is the precipitation of strontium in strong nitric acid.
By the addition of carrier strontium,
this method has been adapted to the determination of radiostrontium. Strontium, barium, and
lead are relatively more insoluble as the concentration is increased. Since other nitrates also
become more insoluble with increased concentration, the selection of the strength to be used
represents a compromise. Based on experimental studies, 75% HNO; was selected as the optimum concentration.
In the analyses 20 mg of carrier strontium is added to each sample before starting the procedure. This may be an excessive quantity, but this amount of carrier can be tolerated in beta
counting and a large excess is helpful when dealing with moderately soluble precipitates such as
the strontium salts used.
|
An experiment was performed to determine the effect of calcium on the recovery of Sr-90.
Solubility measurements indicated that 200 mi of 75% HNO, would cause a loss of 2.6 mg of Sr
or a 13% loss when using 20 mg of Sr carrier. Calcium was found to have a salting effect so
that Sr recovery is improved by operating close to calcium saturation. The solubility of calcium
in 75% HNO;is equivalent to 23.5 grams of CaO perliter. If no calcium is present, a minimum
of HNO, should be used.
Experience showed that the presence of other fission products does not interfere in the
method of analysis used for bone samples.
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10. Place the filter paper on a brass disk and ring assembly (Tracerlab), cover with 0.001 inch
Pliofiim and beta count.
One of the standard methods for separating strontium from calcium and many other metals
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Note.--The fluorothene funnels are a modification of the Tracerlab stainless steel] funne}, designed for
preparing precipitates for counting on filter paper. The glass fiber filters are available from H. Reeve Angel
and Co., Inc., 52 Duane St., New York 7, N. Y., as catalog number X-934-AH. They are more retentive than
paper filters and are unaffected by 75% HNO,.
:
9. Filter through a fluorothene funnel on to a glass fiber filter. Transfer the funnel to a
clean filter flask and wash the acid from the precipitate with anhydrous ethyl!ether.
:
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B. Separation of total radiostrontium from one hundred grams of soil:
The method described below is designed to insure recovery of the radiostrontium regardless
of its state or of the nature of the soil.
However, tests of leaching methods, using 6 N HCl or
1 N ammonium acetate, have shown good recovery and are to be preferred for handling large
samples of soil.
Details of this method are included here partly because the method is being
used for certain cases and partly because of the applicability of a portion of the procedure to
separation of radiostrontium from samples of vegetation and foods.
1. Dry the entire sample in an oven at 110°C.
2. Sample, using standard sampling procedure (quartering process) until approximately
125 grams of soil is obtained as a representative sample.
3. Ignite in a nickel crucible at 900°C.
4. Weigh out 100 grams of the ignited material.
5. Add 400 grams of Na.CO. and mix thoroughly.
6. Fuse in a muffle at 900°C (minimum temperature) for 45 minutes (minimum time), until
the melt is clear and homogeneous.
7. Cool by immersing in a beaker of cold water, withdrawing quickly at first. Continue
immersing and withdrawing until the crucible is cool enough to place on a transite board.
The Na.CO, should not be wet at any time.
8. When the crucible is cool, turn it upside down, tap the bottom with a pestie and allow the
solid fused material to fall into a mortar.
9. Break up the fused material in a hand grinder, transfer to an automatic grinder and
prind to a fine powder.
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