7.7 Nuclear Emulsion Techniques
131
7.7.3 Emulsion Radio Chromatography
An emulsion technique usually known as “Autoradiography” is used in paper chromatography or paper electrophoresis, to locate the separated constituents from a
mixture of radioactive substances and to measure the relative intensity of radiation
present at each constituent. This is achieved by the following procedures.
7.7.3.1 Experimental Procedure for Autoradiography
In this technique, the solution which is to be analyzed or separated is placed on a sheet
of a long filter paper (about 6 in. or longer) in the form of a small spot near one end
of the paper (leaving about 1 in. space from the bottom of the paper). Then the paper
is dried slowly and hanged in a glass jar containing a suitable solvent. The height of
the paper is adjusted such that the solvent touches the bottom of the paper only. Care
has to be taken to ensure that the paper does not move. The solvent is allowed to pass
lengthwise through the paper. Various components of the original mixture move with
the solvent, but at different speeds. After the solvent has moved a sufficient distance,
the paper is dried (e.g., by an infrared lamp). In order to recognize the position of
the original spot and the solvent front, a fresh spot of the radioactive mixture is put
at the original spot, and a line is drawn with the radioactive mixture to mark the
solvent front. For illustrating this procedure, the following experiment was carried
out. A solution containing NaBr and KBr was irradiated in a thermal nuclear reactor.
This mixture was separated by paper chromatography by adopting the procedure as
discussed previously. A solution containing HCl in methanol (1 : 1 v/v) was used as
a solvent to separate the mixture. Location of the constituents (including the solvent
front and position of the original spot) were found by using any of the methods
discussed here:
1. The paper chromatogram was counted by scanning a G.M. counter and count rate
was recorded over a strip chart recorder (Fig. 7.5). This graph shows the positions
of radioactive materials separated at different places on the paper chromatogram.
2. The paper chromatogram was exposed overnight on an X -ray film. This film was
developed and printed (Fig. 7.6a). The photograph was used to calculate the R f
factor, as positions of original spot and solvent front were visible in the print.
3. In another experiment, 11 layers of X -ray films were kept one over other on
the paper chromatogram. This was then exposed overnight. The top (i.e., 11th
layer) X -ray film (Ilford industrial G) was developed and its print was taken
(Fig. 7.6b). This photograph gives an idea about the relative penetrating power
of the radiations emitted by radioactive nuclides present in the mixture. It can be
seen that except for β-radiation emitted by
24 Na, all other radiations emitted by
other isotopes have been able to penetrate 11 layers of the X -ray films.
The R f values obtained from paper chromatogram by G.M. counter and from
X -ray films as well as the energy of radiations emitted by these isotopes are shown
in Table 7.2.
131
7.7.3 Emulsion Radio Chromatography
An emulsion technique usually known as “Autoradiography” is used in paper chromatography or paper electrophoresis, to locate the separated constituents from a
mixture of radioactive substances and to measure the relative intensity of radiation
present at each constituent. This is achieved by the following procedures.
7.7.3.1 Experimental Procedure for Autoradiography
In this technique, the solution which is to be analyzed or separated is placed on a sheet
of a long filter paper (about 6 in. or longer) in the form of a small spot near one end
of the paper (leaving about 1 in. space from the bottom of the paper). Then the paper
is dried slowly and hanged in a glass jar containing a suitable solvent. The height of
the paper is adjusted such that the solvent touches the bottom of the paper only. Care
has to be taken to ensure that the paper does not move. The solvent is allowed to pass
lengthwise through the paper. Various components of the original mixture move with
the solvent, but at different speeds. After the solvent has moved a sufficient distance,
the paper is dried (e.g., by an infrared lamp). In order to recognize the position of
the original spot and the solvent front, a fresh spot of the radioactive mixture is put
at the original spot, and a line is drawn with the radioactive mixture to mark the
solvent front. For illustrating this procedure, the following experiment was carried
out. A solution containing NaBr and KBr was irradiated in a thermal nuclear reactor.
This mixture was separated by paper chromatography by adopting the procedure as
discussed previously. A solution containing HCl in methanol (1 : 1 v/v) was used as
a solvent to separate the mixture. Location of the constituents (including the solvent
front and position of the original spot) were found by using any of the methods
discussed here:
1. The paper chromatogram was counted by scanning a G.M. counter and count rate
was recorded over a strip chart recorder (Fig. 7.5). This graph shows the positions
of radioactive materials separated at different places on the paper chromatogram.
2. The paper chromatogram was exposed overnight on an X -ray film. This film was
developed and printed (Fig. 7.6a). The photograph was used to calculate the R f
factor, as positions of original spot and solvent front were visible in the print.
3. In another experiment, 11 layers of X -ray films were kept one over other on
the paper chromatogram. This was then exposed overnight. The top (i.e., 11th
layer) X -ray film (Ilford industrial G) was developed and its print was taken
(Fig. 7.6b). This photograph gives an idea about the relative penetrating power
of the radiations emitted by radioactive nuclides present in the mixture. It can be
seen that except for β-radiation emitted by
24 Na, all other radiations emitted by
other isotopes have been able to penetrate 11 layers of the X -ray films.
The R f values obtained from paper chromatogram by G.M. counter and from
X -ray films as well as the energy of radiations emitted by these isotopes are shown
in Table 7.2.