and purify these elements are,
chemistry.
in most instances, based on fundamental classical
These methods involve precipitation, coprecipitation, extraction, various
forms of ion exchange, and are based on the classic oxidation-reduction proper-~
ties of the actinides and their similarity to the lanthanide series. The +3
state is characteristic of all the actinide elements, uranium to americium,
and they are capable of being oxidized all the way to +6; in this respect, the
actinides differ from the rare earths. From uranium to americium, the stability
of the +6 state decreases regularly and there is a corresponding increase in
the stability of the +3 state. At americium, the +3 state becomes the predomifMant one, and the only state known to exist for curium in aqueous solutions is
the +3.
The early analytical methods that were developed were used to separate and
purify Pu from alpha emitters and beta~emitting fission products in fresh
fission solutions. Subsequently, it became necessary to separate plutonium in
trace quantities from a variety of environmentally derived matrices. Plutonium
and the other transuranics were not conveniently in solution but in a variety
of chemical and physical forms--some as colloids, some as complexes, and
others in the form of highly refractory oxides fused with macro amounts of
aluminum, iron, silica, etc.
Further, in addition to removal of the artificial
radionuclides, methods had to be developed to also remove the natural elements.
The radiochemical procedures which were developed, therefore, employ the basic
chemical techniques, but differ in a very special manner, due to the necessity
of separation from environmental matrices. Usually, concentration may be
required from large volumes and isolation from macro quantities of stable
elements which differ from matrix to matrix and sample to sample. As a result,
the procedures employed must be tailored to the specific matrix. Over the
years, procedures have become simplified, consisting primarily of a concentration
step, decontamination steps involving coprecipitation and ion exchange, and a
final isolation for counting.
Considerations in the evolution of concentration
techniques are losses due to foaming, spattering, entrainment, formation of
insoluble oxides, polymerization, etc. A successful procedure produces good
yields, clean plates, high purity, with economy of materials and time and use
of the least labor intensive methods.
In the course of these operations, due
to the large volumes and masses of the samples, management of the fumes and
waste liquids produced must be considered. Lastly, for the more sensitive
chemists, some of the odors produced are not exactly "Chanel No. 5."
Much of the early plutonium chemistry, in 1943, at the University of Chicago
Metallurgical Laboratory, was performed with less than 1,000 dpm of plutonium.
Since this was all that was available, recovery techniques were devised for
recycling the plutonium. Techniques employed then to isolate from a variety
of experimental solutions were redox, coprecipitation, and hexone extractions,
with great success. Later, in connection with nuclear weapons tests in the
late 1940s, the transuranics, primarily neptunium and plutonium in the form of
particulates, were recovered from inorganic and organic filter media,
There
were also many bioassay samples to be analyzed.
These were invariably tracerfree.
In the early 1950s, plant uptake of plutonium studies were also performed, Jacobson and Overstreet (1948), again tracer-free Animal studies at
Lovelace and UC Davis and the TG-57 (1957 Safety Tests at NTS) and Roller
Coaster, Major and Wessman (1964), plutonium safety tests
made necessary the
requirement for procedural development on large biological
samples.
HASL
studies of worldwide fallout and the data produced on atmospheri
c and surface
distribution of the actinides led to the development of
standarized procedures
Harley (1957, 1972).
Laboratories contributing to the development and application of transuranic procedures are the USERDA primes,
such as LASL, LLL,
Battelle, etc.; DOD units such as AFTAC, WPAFB, the now defunct
NRDL, and LFE
(Tracerlab).
The procedures discussed herein apply to inorganic matrices
such as soils;
aqueous samples such as water, sea water, and liquid bioassay
samples; and
organics such as vegetation, animal, and filters.
In addition to single
element procedures, some discussion of sequential procedures
is included.
It is interesting to note that current work reported here
also includes
instrumental techniques which, in some instances, relieves
the need for
radiochemistry.
It is also tronic that after years of development of tracer
techniques, because of the desire to measure all transurani
c nuclides in
waste, there is now a need for reliable and accurate tracer-fre
e techniques.
DISSOLUTION AND CONCENTRATION TECHNIQUES
'
The transuranics in environmental samples are usually
low in activity and as a
result, in order to obtain usable data, samples large
in mass or volume must
be taken.
For example, the currently most abundant transuranic in
soil is
plutonium, with a typical average concentration of 0.02
dpm/g (0-20 cm),
Hardy
et al. (1972).
Therefore, in order to recover the nuclide of interest,
it is
necessary to reduce the volume or mass to manageable
amounts and assure its
solubilization.
Some samples such as soil require prior sieving and grinding.
Organic matter must be decomposed.
At an early stage, tracer must be added
and equilibrated and lastly the final solution conditione
d for the initial
radiochemical separation and purification steps.
Since these elements are not
normally volatile, precautions in these Procedures are
primarily mechanical
and involve proper mixing to get a uniform sample and
adjustment of temperatures
and heating cycles to prevent mechanical losses.
In the aqueous phases
acidification 1s required to prevent polymerization or radtocoll
oid formation
and losses due to plating out prior to equilibration.
The methods employed
for volume or mass reduction in organic, inorganic, and
aqueous samples are
shown in Figure 1 and typical concentration steps are shown
in Figure 2.
SOILS
Soil varies widely in physical and inorganic chemical
composition and in the
amount of organic material.
A similar statement can be made about the form of
547