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Effects of surface coatings on the light collection in plastic scintillators used for radioxenon detection
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
2012 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T150, 014007- p.Article in journal (Refereed) Published
Abstract [en]

Atomic Layer Deposition coatings are under investigation to reduce diffusion of radioxenon into plastic scintillators. This paper investigates the impact of such surface coating on the light collection efficiency in a cylindrical geometry. A high and uniform light collection efficiency is important to preserve detector resolution. Monte Carlo simulations and measurements have been performed to study the influence of coating thickness, refractive index, and surface quality. It was found important to achieve a smooth coating, and a good optical match between the refractive indices of the coating and the plastic scintillator. Taking these considerations into account, the detector under study could be coated without significant degradation of its resolution.

Place, publisher, year, edition, pages
2012. Vol. T150, 014007- p.
Keyword [en]
Scintillator detectors, simulations of optical properties, optical ray tracing, thin films, energy resolution
National Category
Physical Sciences
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
URN: urn:nbn:se:uu:diva-163278DOI: 10.1088/0031-8949/2012/T150/014007ISI: 000309605500008OAI: oai:DiVA.org:uu-163278DiVA: diva2:464091
Available from: 2011-12-12 Created: 2011-12-09 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Surface coatings as xenon diffusion barriers on plastic scintillators: Improving Nuclear-Test-Ban Treaty verification
Open this publication in new window or tab >>Surface coatings as xenon diffusion barriers on plastic scintillators: Improving Nuclear-Test-Ban Treaty verification
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis investigates the ability of transparent surface coatings to reduce xenon diffusion into plastic scintillators. The motivation for the work is improved radioxenon monitoring equipment, used with in the framework of the verification regime of the Comprehensive Nuclear-Test-Ban Treaty.

A large part of the equipment used in this context incorporates plastic scintillators which are in direct contact with the radioactive gas to be detected. One problem with such setup is that radioxenon diffuses into the plastic scintillator material during the measurement, resulting in an unwanted memory effect consisting of residual activity left in the detector.

In this work coatings of Al2O3 and SiO2, with thicknesses between 20 and 400 nm have been deposited onto flat plastic scintillator samples, and tested with respect to their Xe diffusion barrier capabilities. All tested coatings were found to reduce the memory effect, and 425 nm of Al2O3 showed the most promise.

This coating was deposited onto a complete detector. Compared to uncoated detectors, the coated one presented a memory effect reduction of a factor of 1000. Simulations and measurements of the expected light collection efficiency of a coated detector were also performed, since it is important that this property is not degraded by the coating. It was shown that a smooth coating, with a similar refractive index as the one of the plastic, should not significantly affect the light collection and resolution. The resolution of the complete coated detector was also measured, showing a resolution comparable to uncoated detectors. The work conducted in this thesis proved that this coating approach is a viable solution to the memory effect problem, given that the results are reproducible, and that the quality of the coating is maintained over time.

Place, publisher, year, edition, pages
Uppsala: Department of Physics and Astronomy, Uppsala University, 2011. 57 p.
Keyword
Plastic scintillator, Radioxenon, Diffusion barrier, Surface coating, Atomic Layer Deposition, Comprehensive Nuclear-Test-Ban Treaty
National Category
Physical Sciences
Research subject
Physics with specialization in Applied Nuclear Physics; Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-163084 (URN)
Presentation
2011-12-02, 2005, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2011-12-12 Created: 2011-12-07 Last updated: 2012-03-27Bibliographically approved
2. Surface Coatings as Xenon Diffusion Barriers for Improved Detection of Clandestine Nuclear Explosions
Open this publication in new window or tab >>Surface Coatings as Xenon Diffusion Barriers for Improved Detection of Clandestine Nuclear Explosions
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis investigates surface coatings as xenon diffusion barriers on plastic scintillators. The motivation for the work is improved radioxenon detection systems, used within the verification regime of the Comprehensive Nuclear-Test-Ban Treaty (CTBT).

One type of radioxenon detection systems used in this context is the Swedish SAUNA system. This system uses a cylindrical plastic scintillator cell to measure the beta decay from radioxenon isotopes. The detector cell also acts as a container for the xenon sample during the measurement.

One problem with this setup is that part of the xenon sample diffuses into the plastic scintillator material during the measurement, resulting in residual activity left in the detector during subsequent measurements. This residual activity is here referred to as the memory effect.

It is here proposed, and demonstrated, that it is possible to coat the plastic scintillator material with a transparent oxide coating, working as a xenon diffusion barrier. It is found that a 425 nm Al2O3 coating, deposited with Atomic Layer Deposition, reduces the memory effect by a factor of 1000, compared an uncoated detector. Furthermore, simulations show that the coating might also improve the light collection in the detector. Finally, the energy resolution of a coated detector is studied, and no degradation is observed.

The focus of the thesis is measurements of the diffusion barrier properties of Al2O3 films of different thicknesses deposited on plastic scintillators, as well as an evaluation of the expected effect of a coating on the energy resolution of the detector. The latter is studied through light transport simulations. As a final step, a complete coated plastic scintillator cell is evaluated in terms of memory effect, efficiency and energy resolution.

In addition, the xenon diffusion process in the plastic material is studied, and molecular dynamics simulations of the Xe-Al2O3 system are performed in order to investigate the reason for the need for a rather thick coating to significantly reduce the memory effect.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 94 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1111
Keyword
Radioxenon, Gas Diffusion Barrier, Plastic Scintillator, Comprehensive Nuclear-Test-Ban Treaty, Atomic Layer Deposition, Al2O3, Molecular Dynamics, Light Transport
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-215562 (URN)978-91-554-8848-2 (ISBN)
Public defence
2014-02-28, 80121, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2014-02-06 Created: 2014-01-14 Last updated: 2014-02-10

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Bläckberg, LisaKlintenberg, Mattias

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