Speaker
Mr
Cole MacDonald
(University of Ottawa)
Description
During nuclear weapons testing several caesium isotopes were released into the environment. Caesium 137 has been used in many studies. However this isotope has a relatively short half-life (30a) and it has already undergone ~50 years of decay. Caesium 135, another fissile isotope, has a much longer half-life ( about 2Ma) and could be used to replace 137Cs and the ratio between the two isotopes of Cs could be used to identify the source of Cs and to calculate the age of the source material.
However Cs-135 can be very difficult to measure. It cannot be gamma counted, as it is a pure beta emitter and beta counting is an impractical approach due to low decay rate. This leaves mass spectrometry as a viable option. While analyses using TIMS and ICPMS have been established, an analytical technique for accelerator mass spectrometry (AMS) still requires development.
The development of an AMS technique for 135Cs requires the development of (1) a beam of Cs anions, (2) a method to separate 135Cs from 135Ba and other ions with the same mass to charge ratio and (3) production of standards and yield tracers to measure the efficiency of the analytical process.
We have used the IsoTrace AMS facility and: (1) Tested a number of different Cs compounds to identify methods to produce Cs beams, (2) Successfully separated 135Cs from 135Ba using an Isobar Separator for Anions (ISA). This reaction chamber selectively reacts 135Ba with oxygen while allowing 135Cs to pass into the accelerator and (3) Used 134Cs as an internal standard and yield tracer.
Currently, the limitations in the analysis of 135Cs are the beam current and cross contamination during sputtering. An array of different Cs molecules are being tested and optimized for greater and more stable beam currents.
However Cs-135 can be very difficult to measure. It cannot be gamma counted, as it is a pure beta emitter and beta counting is an impractical approach due to low decay rate. This leaves mass spectrometry as a viable option. While analyses using TIMS and ICPMS have been established, an analytical technique for accelerator mass spectrometry (AMS) still requires development.
The development of an AMS technique for 135Cs requires the development of (1) a beam of Cs anions, (2) a method to separate 135Cs from 135Ba and other ions with the same mass to charge ratio and (3) production of standards and yield tracers to measure the efficiency of the analytical process.
We have used the IsoTrace AMS facility and: (1) Tested a number of different Cs compounds to identify methods to produce Cs beams, (2) Successfully separated 135Cs from 135Ba using an Isobar Separator for Anions (ISA). This reaction chamber selectively reacts 135Ba with oxygen while allowing 135Cs to pass into the accelerator and (3) Used 134Cs as an internal standard and yield tracer.
Currently, the limitations in the analysis of 135Cs are the beam current and cross contamination during sputtering. An array of different Cs molecules are being tested and optimized for greater and more stable beam currents.
Primary author
Mr
Cole MacDonald
(University of Ottawa)
Co-authors
Dr
Chris Charles
(University of Ottawa)
Dr
Jack Cornett
(University of Ottawa)
Dr
Liam Kieser
(University of Ottawa)
Dr
Xiaolei Zhao
(University of Ottawa)
