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13 Radiochemical Separation Techniques
13.2 Separation and Purification Techniques
The basic methods used for the purification of radioactive samples are those of
analytical chemistry. These analytical methods may have to be modified or carried
out with care in order to achieve maximum radiochemical purity, and it may often be
less harmful to have a few milligrams of inert impurity in the final sample than 10
−9 g
of a radioactive contamination. The speed of the separation technique in some cases
may be more important than high chemical yield or even great chemical purity. A
very good and high yield separation scheme, which requires an hour to perform, is of
little use for isolating and studying a nuclide with a half-life of a few minutes. Also,
the method preferably should not lead to high contamination of apparatus; this may
cause serious losses of active material and give much trouble in decontaminating
the apparatus for further use. Considering these stringent requirements, few specific
techniques are discussed here.
13.3 Co-precipitation
The amount of radioactive nuclides formed in an irradiated target material is often
very low to permit the solubility product of an insoluble compound to be exceeded.
The addition of a chemically identical element (a carrier) in the same chemical form,
allows the solubility product to be exceeded and results in precipitation. An advantage
of this technique is that the amount of material associated with the activity can be
very closely controlled by the addition of the known amount of the carrier.
13.3.1 Carriers for the Separation
In nuclear reactions, other than (n, γ ), the daughter isotope is always a different
chemical species than the parent. Hence, the number of daughter isotope formed
may be of the order of 100–10,000 atoms. Moreover, chemical separation needs
some glassware to carry out the experiment. The radioactive isotope formed during
the nuclear reaction can thus very easily be adsorbed on the surface of glassware,
hence there can be loss of radioactive isotope during chemical maneuvering. In
addition, these atoms may be required to be precipitated or solvent extracted for the
separation. The amount of these radioactive species would be very low to be visible
in precipitation or other techniques. Therefore, the chances of losing the radioactive
atoms become great. However, if after nuclear reactions, the substance is mixed with
an inactive substance (known as carrier) which has the same chemical property as
the tracer, then the radioactive isotope produced in a nuclear reaction is diluted (i.e.,
its specific activity is lowered) and loss due to adsorption etc., during the chemical
separation is minimized.
13 Radiochemical Separation Techniques
13.2 Separation and Purification Techniques
The basic methods used for the purification of radioactive samples are those of
analytical chemistry. These analytical methods may have to be modified or carried
out with care in order to achieve maximum radiochemical purity, and it may often be
less harmful to have a few milligrams of inert impurity in the final sample than 10
−9 g
of a radioactive contamination. The speed of the separation technique in some cases
may be more important than high chemical yield or even great chemical purity. A
very good and high yield separation scheme, which requires an hour to perform, is of
little use for isolating and studying a nuclide with a half-life of a few minutes. Also,
the method preferably should not lead to high contamination of apparatus; this may
cause serious losses of active material and give much trouble in decontaminating
the apparatus for further use. Considering these stringent requirements, few specific
techniques are discussed here.
13.3 Co-precipitation
The amount of radioactive nuclides formed in an irradiated target material is often
very low to permit the solubility product of an insoluble compound to be exceeded.
The addition of a chemically identical element (a carrier) in the same chemical form,
allows the solubility product to be exceeded and results in precipitation. An advantage
of this technique is that the amount of material associated with the activity can be
very closely controlled by the addition of the known amount of the carrier.
13.3.1 Carriers for the Separation
In nuclear reactions, other than (n, γ ), the daughter isotope is always a different
chemical species than the parent. Hence, the number of daughter isotope formed
may be of the order of 100–10,000 atoms. Moreover, chemical separation needs
some glassware to carry out the experiment. The radioactive isotope formed during
the nuclear reaction can thus very easily be adsorbed on the surface of glassware,
hence there can be loss of radioactive isotope during chemical maneuvering. In
addition, these atoms may be required to be precipitated or solvent extracted for the
separation. The amount of these radioactive species would be very low to be visible
in precipitation or other techniques. Therefore, the chances of losing the radioactive
atoms become great. However, if after nuclear reactions, the substance is mixed with
an inactive substance (known as carrier) which has the same chemical property as
the tracer, then the radioactive isotope produced in a nuclear reaction is diluted (i.e.,
its specific activity is lowered) and loss due to adsorption etc., during the chemical
separation is minimized.