SPECIAL REPORT 97-8

Detecting Metallic Primary Explosives

with a Portable X-ray Fluorescence

Spectrometer

Alan D. Hewitt April 1997
Abstract: X-ray fluorescence spectrometry (XRF)

analysis is a practical means of performing in-situ

screening to establish the presence of high concentrations (>0.1% or 1000 ppm) of lead (Pb) and/or mercury (Hg). These two metals are of special military

interest because they are constituents in three primary

explosives: lead azide [Pb(N3)2], lead styphnate

(C6HO6N3Pb), and mercury fulminate [Hg(CNO)2].

The success of in-situ XRF analysis to perform this task

depends on instrumental sensitivity, selectivity, effective sample volume, transportability, and user friendHow to get copies of CRREL technical publications:

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liness. Laboratory experiments established that the

MAP-3 XRF spectrum analyzer (SCITEC Corporation) is

well-suited for this application. This instrument is selfcontained, portable, and equipped with a Co-57

source that allows for a simultaneous analysis of both

the K and L energy lines of Pb and Hg, among other

metals. Laboratory experiments established that high

concentrations of Pb and Hg could be detected in an

active sample area of cylindrical shape, approximately

1.0 cm in diameter and 1.5 cm in depth.
Special Report 97-8

Detecting Metallic Primary Explosives

with a Portable X-ray Fluorescence

Spectrometer

Alan D. Hewitt April 1997

Prepared for

U.S. ARMY ENVIRONMENTAL CENTER

AEC-ET-CR97004

Approved for public release; distribution is unlimited.

US Army Corps

of Engineers

Cold Regions Research &

Engineering Laboratory

®
PREFACE

This report was written by Alan D. Hewitt, Research Physical Scientist, Geological

Sciences Division, Research and Engineering Directorate of the U.S. Army Cold Regions

Research and Engineering Laboratory in Hanover, New Hampshire.

Funding for this work was provided by the U.S. Army Environmental Center, Martin

H. Stutz, Project Monitor. The author thanks James Cragin and Thomas Ranney for critical review of the text.

This publication reflects the views of the author and does not suggest or reflect policy,

practices, programs, or doctrine of the U.S. Army or of the Government of the United

States.

The contents of this report are not to be used for advertising or promotional purposes.

Citation of brand names does not constitute an official endorsement or approval of the

use of such commercial products.

ii
INTRODUCTION

Although the extent of environmental pollution associated with the practices of manufacturing, storage, and disposal of initiators

(primary explosives) does not rival that of secondary explosives (high explosives), because of

the volumes necessary for munitions production,

their high reactivity warrants special attention.

Unlike high explosives, initiators spontaneously

detonate when subjected to mechanical shock,

heat, electrical sparks, or an open flame (Yinon

and Zitrin 1981). It is currently believed that

within the range of 5 to 15% (w/w), a mixture of

the primers lead azide, lead styphnate, or mercury fulminate with an environmental substrate

(i.e., soil) would be sufficient for spontaneous

detonation (Workman 1994).

The presence of lead (Pb) or mercury (Hg),

which is unique to the three initiators, at or near

concentrations critical for spontaneous detonation is well suited for X-ray fluorescence spectrometry (XRF) analysis. This method of chemical analysis relies on fundamental changes in the

electronic configuration of atoms and causes no

physical or chemical alterations to the media

being analyzed. The successful use of XRF analysis for establishing the presence of elevated concentrations of metals in environmental samples

has been well documented (Spittler and Fender

1979, Garby 1991, Puls et al. 1994, Schneider et al.

1995). Moreover, acceptance of XRF analysis as a

screening method is scheduled for the third

update of Test Methods for Evaluation of Solid

Waste (US EPA 1986). XRF analysis is capable of

providing concentration estimates over a range

extending from high percent levels to below 100

mg/kg (ppm). Several manufacturers offer

energy-dispersive XRF spectrometers for in-situ

operations. These transportable instruments

have one or more sources, a detector, and onboard or shoulder-carried spectrum analyzers,

all of which can be operated by battery power for

several hours.

The purpose of this study was to select and

test an XRF instrument for screening sites where

metallic primers may be deposited. The selection

criteria used in this process included appropriate

metal sensitivity and selectivity, area of effective

sample analysis, portability, and user friendliness. Laboratory experiments were designed to

evaluate qualitatively the performance of the

selected XRF system under a variety of conditions and to provide guidelines for field operations.

INSTRUMENT SELECTION CRITERIA

Sensitivity

The concentrations of Pb and/or Hg present

when a metallic primer exists at levels where

spontaneous detonation could occur is some two

to three orders of magnitude above the reported

detection limits (10 to 100 ppm) for most XRF instruments. For example, the lead in lead styphnate, which has the lowest mole fraction of metal

to primer composition, would be present at

about 2.5 × 104 ppm in a 5% mixture. Therefore,

at installations where these primary explosives

have been manufactured, stored, or disposed of,

concentrations of Pb and/or Hg near a 1% level

could be used to infer that a potential explosive

hazard exists.

Detecting Metallic Primary Explosives with

a Portable X-ray Fluorescence Spectrometer

ALAN D. HEWITT
Selectivity

Selectivity of XRF analyzers for individual

metals depends on both the energy emitted by

the primary source and the resolution of the

detector. Portable XRF systems capable of in-situ

analysis rely on one or more radioactive sources

for primary incident radiation. For a metal to be

detected, the incident energy emitted during the

radioactive decay of a primary source must be

greater than the excitation energy of the innershell electrons of the element (or elements) to be

analyzed. Briefly, the electrons most often excited during XRF analysis are located in the K and L

shells. Once excited, these inner-shell electrons

are lost, and electrons from an outer shell fill the

voids created. In the process of the electrons going from an outer to an inner shell, element-specific energies (photons, i.e., X-ray fluorescence)

are emitted. This fluorescent energy is measured

in kilo electron volts (keV; 1 keV = 1000 eV). Subscripts α, β, and γ can accompany the K and L

notations, indicating which outer shell the electrons fell from, thus further specifying the discrete spectral energies measured.

Portable XRF spectrometers come equipped

with silicon (drifted with lithium) [Si(Li)] or

mercuric iodide crystal detectors that have resolutions from 170 to 2500 eV, or gas-proportional

detectors with resolution anywhere from 700 to

3000 eV. Table 1 lists common primary sources and

the analytes that they can excite, along with the K

and L energy lines for Pb and Hg.

Area of metal detection

The effective sample volume measured during XRF analysis is a function of the positioning

of the source and detector and the energy used to

excite or assess the analytes. With regard to instrumental geometry, maximum analysis depth

(penetration) is achieved when the source and

detector are positioned in a parallel configuration. In this orientation the angle between the incident radiation going into the sample matrix

and the fluorescent energy returning to the detector is minimized. Therefore, the least amount

of substrate has to be transversed.

The penetration depth with regard to the incident and fluorescent radiation is inversely

proportional to wavelength and directly proportional to energy. The radiation energy necessary

for exciting electrons, and the energy lost by the

electrons that fill these vacancies, is greater for

the K shell than the L shell for a given element.

Portability, user friendliness, cost

Conceptually, a small, light XRF system would

be best suited for either human-portable or robotic

implementation. Likewise, instrument performance verification and the number of steps to

acquire measurements or view spectra should be

minimal. Because these instruments contain

radioactive sources that can have short half-lives

(< 2 years), rental and upgrade cost should also

be evaluated.

INSTRUMENT SELECTION JUSTIFICATION

The SCITEC MAP-3, an XRF analyzer manufactured for the analysis of lead in paint,

equipped with a Co-57 radioactive source, was

selected for the following reasons. This XRF system allows for simultaneous analysis of both Kand L-shell lines of Pb and Hg and has an ambient-temperature Si(Li) detector with a spectral

resolution of about 2.5 keV. In addition, the

source and detector are positioned next to each

other within the scanner, so they face in the same

direction (almost parallel geometry). All other

2

Table 1. XRF primary sources and emission

energy of metals that have fluorescent energies close to Pb and Hg.

Primary energy Useful for the analysis of

Source (keV) K energies L energies

Fe-55 — Si-V Nb-Ce

(14–23)* (41–58)

Cm-244 — Ti-Se La-Pb

(22–34) (57–82)

Cd-109 87.9 & 22.1 Ba-W Cu-Mo

(56–74) (29–42)

Am-241 59.6 Zn-Nb Hf-U†

(30–41) (72–92)

Co-57 121.9 & 136 Hg-U† W-U†

(80–92) (74–92)

Emission energy (keV)

Metals K L Atomic weight

Ir 64.99 9.173 77

Pt 66.82 9.44 78

Au 68.79 9.71 79

Hg 70.82 10.27 80

Tl 72.86 10.27 81

Pb 74.96 10.55 82

Bi 77.1 10.84 83

Po 79.3 11.1 84

* Range of atomic weights.

† Useful range of emission energies includes Pb and

 Hg.
portable XRF systems available at this time come

equipped only with Fe-55, Cd-109, Cm-244, or

Am-241 radioactive sources and are unable to

excite the K-shell electrons of these two metals.

The low resolution of the MAP-3 analyzer is

probably not important since the metals with

K-line energies within 3 keV of Hg and Pb are relatively scarce (gold [Au], thallium [Tl], and bismuth [Bi]; Table 1).

The complete system, capable of performing

measurements and displaying a spectrum,

comes contained within two portable components (Fig. 1): a scanner 33.7 cm long, weighing

1.6 kg (3.5 lb), and a control console 19.3 cm long

× 20 cm wide × 7.6 cm high, weighing 3.2 kg (7 lb)

with a battery. This instrument is available on a

rental basis for under $3000/mo or it can be purchased for about $15,000. Additional important

features are factory-loaded calibrations (empirical), manual control of analysis time (10 to several

hundred seconds), quantitative determinations

based on counts or spectral display available

within a few seconds of completing an analysis,

storage of up to 325 spectra and quantitative

measurements, and an RS-232 serial interface

port for data transfer. In addition, the instrument

is considered a “low level” risk for stray radiation and operator exposure.

LABORATORY EVALUATION

Following a brief discussion of spectral interpretations and methods of instrumental measurement, some qualitative laboratory experiments will be presented that assessed effective

areas of sample analysis, matrix effects, and

length of analysis relative to the detection of Pb

and Hg.

To perform these various tasks, three different

targets and six different soil types (Table 2) were

used. The targets consisted of lead shot (shotgun

pellets), sealed packets (pillows) of weighed

amounts of lead nitrate [Pb(NO3)2] and/or mercuric chloride (HgCl2), and X-ray cells (small

plastic containers) completely filled with mixtures of soil and lead nitrate. The pillows were

made by heat-sealing weighed quantities of the

above salts in 0.2-mil polypropylene bags (8 mm

× 8 mm) so there would be 0.05, 0.10, 0.25, 0.50, or

1.00 g of the metal present. One pillow was prepared with both the Pb and Hg salts (0.50 g/

each). Samples of Pb in soil were prepared by

first mixing weighed amounts of lead nitrate

with an air-dried soil such that the Pb content

would be roughly 0.625, 1.25, 2.5, 5.0, and 10%,

then completely filling a 40-mm-diameter X-ray

cell.

Spectral interpretation

Illustrations of XRF spectra obtained with the

MAP-3 are shown in Figure 2. The vertical scale

indicates the number of counts (intensity of fluorescent energy measured), and the horizontal

axis displays the 256 channels into which the Xray energy or wavelengths are separated. When

this instrument is equipped with a Co-57 source,

the lowest energy that the system can detect is

about 8.5 keV and the highest is 98 keV. Looking

first at the spectra of a typical soil (Fig. 2a), three

peaks that are common to all analyses are apparent: an electronic noise signal ranging from chan3

Figure 1. The SCITEC MAP-3 XRF analyzer.

a. Scanner.

b. Control console.

Table 2. Soil matrix characteristics.

% Silt Grain size*

Matrix % Sand and clay (mm)

Ottawa sand 100 400

Rocky Mountain Arsenal NA NA NA

Lebanon Landfill 45 55 300

CRREL soil NA NA NA

Tampa Bay sediments 95 5 200

Ft. Edwards clay 100 30

* 95% cutoff.

NA = Not available.

9 0 1 2 3 4 5 6 7 8

Tactile Feel

Buttons

Display

Light
nel 1 to 50, a tungsten (W) K-shell peak in the

channel region 101 due to the composition of the

shutter for the source, and, in the region of channel 176 (85 keV), the Compton backscatter peak.

In addition to these peaks, the three remaining

spectra show either or both of the L- and K-shell

peaks of Pb and Hg. The L-shell peaks for these

two metals appear in the region of channel 26

(10.5 and 10.3 keV) superimposed over an electronic noise signal, and the K-shell peaks appear

at channels 155 ±1 (75.0 keV) and 148 ±1 (70.8

keV) for Pb and Hg, respectively.

Comparing all four spectra in Figure 2 also

shows how the intensity of the Compton peak

changes inversely to the amount of heavy metals

present in the sample. In the spectra of the background soil (no target), the Compton peak has

the highest intensity (400 counts); conversely, the

spectra of a sample with 0.5 g of both Pb and Hg

on the soil surface has the lowest (250 counts).

The Compton peak intensity changes because

the incoherent radiation backscatter that comprises it is caused mainly by light elements (i.e.,

oxygen, silica, etc.) in the sample matrix. As the

amount of heavier elements increases in the

matrix analyzed, the fluorescent energy from

light elements decreases. For instance, when the

4

Figure 2. Spectra obtained with the MAP-3 XRF analyzer: a) a background soil, b) the 0.5-g Pb/Hg target on a soil

surface, c) the Pb target on a soil surface, and d) the Hg target on a soil surface.

Pb and/or Hg K-shell peak intensities are of

equal or greater magnitude than that of the

Compton peak, these metals are present at extremely high concentrations (percent levels).

Instrumental analysis

The SCITEC MAP-3 came preprogrammed

with calibrations for Pb in both paint and soil.

The lead-in-paint calibration, which quantitively

assesses both the L and K lines of Pb, was used to

check the instrument’s performance on a daily

basis. This sensitivity check, which took less than

5 minutes to perform, involved measuring a

block of wood evenly coated with leaded paint.

Standards prepared for the analysis of metals in

soil matrices are homogeneous (finely ground),

but metallic primary explosives most likely exist

as salts. As a salt or salt aggregate, large discrepancies in particle size are likely between primary

explosives and soil matrices. For this reason, the

analysis of the targets mentioned above, based

on the factory calibration for Pb in soil (mg/kg),

served only as a relative measurement of the

amount of this metal. In addition, instrumental

measurements of many of the spectra were manually interpreted by measuring the intensity of

the respective K lines, and sometimes the L lines

5 × 103

4

3

2

1

0

5

4

3

2

1

Counts

0 50 100 150 200 250

Channel

a. Soil Background

b. Pb + Hg 0.5 g/ea

Electronic

Noise WK

Compton

Backscatter

Compton

Backscatter

PbL + HgL

WK

HgK PbK

5 × 103

4

3

2

1

0

5

4

3

2

1

Counts

0 50 100 150 200 250

Channel

c. Pb 0.5 g

d. Hg 0.5 g

WK

Compton

Backscatter

Compton

Backscatter

HgL

WK

HgK

PbK

PbL
and Compton peak, along with the adjacent

baseline noise. Intensities of K- and L-line peaks

were assessed by taking an average of the three

highest intensities (counts) in the appropriate

channel region, while that of the baseline noise

was taken as the average intensity in the three

lowest channels, in the valley either just to the

right or left of the peak. This manual method of

data interpretation was performed because there

was no calibration for Hg, and it provides insight

as to the peak intensities (spectral peak heights)

relative to the background noise and that of the

Compton peak.

Effective surface area of analysis

The effective area of analysis for a discrete

object on a surface was evaluated using a Pb shot

pellet and a large shallow plastic tray (100 × 60

cm) filled 5.0 cm deep with the Lebanon Landfill

(LLF) soil. The Pb pellet (2-mm diameter, 62 mg)

was placed on the soil surface and the scanner

was positioned directly over the pellet to obtain a

maximum instrumental measurement of Pb in

soil, using a 24-s analysis period. When this scanner is placed on the soil, the window for the

source and detector remains some 0.6 cm above

the surface. The position of the scanner (i.e., the

source and detector window) was fixed on the

x/y plane (surface of the soil) with two rulers.

The scanner was then picked up and repositioned by moving it in 0.5-cm increments on the

x/y axis away from the location where the highest measurement was obtained. The maximum

values obtained directly over the pellet were 4 to

5 times greater than the background (no pellet

under the scanner) and were at least 2 times

greater than the background after moving 0.5

cm. Positioning the scanner on the soil surface

1.0 cm away from the point where a maximum

reading had been obtained often resulted in a

reading similar to that of the background. This

experiment indicates that the scanner excites and

receives enough radiation to detect a metal

aggregate lying on the surface over an effective

analysis area of about 1.0 cm2.

Depth of soil penetration

Soil disks

Soil barriers of approximately 0.25, 0.50, 1.0,

1.5, and 2.0 mm were prepared by using an appropriate amount of dry LLF soil. Using only

snap rings and collars from 31-mm polyethylene

X-ray cells, the soil was actually spread over a 22-

mm-diam. cylindrical area and held between

two sheets of 0.2-mil polypropylene. These 6-

mm-high (rim) soil disks were placed between

the XRF spectrometer’s sensor window and a

target consisting of a 0.5-g pillow of Pb. Table 3

shows the amount of Pb measured by both the

MAP-3 (Co-57 source) and an X-Met 920

(Metorex, Inc.; Cd-109 source) XRF spectrometer.

The results of this experiment show that while

the intensity of the L lines rapidly decreases as

the soil barrier increases, the intensity of the K

line is not as severely affected. Indeed, the K-line

intensity remains greater than the Compton peak

(Fig. 3). As will be shown in subsequent tests, the

energy emitted by the Co-57 source and the fluorescent energy from electrons filling the voids

created in the K shell of Pb and Hg can easily

penetrate this depth of soil and more.

Tube tests

Analysis of Pb and Hg through soil of various

depths was also performed using a Lucite tube 3

cm high and 2 cm in diameter. The tube was covered on one end with a sheet of 0.2-mil polypropylene held in place with a rubber band. The

covered end of the tube was positioned 2.8 cm

below the soil surface, in a large plastic jar (11.2

cm diameter × 9.5 cm high). The level of the soil

in the jar came to within 2 cm of its rim, and the

mouth of the jar was just large enough to allow

the sensor end of the MAP-3 scanner to fit inside

and rest on the flat soil surface. The tube was positioned directly below the sensor window

(source and detector window), and the jar was

marked to maintain the alignment between the

scanner and the target from one measurement to

another. For this experiment, a pillow of 0.5 g Pb

was placed in the Lucite tube at 1 or 2 cm below

5

Table 3. Measurements of 0.5 g of Pb on soil surface and through soil ranging from 0.25 mm to 2.0

mm thick.

MAP-3 Metorex 920

 Target Co-57 source Cd-109 source

cover Manual* Instr.† Manual* Instr.†

(mm) PbL PbK Comp.** (ppm) PbLα PbLβ (ppm)

 None 4,300 660 260 24,000 147 150 31,000

0.25 2,600 550 280 15,000 37 57 13,000

0.5 1,000 500 280 9,500 14 30 8,200

1.0 500 510 280 6,900 2.1 9.3 2,000

1.5 250 410 290 5,900 0.18 1.0 270

2.0 ND 400 280 5,600 ND 0.54 113

* Manually measured fluorescent energies, baseline-corrected.

† Instrumental measurements based on Pb (mg/kg) in soil

standards.

** Compton peak.
Figure 3. Illustrations of spectra obtained with the

MAP-3 XRF analyzer for a Pb target beneath barriers

of soil.

6

the rim, and then air-dried soil was transferred

with a spatula to achieve various depths of coverage (the inner wall of the Lucite tube had 0.5-cm

increment markings, and the same soil placed

over the target was also used below it).

Table 4 shows some of the measurements

taken using a 24-s analysis period when a 0.5-g

pillow of Pb was placed 1.0 cm below the rim of

the Lucite tube and six different types of soil were

used for coverings in 0.5-cm increments.

Measurements taken in this fashion required that

the incident and fluorescent radiation pass

through a dry soil barrier or an air void of 1.4, 0.9,

or 0.4 mm, depending of the amount of covering.

The results of this experiment showed that the K

line of Pb could easily be seen through 1.0 cm of

every type of soil tested. Manual measurements

Table 4. Measurements (24 s) of 0.5-g Pb pillow on and below several air-dried soil matrices held in a Lucite tube.

Manual* Instr.† Soil Depth

Soil PbK Comp.** (ppm) target (cm)

Ottawa sand

–20 300 210 no 0

190 280 11000 yes 0

150 300 2300 yes 0.5

130 300 1300 yes 1.0

Rocky Mountain Arsenal

–15 300 –250 no 0

210 260 12000 yes 0

205 300 3500 yes 0.5

165 300 3000 yes 1.0

Lebanon Landfill

–35 280 380 no 0

190 260 10000 yes 0

135 280 2400 yes 0.5

125 280 2200 yes 1.0

CRREL soil

–35 260 –400 no 0

175 210 12000 yes 0

210 260 3800 yes 0.5

155 260 4500 yes 1.0

Tampa Bay sediments

–30 280 –390 no 0

220 260 11000 yes 0

130 280 2600 yes 0.5

120 280 1900 yes 1.0

Ft. Edwards clay

–10 220 89 no 0

145 210 11000 yes 0

130 220 2600 yes 0.5

110 220 3300 yes 1.0

* Manually measured fluorescent energies, baselinecorrected.

† Instrumental measurements based on Pb (mg/kg)

in soil standards.

** Compton peak.

of the background soil (no metal target present)

resulted in negative values because the signal intensity is actually lower at the appropriate channels for Pb and Hg than the channels selected for

baseline correction.

Although no results are presented, this experiment was also performed with the 0.5-g Pb pillow positioned at a depth of 2.0 cm (2.4 cm from

the detector source window). Under these conditions, the K line for Pb could only be distinguished from the baseline when there was either

a 0.5-cm soil barrier or none at all. The results of

these experiments indicate that the scanner does

not have to be in direct contact with the surface

in order to measure these metals on or below the

surface.

5 × 103

4

3

2

1

0

5

4

3

2

1

0

5

4

3

2

1

0 50 100 150 200 250

Channel

Counts

a. 0.25-mm Soil Barrier (0.5 g Pb)

b. 1.0-mm Soil Barrier (0.5 g Pb)

c. 2.0-mm Soil Barrier (0.5 g Pb)

PbL

PbL

PbL

PbK

PbK

PbK
7

Modified X-ray cell test

A third experiment used several polyethylene

31-mm X-ray cells, modified so that they were

only 0.5, 1.0, and 1.5 cm high. Each was covered

on the bottom with a single sheet of 0.2-mil

polypropylene. After packing the modifed cells

with soil, they were buried in the large soil-filled

jar so that the top rim was flush with the surface.

The cells were buried with and without the packets of metal salts positioned beneath. With these

cells the mass (density) of soil between the

source and the metal target could be established,

and soil moisture experiments could be performed.

Table 5 shows the manually measured peak

intensities for the K lines of Pb and Hg on and

beneath an air-dried soil and for Pb beneath a

soil of 20 and 40% moisture content. All measurements used a 24-s analysis period, and only the

CRREL soil was used. As indicated by the previous experiment, the K lines of these metals were

detected above the baseline through barriers up

to 1 cm in thickness, even when the moisture

content was increased.

In Table 5, the measured intensities of Pb buried beneath the air-dried CRREL soil were lower

than established in the previous experiment

(Table 4). An explanation for this decrease in signal intensity between experiments is that greater

soil densities most likely were present in the

modified cell experiment. In addition, measurements through the moistened soil barriers appeared to decrease the Pb-line intensity, and the

measurement of this line became inconclusive

when the barrier was increased to 1.5 cm.

Table 6 shows values for both Pb and Hg

based on manually measured intensities and for

instrumental measurement of Pb using a 96-s

analysis period. The targets for this experiment

consisted of pillows containing 0.5 g of both of

these metals, or just Pb. While the findings of this

experiment again indicate that both of these metals could be detected if present as a 0.5-g aggregate or larger on or near the surface, to achieve

detection at depths greater than 1.0 cm beneath

the soil surface, the measurement time had to be

increased.

Table 5. Measurements (24 s)

of 0.5-g pillows of Hg and

Pb uncovered and below

disks of air-dried and moist

CRREL soil.

Hg

Soil

Manual* depth

Soil HgK Comp.† (cm)

CRREL air dried

395 180 0.0

75 240 0.5

45 250 1.0

5 295 1.5

Pb

Soil

Manual* depth

Soil PbK Comp.† (cm)

CRREL air dried

500 250 0.0

120 280 0.5

65 280 1.0

15 280 1.5

CRREL 20% moisture

80 290 0.5

15 290 1.0

0 290 1.5

CRREL 40% moisture

100 290 0.5

40 290 1.0

0 290 1.5

* Manually measured fluorescent

energies, baseline-corrected.

† Compton peak.

Table 6. Measurements (96 s) of Hg and Pb below disks of air-dried and moist soil matrices.

Manual* Instr.†

PbK HgK Comp.** (ppm) Moisture/depth (cm)

Lebanon Landfill (mean density 1.5 g/cm3)

240 400 750 5000 AD†† / 0.5

110 170 860 2500 AD†† / 1.0

10 80 890 1400 AD†† / 1.5

410 — 920 2230 20% / 0.5

170 — 890 1200 20% / 1.0

70 — 870 1050 20% / 1.5

440 — 910 3000 40% / 0.5

180 — 890 1400 40% / 1.0

70 — 830 820 40% / 1.5

Ft. Edwards clay (mean density 1.3 g/cm3)

280 400 760 5200 AD†† / 0.5

120 190 840 2700 AD†† / 1.0

20 70 860 1200 AD†† / 1.5

500 — 950 2800 20% / 0.5

200 — 910 1900 20% / 1.01

50 — 890 610 20% / 1.5

380 — 960 1800 40% / 0.5

210 — 940 1200 40% / 1.0

30 — 910 690 40% / 1.5

* Manually measured fluorescent energies, baselinecorrected.

† Instrumental measurements based on Pb (mg/kg) in

soil standards.

** Compton peak.

†† Air dried.
8

Table 7. Measurements of Pb in soil mixtures using different analysis periods.

Analysis

Sample period Manual* Instr.†

(%) (s) PbK Comp.** (ppm)

Background 96 –50 1400 354

0.625 96 185 835 3000

0.625 10 15 85 3400

1.25 96 315 790 5000

1.25 10 25 85 5100

2.5 96 700 830 6400

2.5 10 60 90 6300

5.0 96 980 740 7100

5.0 10 115 65 7100

10 96 1500 825 8500

10 10 170 80 8400

* Manually measured fluorescent energies,

baseline-corrected.

† Instrumental measurements based on Pb

(mg/kg) in soil standards.

** Compton peak.

Table 8. Measurements of Hg and Pb on and

below disks of Lebanon Landfill soil using different periods of analysis.

Hg

Analysis

Manual* Target Depth period

HgK Comp** (g) Moisture (cm) (s)

–50 920 none AD†† 0.5 96

–15 105 none AD†† 0.5 10

210 840 0.25 AD†† 0.5 96

30 100 0.25 AD†† 0.5 10

115 869 0.5 AD†† 1.0 96

5 90 0.5 AD†† 1.0 10

Pb

Analysis

Manual* Instr.† Target Depth period

 Pb Comp.** (ppm) (g) Moisture (cm) (s)

–40 920 380 none AD†† 0.5 96

–5 105 –930 none AD†† 0.5 10

265 930 1900 0.25 20% 0.5 96

25 85 2600 0.25 20% 0.5 10

490 800 3100 0.5 20% 0.5 96

45 75 5100 0.5 20% 0.5 10

135 880 1400 0.5 AD†† 1.0 96

10 95 1200 0.5 AD†† 1.0 10

* Manually measured fluorescent energies, baselinecorrected.

† Instrumental measurements based on Pb (mg/kg) in soil

standards.

** Compton peak.

†† Air dried.

Detection level of rapid analysis

The sensitivity of elemental detection in environmental matrices performed by XRF depends

upon several factors, including the length of analysis time. The sensitivity for rapid analyses with

the MAP-3 scanner was assessed by analyzing

mixtures of the LLF soil and Pb(NO3)2 held in

XRF cups and pillows of both the Pb and Hg salts

beneath the modified XRF cups (Tables 7 and 8)

for either 10 or 96 seconds. The 10-s measurement

period is the fastest analysis time for this instrument. The objective of this experiment was not to

establish the smallest amount of Pb or Hg that

could be measured, but to determine if percent

levels could be quickly detected.

The results in Table 7 show that Pb was easily

detectable using a 10-s analysis period when

mixed with soil so that ≥0.625% was present.

Likewise, it appears that 0.5-g quantities of these

two metals could be rapidly detected even when

covered with 0.5 cm of soil (Table 8).

A comparison between the changes in response

relative to metal concentration as seen by the

manual and instrumental measurement methods

is also shown in Table 7. For a 16-fold increase in

Pb, the manual method established an 8.1- to 11-

fold increase in PbK peak intensity, but the Pb

concentrations (mg Pb/kg) determined by the

calibrated instrument method only showed a 2.8-

to 2.5-fold increase. The large discrepancy in

range of relative response between the two methods of analysis indicates that a different approach

to instrumental calibration would be necessary

before quantitative measurements could be performed. Ideally, correction factors could be also

be applied so that measured metal concentrations

could be converted readily to estimations of primer concentration [i.e., 1.4 times for Pb(N3)2 and

Hg(CNO)2 or 2 times for C6HO6N3Pb].

SUMMARY

This study shows that the MAP-3 XRF analyzer

is well suited for rapidly determining if either

lead or mercury exists on or near the surface in

high concentrations (percent levels). This system

has several features that are not currently

matched by other commercially available portable XRF spectrometers, most importantly the use

of a Co-57 source. This source, coupled with the

instrument’s capability for rapid analyses and a

complete spectral display of both the K and L

lines of energy for these two metals, not only provides immediate information as to the concentrations present, but their location within the first 1.5

cm of the surface as well. In addition, the manufacturer can provide calibrations for Hg in soil

upon request.
9

The design of this instrument is well suited for

in-situ manual operations and could also be

adapted for robotic implementation. Two likely

adaptations are increasing the distance between

the scanner and analyzer console by acquiring a

longer connecting cable and changing the software to allow for rapid quantification of both the

K and L lines for both of Pb and Hg in soil matrices, as currently performed for the analysis of Pb

in paint.

Sensitivity of XRF analysis increases with

length of analysis up to a period of several minutes. Unique to this system (Co-57 source) is that

not only does the ability to detect lower concentrations at the immediate surface increase with

analysis time, but the ability to detect aggregates

within the first 1.5 cm also increases. If site plan

objectives call for detection of percent levels on

the surface, then a 10-s analysis period is sufficient. However, if the first 1.5 cm is of concern,

then measurement periods of 1.5 minutes or

longer are necessary. The use of portable XRF

systems that cannot be equipped with a Co-57

source for screening sites for primary explosives

is not recommended.

LITERATURE CITED

Garby, J.C. (1991) Comparison of mobile laboratory XRF and CLP split sample lead results from

a superfund site remediation in New Jersey. In

Proceedings of the 2nd International Symposium

Field Screening for Hazardous Waste and Toxic

Chemicals, 12–14 February, Las Vegas, Nevada.

ICAIR, Life Systems, Inc., p. 671–672.

Puls, R., D.A. Clark, C. Carlson, and J. Vardy (1994)

Characterization of chromium-contaminated

soils using field-portable X-ray fluorescence.

Ground Water Monitoring and Remediation, Summer, p. 111–115.

Schneider, J.F., J.D. Taylor, D.A. Bass, S.D. Zellmer, and M. Rieck (1995) Evaluation of a fieldportable X-ray fluorescence spectrometer for the

determination of lead contamination in soil.

American Environmental Laboratory, 6(10): 35–36.

Spittler, T.M., and W.A. Fender (1979) A study of

soil contamination and plant lead uptake in Boston urban gardens. Communications in Soil Science

and Plant Analysis, 10(9): 1195–1210.

US EPA (1986) Test Methods for Evaluating Solid

Waste. U.S. Environmental Protection Agency,

vol. 1B, SW-846.

Workman, W.R. (1994) Reactivity testing of primary explosives in soil, final report. Global Environmental Solutions, Inc., Roy F. Weston, Inc.,

U.S. Army Environmental Center Report No.

SFIM-AEC-TS-CR-94057.

Yinon, J., and S. Zitrin (1981) The Analysis of Explosives. New York: Pergamon Press, Inc., Maxwell

House.
April 1997

Detecting Metallic Primary Explosives with a

Portable X-ray Fluorescence Spectrometer

Alan D. Hewitt

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road Special Report 97-8

Hanover, New Hampshire 03755-1290

U.S. Army Environmental Center

Aberdeen Proving Ground, Maryland 21010-5401 AEC-ET-CR97004

Approved for public release; distribution is unlimited.

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Prescribed by ANSI Std. Z39-18

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Lead

Mercury

Primary explosives

X-ray fluorescence spectrometry (XRF) analysis is a practical means of performing in-situ screening to establish the presence of high concentrations (>0.1% or 1000 ppm) of lead (Pb) and/or mercury (Hg). These two

metals are of special military interest because they are constituents in three primary explosives; lead azide

[Pb(N3)2], lead styphnate (C6HO6N3Pb), and mercury fulminate [Hg(CNO)2]. The success of in-situ XRF

analysis to perform this task depends on instrumental sensitivity, selectivity, effective sample volume, transportability, and user friendliness. Laboratory experiments established that the MAP-3 XRF spectrum analyzer

(SCITEC Corporation) is well-suited for this application. This instrument is self-contained, portable, and

equipped with a Co-57 source that allows for a simultaneous analysis of both the K and L energy lines of Pb

and Hg, among other metals. Laboratory experiments established that high concentrations of Pb and Hg

could be detected in an active sample area of cylindrical shape, approximately 1.0 cm in diameter and 1.5 cm

in depth.

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X-ray fluorescence spectrometer 15

XRF

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