Detecting Metallic Primary Explosives with
a Portable X-ray Fluorescence Spectrometer
ALAN D. HEWITT
INTRODUCTION
mg/kg (ppm). Several manufacturers offer
energy-dispersive XRF spectrometers for in-situ
Although the extent of environmental pollu-
operations. These transportable instruments
tion associated with the practices of manu-
have one or more sources, a detector, and on-
facturing, storage, and disposal of initiators
board or shoulder-carried spectrum analyzers,
(primary explosives) does not rival that of sec-
all of which can be operated by battery power for
ondary explosives (high explosives), because of
several hours.
the volumes necessary for munitions production,
The purpose of this study was to select and
their high reactivity warrants special attention.
test an XRF instrument for screening sites where
Unlike high explosives, initiators spontaneously
metallic primers may be deposited. The selection
detonate when subjected to mechanical shock,
criteria used in this process included appropriate
heat, electrical sparks, or an open flame (Yinon
metal sensitivity and selectivity, area of effective
and Zitrin 1981). It is currently believed that
sample analysis, portability, and user friendli-
within the range of 5 to 15% (w/w), a mixture of
ness. Laboratory experiments were designed to
the primers lead azide, lead styphnate, or mer-
evaluate qualitatively the performance of the
cury fulminate with an environmental substrate
selected XRF system under a variety of condi-
(i.e., soil) would be sufficient for spontaneous
tions and to provide guidelines for field opera-
detonation (Workman 1994).
tions.
The presence of lead (Pb) or mercury (Hg),
which is unique to the three initiators, at or near
concentrations critical for spontaneous detona-
INSTRUMENT SELECTION CRITERIA
tion is well suited for X-ray fluorescence spec-
Sensitivity
trometry (XRF) analysis. This method of chemi-
The concentrations of Pb and/or Hg present
cal analysis relies on fundamental changes in the
when a metallic primer exists at levels where
electronic configuration of atoms and causes no
spontaneous detonation could occur is some two
physical or chemical alterations to the media
to three orders of magnitude above the reported
being analyzed. The successful use of XRF analy-
detection limits (10 to 100 ppm) for most XRF in-
sis for establishing the presence of elevated con-
struments. For example, the lead in lead styph-
centrations of metals in environmental samples
nate, which has the lowest mole fraction of metal
has been well documented (Spittler and Fender
to primer composition, would be present at
1979, Garby 1991, Puls et al. 1994, Schneider et al.
about 2.5 104 ppm in a 5% mixture. Therefore,
1995). Moreover, acceptance of XRF analysis as a
at installations where these primary explosives
screening method is scheduled for the third
have been manufactured, stored, or disposed of,
update of Test Methods for Evaluation of Solid
concentrations of Pb and/or Hg near a 1% level
Waste (US EPA 1986). XRF analysis is capable of
could be used to infer that a potential explosive
providing concentration estimates over a range
hazard exists.
extending from high percent levels to below 100
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