8.2 Solid Sample Source
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artificial centers help the solids (i.e., radioactive materials) to crystallize in many
small crystals instead of a few big ones. Big crystals cause loss of activity due to
uneven spread over surface of the sample holder.
8.2.3 Source from a Slurry
In most of the radiochemical work, we come across with a problem of counting
freshly prepared precipitate. Following procedure is adopted for making a sample
source for counting purpose. From the solution of radioactive material, we precipitate
the desired chemical, which is filtered and washed several times with suitable solvent.
Precipitate is transferred to a test tube and a slurry is made in some suitable solvent
(e.g., water, acetone, methanol, etc.). Slurry is transferred slowly with a micro-pipette
to the planchet and then it is dried under the infrared lamp. Care is taken to get uniform
deposit of the precipitate over the planchet (Fig. 8.1A). The planchet along with the
dried solid is then measured for its activity, by a suitable technique. In order to prevent
loss of activity by splashing while drying the sample, the source is dried in a gentle
air stream at about 40
◦ C and is protected from dirt. Crystals of the solid sample
can be stabilized by adding a few drops of binding agent, prior to drying (e.g., 0.5%
collodin in acetone or 2% isobutylmethy-lacrylate polymer in ethylacetate). Addition
of a trace of secptine to the slurry prior to drying prevents the dried source to not
become powdery. A trace of detergent, such as teepol, often assists preparation of
even deposits. Cracking of the solid sources while drying can often be prevented
by addition of a few drops of celite, which is very useful when drying gelatinous
precipitates.
Alternatively, the slurry can be transferred to a filter paper fitted in a micro-funnel;
this is convenient when the solid material has to be washed thoroughly. The filter
paper is not allowed to dry until the entire process of transferring the slurry and
washing, etc., has been completed. The filter paper along with the precipitate is
transferred to a planchet coated with thin layer of wax. Waxing the inside surface
of the planchet allows the filter paper to remain flat while slowly drying under the
infrared lamp. This method is most successful because self-absorption can be made
very negligible.
Summary
The discussions made in this chapter revealed that source preparation is one
of the important parameter to get a reproducible result, especially when series
of samples are to be counted or when specific activity of the sample is to be
determined. In this chapter, we have learnt a detailed account of various methods normally used for the preparation of sample source. In the next chapter, we
shall discuss the factors other than sample preparation, affecting the efficiency
of counting.
145
artificial centers help the solids (i.e., radioactive materials) to crystallize in many
small crystals instead of a few big ones. Big crystals cause loss of activity due to
uneven spread over surface of the sample holder.
8.2.3 Source from a Slurry
In most of the radiochemical work, we come across with a problem of counting
freshly prepared precipitate. Following procedure is adopted for making a sample
source for counting purpose. From the solution of radioactive material, we precipitate
the desired chemical, which is filtered and washed several times with suitable solvent.
Precipitate is transferred to a test tube and a slurry is made in some suitable solvent
(e.g., water, acetone, methanol, etc.). Slurry is transferred slowly with a micro-pipette
to the planchet and then it is dried under the infrared lamp. Care is taken to get uniform
deposit of the precipitate over the planchet (Fig. 8.1A). The planchet along with the
dried solid is then measured for its activity, by a suitable technique. In order to prevent
loss of activity by splashing while drying the sample, the source is dried in a gentle
air stream at about 40
◦ C and is protected from dirt. Crystals of the solid sample
can be stabilized by adding a few drops of binding agent, prior to drying (e.g., 0.5%
collodin in acetone or 2% isobutylmethy-lacrylate polymer in ethylacetate). Addition
of a trace of secptine to the slurry prior to drying prevents the dried source to not
become powdery. A trace of detergent, such as teepol, often assists preparation of
even deposits. Cracking of the solid sources while drying can often be prevented
by addition of a few drops of celite, which is very useful when drying gelatinous
precipitates.
Alternatively, the slurry can be transferred to a filter paper fitted in a micro-funnel;
this is convenient when the solid material has to be washed thoroughly. The filter
paper is not allowed to dry until the entire process of transferring the slurry and
washing, etc., has been completed. The filter paper along with the precipitate is
transferred to a planchet coated with thin layer of wax. Waxing the inside surface
of the planchet allows the filter paper to remain flat while slowly drying under the
infrared lamp. This method is most successful because self-absorption can be made
very negligible.
Summary
The discussions made in this chapter revealed that source preparation is one
of the important parameter to get a reproducible result, especially when series
of samples are to be counted or when specific activity of the sample is to be
determined. In this chapter, we have learnt a detailed account of various methods normally used for the preparation of sample source. In the next chapter, we
shall discuss the factors other than sample preparation, affecting the efficiency
of counting.