13.8 Activation Analysis
215
out. Hold-back carriers are also added for the other undesirable elements which have
been activated. A similar chemical process is used for the irradiated reference sample.
The comparison of the activities of the separated constituent of the sample with the
reference one can get the amount of the sought element present in the original sample.
13.8.3 Advantages/Disadvantages of This Technique
1. An advantage of this method is that the sensitivity for different elements can be
increased or decreased by a suitable choice of irradiation time.
2. It is highly selective because the choice of the carriers depends upon the element
of the interest and has no effect on any other impurities present in the sample.
However, the efficiency of the process and the purity of the element separated
should always be checked by radiochemical methods.
3. Errors in the determination may be somewhat larger with species of low natural
abundance and where poor counting statistics are obtained. The counting of low
energy particulate radiation is sometimes a problem. There are also cases where
more than one elements in the sample give rise to the same species on irradiation;
for example, Aluminum-27 [by the reaction
27 Al (n, α)
24 Na] and Sodium-23 [by
the reaction
23 Na (n, γ )
24 Na] both give Sodium-24 when irradiated in a reactor,
which makes the determination of traces of sodium in aluminum impracticable
by this method.
4. In the activation analysis, the neutron flux should be as high as possible, otherwise
the activity produced due to a micro-component may be very low and not easy
to detect and measure. This limits the use of ordinary laboratory neutron source,
which usually gives a neutron flux of up to only about 10
5 neutron cm
−2 sec
−1 .
On the other hand, neutron generators based on the following reactions are useful
and give a neutron flux of about 10
9 neutron cm
−2 sec
−1 .
3 H 1 +
2 H 1 −→
4 He 2 +
1 n 0 + 14 MeV
Hence fast as well as slow neutron activation analysis can be carried out. Since
neutron generator can be installed in the laboratory, non-destructive experiments can
be carried out with great precision. However, an adequate shielding of the generator
is essential. In addition, the tritium target material has a short life of about 12 h
and therefore, requires regular charging quite often. Both of these factors make
the neutron generator expensive. Nevertheless, for shorter irradiation work neutron
generators can be used.
215
out. Hold-back carriers are also added for the other undesirable elements which have
been activated. A similar chemical process is used for the irradiated reference sample.
The comparison of the activities of the separated constituent of the sample with the
reference one can get the amount of the sought element present in the original sample.
13.8.3 Advantages/Disadvantages of This Technique
1. An advantage of this method is that the sensitivity for different elements can be
increased or decreased by a suitable choice of irradiation time.
2. It is highly selective because the choice of the carriers depends upon the element
of the interest and has no effect on any other impurities present in the sample.
However, the efficiency of the process and the purity of the element separated
should always be checked by radiochemical methods.
3. Errors in the determination may be somewhat larger with species of low natural
abundance and where poor counting statistics are obtained. The counting of low
energy particulate radiation is sometimes a problem. There are also cases where
more than one elements in the sample give rise to the same species on irradiation;
for example, Aluminum-27 [by the reaction
27 Al (n, α)
24 Na] and Sodium-23 [by
the reaction
23 Na (n, γ )
24 Na] both give Sodium-24 when irradiated in a reactor,
which makes the determination of traces of sodium in aluminum impracticable
by this method.
4. In the activation analysis, the neutron flux should be as high as possible, otherwise
the activity produced due to a micro-component may be very low and not easy
to detect and measure. This limits the use of ordinary laboratory neutron source,
which usually gives a neutron flux of up to only about 10
5 neutron cm
−2 sec
−1 .
On the other hand, neutron generators based on the following reactions are useful
and give a neutron flux of about 10
9 neutron cm
−2 sec
−1 .
3 H 1 +
2 H 1 −→
4 He 2 +
1 n 0 + 14 MeV
Hence fast as well as slow neutron activation analysis can be carried out. Since
neutron generator can be installed in the laboratory, non-destructive experiments can
be carried out with great precision. However, an adequate shielding of the generator
is essential. In addition, the tritium target material has a short life of about 12 h
and therefore, requires regular charging quite often. Both of these factors make
the neutron generator expensive. Nevertheless, for shorter irradiation work neutron
generators can be used.