Bogen and Welford (1971) obtained good results using LSC for total beta and
alpha assay.
Ludwick (1960) applied LSC to beta counting of 24!pu.
Price
(1972) reports that he obtained 100% counting efficiency for 239py, 24 1am,
244om and 92% for 237Np using a TTWC liquid scintillating gel. McDowell et
al, (1974) have reported on the use of a combined solvent extract ion-liquid
scintillation method for Pu and U determination in environmental samples.
Alpha counting efficiencies of 100% and an energy resolution of 260 to 300%
keV are quoted.
Scintillations produced by Pu alpha particles on a ZnS screen, coupled to a
photomultiplier, are reported by Hallden and Harley (1960), Kooi and Holistein
(1962).
An extensively applied method for ?“!am is to detect the 60-KeV gamma
in a NaI(T1) scintillation well counter as described by Bubernak et al. (1956),
Cline (1967), Filer (1974), and Wallace (1972).
Numerous other detector and
sample counting geometries have been discussed, including a thin NaI(Tl) wafer
detector and plastic jar containing dissolved soil solutions, 10 g per 100 g
of solution, as reported by Major et al. (1974), on the use of a solid state
planar germanium detector for 10-g soil samples as given by Essington et al.
(1976).
Heimbuch and Gee (1962) developed a scintillating ion exchange resin
which they applied to the assay of plutonium.
Gee et al. (1967) used Alpha-a-Cal,
an acetate base backed with a 2-3 mg/cm? ZnS, to enchance registration of Am
alpha particles on film with several orders of magnitude increase in sensitivity.
Schwendiman and Healy (1958), Campbell and Moss (1963), and Everett et al.
(1964) all describe the use of nuclear track plates for high sensitivity
measurements of Pu in urine.
Isotope dilution surface ionization mass spectrometry has been applied to
environmental samples as low as 0.006 dpm by Dupzyk et al. (1972) measuring
239pu, 240py, and 24!pu with 242pu tracer.
Hoffman et al. (1971) used a
similar technique to detect ?""Pu in nature.
Noshkin et al. (1974) used 235np
tracer and mass spectrometry to measure *3’Np in sediment samples.
Exposure to neutrons in a reactor and the search for activation or fission
products or tracks have also been used, Larson and Oldham (1974a), to provide
highly sensitive analysis of the actinides.
Some of the early instrumental
techniques are those of Jacobson and Overstreet (1948) in which he used a
linear amplifer system co assay 739Pu.
SUMMARY
There are numerous procedures for the analysis of transuraniums (TU) in environmental samples, and in environmental type samples from laboratory or field
studies.
There are many variations on reported methods and so many ways to
achieve the final result accurately that none can be singled out as the preferred
method.
Ie is known, also, that in actual laboratory operation, there are deviations
from published procedures due to sample variations and procedure improvements
and publication lag.
Also, the accuracy and precision of the final data is
known to be much dependent upon individual experience, competence, and quality
control.
Possibly, the driving force for continual changes, besides scientific inquiry,
is to minimize analysis costs.
By their very nature, sensitive TU analysis
costs have always been expensive. A comparison of available 1976-cost data to
that of 1963 Roller Coaster Project costs was made. Analysis for 239py in
10 g of soil is now being performed with lower labor cost, and slightly reduced
material costs.
The net overall cost is slightly lower.
For small filter
samples, labor is lower, material higher, and the net change is to a slightly
higher cost.
Both cost figures show significant procedure and operational
cost reductions have been well ahead of the 13-year span of inflation.
Cost
figures at other facilities are not available but they would also be influenced
by changes in overall technology at that facility.
Possibly, a laboratory performing gross analyses in 1963 would have expertenced
a significant rise in costs in converting to isotope dilution analyses, exclusive
of equipment costs.
Presently there is a wealth of procedures available for Pu and Am, although
not for Np and Cm.
There is progress in sensitivity, accuracy, and cost
reduction.
Relative to the use of TU analyses as a tool in various studies
and as a regulatory requirement, it is expected there will continue to be a
need for procedure improvement studies.
Rhodes (1957) studied the absorption
of Pu in soil with a parallel plate alpha counter.
Buenger et al. (1962)
detected Pu alphas by a 2 7 proportional counter.
Sill and Williams (1971)
used surface barrier detectors for direct alpha spectrometry of environmental
samples. Melgard et al. (1968) preferred Frisch grid chambers to surface
barrier detectors because of buildup of daughter product contamination from
samples was not permanent and uniformity of plates was not required.
Development of the multichannel analyzers and the associated data acquisition systems
has made APHA by either surface barrier or Frisch grid chambers the preferred
method for environmental alpha counting.
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