| 1. |
- Piscitelli, Francesco, et al.
(författare)
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Neutron reflectometry on highly absorbing films and its application to (B4C)-B-10-based neutron detectors
- 2016
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Ingår i: Royal Society of London. Proceedings A. Mathematical, Physical and Engineering Sciences. - : The Royal Society. - 1364-5021 .- 1471-2946. ; 472:2185
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Tidskriftsartikel (refereegranskat)abstract
- Neutron reflectometry is a powerful tool used for studies of surfaces and interfaces. The absorption in the typical studied materials is neglected and this technique is limited only to the reflectivity measurement. For strongly absorbing nuclei, the absorption can be directly measured by using the neutron-induced fluorescence technique which exploits the prompt particle emission of absorbing isotopes. This technique is emerging from soft matter and biology where highly absorbing nuclei, in very small quantities, are used as a label for buried layers. Nowadays, the importance of absorbing layers is rapidly increasing, partially because of their application in neutron detection; a field that has become more active also due to the He-3-shortage. We extend the neutron-induced fluorescence technique to the study of layers of highly absorbing materials, in particular (B4C)-B-10. The theory of neutron reflectometry is a commonly studied topic; however, when a strong absorption is present the subtle relationship between the reflection and the absorption of neutrons is not widely known. The theory for a general stack of absorbing layers has been developed and compared to measurements. We also report on the requirements that a (B4C)-B-10 layer must fulfil in order to be employed as a converter in neutron detection.
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| 2. |
- Fritioff, T., et al.
(författare)
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Purification of radioactive neutron-rich argon beams using an ion source in charge breeding mode
- 2006
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576 .- 0167-5087. ; 556:1, s. 31-37
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of nuclear properties of some neutron-rich asymmetric fission isotopes at an ISOL laboratory present a severe problem when a plasma ion source is used as the primary ion-source. The problem is associated with intense multi-charged symmetric fission contaminants that cannot be mass-separated from asymmetric fission products. In this work we demonstrate how this problem can be overcome on-line by using an electron cyclotron resonance ion source (ECRIS) as a charge-breeding secondary ion-source. Mixed Ar+/Kr2+/Xe3+ radioactive beams from an plasma ion-source were injected into the PHOENIX ECRIS that currently is installed at the ISOLDE facility at CERN in order to improve the ratio of Ar to the background contaminants of Kr and Xe. The signal to noise ratio was improved by more than two orders of magnitude after charge-breeding and mass-separation of the Ar8+, Ar9+ beams. The information on the decay of the Ar-48 nucleus obtained in these tests is useful for a better understanding of the origin of the Ca-48/Ca-46 meteorite isotopic anomaly. Potential applications of the method are discussed.
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| 3. |
- Hidvegi, Attila, et al.
(författare)
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A system for distributing high-speed synchronous high-precision clock and trigger data over large distances
- 2008
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Ingår i: Nuclear Science Symposium Conference Record, 2008. NSS '08. IEEE. - 9781424427147 ; , s. 2581-2584
-
Konferensbidrag (refereegranskat)abstract
- The distribution of precise timing throughout the European X-ray Free Electron Laser project [1] (XFEL) and its triggering system is a very challenging part of the system design. ADCs in data acquisition systems and DACs in control systems will require very high precision clocks. The clocks need to be synchronous to each other, both in frequency and phase, with a jitter performance better than 5 ps (RMS). At some high-speed ADCs it might even need a precision down to 0.1 ps. The frequencies that must be available are the main 1.3 GHz and some frequencies below, which are all derived from the main frequency. The phase needs to be adjustable to allow synchronization between separate devices. Triggering information needs to be distributed over the system, so that controlling instructions can be carried out at a very precise time. This is very important since the beam will travel with the speed of light, and there is no possibility for information to be sent back and forth. This requires an absolute timing to be distributed over the system. Both the main clock and triggering information will be transmitted over the same fiber cable, one to each device. An advanced synchronization method needs to be developed to synchronize the phases of the clocks throughout the whole system. The delay through the cable can change with temperature, and due to long cables the total change through a single cable can be significant. It is essential that the clocks are stable and not drifting away from each other. Therefore a continuous calibration method is needed, ensuring that the clocks are synchronous throughout the whole system. A prototype of such a system is being developed and a first version is expected to be completed in 2009 Ql.
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| 4. |
- Reza, Salim, 1985-, et al.
(författare)
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Smart dosimetry by pattern recognition using a single photon counting detector system in time over threshold mode
- 2012
-
Ingår i: Journal of Instrumentation. - 1748-0221 .- 1748-0221. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- The function of a dosimeter is to determine the absorbed dose of radiation, for those cases in which, generally, the particular type of radiation is already known. Lately, a number of applications have emerged in which all kinds of radiation are absorbed and are sorted by pattern recognition, such as the Medipix2 application in [1]. This form of smart dosimetry enables measurements where not only the total dosage is measured, but also the contributions of different types of radiation impacting upon the detector surface. Furthermore, the use of a photon counting system, where the energy deposition can be measured in each individual pixel, ensures measurements with a high degree of accuracy in relation to the pattern recognition. In this article a Timepix [2] detector system has been used in the creation of a smart dosimeter for Alpha, Beta and Gamma radiation. When a radioactive particle hits the detector surface it generates charge clusters and those impacting upon the detector surface are read out and image processing algorithms are then used to classify each charge cluster. The individual clusters are calculated and as a result, the dosage for each type of radiation is given. In some cases, several particles can impact in roughly the same place, forming overlapping clusters. In order to handle this problem, a cluster separation method has been added to the pattern recognition algorithm. When the clusters have been separated, they are classified by shape and sorted into the correct type of radiation. The algorithms and methods used in this dosimeter have been developed so as to be simple and computationally effective, in order to enable implementation on a portable device. © 2012 IOP Publishing Ltd and SISSA.
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| 5. |
- Lestinsky, M., et al.
(författare)
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Physics book: CRYRING@ESR
- 2016
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Ingår i: European Physical Journal: Special Topics. - : Springer Science and Business Media LLC. - 1951-6401 .- 1951-6355. ; 225:5, s. 797-882
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Forskningsöversikt (refereegranskat)abstract
- The exploration of the unique properties of stored and cooled beams of highly-charged ions as provided by heavy-ion storage rings has opened novel and fascinating research opportunities in the realm of atomic and nuclear physics research. Since the late 1980s, pioneering work has been performed at the CRYRING at Stockholm (Abrahamsson et al. 1993) and at the Test Storage Ring (TSR) at Heidelberg (Baumann et al. 1988). For the heaviest ions in the highest charge-states, a real quantum jump was achieved in the early 1990s by the commissioning of the Experimental Storage Ring (ESR) at GSI Helmholtzzentrum für Schwerionenforschung (GSI) in Darmstadt (Franzke 1987) where challenging experiments on the electron dynamics in the strong field regime as well as nuclear physics studies on exotic nuclei and at the borderline to atomic physics were performed. Meanwhile also at Lanzhou a heavy-ion storage ring has been taken in operation, exploiting the unique research opportunities in particular for medium-heavy ions and exotic nuclei (Xia et al. 2002).
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| 6. |
- Thiele, Illia, 1989, et al.
(författare)
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Electron Beam Driven Generation of Frequency-Tunable Isolated Relativistic Subcycle Pulses
- 2019
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 122
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 American Physical Society. We propose a novel scheme for frequency-tunable subcycle electromagnetic pulse generation. To this end a pump electron beam is injected into an electromagnetic seed pulse as the latter is reflected by a mirror. The electron beam is shown to be able to amplify the field of the seed pulse while upshifting its central frequency and reducing its number of cycles. We demonstrate the amplification by means of 1D and 2D particle-in-cell simulations. In order to explain and optimize the process, a model based on fluid theory is proposed. We estimate that using currently available electron beams and terahertz pulse sources, our scheme is able to produce millijoule-strong midinfrared subcycle pulses.
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| 7. |
- Abata, E., et al.
(författare)
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Study of energy response and resolution of the ATLAS barrel calorimeter to hadrons of energies from 20 to 350 GeV
- 2010
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576 .- 0167-5087. ; 621:1-3, s. 134-150
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Tidskriftsartikel (refereegranskat)abstract
- A fully instrumented slice of the ATLAS detector was exposed to test beams from the SPS (Super Proton Synchrotron) at CERN in 2004. In this paper, the results of the measurements of the response of the barrel calorimeter to hadrons with energies in the range 20-350 GeV and beam impact points and angles corresponding to pseudo-rapidity values in the range 0.2-0.65 are reported. The results are compared to the predictions of a simulation program using the Geant 4 toolkit. (C) 2010 Published by Elsevier B.V.
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| 8. |
- Abat, E., et al.
(författare)
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Photon reconstruction in the ATLAS Inner Detector and Liquid Argon Barrel Calorimeter at the 2004 Combined Test Beam
- 2011
-
Ingår i: Journal of Instrumentation. - 1748-0221. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- The reconstruction of photons in the ATLAS detector is studied with data taken during the 2004 Combined Test Beam, where a full slice of the ATLAS detector was exposed to beams of particles of known energy at the CERN SPS. The results presented show significant differences in the longitudinal development of the electromagnetic shower between converted and unconverted photons as well as in the total measured energy. The potential to use the reconstructed converted photons as a means to precisely map the material of the tracker in front of the electromagnetic calorimeter is also considered. All results obtained are compared with a detailed Monte-Carlo simulation of the test-beam setup which is based on the same simulation and reconstruction tools as those used for the ATLAS detector itself.
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| 9. |
- Bengtsson, Lars, 1963
(författare)
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Embedded Measurement Systems
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The subject of Embedded Measurement Systems (EMS) is the merging of embedded systems and electrical measurement systems. This indicates that EMSs are hardware-software systems dedicated to measuring one or a few physical quantities. Applications are numerous; EMSs measure the temperature in refrigerators, freezers, irons, ovens and automobile combustion engines, they sense vibrations in tilt alarms and game consoles, they measure airflow in engines and ventilation systems, they measure shock impact in crash detectors and are used as shock and temperature loggers for transport goods, they measure air pressure in airplane cabins, humidity in air-conditioned environments, they measure liquid levels in fuel tanks, they detect smoke in fire alarms, they measure the viscosity of lubricant oil in engines, they measure the rotation speed of spinning wheels (in any engine), they measure torque in engines and are used as heart rate and ECG detectors in medicine etc. The commercial demand for ever cheaper products and worldwide environmental legislations force vendors to continuously look for more cost-efficient and less power-consuming solutions for their embedded measurement systems. This thesis is concerned most of all with the implementation of cost-efficient/low-power measurement systems in embedded controllers. This includes some novel ideas in voltage, time and resistance measurements with embedded controllers and it will demonstrate how these quantities, analog in nature, can be measured accurately and precisely by inherently digital embedded controllers.
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| 10. |
- Abat, E., et al.
(författare)
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Combined performance studies for electrons at the 2004 ATLAS combined test-beam
- 2010
-
Ingår i: Journal of Instrumentation. - : Institute of Physics (IOP). - 1748-0221. ; 5, s. P11006-
-
Tidskriftsartikel (refereegranskat)abstract
- In 2004 at the ATLAS (A Toroidal LHC ApparatuS) combined test beam, one slice of the ATLAS barrel detector (including an Inner Detector set-up and the Liquid Argon calorimeter) was exposed to particles from the H8 SPS beam line at CERN. It was the first occasion to test the combined electron performance of ATLAS. This paper presents results obtained for the momentum measurement p with the Inner Detector and for the performance of the electron measurement with the LAr calorimeter (energy E linearity and resolution) in the presence of a magnetic field in the Inner Detector for momenta ranging from 20 GeV/c to 100 GeV/c. Furthermore the particle identification capabilities of the Transition Radiation Tracker, Bremsstrahlungs-recovery algorithms relying on the LAr calorimeter and results obtained for the E/p ratio and a way how to extract scale parameters will be discussed.
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| 11. |
- Göök, A., et al.
(författare)
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Application of the ShockleyRamo theorem on the grid inefficiency of Frisch grid ionization chambers
- 2012
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 664:1, s. 289-293
-
Tidskriftsartikel (refereegranskat)abstract
- The concept of grid inefficiency in Frisch grid ionization chambers and its influence on the anode pulse shape is explained in terms of the ShockleyRamo theorem for induced charges. The grid inefficiency correction is deduced from numerically calculated weighting potentials. A method to determine the correction factor experimentally is also presented. Experimental and calculated values of the correction factor are shown to be in good agreement.
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| 12. |
- Milstead, David A., et al.
(författare)
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Modelling radiation damage to pixel sensors in the ATLAS detector
- 2019
-
Ingår i: Journal of Instrumentation. - : IOP PUBLISHING LTD. - 1748-0221. ; 14:6
-
Tidskriftsartikel (refereegranskat)abstract
- Silicon pixel detectors are at the core of the current and planned upgrade of the ATLAS experiment at the LHC. Given their close proximity to the interaction point, these detectors will be exposed to an unprecedented amount of radiation over their lifetime. The current pixel detector will receive damage from non-ionizing radiation in excess of 1015 1 MeV neq/cm2, while the pixel detector designed for the high-luminosity LHC must cope with an order of magnitude larger fluence. This paper presents a digitization model incorporating effects of radiation damage to the pixel sensors. The model is described in detail and predictions for the charge collection efficiency and Lorentz angle are compared with collision data collected between 2015 and 2017 (≤ 10 1 MeV neq/cm2). © 2019 CERN for the benefit of the ATLAS collaboration. Published by IOP Publishing Ltd on behalf of Sissa Medialab. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.
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| 13. |
- Gonoskov, Arkady, 1984, et al.
(författare)
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Employing machine learning for theory validation and identification of experimental conditions in laser-plasma physics
- 2019
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 9:1
-
Tidskriftsartikel (refereegranskat)abstract
- The validation of a theory is commonly based on appealing to clearly distinguishable and describable features in properly reduced experimental data, while the use of ab-initio simulation for interpreting experimental data typically requires complete knowledge about initial conditions and parameters. We here apply the methodology of using machine learning for overcoming these natural limitations. We outline some basic universal ideas and show how we can use them to resolve long-standing theoretical and experimental difficulties in the problem of high-intensity laser-plasma interactions. In particular we show how an artificial neural network can “read” features imprinted in laser-plasma harmonic spectra that are currently analysed with spectral interferometry.
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| 14. |
- Aartsen, M. G., et al.
(författare)
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Computational techniques for the analysis of small signals in high-statistics neutrino oscillation experiments
- 2020
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 977
-
Tidskriftsartikel (refereegranskat)abstract
- The current and upcoming generation of Very Large Volume Neutrino Telescopes - collecting unprecedented quantities of neutrino events - can be used to explore subtle effects in oscillation physics, such as (but not restricted to) the neutrino mass ordering. The sensitivity of an experiment to these effects can be estimated from Monte Carlo simulations. With the high number of events that will be collected, there is a trade-off between the computational expense of running such simulations and the inherent statistical uncertainty in the determined values. In such a scenario, it becomes impractical to produce and use adequately-sized sets of simulated events with traditional methods, such as Monte Carlo weighting. In this work we present a staged approach to the generation of expected distributions of observables in order to overcome these challenges. By combining multiple integration and smoothing techniques which address limited statistics from simulation it arrives at reliable analysis results using modest computational resources.
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| 15. |
- Agåker, Marcus, et al.
(författare)
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Spectroscopy in the vacuum-ultraviolet
- 2011
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Ingår i: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 5:5, s. 248-248
-
Tidskriftsartikel (refereegranskat)
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| 16. |
- Gatchell, Michael, et al.
(författare)
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Commissioning of the DESIREE storage rings - a new facility for cold ion-ion collisions
- 2014
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Ingår i: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013). - : Institute of Physics (IOP). ; 488:1
-
Konferensbidrag (refereegranskat)abstract
- We report on the ongoing commissioning of the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. Beams of atomic carbon anions (C-) and smaller carbon anion molecules (C-2(-), C-3(-), C-4(-) etc.) have been produced in a sputter ion source, accelerated to 10 keV or 20 keV, and stored successfully in the two electrostatic rings. The rings are enclosed in a common vacuum chamber cooled to below 13 Kelvin. The DESIREE facility allows for studies of internally relaxed single isolated atomic, molecular and cluster ions and for collision experiments between cat-and anions down to very low center-of-mass collision energies (meV scale). The total thermal load of the vacuum chamber at this temperature is measured to be 32 W. The decay rates of stored ion beams have two components: a non-exponential component caused by the space charge of the beam itself which dominates at early times and an exponential term from the neutralization of the beam in collisions with residual gas at later times. The residual gas limited storage lifetime of carbon anions in the symmetric ring is over seven minutes while the 1/e lifetime in the asymmetric ring is measured to be about 30 seconds. Although we aim to improve the storage in the second ring, the number of stored ions are now sufficient for many merged beams experiments with positive and negative ions requiring milliseconds to seconds ion storage.
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| 17. |
- Lei, Fuchuan, 1987, et al.
(författare)
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Power-efficient hyperparametric oscillation via bound states in the continuum
- 2023
-
Ingår i: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023.
-
Konferensbidrag (refereegranskat)abstract
- Optical hyperparametric oscillation (h-OPO) emerges in a driven Kerr cavity because of modulation instability. Two pump photons are converted into a pair of two correlated photons at new wavelengths. For many realistic applications, efficient operation of h-OPO is required, especially at high-power regime. Currently, the pump-to-signal conversion efficiency is fundamentally limited mainly by two factors: parasitic mode competition [1] and attainable cavity intrinsic Q (Qi) to coupling Q (Qc) ratio [2].
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| 18. |
- Eriksson, Daniel, et al.
(författare)
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A prototype for the upgraded readout electronics of TileCal
- 2012
-
Ingår i: Journal of Instrumentation. - 1748-0221 .- 1748-0221. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- Upgrade plans for the ATLAS hadronic tile calorimeter (TileCal) at the LHC include full granularity readout to the 1st level trigger. R&D activities at different laboratories target different parts of the upgraded system. We are developing a possible implementation of the future readout electronics to be included in a full functional demonstrator. This must be capable of adapting to each of the three different front-end alternatives being considered. Prototypes of the two PCBs that will be in charge of digitization, control and communication have been developed. The design is redundant and uses FPGAs with fault tolerant firmware for control and protocol conversion. Communication and clock synchronization between on and offdetector electronics is implemented via high speed optical links using the GBT protocol.
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| 19. |
- Rebolledo Salgado, Israel, 1992, et al.
(författare)
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Nonlinear Broadening of Electro-Optic Frequency Combs in All-Normal Dispersion Si 3 N 4 Waveguides
- 2021
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Ingår i: 2021 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2021.
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Konferensbidrag (refereegranskat)abstract
- Dispersion-engineered silicon nitride waveguides are often used for broadening of frequency combs. Previous experiments have focused on anomalous dispersion waveguides pumped by femtosecond laser pulses, whereby coherent supercontinuum generation relies on soliton compression and dispersive wave emission (see e.g. [1] ). This regime of operation does not work well with high-repetition rate sources, such as microcombs or electro-optic (EO) combs, because the pulse duration is not sufficiently short to drive coherent broadening in anomalous dispersion media. Indeed, octave-spanning coherent broadening of high-repetition rate sources has been attained in anomalous dispersion silicon nitride waveguides, but this required using a pre-broadening stage in a normal-dispersion highly nonlinear fiber (HNLF) [2]. Implementing this stage in a silicon nitride waveguide is the topic we address in this contribution.
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| 20. |
- Ferri, Julien, 1990, et al.
(författare)
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Enhanced target normal sheath acceleration using colliding laser pulses
- 2019
-
Ingår i: Communications Physics. - : Springer Science and Business Media LLC. - 2399-3650. ; 2
-
Tidskriftsartikel (refereegranskat)abstract
- Laser-solid interaction can lead to the acceleration of protons to tens of MeV. Here, we show that a strong enhancement of this acceleration can be achieved by splitting the laser pulse to two parts of equal energy and opposite incidence angles. Through the use of two- and three-dimensional Particle-In-Cell simulations, we find that the multi-pulse interaction leads to a standing wave pattern at the front side of the target, with an enhanced electric field and a substantial modification of the hot electron generation process. This in turn leads to significant improvement of the proton spectra, with an almost doubling of the accelerated proton energy and five-fold enhancement of the number of protons. The proposed scheme is robust with respect to incidence angles for the laser pulses, providing flexibility to the scheme, which should facilitate its experimental implementation.
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| 21. |
- Isaksson, Oscar, et al.
(författare)
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An optical levitation system for a physics teaching laboratory
- 2018
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Ingår i: American Journal of Physics. - : American Association of Physics Teachers (AAPT). - 0002-9505 .- 1943-2909. ; 86:2, s. 135-142
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Tidskriftsartikel (refereegranskat)abstract
- We describe an experimental system based on optical levitation of an oil droplet. When combined with an applied electric field and a source of ionizing radiation, the setup permits the investigation of physical phenomena such as radiation pressure, light diffraction, the motion of a charged particle in an oscillating electric field, and the interaction of ionizing radiation with matter. The trapping occurs by creating an equilibrium between a radiation pressure force and the force of gravity. We have found that an oil droplet can be trapped for at least nine hours. The system can be used to measure the size and total electric charge on the trapped droplet. The intensity of the light from the trapping laser that is scattered by the droplet is sufficient to allow the droplet to be easily seen with the naked eye, covered by laser alignment goggles. When oscillating under the influence of an ac electric field, the motion of the droplet can be described as that of a driven, damped harmonic oscillator. The magnitude and polarity of the charge can be altered by exposing the droplet to ionizing radiation from a low-activity radioactive source. Our goal was to design a hands-on setup that allows undergraduate and graduate students to observe and better understand fundamental physical processes. (C) 2018 American Association of Physics Teachers.
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| 22. |
- Litvinov, Yu.A., et al.
(författare)
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Nuclear physics experiments with ion storage rings
- 2013
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Ingår i: Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X. ; 317:PART B, s. 603-616
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Tidskriftsartikel (refereegranskat)abstract
- In the last two decades a number of nuclear structure and astrophysics experiments were performed at heavy-ion storage rings employing unique experimental conditions offered by such machines. Furthermore, building on the experience gained at the two facilities presently in operation, several new storage ring projects were launched worldwide. This contribution is intended to provide a brief review of the fast growing field of nuclear structure and astrophysics research at storage rings.
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| 23. |
- Lundholm, Ida V., et al.
(författare)
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Considerations for three-dimensional image reconstruction from experimental data in coherent diffractive imaging
- 2018
-
Ingår i: IUCrJ. - : International Union of Crystallography. - 2052-2525. ; 5, s. 531-541
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Tidskriftsartikel (refereegranskat)abstract
- Diffraction before destruction using X-ray free-electron lasers (XFELs) has the potential to determine radiation-damage-free structures without the need for crystallization. This article presents the three-dimensional reconstruction of the Melbournevirus from single-particle X-ray diffraction patterns collected at the LINAC Coherent Light Source (LCLS) as well as reconstructions from simulated data exploring the consequences of different kinds of experimental sources of noise. The reconstruction from experimental data suffers from a strong artifact in the center of the particle. This could be reproduced with simulated data by adding experimental background to the diffraction patterns. In those simulations, the relative density of the artifact increases linearly with background strength. This suggests that the artifact originates from the Fourier transform of the relatively flat background, concentrating all power in a central feature of limited extent. We support these findings by significantly reducing the artifact through background removal before the phase-retrieval step. Large amounts of blurring in the diffraction patterns were also found to introduce diffuse artifacts, which could easily be mistaken as biologically relevant features. Other sources of noise such as sample heterogeneity and variation of pulse energy did not significantly degrade the quality of the reconstructions. Larger data volumes, made possible by the recent inauguration of high repetition-rate XFELs, allow for increased signal-to-background ratio and provide a way to minimize these artifacts. The anticipated development of three-dimensional Fourier-volume-assembly algorithms which are background aware is an alternative and complementary solution, which maximizes the use of data.
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| 24. |
- Spartà, R., et al.
(författare)
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Probing proton halo effects in the 8 B+ 64 Zn collision around the Coulomb barrier
- 2021
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 820
-
Tidskriftsartikel (refereegranskat)abstract
- Proton halo effects in the 8B+64Zn reaction at an energy around 1.5 times the Coulomb barrier have been studied at HIE-ISOLDE CERN using, for the first time, the only existing postaccelerated 8B beam. This, together with the use of a high granularity and large solid angle detection system, allowed for a careful mapping of the elastic angular distribution, especially in the Coulomb-nuclear interference region. Contrary to what is observed for the one-neutron halo nucleus 11Be on the same target in a similar energy range, the analysis of the elastic scattering angular distribution shows only a modest suppression of the Coulomb-nuclear interference peak, with no remarkable enhancement of the total reaction cross-section. Inclusive angular and energy distributions of 7Be produced in direct reaction processes have also been measured. The comparison of these data with the results of theoretical calculations for the elastic and non-elastic breakup contributions indicate that both processes are important. Overall, the experimental data suggest a 8B collision dynamics at the barrier very different from the one of neutron halo nuclei, showing only modest effects of coupling to continuum. This behaviour can be interpreted as due to the presence of the additional Coulomb interactions halo-core and halo-target together with the presence of the centrifugal barrier felt by the valence proton of 8B.
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| 25. |
- Warbinek, Jessica, et al.
(författare)
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A graphene-based neutral particle detector
- 2019
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 114:6
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Tidskriftsartikel (refereegranskat)abstract
- A neutral particle detector is presented, in which the traditionally used target material, indium tin oxide (ITO), is replaced by graphene. The graphene-based detector enables collinear photodetachment measurements at a significantly shorter wavelength of light down to 230nm compared to ITO-based detectors, which are limited at 335 nm. Moreover, the background signal from the photoelectric effect is drastically reduced when using graphene. The graphene based detector, reaching 1.7 eV further into the UV energy range, allows increased possibilities for photodetachment studies of negatively charged atoms, molecules, and clusters. Published under license by AIP Publishing.
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