8.1 Sample Preparation Techniques
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in determination of the half-life of some uranium isotopes. The electrolytic deposition can be done with or without the use of carriers. For example, a very thin film
of Silver-110 can be obtained by deposition of Silver-110 on a gold cathode from a
slightly ammoniacal solution of silver argentocyanide labeled with Silver-110. This
gives about 97.98% of Silver-110 deposition. This deposition can be made with or
without the presence of natural silver as a carrier. Source prepared without the carrier
would suffer negligible loss due to self-absorption.
8.1.5 Vacuum Evaporation Technique
Using vacuum evaporation technique, the source can be prepared by volatilizing by
heating under reduced pressure.
The sample gets deposited over the substrate. Sometimes difficulties arise as the
evaporated layer becomes thicker at the substrate, leading to pulling of the sample.
Thus, source quality is determined by quality of backing on which the thin source
has been prepared. If plastic foil is used as a substrate, it must be cooled by placing
a thick copper plate in contact with the substrate. Size and area of the deposit can be
controlled by placing a mask of the required size over the substrate during evaporation process. Although this technique gives a thin film of a material, it increases the
decontamination problem, because during vacuum evaporation in the vacuum chamber, the material gets deposited on the glass jar and other places. Before selecting
this technique, the above problem must be taken into consideration.
8.1.6 Electrospraying Technique
Electrospraying technique can also be used for thin source preparation. This technique makes use of the fact that when a potential is applied between a capillary
containing a polar liquid and a plate at ground potential, the liquid is ejected from
the capillary as a fine spray. A solvent with a sufficiently high vapor pressure is
chosen so that it gets evaporated before reaching the ground plate. The dissolved
material then gets deposited as a thin layer. In this case, as well, the quality of source
is partly influenced by the quality of substrate. Generally, a positive high tension of
5–10 kV is applied to the capillary.
8.2 Solid Sample Source
We learnt some special methods for sample preparation, but these are not commonly
used in radiochemical work. Most of the time we prepare solid sample source for
measuring the activity. Now, we shall devote our discussion on solid sample preparation.
141
in determination of the half-life of some uranium isotopes. The electrolytic deposition can be done with or without the use of carriers. For example, a very thin film
of Silver-110 can be obtained by deposition of Silver-110 on a gold cathode from a
slightly ammoniacal solution of silver argentocyanide labeled with Silver-110. This
gives about 97.98% of Silver-110 deposition. This deposition can be made with or
without the presence of natural silver as a carrier. Source prepared without the carrier
would suffer negligible loss due to self-absorption.
8.1.5 Vacuum Evaporation Technique
Using vacuum evaporation technique, the source can be prepared by volatilizing by
heating under reduced pressure.
The sample gets deposited over the substrate. Sometimes difficulties arise as the
evaporated layer becomes thicker at the substrate, leading to pulling of the sample.
Thus, source quality is determined by quality of backing on which the thin source
has been prepared. If plastic foil is used as a substrate, it must be cooled by placing
a thick copper plate in contact with the substrate. Size and area of the deposit can be
controlled by placing a mask of the required size over the substrate during evaporation process. Although this technique gives a thin film of a material, it increases the
decontamination problem, because during vacuum evaporation in the vacuum chamber, the material gets deposited on the glass jar and other places. Before selecting
this technique, the above problem must be taken into consideration.
8.1.6 Electrospraying Technique
Electrospraying technique can also be used for thin source preparation. This technique makes use of the fact that when a potential is applied between a capillary
containing a polar liquid and a plate at ground potential, the liquid is ejected from
the capillary as a fine spray. A solvent with a sufficiently high vapor pressure is
chosen so that it gets evaporated before reaching the ground plate. The dissolved
material then gets deposited as a thin layer. In this case, as well, the quality of source
is partly influenced by the quality of substrate. Generally, a positive high tension of
5–10 kV is applied to the capillary.
8.2 Solid Sample Source
We learnt some special methods for sample preparation, but these are not commonly
used in radiochemical work. Most of the time we prepare solid sample source for
measuring the activity. Now, we shall devote our discussion on solid sample preparation.