Nuclear Forensics: Deciphering nuclear device components within post-detonation materials


Antonio Simonetti

Associate Professor, Department of Civil and Environmental Engineering and Earth Sciences,
University of Notre Dame


Nuclear Forensics is defined as “the technical means by which nuclear materials, whether
intercepted intact or retrieved from post-explosion debris, are characterized (as to composition,
physical condition, age, provenance, history) and interpreted (as to provenance, industrial
history, and implications for nuclear device design).” Detailed investigation of post detonation
material (PDM) is critical in preventing and/or responding to nuclear-based terrorist
activities/threats. However, accurate identification of nuclear device components within PDM
typically requires a variety of instrumental approaches and sample characterization strategies; the
latter may include radiochemical separations, mass spectrometry, decay counting measurements,
microscopy, and expertise from various fields, such as chemistry, geology, and physics. Cleverly
designed approaches can simultaneously provide insight into a material’s ‘‘age’’ (i.e., time
elapsed since last purification), actinide concentrations, and relevant isotopic ratios/enrichment
values. Consequently, these signatures are invaluable in determining the origin, processing
history, and intended purpose of a nuclear material, and are data that will be used by pertinent
law enforcement agencies.


The ultimate technical objective of nuclear forensic analysis is to determine the source attributes
of the pertinent radioactive specimens, which for the purposes of this lecture shall be limited to
PDMs. Specifically, the results and discussion presented in this chapter shall focus on recent,
detailed, in-situ (micron-scale) investigations of ‘Trinitite’; the PDM resulting from the first
atomic weapon test ‘Trinity’ conducted on the White Sands Proving Grounds (south of Alamogordo, NM)
at 5:29:45 a.m. on July 16, 1945. PDMs from historic test sites, such as trinitite, provide an
excellent opportunity to establish and verify forensic protocols, as the nature of the device
components employed are relatively well documented. Timely forensic investigations of PDMs are
needed to reveal the elemental and isotopic compositions of the device and associated components so
that source attribution can be made rapidly and accurately. Deciphering the chemical/isotopic
composition of a nuclear device from PDMs in a relatively rapid manner will also serve as a strong
deterrent to nuclear terrorism. However, factors that complicate forensic analysis of PDMs include
the inherent heterogeneity (mineralogical, chemical, isotopic) of the materials present at ground
zero, and possible overlapping signatures of the natural and anthropogenic (device) components.
Moreover, traditional investigative methods for post-detonation are time-consuming, and those
involving bulk sample digestion followed by chemical separation tend to homogenize (average) the
chemical and isotopic signatures; hence obliterating valuable forensic information present at the
micron-scale.


To date, my research team has focused its efforts into the detailed, micron-scale mineralogical,
chemical, and isotopic characterization of ~70 samples of trinitite. Most of the results presented
in this chapter were obtained using extra thick (~70 to 100 microns) standard petrographic thin
sections of trinitite; in contrast, gamma spectroscopy experiments were conducted using bulk
trinitite samples. Results reported here were obtained from various in-situ, microanalytical
techniques that provide relatively rapid, spatially resolved chemical and isotopic data of
trinitite; several are based on laser ablation- inductively coupled plasma mass spectrometry
(LA-ICP-MS). Of importance, these in-situ results document the inherent and significant
chemical/isotopic variability present within individual trinitite samples at the 10s to 100s micron
scale.