| 1. |
- Bläckberg, Lisa, et al.
(författare)
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Assisted self-healing in ripped graphene
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:19, s. 195434-
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Tidskriftsartikel (refereegranskat)abstract
- A monolayer of sp(2)-bonded carbon (graphene) is a material with great technological promise because of, for example, its transport, electrical, optical, and mechanical properties. In this work noble gas diffusion through ripped graphene sheets is explored. The motivation is improved detection systems used worldwide to verify compliance of the Comprehensive Nuclear-Test-Ban Treaty. It is demonstrated that even ripped graphene sheets and/or nonoverlapping graphene flakes inhibit noble gas diffusion. The latter has been shown for He and Xe where an infinitely long rip was constructed to have Stone-Wales edges. It is also shown that the ripped graphene layer self-heal in an alternating pentagon, hexagon, heptagon (5-6-7) and 7-6-5 pattern perpendicular to the rip. Moreover, the noble gas (He and Xe) assists in the healing process of wider rips.
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| 2. |
- Bläckberg, Lisa, et al.
(författare)
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Effects of surface coatings on the light collection in plastic scintillators used for radioxenon detection
- 2012
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T150, s. 014007-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Bläckberg, Lisa, et al.
(författare)
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Investigations of surface coatings to reduce memory effect in plastic scintillator detectors used for radioxenon detection
- 2011
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 656:1, s. 84-91
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Bläckberg, Lisa, 1982-, et al.
(författare)
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Light spread manipulation in scintillators using laser induced optical barriers
- 2018
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Ingår i: IEEE Transactions on Nuclear Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9499 .- 1558-1578. ; 65:8, s. 2208-2215
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Tidskriftsartikel (refereegranskat)abstract
- We are using the Laser Induced Optical Barriers (LIOB) technique to fabricate scintillator detectors with combined performance characteristics of the two standard detector types, mechanically pixelated arrays and monolithic crystals. This is done by incorporation of so-called optical barriers that have a refractive index lower than that of the crystal bulk. Such barriers can redirect the scintillation light and allow for control of the light spread in the detector. Previous work has shown that the LIOB technique has the potential to achieve detectors with high transversal and depth of interaction (DOI) resolution simultaneously in a single-side readout configuration, suitable for high resolution PET imaging. However, all designs studied thus far present edge effect issues similarly as in the standard detector categories. In this work we take advantage of the inherent flexibility of the LIOB technique and investigate alternative barrier patterns with the aim to address this problem. Light transport simulations of barrier patterns in LYSO:Ce, with deeper barrier walls moving towards the detector edge show great promise in reducing the edge effect, however there is a trade-off in terms of achievable DOI information. Furthermore, fabrication and characterization of a 20 mm thick LYSO:Ce detector with optical barriers forming a pattern of 1×1×20mm3 pixel like structures show that light channeling in laser-processed detectors in agreement with optical barriers with refractive index between 1.2 and 1.4 is achievable.
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| 5. |
- Bläckberg, Lisa, et al.
(författare)
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Measurements of memory effect and resolution for an Al2O3 coated plastic scintillator used for radioxenon detection
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 6. |
- Bläckberg, Lisa, et al.
(författare)
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Memory effect, resolution, and efficiency measurements of an Al2O3 coated plastic scintillator used for radioxenon detection
- 2013
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 714, s. 128-135
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Tidskriftsartikel (refereegranskat)abstract
- 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 with the coated detector show both energy resolution and efficiency comparable to uncoated detectors, and a memory effect reduction of a factor of 1000. Provided that the quality of the detector is maintained for a longer period of time, Al2O3 coatings are believed to be a viable solution to the memory effect problem in question.
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| 7. |
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| 8. |
- Bläckberg, Lisa, 1982-, et al.
(författare)
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Scintillator-based Photon Counting Detector : is it feasible?
- 2016
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Ingår i: 2016 IEEE Nuclear Science Symposium, Medical Imaging Conference And Room-Temperature Semiconductor Detector Workshop (Nss/Mic/Rtsd). - 9781509016426 - 9781509016433
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Konferensbidrag (refereegranskat)abstract
- By utilizing finely pitched scintillator arrays where the scintillator has high atomic number and density, fast decay time, and high light output, realizing a scintillator-based Photon Counting Detector (PCD) is conceptually feasible. Fabrication of fine-pitched scintillator arrays however, has been the bottleneck for realizing such detectors. Combining the novel scintillator fabrication technique called laser-induced optical barriers (LIOB) where optical barriers can be placed inside a transparent crystal and act as a reflector without removing the material, with laser ablation, we are now able to overcome the obstacles for developing scintillator-based PCD. In this regard, we are developing an LYSO-based PCD where the LYSO crystal is laser pixelated to sub-mm pixels. The scintillator array will be coupled to an application specific integrated circuit (ASIC) where each ASIC pixel has built-in photodiode, amplifiers and 3-4 energy windows and their associated counters. We have simulated light transport for different scenarios where the crystal is pixelated by a combination of LIOB and laser cut techniques, where the 2 mm thick crystal is first pixelated by LIOB to a depth and then the rest is pixelated by the ablation technique. We also simulated the fraction of collected light in the same scintillator pixel by modeling various surface properties of the pixel cuts as well as optical barrier surface roughness and refractive index (RI). Simulation results show that up to similar to 70% of the scintillation light will be contained in the same pixel when only using the LIOB technique with barrier refractive index of 1.0. These results suggest that laser processed arrays can potentially change the paradigm in PCD development as they can replace the traditional array production and thus allow for scintillator-based PCD development in a more robust and cost-effective manner.
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| 9. |
- Bläckberg, Lisa, 1982-, et al.
(författare)
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Simulation study of light transport in laser-processed LYSO:Ce detectors with single-side readout
- 2017
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 62:21, s. 8419-8440
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Tidskriftsartikel (refereegranskat)abstract
- A tightly focused pulsed laser beam can locally modify the crystal structure inside the bulk of a scintillator. The result is incorporation of so-called optical barriers with a refractive index different from that of the crystal bulk, that can be used to redirect the scintillation light and control the light spread in the detector. We here systematically study the scintillation light transport in detectors fabricated using the laser induced optical barrier technique, and objectively compare their potential performance characteristics with those of the two mainstream detector types: monolithic and mechanically pixelated arrays. Among countless optical barrier patterns, we explore barriers arranged in a pixel-like pattern extending all-the-way or half-way through a 20 mm thick LYSO:Ce crystal. We analyze the performance of the detectors coupled to MPPC arrays, in terms of light response functions, flood maps, line profiles, and light collection efficiency. Our results show that laser-processed detectors with both barrier patterns constitute a new detector category with a behavior between that of the two standard detector types. Results show that when the barrier-crystal interface is smooth, no DOI information can be obtained regardless of barrier refractive index (RI). However, with a rough barrier-crystal interface we can extract multiple levels of DOI. Lower barrier RI results in larger light confinement, leading to better transverse resolution. Furthermore we see that the laser-processed crystals have the potential to increase the light collection efficiency, which could lead to improved energy resolution and potentially better timing resolution due to higher signals. For a laser-processed detector with smooth barrier-crystal interfaces the light collection efficiency is simulated to >42%, and for rough interfaces >73%. The corresponding numbers for a monolithic crystal is 39% with polished surfaces, and 71% with rough surfaces, and for a mechanically pixelated array 35% with polished pixel surfaces and 59% with rough surfaces.
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| 10. |
- Bläckberg, Lisa, 1982-, et al.
(författare)
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Simulation Study of Partially Laser-Processed LYSO:Ce with Single-Side Readout
- 2017
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Ingår i: 2017 IEEE Nuclear Science Symposium And Medical Imaging Conference (NSS/MIC). - 9781538622827
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Konferensbidrag (refereegranskat)abstract
- Laser Induced Optical Barriers (LIOB) can be used to locally engineer the refractive index of a scintillator crystal, leading to the incorporation of so-called optical barriers. Given that the optical barriers may be placed in virtually any pattern inside the scintillator, light transport simulations are important tools for pattern optimization for a given end-application. In this work we simulate the light spread in a 20 mm thick LYSO:Ce detector with optical barriers in a pixel-like pattern half way through its thickness, read out by a photodetector array on one side. We compare the detector performance in terms of DOI and transversal resolution, depending on which side of the detector is chosen for light extraction. Our results show that reading the detector from the laser-processed side yields higher DOI resolution, at the expense of XY resolution, compared to the opposite configuration.
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