APPENDIX A
RADIOCHEMICAL DETERMINATIONS
Most of the determinations of Sr—90 at low concentrations in the various materials of interest
have been carried out in three laboratories: Institute for Nuclear Studies, University of Chicago
(W. F. Libby) ; Lamont Geophysical Observatory, Columbia University (J. L. Kulp); and Division
of Health and Safety, New York Operations Office, U.S. Atomic Energy Commission (J. H. Harley).
While the methods used by these laboratories were evolved with some degree of collaboration,
differences in detail make it desirable to include here descriptions of all three. For this purpose, minor changes have been made in descriptions submitted by the respective investigators for
other purposes.
1. UNIVERSITY OF CHICAGO
A. Preliminary treatment of samples:
Before any chemical preparation was done, most of the solid samples were dried or burned
in an oven or incinerator and then reduced to ash in a muffle furnace at 900° C. Samples treated
in this way included the human,alfalfa, cheese and milk specimens. The Bureau of Plant
Industry at Beltsville, Md., processed the soil samples and sent them in the form of calcium
oxalate.
The water samples, including the rain, snow, lake, river and ocean samples, were filtered
to remove solid material.
B. Chemical preparation of samples:
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The ashed samples were dissolved in concentrated HCl, and concentrated HNO; was also
added if the sample did not go into solution satisfactorily. The residue, if any, was then
filtered off, and, with the exception of the human group, strontium carrier was added to the
solution, which was then milked with yttrium.
The alfalfa samples werestill highly contaminated after the first milking. Repeated ferric
phosphate precipitations were made to remove the rare earth contaminants. The strontium
carrier which had been added was isolated using Harley’s method (see p. 33 of this appendix),
and then purified.
The soil samples in the form of calcium oxalate were dried, ignited to oxides, dissolved in
concentrated HCl, diluted with water, and milked. The milking technique adopted by the
Chicago group for the determination of the Sr—90 content of various types of sample essentially
consists of obtaining an HC! solution of the sample, adding carrier for the yttrium, separating
the Y-90 daughter of the Sr—90 present in the sample by a phosphate precipitation of the
carrier, and determining the amount of Y-90 and therefore also of Sr-90 present by absolute
counting.
The technique outlined above was tested and shown toyield satisfactory results using both
inactive yttrium and neodymium as carriers for the Y-90 and in both the presence and the
absence of calcium in the solution. The following example of a test experiment performed
with neodymium carrier and in the absence of calcium serves to illustrate the details of the