by
(NMT-1.) Others
accurate data (~0.5% to 3.0% RSD) will meet using a tantalum (Ta) secondary cathode.
contributing to
customer needs, or when very rapid results A radiofrequency-powered GD ion source
this work are Wei
are required, isotope ratio analysis can be also permits direct sputter atomization of
Hang and Vahid
undertaken by other means. Quantitative insulating materials.
Majid (CST-9)
elemental and isotopic data can be obtained Mass bias in mass spectrometry arises
and E. Larry directly from the sample surface through the when physical phenomena present during ion-
Callis, Debbie use of cathodic sputtering (glow discharge ization, sampling, or analysis result in the pref-
Figg, Diane mass spectrometry—GDMS), laser ablation erential loss of either light or heavy ions from
McDaniel, and (laser ablation inductively coupled plasma an ion population. Thus, the measured isotope
Cris Lewis mass spectrometry—LA-ICPMS), or by ion ratio is different from the actual value. Al-
beam bombardment (secondary ion mass spec- though mass bias in ICPMS and GDMS is a
(NMT-1).
trometry—SIMS). In this article, we describe predictable function of element mass and can
the capabilities of two plasma-based isotope be corrected, it is generally far more severe
ratio analysis techniques: GDMS and ICPMS. than in TIMS. For this reason, isotope ratio
ICPMS is the method of choice for most measurements made using plasma-source
trace element determinations in radioactive mass spectrometry are inherently less accurate
materials at LANL. The ICP ion source is an than TIMS measurements.
extremely efficient ion generator that operates Extensive research has been done on iso-
at near-atmospheric (~760 torr) pressures. tope ratio analysis using both double-focusing
Nearly complete analytical coverage of the single collector and “multicollector” ICPMS.
periodic table is available from ICPMS. The latter are equipped with up to nine inde-
Samples may be introduced as solutions, pendent detectors that measure multiple ion
slurries, or suspensions of very fine particles beams simultaneously and can attain sensitiv-
generated by laser ablation. Samples are nebu- ity and precision that rivals that of
lized, ignited in an rf-generated argon plasma multicollector TIMS instruments. Even so,
at >7000oC, and sampled into the mass spec- single-collector, double-focusing ICPMS (and
trometer through a series of cones. The sam- GDMS) instruments are far less expensive,
pling cones, along with a powerful differential easier to maintain, and offer exceptional ana-
pumping system, permit ions to make the lytical versatility. For “real-world” samples, a
transition from the high-pressure ion source double-focusing, single-collector ICPMS is ca-
region to the low-pressure (~10-7 to 10-8 torr) pable of accuracy and precision of 0.5% to 2.0%
mass analysis region. RSD, depending on the actual concentration of
In a glow discharge (GD) ion source, direct the isotopes in the unknown. Isotope dilution
atomization and ionization are achieved via analysis, preconcentration, and on-line separa-
cathodic sputtering of the sample surface in a tions for key elements are also possible using
low-pressure (0.1 to 10 torr) argon atmo- solution-based ICPMS.
sphere. Unlike other direct sampling tech- In contrast, only a few investigators have
niques (e.g., SIMS or LA-ICPMS), the GD ion used GDMS to measure isotope ratios. NMT-1
source exhibits relatively uniform elemental researchers have measured isotope ratios of
response and can rapidly produce quantitative several elements (B, W, Tl, Pb, U) in a variety
trace analyses (parts per billion) without the of metal and glass standards using a double-
8 Nuclear Materials Research and Technology/Los Alamos National Laboratory
2nd quarter 1999
focusing, single-collector GDMS instrument.
The mass ranges can be selected and scanned
by changing the magnetic field intensity.
Total elapsed time required for each analysis
(i.e., 8 to 10 sets of 8 to 15 scans) was 30 to 40
minutes. All uncertainties are reported at the
2-s level.
First, we performed isotope ratio analyses
of tungsten (W, 0.102 wt. %) and lead (Pb, 240
ppm) in a steel standard (NIST SRM 1264a).
The precision of W isotope ratios measured
using GDMS was ~0.4% to 1.5% RSD, and the
accuracy was <1% RSD. Mass bias in Pb iso-
topes was estimated using the departure of the
186W/183W ratio from the known value, and
assuming an exponential mass fractionation
law. The precision of Pb isotope ratios in SRM
1264a, measured by GDMS, was ~1.5% to 3.6%
RSD.
For the next set of analyses, we analyzed a
Na-Ca-Al silicate-based glass-ceramic stan-
dard (NIST SRM 611) using a Ta secondary were less precise (2.3% to 9.3% RSD) and less Figure 1. Scanning
cathode (Figure 1). The standard glass con- accurate (0.4% to -7.8% RSD) than the Pb and electron micro-
tains trace amounts of Pb (426 ppm), Tl (62 Tl measurements. However, the uranium iso- scope image of a
ppm), and U (461.5 ppm). Furthermore, the tope ratio data are still useful. The GDMS sputter crater in
isotope ratios of Pb (208Pb/206Pb and 207Pb/ analyses indicated that the U in the glass stan- glass after 5 hrs.
206Pb) in this material have been characterized dard was depleted in 235U (235U/238U = 2.2· 10-3 of analysis using
using TIMS. Isobaric interference from to 2.5· 10-3). This was confirmed by NIST per- a secondary
(TaNa)+ ion clusters (mass = 203.9378 amu) sonnel and in published reports. Note that the cathode. The
prevented the collection of 204Pb at a mass characterization of depleted U in the glass stan- bright areas
resolution of 1500, although the remaining Pb dard took less than 1 hour by GDMS. around the perim-
eter of the crater
isotopes (206Pb, 207Pb, 208Pb) were interference-
Conclusions are coated with
free. Mass bias, measured using 205Tl/203Tl,
Ta sputtered from
varied from –0.7% to +0.9% over 9 runs, much Most commercial, magnetic-sector ICPMS
the secondary
lower than typical values for ICPMS (> 1.5%). and GDMS instruments are single-collector,
cathode.
These data also support our theoretical calcu- double-focusing mass spectrometers designed
lations, which predict that mass bias in the GD for rapid determinations of trace and major ele-
ion source is less severe than in the ICP ion ments. However, sector GDMS and ICPMS
source. The GDMS Pb isotope determinations may also be used to acquire reasonably precise
were typically accurate to within 1% of TIMS and accurate (0.5% to 2.0% RSD) isotope ratios
Pb isotope measurements and precise to < 2% on trace and major elements. Both techniques
RSD. are very rapid and require minimal sample
GDMS permits the collection of multi-ele- preparation but with decreased sensitivity, ac-
ment isotope ratio data in a single run; thus, a curacy, and precision relative to TIMS. Moder-
uranium isotope ratio (235U/238U) was also ate-precision data may be useful in some
measured in the glass standard, along with Pb applications; however, isotope ratios acquired
and Tl. The extremely low abundance of 235U using GDMS and ICPMS may be most useful
(ca. 1 ppm) resulted in low signal intensities, as screening techniques before TIMS data are
and the 235U/238U ratios obtained by GDMS obtained from selected samples.
9
Nuclear Materials Research and Technology/Los Alamos National Laboratory
Actinide Research Quarterly
NMT Division Completes Annual Division Review
On May 11–14, 1999, NMT Division held l Synthesis and Characterization of
its Science and Technology Assessment (also Uranium(IV)-bearing Members of the (NZP)
called the “Division Review”) at the J. Robert Structural Family, H. T. Hawkins, D. R. Spear-
Oppenheimer Study Center and TA-55. This ing, and D. K. Veirs (NMT-6); J. A. Danis and
year’s topics included pollution prevention, W. H. Runde (CST-7); D. M. Smith (CST-11);
analytical chemistry, separations science, ma- C. D. Tait (CST-4); M. N. Spilde (University of
Reported by
terials science, and nuclear materials manage- New Mexico); and B. E. Scheetz (Pennsylvania
Octavio Ramos,
ment. In addition, there were 43 poster papers State)
CIC-1.
covering a broad range of NMT’s scientific l Coordination Chemistry of Hexa-va-
Photos by
and technological activities. lent Actinide Ions (Uranium, Neptunium, and
Gary Warren,
On May 11 the Division Review Commit- Plutonium) Under Highly Alkaline Condi-
CIC-9.
tee (see Figure 1) met with Laboratory and tions, D. L. Clark (NMT-DO); S. D. Conradson
NMT management for an executive opening (MST-11); D. W. Koegh and B. L. Scott (CST-
session, which was followed by morning over- 18); R. J. Donohoe, D. E. Morris, and C. D. Tait
view sessions presented by Nuclear Weapons (CST-4); M. P. Neu (CST-11); and R. D. Rogers
Directorate Deputy James A. Mercer-Smith (CST-7)
and NMT Division Director Bruce Matthews. l M agnetic Separation for Nuclear Mate-
The afternoon session covered topics such as rial Detection and Surveillance, L. A. Worl and
facilities and infrastructure, NMT’s major pro- D. Padilla (NMT-6); D. Devlin (MST-7); and
grams, and personnel and collaborations. D. D. Hill and F. C. Prenger (ESA-EPE)
For the next day and a half, the committee l Membranes for Selective Metal Ion
listened to a number of presentations, includ- Separation, G. D. Jarvinen, M. E. Barr, and
ing an update from the Seaborg Institute; an J. S. Young (NMT-6); T. M. Mcleskey,
overview of analytical chemistry; highlights D. S. Ehler, N. N. Sauer, and Q. T. Le
from separations science actitivities, materials (CST-18); N. C. Schroeder, K. D. Abney,
science, and nuclear materials management; R. M. Chamberlin, E. A. Bluhm, and E. Bauer
Figure 1. Division
and an overview of waste treatment, environ- (CST-11); T. W. Robinson and B. F. Smith
Review Committee
mental compliance, and pollution prevention. (CST-12); R. C. Dye, B. S. Jorgensen, and
Members (left to
Poster sessions presented the second after- D. R. Pesiri (MST-7); A. Redondo, L. R. Pratt,
right) Dr. Ned
noon showcased NMT’s science and technol- and S. L. Rempe (T-12)
Wogman (chair),
ogy activities and accomplishments. This year, l Electronic Structure of Plutonium
Dr. Darleane
the committee selected five posters it felt were Metal: High-resolution Core Level and Reso-
Hoffman, Dr. Todd
outstanding. The top five were as follows: nant Valence Band Photoemission Spectros-
LaPorte, Dr. Lamar
copy at the Advanced Light Source,
Miller, Dr. Robert
J. H. Terry, Jr., R. K. Schulze, T. G. Zocco,
Uhrig, Dr.Anthony
and D. Farr (NMT-11); J. Lashley (MST-8);
Rollett, Dr. Rich-
E. Rotenberg and D. Shuh (Lawrence Berkeley
ard Bartsch, and
National Laboratory); and J. Tobin (Lawrence
Dr. Darryl
Livermore National Laboratory)
DesMarteau.
10 Nuclear Materials Research and Technology/Los Alamos National Laboratory