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| Titel |
Evaluation of environmental radioxenon isotopical signals from a singular large source emitter |
| VerfasserIn |
P. R. J. Saey, T. W. Bowyer, M. Aldener, A. Becker, M. W. Cooper, K. Elmgren, A. Faanhof, J. C. Hayes, B. Hosticka, L. S. Lidey |
| 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 |
250027536
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| Zusammenfassung |
| Abstract
In the framework of the verification of the Comprehensive Nuclear-Test-Ban
Treaty (CTBT) the atmospheric background of environmental radioxenon is been
studied near areas that could be affected by man-made sources. It was recently shown
that radiopharmaceutical facilities (RPF) make a major contribution to the general
background of 133Xe and other xenon isotopes both in the northern and southern
hemisphere. The daily IMS noble gas measurements around the globe are influenced from
such anthropogenic sources that could mask radioxenon signals from a nuclear
explosion.
To distinguish a nuclear explosion signal from releases from civil nuclear facilities, not
only the activity concentration but also the ratio of different radioxenon isotopes (131mXe,
133mXe, 133Xe and 135Xe) plays a crucial role, since the ratios can be used to discriminate
source types.
Theoretical release and ratio studies were recently published, but no measurements close
to radiopharmaceutical facilities have ever been performed.
The world’s fourth largest radiopharmaceutical facility, NTP Radioisotopes Ltd, is located
in Pelindaba, South Africa. Other than a small nuclear power plant, located 1300 km
southwest, near Cape Town and a small research reactor in the DR of Congo, located 2700
km northwest, this is the only facility that is known to emit any radioxenon on the African
continent south of the Equator. This source is likely very dominant with respect to xenon
emission. This makes it a point source, which is a unique situation, as all other worldwide
large radiopharmaceutical facilities are situated in regions surrounded by many other nuclear
facilities.
Between 10 November and 22 December 2008, radioxenon was measured continuously
with a radioactive xenon measurement system, at the North-West University, Mafikeng, South
Africa, which is situated 250 km northwest of Pelindaba. Fifty-six 12-hour samples were
measured with a beta-gamma coincidence detector, of which 55 contained 133Xe with values
between 0.11 and 27.1 mBq/m3. Eleven samples contained 135Xe and three samples
133mXe. It is furthermore worth mentioning that none of the samples contained
131mXe.
In parallel, stack samples were taken at the NTP facility on an almost daily basis and
measured with a high purity germanium gamma detector nearby at a local laboratory of
NECSA. These stack measurements correspond to a daily release of around 1-10 TBq. This is
consistent with typical release rates published for this type of facility and well below
exposure guidelines thus not dangerous to the public. On the other hand it is expected to be
high enough to increase the radioxenon background in wide regions around such facilities and
has a potential impact on the monitoring capability of the highly sensitive CTBT xenon
monitoring systems.
This paper will report on the activities measured at the facility stack and in Mafikeng,
which allows for analysis and comparison with activity predictions based on atmospheric
transport modelling. Finally the activity ratios measured shall be discussed in view
of their implication for the xenon monitoring capability of the CTBT verification
regime.
Disclaimer
The views expressed in this publication are those of the authors and do not necessarily
reflect the views of the CTBTO Preparatory Commission or any of the institutions mentioned
herein.
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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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