ll. COLUMBIA UNIVERSITY
A. Chemicai treatment:
The program undertaken at Lamont Cbservatory required analysis for the determination
of Sr-90 in a variety of sample types. The counting equipment, designed specifically for this
program, dictated to some degree the kinds of samples necessary for maximum efficiency of
operation. Thus chemical procedures were developed which (a) would be adaptable to all of
the sample types anticipated, (b) would be rapid and quantitative, and, (c) would result in a
precipitate suitable for the mounting technique described in the next section.
Because of its characteristic granular texture and relatively non-absorptive properties, it
was decided to count the samples as yttrium oxalate Y.(C.0,);‘9H,O.
Two further advantages
of this compound are its high molecular weight, resulting in relatively large samples, and its
precipitation at low pH (less than 1), where the oxalates of iron and other interfering cations
are soluble.
The samples fall into two categories; those naturally occurring as calcium phosphate, and
all other. In all cases a pure calcium salt was first prepared. Cheese, bone, and plant samples
were burned to ash in stainless steel chambers, the ash dissolved in concentrated HCl, and
solids filtered off. Caicium phosphate along with strontium phosphate was then precipitated
by addition of H;PO, and NH,OH. Generally these were purified by several re-precipitations
and filtrations after which they were dried and weighed to determine calcium content.
Soil samples were leached for five minutes in 50% HCl solution with stirring. The liquid
was filtered off, evaporated to dryness and ignited to remove organic debris. The ash was then
dissolved in concentrated HCl, and filtered, and CaCO, precipitated by addition of concentrated
Na.CO,;,. Again several re-crystallizations were carried out for purification purposes, after
which the solid was dried and weighed to determine calcium content.
B. Milking:
The milking procedure was done by two methods for carbonate and phosphate samples,
respectively.
The carbonate samples were milked by addition of yttrium carrier in acid solution, and precipitation of yttrium hydroxide at pH of 9. The filtrate was then set aside for accumulation of
Y-90 and later milking. The Y(OH). was dissolved off the filter paper by 50% HCl, and then
NH,OH added dropwise to just recrystallize the hydroxide. One or two drops of concentrated
HC! was then added to just dissolve it again, and concentrated oxalic acid then added to precipi-
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After leaching, the solid material was then
burned to ash and the ash similarly treated. In most cases there was insufficient calcium present
for good CaCO; precipitation, so weighed SrCl.:6 H.O was added as carrier and the resulting
SrCO; precipitate was stored.
Water samples were treated by addition of SrCl.°6 H.O as carrier and precipitation of SrCOs.
The water samples were not filtered before the addition of the strontium carrier for the purpose
of base exchanging any adsorbed Sr-90 on the solid material carried down by the rain. A
portion of each sample was used to prepare special concentrated Na.CO;solution for precipitation; thus with the exception of the negligible amount of water in the SrCl.'6 H.O carrier, no
other water was added to the samples.
By these methods, all of the samples were purified to either phosphates or carbonates,
and were then put into solution in small volumes of HCl.
“, WEE.
exactly the same manner as described for soils.
ah
Shell samples were dissolved in HCl, filtered, evaporated to dryness and ignited to remove
organic matter. The salt was redissolved and CaCO; precipitated and determined as outlined
for soils.
Plant samples were treated in two ways. Leach samples were prepared from plants in