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material as a whole. In some cases, bulk analysis is necessary to have sufficient material to adequately detect and quantify trace constituents. Imaging analysis tools provide high magnification images or maps of the material and can confirm sample homogeneity or heterogeneity. Imaging will also capture the spatial and textural heterogeneities vital to fully characterize a sample. Such morphological information can often provide additional insight into the nature of the material. If imaging analysis confirms that the sample is heterogeneous, then microanalysis tools can quantitatively or semi-quantitatively characterize the individual constituents of the bulk material. The category of microanalysis tools also includes surface analysis tools, which can detect trace surface contaminants or measure the composition of thin layers or coatings, either of which could be important for interpretation.

The ITWG has achieved general consensus on the proper sequencing of techniques so as to provide the most valuable information as early as possible in the interpretation process (see Table 1). This consensus was achieved through discussion and consultation at regular meetings, as well as from experience developed from two round robin analyses.

Table 1 Sequence for Nuclear Forensics Techniques/Methods*

Techniques/Methods

24-Hours

1-Week

2-Months

Radiological

Estimated total activity

Dose Rate (α, γ, n)

Surface Contamination

 

 

Physical Characterization

Visual Inspection

Radiography

Photography

Weight

Dimension

Optical Microscopy

Density

SEM (EDX)

XRD

TEM (EDX)

Traditional Forensic Analysis

Fingerprints,

Environmentally sensitive samples

Fibers

 

Isotope Analysis

γ-spectroscopy

α-spectroscopy

Mass spectrometry (SIMS, TIMS, MC-ICP-MS)

Radiochemical separations

Elemental/Chemical

 

ICP-MS

XRF

Assay (titration, IDMS)

GC/MS

*All times above refer to time after receipt of sample(s) at the nuclear forensics laboratory.

Traditional Forensic Analysis

Traditional forensic analysis, like radioactive materials analysis, is an iterative process, in which the results from one analysis are used to guide the selection of subsequent analyses. The forensic analyst must carefully examine all of the items seized at the incident site in order to uncover as much information as possible. Unlikely and apparently unrelated evidence often are key to the successful prosecution of a case. Once again, all sampling and analysis must be



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