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10 Identification of Radioactive Isotopes
Alternatively, the absorption curve of various β-particles of known but different
energies can be taken by the method described earlier. Accordingly, their corresponding R max can be calculated by either of the methods described earlier. From these
results, a calibration graph between the experimentally determined R max and its corresponding E max energy (taken from standard table of isotopes) can be plotted, which
then be used to determine the E max from experimentally determined R max value of a
radioactive isotope.
10.5 Determination of Energy of α-Particles or γ -Rays
Energy of α-particles and γ -rays being monochromatic can be very easily determined by observing their energy spectrum with the help of the pulse-height analyzer.
Measurement of activity is determined either by a gas-flow proportional counter or
a scintillation counter, details of which are discussed in the previous chapters. For
γ -rays, one can take help of absorption curve technique (Sect. 10.4), as well as to
evaluate the energy of γ -ray.
However, there will be a need to calibrate the pulse height- analyzer in terms
of energy (MeV), so that the peak position of either α-particles and γ -rays can be
assigned appropriate energy in terms of MeV. This is done by taking the spectra of
α-particles and γ -rays of known energy and the peak position of the spectra is plotted
against their corresponding energy. These calibration graphs would be valid for the
set conditions under which spectra were taken. Once the conditions are changed, the
calibration curve becomes invalid.
10.6 Photographic Emulsion Technique
In a few special cases, photographic emulsion can also be a useful technique to
determine the energy of α-particles from the α-tracks (i.e., distance traveled by αparticles over a photographic film/plate in lateral direction).
In this technique, a photographic plate is either impregnated with a radioactive
solution and allowed to stand for some time or a solid source is kept over a photographic plate for a certain period (depending on the energy, activity, and half-life
of the source) before developing. The photographic film/plate is then developed
and washed. On developing, small grains with several tails (known as α-tracks) are
observed. By comparing the length of a track with a standard α-track obtained with
α-particle of known energy, the energy of unknown α-particle can be determined.
Careful and uniform processing of the exposed film is an important part of the emulsion technique. Unless properly carried out, this technique may lead to serious errors
or loss of significant results.
10 Identification of Radioactive Isotopes
Alternatively, the absorption curve of various β-particles of known but different
energies can be taken by the method described earlier. Accordingly, their corresponding R max can be calculated by either of the methods described earlier. From these
results, a calibration graph between the experimentally determined R max and its corresponding E max energy (taken from standard table of isotopes) can be plotted, which
then be used to determine the E max from experimentally determined R max value of a
radioactive isotope.
10.5 Determination of Energy of α-Particles or γ -Rays
Energy of α-particles and γ -rays being monochromatic can be very easily determined by observing their energy spectrum with the help of the pulse-height analyzer.
Measurement of activity is determined either by a gas-flow proportional counter or
a scintillation counter, details of which are discussed in the previous chapters. For
γ -rays, one can take help of absorption curve technique (Sect. 10.4), as well as to
evaluate the energy of γ -ray.
However, there will be a need to calibrate the pulse height- analyzer in terms
of energy (MeV), so that the peak position of either α-particles and γ -rays can be
assigned appropriate energy in terms of MeV. This is done by taking the spectra of
α-particles and γ -rays of known energy and the peak position of the spectra is plotted
against their corresponding energy. These calibration graphs would be valid for the
set conditions under which spectra were taken. Once the conditions are changed, the
calibration curve becomes invalid.
10.6 Photographic Emulsion Technique
In a few special cases, photographic emulsion can also be a useful technique to
determine the energy of α-particles from the α-tracks (i.e., distance traveled by αparticles over a photographic film/plate in lateral direction).
In this technique, a photographic plate is either impregnated with a radioactive
solution and allowed to stand for some time or a solid source is kept over a photographic plate for a certain period (depending on the energy, activity, and half-life
of the source) before developing. The photographic film/plate is then developed
and washed. On developing, small grains with several tails (known as α-tracks) are
observed. By comparing the length of a track with a standard α-track obtained with
α-particle of known energy, the energy of unknown α-particle can be determined.
Careful and uniform processing of the exposed film is an important part of the emulsion technique. Unless properly carried out, this technique may lead to serious errors
or loss of significant results.