FORENSIC ANALYSIS OF TRINITITE POST-DETONATION MATERIALS AT HIGH SPATIAL RESOLUTION: DEVELOPING METHODS FOR SOURCE ATTRIBUTION

In the event of a rogue nuclear attack, accurate and timely investigation of post-detonation materials (PDMs) is crucial for source attribution. Therefore, the ability to identify chemical and isotopic signatures from the device using PDMs is an important area of research in forensic geology. Hence, analysis of historic PDMs is critical in the establishment of analytical methods and protocols since the chemical and isotopic composition of the device is known. Specifically, our research has focused on Trinitite, PDMs formed following the world’s first nuclear detonation (Trinity test) on July 16, 1945 (White Sands Missile Range, NM). The device (nicknamed “Gadget”) featured a ²³⁹Pu core and upon detonation created temperatures >8000K within the mushroom cloud; consequently the blast tower, components of the bomb, and natural arkosic sand at the test site were melted to form Trinitite PDMs.

Detailed analysis of Trinitite has involved the use of petrographic microscopy and alpha-track radiography to locate areas of high alpha activity within thin sections; the latter are the result of abundant residual, device-related U and Pu. Micro-X-ray fluorescence (XRF) was used to map out the abundances of major elements. Additional imaging of the samples has included scanning electron microscopy (SEM) and compositional data obtained by backscatter electron (BSE) mapping. Electron microprobe analysis (EMPA) was then employed for more precise and accurate determination of major element abundances. Trace element concentrations were obtained at high spatial resolution (10s to 100s micron scale) using laser ablation inductively coupled mass spectrometry (LA-ICP-MS).

The abundances of various bomb- and/or blast site-related trace metals (i.e., Cr, Co, Cu, Pb) and those derived predominantly from the natural geological background (i.e., Zr, La, Th) indicate significant correlations amongst themselves. For example, in areas with high alpha emissions, measured U and Pu ion signals are positively correlated. These results support the hypothesis that subsequent bomb detonation, elements originating from both the arkosic sand (natural background) and bomb components (anthropogenic sources) mixed and were incorporated into Trinitite PDMs.