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Surface coatings as xenon diffusion barriers on plastic scintillators: Improving Nuclear-Test-Ban Treaty verification
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.
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 [en]
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: urn:nbn:se:uu:diva-163084OAI: oai:DiVA.org:uu-163084DiVA: diva2:464100
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
List of papers
1. Investigations of surface coatings to reduce memory effect in plastic scintillator detectors used for radioxenon detection
Open this publication in new window or tab >>Investigations of surface coatings to reduce memory effect in plastic scintillator detectors used for radioxenon detection
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2011 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 656, no 1, 84-91 p.Article in journal (Refereed) Published
Abstract [en]

In this work Al(2)O(3) and SiO(2) coatings are tested as Xe diffusion barriers on plastic scintillator substrates. The motivation is improved beta-gamma coincidence detection systems, used to measure atmospheric radioxenon within the verification regime of the Comprehensive Nuclear-Test-Ban Treaty. One major drawback with the current setup of these systems is that the radioxenon tends to diffuse into the plastic scintillator material responsible for the beta detection, resulting in an unwanted memory effect. Here, coatings with thicknesses between 20 and 900 nm have been deposited onto plastic scintillators, and investigated using two different experimental techniques. The results show that all tested coatings reduce the Xe diffusion into the plastic. The reduction is observed to increase with coating thickness for both coating materials. The 425 nm Al(2)O(3) coating is the most successful one, presenting a diffusion reduction of a factor 100, compared to uncoated plastic. In terms of memory effect reduction this coating is thus a viable solution to the problem in question.

Keyword
Radioxenon, Gas diffusion barrier, Plastic scintillator, Comprehensive Nuclear-Test-Ban Treaty, Atomic layer deposition, Plasma enhanced chemical vapor deposition
National Category
Natural Sciences Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-161431 (URN)10.1016/j.nima.2011.07.038 (DOI)000296129100011 ()
Available from: 2011-11-16 Created: 2011-11-14 Last updated: 2017-12-08Bibliographically approved
2. Effects of surface coatings on the light collection in plastic scintillators used for radioxenon detection
Open this publication in new window or tab >>Effects of surface coatings on the light collection in plastic scintillators used for radioxenon detection
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.

Keyword
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:nbn:se:uu:diva-163278 (URN)10.1088/0031-8949/2012/T150/014007 (DOI)000309605500008 ()
Available from: 2011-12-12 Created: 2011-12-09 Last updated: 2017-12-08Bibliographically approved
3. Measurements of memory effect and resolution for an Al2O3 coated plastic scintillator used for radioxenon detection
Open this publication in new window or tab >>Measurements of memory effect and resolution for an Al2O3 coated plastic scintillator used for radioxenon detection
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

A cylindrical plastic scintillator cell, used for radioxenon monitoring within the verification regime of the Comprehensive Nuclear-Test-Ban Treaty, has been coated with 425 nm Al2O3 using low temperature Atomic Layer Deposition, and its performance has been evaluated. The motivation is to reduce the memory effect caused by radioxenon diffusing into the plastic scintillator material during measurements, resulting in an elevated detection limit. Measurements of the coated detector show a resolution comparable to uncoated detectors, and a memory effect reduction of a factor of 1000. If these results are reproducible, and the quality of the detector is maintained for a longer period of time, the Al2O3 coating method is believed to be viable solution to the memory effect problem in question.

Keyword
Plastic scintillator, Comprehensive Nuclear-Test Ban Treaty, Atomic Layer Deposition, Al2O3, Diffusion barrier, Radioxenon, Energy Resolution
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-163280 (URN)
Available from: 2011-12-12 Created: 2011-12-09 Last updated: 2012-04-03

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