portable XRF systems available at this time come
LABORATORY EVALUATION
equipped only with Fe-55, Cd-109, Cm-244, or
Am-241 radioactive sources and are unable to
Following a brief discussion of spectral inter-
excite the K-shell electrons of these two metals.
pretations and methods of instrumental mea-
The low resolution of the MAP-3 analyzer is
surement, some qualitative laboratory experi-
probably not important since the metals with
ments will be presented that assessed effective
K-line energies within 3 keV of Hg and Pb are rel-
areas of sample analysis, matrix effects, and
atively scarce (gold [Au], thallium [Tl], and bis-
length of analysis relative to the detection of Pb
muth [Bi]; Table 1).
and Hg.
The complete system, capable of performing
To perform these various tasks, three different
measurements and displaying a spectrum,
targets and six different soil types (Table 2) were
comes contained within two portable compo-
used. The targets consisted of lead shot (shotgun
nents (Fig. 1): a scanner 33.7 cm long, weighing
pellets), sealed packets (pillows) of weighed
1.6 kg (3.5 lb), and a control console 19.3 cm long
amounts of lead nitrate [Pb(NO3)2] and/or mer-
curic chloride (HgCl2), and X-ray cells (small
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
a. Scanner.
Ft. Edwards clay
100
30
Tactile Feel
* 95% cutoff.
Buttons
NA = Not available.
plastic containers) completely filled with mix-
0
1
2
3
tures of soil and lead nitrate. The pillows were
4
5
6
7
8
made by heat-sealing weighed quantities of the
9
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 pre-
pared with both the Pb and Hg salts (0.50 g/
Display
each). Samples of Pb in soil were prepared by
Light
first mixing weighed amounts of lead nitrate
b. Control console.
with an air-dried soil such that the Pb content
Figure 1. The SCITEC MAP-3 XRF analyzer.
would be roughly 0.625, 1.25, 2.5, 5.0, and 10%,
then completely filling a 40-mm-diameter X-ray
cell.
20 cm wide 7.6 cm high, weighing 3.2 kg (7 lb)
with a battery. This instrument is available on a
Spectral interpretation
Illustrations of XRF spectra obtained with the
rental basis for under 00/mo or it can be pur-
MAP-3 are shown in Figure 2. The vertical scale
chased for about ,000. Additional important
indicates the number of counts (intensity of fluo-
features are factory-loaded calibrations (empiri-
rescent energy measured), and the horizontal
cal), manual control of analysis time (10 to several
axis displays the 256 channels into which the X-
hundred seconds), quantitative determinations
ray energy or wavelengths are separated. When
based on counts or spectral display available
this instrument is equipped with a Co-57 source,
within a few seconds of completing an analysis,
the lowest energy that the system can detect is
storage of up to 325 spectra and quantitative
about 8.5 keV and the highest is 98 keV. Looking
measurements, and an RS-232 serial interface
first at the spectra of a typical soil (Fig. 2a), three
port for data transfer. In addition, the instrument
peaks that are common to all analyses are appar-
is considered a "low level" risk for stray radia-
ent: an electronic noise signal ranging from chan-
tion and operator exposure.
3
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