nuclear forensic applications involving high-spatial
TRANSCRIPT
0 2 4 6 8
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K2O
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5A 8.86b 5A 6.06a
4F 8.86c 4D 9.18b
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)
CaO (wt.%)
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4F 8.86c 4D 9.18b
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5A 8.86b 5A 6.06a
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NUCLEAR FORENSIC APPLICATIONS INVOLVING HIGH-SPATIAL-RESOLUTION ANALYSIS OF TRINITITE CROSS-SECTIONSPatrick H. DONOHUE1 ([email protected]), Antonio SIMONETTI1, Sara MANA1,2, Elizabeth C. KOEMAN1, Peter C. BURNS1
1Civil & Environmental Engineering & Earth Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556; 2Department of Earth & Environmental Sciences, University of Iowa, 121 Trowbridge Hall, Iowa City, IA 52242
MOTIVATIONTrinitite is a relatively well-characterized PDM – the
bomb design and isotopic composition of the nuclear fuel used in the explosion are known – and it originated in a geologically simple environment.
Trinitite composition is influenced primarily by melting of the heterogeneous local arkosic sand and incorporation of anthropogenic components (e.g., blast tower, bomb material) (Bellucci et al. 2014).
Lateral heterogeneity in Trinitite is well noted, but lesser studied is the vertical trace element and radioisotope distributions.
We hypothesize that their near-surface (upper few mm) geochemistry would reflect greater contribution from blast products (e.g., Pu, U).
ANALYTICAL METHODS
EDAX Orbis Micro X-Ray Fluorescence (μXRF) Imaging »Voltage (35-40 kV) and amperage (250-350 μA) were adjusted to yield >10,000 counts and 30%-50% deadtime for a 30 μm beam size. » Final images have resolutions of ~40-50 microns/pixel.
Alpha Track Radiography (Method of Wallace et al. 2013) »CR-39 Plastic detectors were overlain on sample thin sections for 7-10 days. » Etched in 6.25 M NaOH at 98 °C for 4 hours. » Imaged & mosaiced to overlay on sample images.
Qualitative Sample aSSeSSment
Electron microprobe (EMP) Transects »Cameca SX50 electron microprobe;• University of Chicago, Chicago, Illinois. » 15 kV accelerating potential. » 30 nA probe current. » 15 μm spot size.
Laser Ablation (LA)-ICP-MS Transects »Thermo Finnegan Element2 high-resolution ICP-MS. »NewWave UP213 Nd:YAG laser ablation system. » 5 Hz pulse rate; 40 μm spot size; fluence of 10-11 J cm-2. »Time resolved signal analysis with GLITTER© program.
SAMPLES
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240 P
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9 Pu
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bomb ratio
natural ratio
240 P
u/23
9 Pu
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rect
ed)
239Pu (cps)
5A 8.86b
5A 6.06a
4F 8.86c 4D 9.18b
bomb ratio
(a) (b)
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Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
5A 8.86b
chon
drite
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La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
5A 6.06a
La
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La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
4F 8.86
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La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
chon
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This research was funded by DOE/NNSA grant PDP11-40/DE-NA0001112. We thank Dr. Ian Steele for lending expertise and time in obtaining electron microprobe
analyses at the University of Chicago (Chicago, Illinois). Sandy Dillard of the Brazos Valley Petrographic Thin Section Services Lab (Bryan, Texas) is thanked for production of thin sections of Trinitite. We also wish to thank the Center for Environmental Science and Technology at the University of Notre Dame for use of the EDAX Orbis XRF. Trinitite samples in this study were purchased from the Mineralogical Research Corporation (www.minresco.com).
major and trace element analySiS
4F 8.864D 9.18b
Three vertical cut thin sections (4D 9.18b; 4F 8.86; 5A 8.86b) and one horizontally cut section (5A 6.06a).
Photomosaics are overlain by transect paths (yellow) and alpha tracks (red) that reflect high alpha track activity.
Ho
rizo
nta
l C
ut 5A 6.06a5A 8.86b
Fig 3a) Variable contribution from dominant quartz lithology in arkosic sand is reflected in high SiO2 content.
MAJOR ELEMENTS
VERTICAL PROFILES
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CaO (wt.%)
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corrected 240Pu/239Pu corrected 240Pu/239Pu corrected 240Pu/239Pu corrected 240Pu/239Pu
bomb ratio natural ratio
4D 9.18b 4F 8.86 5A 8.86b 5A 6.06a
Fig. 7) CaO variation by depth within sample for the three transects of each sample. Most transects follow similar patterns of enrichment.
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corrected 240Pu/239Pu corrected 240Pu/239Pu corrected 240Pu/239Pu corrected 240Pu/239Pu
bomb ratio natural ratio
4D 9.18b 4F 8.86 5A 8.86b 5A 6.06a
Fig. 8) U-concentration is generally similar to unmelted sand (dashed gray line). High U-concentrations are limited to the upper 2 mm.
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corrected 240Pu/239Pu corrected 240Pu/239Pu corrected 240Pu/239Pu corrected 240Pu/239Pu
bomb ratio natural ratio
4D 9.18b 4F 8.86 5A 8.86b 5A 6.06a
Fig. 10) Near surface 240Pu/239Pu ratios are similar to the Trinity device (0.013-0.016), though low 240Pu/239Pu ratios are also present at depth.
REFERENCES ACKNOWLEDGMENTSBellucci, J.J., Simonetti, A., Koeman, E.C., Wallace, C., and Burns, P.C., 2014, A detailed geochemical investigation of post-nuclear detonation Trinitite glass at high spatial resolution: Delineating anthropogenic vs. natural components: Chemical Geology, v. 365, p. 69–86.
Wallace, C., Bellucci, J.J., Simonetti, A., Hainley, T., Koeman, E.C., and Burns, P.C., 2013, A multi-method approach for determination of radionuclide distribution in Trinitite: Journal of Radioanalytical and Nuclear Chemistry, v. 298, p. 993–1003.
Fig. 4) CI-normalized REE-profiles (green fields) are generally parallel to unmelted sand (black line; Bellucci et al. 2014). Some analyses (gray lines) reflect significant contributions from minerals.
(a) (b) (c)
Poster #67T123. Advances in Nuclear ForensicsGSA 2014, Vancouver, B.C., Canada
Fig. 9) Regions with a) <1000 cps 239Pu are more likely to reflect natural Pu or give erroneously low 240Pu/239Pu ratios, whereas b) high Pu signal (>1000 cps) yields a consistent 240Pu/239Pu ratio similar to the Trinity device.
TRACE ELEMENTS
Pu-240/239 RATIO
Fig 3c) There is a positive Fe and Ti correlation in all samples.
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CaO (wt.%)
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5A 6.06a
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Fig. 5) High CaO correlates with elevated (a) U and (b) Pu.
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Fig. 6) Constant Zr-Hf ratios across all samples indicates zircon control.
Even at high spatial resolution, Trinitite demonstrates trace element homogeneity at hand specimen scale.
Potential bomb signatures (Pu and U) occur at several millimeters depth in sections.
The upper 2mm of Trinitite is more likely to be enriched in bomb and anthropogenic related trace elements.
SiμXRF Colors
CaFeAlK
Fig. 3b) Minor elements are strongly controlled by a few minerals (e.g., Plagioclase for K2O).
CONCLUSIONS
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CaO (wt.%)
5A 8.86b
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Pb (p
pm)
Cu (ppm)
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K2O
(wt.%
)
CaO (wt.%)
5A 8.86b 5A 6.06a
4F 8.86c 4D 9.18b
0.001
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SiO2 (wt.%)
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Al 2
O3
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FeO (wt.%)