MATERIALS AND METHODS
Particulate air samplers are run continuously at two perimeter locations
and at one off-site location.
Collections are made on a polystyrene
filter medium.
Individual samples are combined by location on a monthly
basis to give a typical filtered air volume of about 25,000 m3.
Samples
are ignited at 600° C. to remove organic matter and prepared for analysis
by using a leach procedure employing combinations of hydrochloric,
hydrofluoric, and nitric acids.
A radiochemical separation procedure is
used to sequentially isolate plutonium, thorium, and uranium.
After
separation, the fractions are electrodeposited and their isotopic composition determined by alpha spectrometry. Chemical recoveries are monitored
by added known amounts of plutonium-242, thorium-234, and uranium-232
prior to ignition.
The monthly amount of plutonium deposited on the surface from the air is
also determined by the above method.
Wet and dry deposited material is
collected in a container of known area and the residue analyzed for
plutonium.
Surface soil of known area is analyzed for plutonium, uranium, and
thorium.
After drying, grinding, and mixing, an aliquot of soil is
analyzed by a leach method similar to that used above for the air-filter
residues.
RESULTS AND DISCUSSION
The concentration of plutonium-239,240 in air at ANL (Sedlet et al.,
1973, 1974, 1975; Golchert et al., 1976, 1977) for the last five years
is depicted in Figure 1.
The fluctuations are primarily due to recent
atmospheric nuclear tests conducted by the People's Republic of China.
The approximate dates of these tests are indicated by arrows at the
bottom of the figures. The concentrations in air of other fission
products for which measurements were made, t.e., strontium-89, strontium-90,
ete., show a similar distribution.
Measurements of this type for this
period and earlier have been made by the Environmental Measurements
Laboratory (EML) (Hardy, 1978), formerly HASL, at various locations.
The monthly variations exhibit the expected maximum in the spring and
the magnitude of the peak is determined by the quantity and yield of
atmospheric testing the previous year.
Another way of looking at this
type of information is to examine ground deposition of plutonium-239, 240
for the same period. This is illustrated in Figure 2. This data was
generated by analyzing the contents of a known area sample collector for
plutonium and expressing the results in terms of deposition (pCi/m*).
724