Browsing by Author "Veenhof, Robert J."

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Charge transfer properties through graphene for applications in gaseous detectors
(Elsevier, 2016-07-11) Franchino, S.; Gonzalez-Diaz, Diego; Hall-Wilton, Richard; Jackman, Richard; Muller, H.; Nguyen, T. T.; de Oliveira, R.; Oliveri, Eraldo; Pfeiffer, Dorothea; Resnati, F.; Ropelewski, L.; Smith, Joe; van Stenis, M.; Streli, Christina; Thuiner, P.; Veenhof, Robert J.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 6603742499
Graphene is a single layer of carbon atoms arranged in a honeycomb lattice with remarkable mechanical and electrical properties. Regarded as the thinnest and narrowest conductive mesh, it has drastically different transmission behaviours when bombarded with electrons and ions in vacuum. This property, if confirmed in gas, may be a definitive solution for the ion back-flow problem in gaseous detectors. In order to ascertain this aspect, graphene layers of dimensions of about 2 x 2 cm(2), grown on a copper substrate, are transferred onto a flat metal surface with holes, so that the graphene layer is freely suspended. The graphene and the support are installed into a gaseous detector equipped with a triple Gaseous Electron Multiplier (GEM), and the transparency properties to electrons and ions are studied in gas as a function of the electric fields. The techniques to produce the graphene samples are described, and we report on preliminary tests of graphene-coated GEMs.
Charge transfer properties through graphene layers in gas detectors
(IEEE, 2014) Thuiner, Patrik; Hall-Wilton, Richard John; Jackman, Richard B.; Müller, Hans; Nguyen, Thuong Thuong; Oliveri, Eraldo; Pfeiffer, Dorothea Andreas; Resnati, Filippo; Ropelewski, Leszek; Smith, J. A.; Van Stenis, Miranda; Veenhof, Robert J.; Uludağ Üniversitesi/Fen Edebiyat Fakültesi/Fizik Bölümü.
Graphene is a single layer of carbon atoms arranged in a honeycomb lattice with remarkable mechanical, electrical and optical properties. For the first time graphene layers suspended on copper meshes were installed into a gas detector equipped with a gaseous electron multiplier. Measurements of low energy electron and ion transfer through graphene were conducted. In this paper we describe the sample preparation for suspended graphene layers, the testing procedures and we discuss the preliminary results followed by a prospect of further applications.
A dynamic method for charging-up calculations: The case of GEM
(IOP Publishing, 2014-06-26) Correia, Pedro M. M.; Oliveira, Carlos A. B.; Azevedo, C. D. R.; Silva, Ana Luísa M.; Nemallapudi, Mythra Varun; Veloso, J. F. C. A.; Veenhof, Robert J.; Uludağ Üniversitesi/Fen Edebiyat Fakültesi/Fizik Bölümü.; 6603742499
The simulation of Micro Pattern Gaseous Detectors (MPGDs) signal response is an important and powerful tool for the design and optimization of such detectors. However, several attempts to exactly simulate the effective gas gain have not been completely successful. Namely, the gain stability over time has not been fully understood. Charging-up of the insulator surfaces have been pointed as one of the responsible for the difference between experimental and Monte Carlo results. This work describes two iterative methods to simulate the charging-up in one MPGD device, the Gas Electron Multiplier (GEM). The first method, which uses a constant step size for avalanches time evolution, is very detailed but slow to compute. The second method instead uses a dynamic step-size that improves the computing time. Good agreement between both methods was achieved. Comparison with experimental results shows that charging-up plays an important role in detectors operation, explaining the time evolution of the gain. However it doesn't seem to be the only responsible for the difference between measurements and Monte Carlo simulations.
Experimental ion mobility measurements for the LCTPC collaboration - Ar-CF4 mixtures
(IOP Publishing, 2018-03-28) Santos, M. A.G.; Kaja, Magdalena A.; Cortez, André F.V.; Neves, Pedro N.B.; Santos, Filomena P.; Borges, F. I.G.M.; Conde, Carlos A.N.; Veenhof, Robert J.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 6603742499
In this paper we present the results of the ion mobility measurements made in pure carbon tetrafluoride (CF4) and gaseous mixtures of argon with carbon tetrafluoride (Ar-CF4) for pressures ranging from 6 to 10 Torr (8-10.6 mbar) and for low reduced electric fields in the 10 Td to 25 Td range (2.4-6.1 kV center dot cm(-1)center dot bar(-1)), at room temperature. The time of arrival spectra revealed only one peak throughout the entire range studied which was attributed to CF3+. However, for Ar concentrations above 70%, a bump starts to appear at the left side of the main peak for reduced electric fields higher than 15 Td, which was attributed to impurities. The reduced mobilities obtained from the peak centroid of the time-of-arrival spectra are presented for Ar concentrations in the 5%-95% range.
Experimental ion mobility measurements in Ar-N2
(IOP Publishing Ltd, 2018-10-12) Santos, M. A.G.; Cortez, André F.V.; Perdigoto, J. M.C.; Escada, J.; Neves, P. N. B.; Santos, F. P.; Conde, C. A. N.; Borges, F. I. G. M.; Veenhof, Robert J.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 6603742499
Data on ion mobility is important to improve the performance of large volume gaseous detectors, since the detector signal can be influenced by the drift of the ions, namely in the cases where charge multiplication is used, for example in Multi-Wire Proportional Chambers (MWPCs) and in some Time Projection Chambers (TPCs). In the present work the results for the ion mobility measurements in Ar-N-2 mixtures are presented, using an experimental setup and method already tested in previous work. The results for this mixture show the presence of only one peak for all gas ratios of Ar-N-2, for reduced electric fields, E/N, in the range of 10-25 Td (2.4-6.1 kV.cm(-1).bar(-1)), and 8 Torr (10.6 mbar) pressure, at room temperature.
Experimental Ion Mobility measurements in Ne-CO2 and CO2-N-2 mixtures
(IOP Publishing, 2016-04-27) Encarnaçao, Pedro M.C.C.; Cortez, André F.V.; Neves, Pedro N.B.; Santos, Filomena P.; Trindade, Alexandre M.F.; Borges, F. I.G.M.; Conde, Carlos A.N.; Veenhof, Robert J.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 6603742499
In this paper we present the experimental results for the mobility, K-0, of ions in neon-carbon dioxide (Ne-CO2) and carbon dioxide-nitrogen (CO2-N-2) gaseous mixtures for total pressures ranging from 8-12 Torr, reduced electric fields in the 10-25 Td range, at room temperature. Regarding the Ne-CO2 mixture only one peak was observed for CO2 concentrations above 25%, which has been identified as an ion originated in CO2, while below 25% of CO2 a second-small peak appears at the left side of the main peak, which has been attributed to impurities. The mobility values for the main peak range between 3.51 +/- 0.05 and 1.07 +/- 0.01 cm(2)V(-1)s(-1) in the 10%-99% interval of CO2, and from 4.61 +/- 0.19 to 3.00 +/- 0.09 cm(2)V(-1)s(-1) for the second peak observed (10%-25% of CO2). For the CO2-N-2, the time-of-arrival spectra displayed only one peak for CO2 concentrations above 10%, which was attributed to ions originated in CO2, namely CO2+ (CO2), with a second peak appearing for CO2 concentrations below 10%. This second peak, with higher mobility, was attributed to CO2+ ions. The mobility values of the main peak range between 2.11 +/- 0.04 and 1.10 +/- 0.03 cm(2)V(-1)s(-1) in the 1%-99% interval of CO2, while the second peak's from 2.26 +/- 0.02 and 1.95 +/- 0.04 cm(2)V(-1)s(-1) (1%-10% of CO2). The inverse of the mobility displays an aproximately linear dependence on the CO2 concentration in the mixture.
Experimental ion mobility measurements in Ne-N-2
(IOP Publishing, 2016-11-21) Cortez, Andre F. V.; Encarnacao, Pedro M. C. C.; Neves, Priscilla Natalie B.; Santos, Filomena P.; Borges, Filipa I. G. M.; Conde, Carlos A. N.; Veenhof, Robert J.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 6603742499
Data on ion mobility is important to improve the performance of large volume gaseous detectors, such as the ALICE TPC or in the NEXT experiment. In the present work the method, experimental setup and results for the ion mobility measurements inNe-N-2 mixtures are presented. The results for this mixture show the presence of two peaks for different gas ratios of Ne-N-2, low reduced electric fields, E/N, 10-20 Td (2.4-4.8 kV.cm (-1).bar (-1)), low pressures 6-8 Torr (8-10.6 mbar) and at room temperature.
Experimental ion mobility measurements in Xe-C2H6
(IOP Publishing, 2017-09-26) Perdigoto, J. M.C.; Cortez, A.F.V.; Neves, P.N.B.; Santos, F.P.; Borges, F.I.G.M.; Conde, C.A.N.; Veenhof, Robert J.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 6603742499
In this paper we present the results of the ion mobility measurements made in gaseous mixtures of xenon (Xe) with ethane (C2H6) for pressures ranging from 6 to 10 Torr (8-10.6 mbar) and for low reduced electric fields in the 10 Td to 25 Td range (2.4-6.1 kV.cm(-1) . bar(-1)), at room temperature. The time of arrival spectra revealed two peaks throughout the entire range studied which were attributed to ion species with 3-carbons (C3H5+, C3H6+ C3H8+ and C3H9+) and with 4-carbons (C4H7+, C4H9+ and C4H10+). Besides these, and for Xe concentrations above 70%, a bump starts to appear at the right side of the main peak for reduced electric fields higher than 20 Td, which was attributed to the resonant charge transfer of C2H6+ to C2H6 that affects the mobility of its ion products (C3H8+ and C3H9+). The time of arrival spectra for Xe concentrations of 20%, 50%, 70% and 90% are presented, together with the reduced mobilities as a function of the Xe concentration calculated from the peaks observed for the low reduced electric fields and pressures studied.
Experimental ion mobility measurements in Xe-CF4 mixtures
(IOP Publishing, 2018-04) Cortez, André F.V.; Kaja, Magdalena A.; Escada, J. M.D.; Santos, M. A.G.; Neves, Pedro N.B.; Santos, Filomena P.; Borges, F. I.G.M.; Conde, Carlos A.N.; Veenhof, Robert J.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 6603742499
In this paper we present the results of the ion mobility measurements made in gaseous mixtures of xenon with carbon tetrafluoride (Xe-CF4) for pressures ranging from 6 to 10 Torr (8-10.6 mbar) and for low reduced electric fields in the 10 to 25 Td range (2.4-6.1 kV.cm(-1).bar(-1)), at room temperature. The time-of-arrival spectra revealed one or two peaks depending on the gas relative abundances, which were attributed to CF3+ and to Xe-2(+) ions. However, for Xe concentrations above 60%, only one peak remains (Xe-2(+)). The reduced mobilities obtained from the peak centroid of the time-of-arrival spectra are presented for Xe concentrations in the 5%-95% range.
Experimental ion mobility measurements in Xe-CH4
(IOP Publishing, 2017-07-24) Perdigoto, J. M.C.; Cortez, André F.V.; Neves, Pedro N.B.; Santos, Filomena P.; Borges, F. I.G.M.; Conde, Carlos A.N.; Veenhof, Robert J.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 6603742499
Data on ion mobility is important to improve the performance of large volume gaseous detectors. In the present work, the method, experimental setup and results for the ion mobility measurements in Xe-CH4 mixtures are presented. The results for this mixture show the presence of two distinct groups of ions. The nature of the ions depend on the mixture ratio since they are originated by both Xe and CH4. The results here presented were obtained for low reduced electric fields, E/N, 10-25 Td (2.4-6.1 kV.cm(-1).bar 1), at low pressure (8 Torr) (10.6 mbar), and at room temperature.
Experimental ion mobility measurements in Xe-CO2
(IOP Publishing, 2017-06) Cortez, Andre F.V.; Santos, M. A.G.; Nath, Patra Rajendra; Neves, Pedro N.B.; Santos, Filomena P.; Borges, F. I.G.M.; Conde, Carlos A.N.; Veenhof, Robert J.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 6603742499
Data on ion mobility is important to improve the performance of large volume gaseous detectors. In the present work the method, experimental setup and results for the ion mobility measurements in Xe-CO2 mixtures are presented. The results for this mixture show the presence of only one peak for all gas ratios of Xe-CO2, low reduced electric fields, E/N, 10-25 Td (2.4-6.1 kV·cm-1·bar-1), low pressures 6-8 Torr (8-10.6 mbar), at room temperature.
High-precision gas gain and energy transfer measurements in Ar-CO2 mixtures
(Elsevier, 2014-12-21) Kowalski, Tadeusz Z.; Şahin, Özkan; Veenhof, Robert J.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 0000-0003-3940-7222; AAH-6445-2021; 36053592700; 6603742499
Ar-CO2 is a Penning mixture since a fraction of the energy stored in Ar 3p(5)3d and higher excited states can be transferred to ionize CO2 molecules. In the present work, concentration and pressure dependence of Penning transfer rate and photon feedback parameter in Ar-CO2 mixtures have been investigated with recent systematic high-precision gas gain measurements which cover the range 1-50% CO2 at 400, 800, 1200, 1800 hPa and gas gain from 1 to 5 x 10(5).
Interfacing Geant4, Garfield++ and Degrad for the simulation of gaseous detectors
(Elsevier, 2019-04-29) Pfeiffer, Dorothea Andreas; de Keukeleere, Lennert; Azevedo, C. D.R.; Belloni, Francesca; Biagi, Stephen F.; Grichine, Vladimir M.; Hayen, Leendert; Hanu, Andrei R.; Hřivnáčová, I.; Ivanchenko, Vladimir N.; Krylov, Vladyslav V.; Schindler, Heinrich; Veenhof, Robert J.; Uludağ Üniversitesi.; 6603742499
For several years, attempts have been made to interface Geant4 and other software packages with the aim of simulating the complete response of a gaseous particle detector. In such a simulation, Geant4 is always responsible for the primary particle generation and the interactions that occur in the non-gaseous detector material. Garfield++ on the other hand always deals with the drift of ions and electrons, amplification via electron avalanches and finally signal generation. For the ionizing interaction of particles with the gas, different options and physics models exist. The present paper focuses on how to use Geant4, Garfield++ (including its Heed and SRIM interfaces) and Degrad to create the electron-ion pairs stemming from the ionization of the gas. Software-wise, the proposed idea is to use the Geant4 physics parameterization feature, and to implement a Garfield++ or Degrad based detector simulation as an external model. With a Degrad model, detailed simulations of the X-ray interaction in gaseous detectors, including shell absorption by photoelectric effect, subsequent Auger cascade, shake-off and fluorescence emission, become possible. A simple Garfield++ model can be used for photons (Heed), heavy ions (SRIM) and relativistic charged particles or MIPs (Heed). For non-relativistic charged particles, more effort is required, and a combined Geant4/Garfield++ model must be used. This model, the Geant4/Heed PAI model interface, uses the Geant4 PAI model in conjunction with the Heed PAI model. Parameters, such as the lower production cut of the Geant4 PAI model and the lowest electron energy limit of the physics list have to be set correctly. The paper demonstrates how to determine these parameters for certain values of the W parameter and Fano factor of the gas mixture. The simulation results of this Geant4/Heed PAI model interface are then verified against the results obtained with the stand-alone software packages.
Mesh geometry impact on Micromegas performance with an Exchangeable Mesh prototype
(Elsevier, 2016-07-11) Kuger, Fabian; Bianco, Michele; Iengo, Paolo; Sekhniaidze, Givi; Wotschack, Joerg; Veenhof, Robert J.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 6603742499
The reconstruction precision of gaseous detectors is limited by losses of primary electrons during signal formation. In addition to common gas related losses, like attachment, Micromegas suffer from electron absorption during its transition through the micro mesh. This study aims for a deepened understanding of electron losses and their dependency on the mesh geometry. It combines experimental results obtained with a novel designed Exchangeable Mesh Micromegas (ExMe) and advanced microscopic tracking simulations (ANSYS and Garfield+ +) of electron drift and mesh transition.
PICOSEC: Charged particle timing at sub-25 picosecond precision with a Micromegas based detector
(Elsevier, 2018-09-21) Veenhof, Robert J.; Uludağ Üniversitesi/Fen - Edebiyat Fakültesi/Fizik Bölümü.; GJK-8031-2022; 6603742499
The prospect of pileup induced backgrounds at the High Luminosity LHC (HL-LHC) has stimulated intense interest in developing technologies for charged particle detection with accurate timing at high rates. The required accuracy follows directly from the nominal interaction distribution within a bunch crossing (sigma(2) similar to 5 cm, sigma(t) similar to 170 ps). A time resolution of the order of 20-30 ps would lead to significant reduction of these backgrounds. With this goal, we present a new detection concept called PICOSEC, which is based on a "two-stage'' Micromegas detector coupled to a Cherenkov radiator and equipped with a photocathode. First results obtained with this new detector yield a time resolution of 24 ps for 150 GeV muons, and 76 ps for single photoelectrons.
Secondary avalanches in gas mixtures
(Elsevier, 2013-08-01) Veenhof, Robert J.; Şahin, Özkan; Tapan, İlhan; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Anabilim Dalı.; 0000-0003-3940-7222; AAH-6445-2021; I-9715-2017; 36053592700; 8905787000
Avalanche development in gas-based detectors relies not only on direct ionisation but also on excitation of noble gas atoms. Some quencher molecules can be ionised when they collide with excited atoms, a process on which we reported earlier In Alternatively, excited atoms can decay by photon emission. If these photons are insufficiently absorbed by the quencher, yet capable of ionising, then they may escape from the avalanche region and start secondary avalanches. This process, called photon feedback, leads to an over-exponential increase of the gas gain which limits the working range. In this paper, we derive photon feedback parameters from published gain measurements for several gas mixtures and fit these parameters in a model which describes their dependence on the quencher concentration and the pressure.
Systematic gas gain measurements and Penning energy transfer rates in Ne-CO2 mixtures
(IOP Publishing, 2015-12-08) Kowalski, Tadeusz Z.; Şahin, Özkan; Veenhof, Robert J.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 0000-0003-3940-7222; AAH-6445-2021; I-9715-2017; 36053592700; 6603742499
In Ne-CO2 mixtures, excitation energy of Ne atom can be used to ionize CO2 molecule by the mechanisms called Penning transfers. In the present work, we have measured the gas gain systematically in various Ne-CO2 mixtures (Ne + 0 : 6-60 % CO2) at 0.4, 0.8, 1.2, 1.8 atm. The experimental data have been fitted to investigate the Penning energy transfer rates and the secondary processes playing a role in avalanche formations.