706
M. Dohlus et al.
11.2.4 Accelerator Mass Spectroscopy
Many methods and also facilities which were developed for solving basic scientific
questions have also found their way into the applications. One of these methods
is the Accelerator Mass Spectrometry (AMS). It was developed for the measuring
of very small ratios of radioisotopes to stable isotope concentrations by detecting
atoms, rather than by detecting their radioactive decay. The samples which contain
the isotopes under investigation are incorporated in the ion source either in gaseous
form or as solid material in a sputter source. One characteristic isotope is 14 C,
which has a half life of 5760 years, and is used for age determination in many
organic substances. Trees, e.g., incorporate also 14 C as long as they live. From
the analysis of the amount of remaining 14 C the age of a piece of wood can be
determined.
Tracing the radioactivity in organic substances can also determine e.g.
metabolism or the paths of drugs and medicine. By measuring the concentration
of the parent ions in beams, rather than their detecting radioactive decay products,
AMS can determine values within the low 10 −16 range for the ratio of 14 C/ 12 C.
The accuracy is of the order of 0.3%. The measurements need much less time
than detecting the radioactive decay products, an important factor in industrial
application.
For industrial applications particularly compact instruments have been developed
[42, 43].
As example—in Fig. 11.22 the installation of VERA (Vienna Environmental
Research Accelerator) [42]—as a quite universal installation is shown. In this
installation the measurement of negative as well as positive ions is possible.
Particularly for the detection of 14 C the measurement of negative ions is important.
The mass difference of 14 C and 14 N is so small that a magnetic separation of both
is impossible, but since nitrogen forms no negatively charged ions 14 C appears as a
very pure line in the spectrum.
Therefore the detection of 14 C allows the analysis of pharmaceuticals which is
one of the dominant industrial applications of AMS.
11.2.5 Conclusion
The present experience has shown that accelerators with energies below 100 MeV
fulfill the needs of industrial applications because electron and ion beams can steer
fabrication processes in much smaller areas compared to conventional methods.
Particularly the well-defined energies and doses are essential for tailoring layered
structures in some cases also with isolating layers.
M. Dohlus et al.
11.2.4 Accelerator Mass Spectroscopy
Many methods and also facilities which were developed for solving basic scientific
questions have also found their way into the applications. One of these methods
is the Accelerator Mass Spectrometry (AMS). It was developed for the measuring
of very small ratios of radioisotopes to stable isotope concentrations by detecting
atoms, rather than by detecting their radioactive decay. The samples which contain
the isotopes under investigation are incorporated in the ion source either in gaseous
form or as solid material in a sputter source. One characteristic isotope is 14 C,
which has a half life of 5760 years, and is used for age determination in many
organic substances. Trees, e.g., incorporate also 14 C as long as they live. From
the analysis of the amount of remaining 14 C the age of a piece of wood can be
determined.
Tracing the radioactivity in organic substances can also determine e.g.
metabolism or the paths of drugs and medicine. By measuring the concentration
of the parent ions in beams, rather than their detecting radioactive decay products,
AMS can determine values within the low 10 −16 range for the ratio of 14 C/ 12 C.
The accuracy is of the order of 0.3%. The measurements need much less time
than detecting the radioactive decay products, an important factor in industrial
application.
For industrial applications particularly compact instruments have been developed
[42, 43].
As example—in Fig. 11.22 the installation of VERA (Vienna Environmental
Research Accelerator) [42]—as a quite universal installation is shown. In this
installation the measurement of negative as well as positive ions is possible.
Particularly for the detection of 14 C the measurement of negative ions is important.
The mass difference of 14 C and 14 N is so small that a magnetic separation of both
is impossible, but since nitrogen forms no negatively charged ions 14 C appears as a
very pure line in the spectrum.
Therefore the detection of 14 C allows the analysis of pharmaceuticals which is
one of the dominant industrial applications of AMS.
11.2.5 Conclusion
The present experience has shown that accelerators with energies below 100 MeV
fulfill the needs of industrial applications because electron and ion beams can steer
fabrication processes in much smaller areas compared to conventional methods.
Particularly the well-defined energies and doses are essential for tailoring layered
structures in some cases also with isolating layers.