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| Titel |
Understanding radioxenon isotopical ratios originating from radiopharmaceutical facilities |
| VerfasserIn |
P. R. J. Saey, A. Ringbom, T. W. Bowyer, A. Becker, L.-E. De Geer, M. Nikkinen, R. F. Payne |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250027769
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| Zusammenfassung |
| It was recently shown that radiopharmaceutical facilities (RPF) are major contributors to the
general background of 133Xe and other xenon isotopes both in the northern and southern
hemisphere. To distinguish a nuclear explosion signal from releases from civil nuclear
facilities, not only the activity concentrations but also the ratios of the four different CTBT
relevant radioxenon isotopes (131mXe, 133mXe, 133Xe and 135Xe) have to be well
understood.
First measurements taken recently in and around two of the world’s largest RPF’s:
NTP at Pelindaba, South Africa and IRE at Fleurus, Belgium have been presented.
At both sites, also stack samples were taken in close cooperation with the facility
operators.
The radioxenon in Belgium could be classified in four classes: the normal European
background (133Xe activity between 0 – 5 mBq/m3) on one hand and then the samples where
all four isotopes were detected with 133mXe/131mXe > 1.
In northern South Africa the Pelindaba RPF is in practice the sole source of radioxenon. It
generated a background of 133Xe at the measurement site some 230 km to the west of the
RPF of 0 – 5 mBq/m3. In the cases where the air from the Pelindaba facility reached the
measurement site directly and in a short time period, the 133Xe was higher, also 135Xe was
present and in some samples 133mXe as well.
The ratios of the activity concentrations of 135Xe/133Xe vs. 133mXe/131mXe (Multiple
Isotope Ratio Plot - MIRC) have been analysed. For both facilities, the possible theoretical
ratio’s for different scenarios were calculated with the information available and compared
with the measurements.
It was found that there is an excess of 131mXe present in the European samples compared
to theoretical calculations. A similar excess has also been seen in samples measured in
northern America. In South Africa, neither the environmental samples nor the stack ones
contained 131mXe at measurable levels. This can probably be explained by different
processes and delay lines at the different RPF’s.
From the measurements it can be concluded that probably special 131I production lines
emit more of the daughter nucleus 131mXe and push the 133mXe/131mXe ratios into the area
of the MIRC plot that signifies reactor operation. Thereby it might mask a possible nuclear
explosion signal.
A fresh RFP signal will in many cases be more similar to a nuclear explosion one in a
135Xe/133Xe vs. 133mXe/133Xe plot, as the impact of a possibly anomalous emission history
of 131mXe is here avoided. The thus reduced significance of the isotope 131mXe and its
implication for monitoring the CTBT is discussed.
Disclaimer
The views expressed in this publication is this of the authors and do not necessarily reflect
the views of the CTBTO Preparatory Commission or any of the institutions mentioned
herein.
Acknowledgement
This project is performed in the framework of European Council Joint Action no.
2007/468/CFSP on support for activities of the Preparatory Commission of the
Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO) monitoring and verification
capabilities in the framework of the implementation of the European Union Strategy against
Proliferation of Weapons of Mass Destruction. |
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