0 2 4 6 8 10 12 14 16 0 5 10 15 20 25 30 K 2 O (wt.%) CaO (wt.%) 100 FeO (wt.%) 0 2 4 6 8 10 12 20 40 60 80 100 FeO (wt.%) SiO 2 (wt.%) 25 0.001 0.01 0.1 1 10 100 0 2 4 6 8 10 12 TiO 2 (wt.%) FeO (wt.%) Al O (wt.%) NUCLEAR FORENSIC APPLICATIONS INVOLVING HIGH-SPATIAL-RESOLUTION ANALYSIS OF TRINITITE CROSS-SECTIONS Patrick H. DONOHUE 1 ([email protected]), Antonio SIMONETTI 1 , Sara MANA 1,2 , Elizabeth C. KOEMAN 1 , Peter C. BURNS 1 1 Civil & Environmental Engineering & Earth Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556; 2 Department of Earth & Environmental Sciences, University of Iowa, 121 Trowbridge Hall, Iowa City, IA 52242 MOTIVATION Trinitite 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 » ermo 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 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 100 1000 10000 Pu-240/239 ratios of points with 239 Pu > 200 0.001 0.01 0.1 1 10 1 10 100 1000 10000 240 Pu/ 239 Pu (corrected) 239 Pu (cps) bomb ratio natural ratio 240 Pu/ 239 Pu (corrected) 239 Pu (cps) 5A 8.86b 5A 6.06a 4F 8.86c 4D 9.18b bomb ratio (a) (b) 1 10 100 1000 Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 5A 8.86b 0.1 1 10 100 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 5A 6.06a La 1 10 100 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 4F 8.86 1 10 100 1000 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 4D 9.18b Pu (cps) 0 2 4 6 8 10 12 14 16 18 20 0 5 10 15 20 25 30 U (ppm) CaO (wt.%) 5A 8.86b 5A 6.06a 4F 8.86c 4D 9.18b 400 is 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 in 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 8.86 4D 9.18b ree 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. Horizontal Cut 5A 6.06a 5A 8.86b Fig 3a) Variable contribution from dominant quartz lithology in arkosic sand is reflected in high SiO 2 content. MAJOR ELEMENTS VERTICAL PROFILES 0 1 2 3 4 5 6 7 8 9 0 5 10 15 20 25 30 CaO (wt.%) 0 1 2 3 4 5 6 7 8 9 10 11 0 5 10 15 20 25 30 CaO (wt.%) 0 1 2 3 4 5 6 7 8 9 10 11 0 5 10 15 20 25 30 CaO (wt.%) 0 1 2 3 4 5 6 7 8 0 5 10 15 20 25 30 depth (mm) CaO (wt.%) distance from edge (mm) 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. 0 1 2 3 4 5 6 7 8 9 0 2 4 6 8 10 12 14 U (ppm) 0 1 2 3 4 5 6 7 8 9 10 11 0 4 8 12 16 20 distance from edge (mm) U (ppm) 0 1 2 3 4 5 6 7 8 9 10 11 0 2 4 6 8 10 12 14 U (ppm) 0 1 2 3 4 5 6 7 8 0 2 4 6 8 10 12 14 depth (mm) U (ppm) 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. 0 1 2 3 4 5 6 7 8 9 0.001 0.01 0.1 1 10 0 1 2 3 4 5 6 0.001 0.01 0.1 1 10 0 1 2 3 4 5 6 7 8 9 10 11 0.001 0.01 0.1 1 10 0 1 2 3 4 5 6 7 8 0.001 0.01 0.1 1 10 distance from edge (mm) depth (mm) corrected 240 Pu/ 239 Pu corrected 240 Pu/ 239 Pu corrected 240 Pu/ 239 Pu corrected 240 Pu/ 239 Pu bomb ratio natural ratio 4D 9.18b 4F 8.86 5A 8.86b 5A 6.06a Fig. 10) Near surface 240 Pu/ 239 Pu ratios are similar to the Trinity device (0.013-0.016), though low 240 Pu/ 239 Pu ratios are also present at depth. REFERENCES ACKNOWLEDGMENTS Bellucci, 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 #67 T123. Advances in Nuclear Forensics GSA 2014, Vancouver, B.C., Canada Fig. 9) Regions with a) <1000 cps 239 Pu are more likely to reflect natural Pu or give erroneously low 240 Pu/ 239 Pu ratios, whereas b) high Pu signal (>1000 cps) yields a consistent 240 Pu/ 239 Pu ratio similar to the Trinity device. TRACE ELEMENTS Pu-240/239 RATIO Fig 3c) ere is a positive Fe and Ti correlation in all samples. 1 10 100 1000 10000 0 5 10 15 20 25 30 Pu (cps) CaO (wt.%) Fig. 5) High CaO correlates with elevated (a) U and (b) Pu. 0.01 0.1 1 10 100 1000 1 10 100 1000 10000 Hf (ppm) Zr (ppm) 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. e upper 2mm of Trinitite is more likely to be enriched in bomb and anthropogenic related trace elements. Si μXRF Colors Ca Fe Al K Fig. 3b) Minor elements are strongly controlled by a few minerals (e.g., Plagioclase for K 2 O). CONCLUSIONS 5A 8.86b 5A 6.06a 4F 8.86c 4D 9.18b 5A 8.86b 5A 6.06a 4F 8.86c 4D 9.18b