J. Correa

Bio: J. Correa is an academic researcher from University of Hamburg. The author has contributed to research in topics: Detector & Neutron detection. The author has an hindex of 13, co-authored 38 publications receiving 671 citations.

B4C thin films for neutron detection

Abstract: Due to the very limited availability of 3He, new kinds of neutron detectors, not based on 3He, are urgently needed. Here, we present a method to produce thin films of 10B4C, with maximized detection efficiency, intended to be part of a new generation of large area neutron detectors. B4C thin films have been deposited onto Al-blade and Si wafer substrates by dc magnetron sputtering from natB4C and 10B4C targets in an Ar discharge, using an industrial deposition system. The films were characterized with scanning electron microscopy, elastic recoil detection analysis, x-ray reflectivity, and neutron radiography. We show that the film-substrate adhesion and film purity are improved by increased substrate temperature and deposition rate. A deposition rate of 3.8 A/s and substrate temperature of 400 °C result in films with a density close to bulk values and good adhesion to film thickness above 3 μm. Boron-10 contents of almost 80 at. % are obtained in 6.3 m2 of 1 μm thick 10B4C thin films coated on Al-blades. Initial neutron absorption measurements agree with Monte Carlo simulations and show that the layer thickness, number of layers, neutron wavelength, and amount of impurities are determining factors. The study also shows the importance of having uniform layer thicknesses over large areas, which for a full-scale detector could be in total ∼1000 m2 of two-side coated Al-blades with ∼1 μm thick 10B4C films.

Femtosecond response of polyatomic molecules to ultra-intense hard X-rays

Abstract: Upon exposure to ultra-intense, hard X-ray pulses, polyatomic molecules containing one heavy atom reach a much higher degree of ionization than do individual heavy atoms, contrary to previous assumptions X-ray free-electron lasers offer many new applications such as the ability to structurally probe fast biological processes This requires the use of hard and intense X-ray pulses, but the behaviour of matter under such conditions has not been fully explored Artem Rudenko et al show that when exposing small polyatomic molecules that contain one heavy atom to hard X-ray pulses with ultra-high intensities, the response is qualitatively different from what is seen in experiments carried out under less extreme conditions The observed ionization of the molecule is considerably enhanced compared to that of an individual heavy atom under the same conditions, owing to ultrafast charge transfer within the molecule that replenishes the electrons removed from the heavy atom, enabling further ionization Being able to account for this effect will aid further use of X-ray free-electron lasers for studying biological systems X-ray free-electron lasers enable the investigation of the structure and dynamics of diverse systems, including atoms, molecules, nanocrystals and single bioparticles, under extreme conditions1,2,3,4,5,6,7 Many imaging applications that target biological systems and complex materials use hard X-ray pulses with extremely high peak intensities (exceeding 1020 watts per square centimetre)3,5 However, fundamental investigations have focused mainly on the individual response of atoms and small molecules using soft X-rays with much lower intensities8,9,10,11,12,13,14,15,16,17 Studies with intense X-ray pulses have shown that irradiated atoms reach a very high degree of ionization, owing to multiphoton absorption8,12,13,18, which in a heteronuclear molecular system occurs predominantly locally on a heavy atom (provided that the absorption cross-section of the heavy atom is considerably larger than those of its neighbours) and is followed by efficient redistribution of the induced charge14,15,16,17,19,20 In serial femtosecond crystallography of biological objects—an application of X-ray free-electron lasers that greatly enhances our ability to determine protein structure2,3—the ionization of heavy atoms increases the local radiation damage that is seen in the diffraction patterns of these objects21,22 and has been suggested as a way of phasing the diffraction data23,24 On the basis of experiments using either soft or less-intense hard X-rays14,15,16,17,18,19,25, it is thought that the induced charge and associated radiation damage of atoms in polyatomic molecules can be inferred from the charge that is induced in an isolated atom under otherwise comparable irradiation conditions Here we show that the femtosecond response of small polyatomic molecules that contain one heavy atom to ultra-intense (with intensities approaching 1020 watts per square centimetre), hard (with photon energies of 83 kiloelectronvolts) X-ray pulses is qualitatively different: our experimental and modelling results establish that, under these conditions, the ionization of a molecule is considerably enhanced compared to that of an individual heavy atom with the same absorption cross-section This enhancement is driven by ultrafast charge transfer within the molecule, which refills the core holes that are created in the heavy atom, providing further targets for inner-shell ionization and resulting in the emission of more than 50 electrons during the X-ray pulse Our results demonstrate that efficient modelling of X-ray-driven processes in complex systems at ultrahigh intensities is feasible

Investigation of gamma-ray sensitivity of neutron detectors based on thin converter films

Abstract: Currently, many detector technologies for thermal neutron detection are in development in order to lower the demand for the rare 3He gas. Gas detectors with solid thin film neutron converters readout by gas proportional counter method have been proposed as an appropriate choice for applications where large area coverage is necessary. In this paper, we investigate the probability for γ-rays to generate a false count in a neutron measurement. Simulated results are compared to measurement with 10B thin film prototypes and a 3He detector. It is demonstrated that equal γ-ray rejection to that of 3He tubes is achieved with the new technology. The arguments and results presented here are also applicable to gas detectors with converters other than solid 10B layers, such as 6Li layers and 10BF3 gas.

B-10 multi-grid proportional gas counters for large area thermal neutron detectors

Abstract: He-3 was a popular material in neutrons detectors until its availability dropped drastically in 2008. The development of techniques based on alternative convertors is now of high priority for neutron research institutes. Thin films of B-10 or (B4C)-B-10 have been used in gas proportional counters to detect neutrons, but until now, only for small or medium sensitive area. We present here the multi-grid design, introduced at the ILL and developed in collaboration with ESS for LAN (large area neutron) detectors. Typically thirty (B4C)-B-10 films of 1 mu m thickness are used to convert neutrons into ionizing particles which are subsequently detected in a proportional gas counter. The principle and the fabrication of the multi-grid are described and some preliminary results obtained with a prototype of 200 cm x 8 cm are reported; a detection efficiency of 48% has been measured at 2.5 angstrom with a monochromatic neutron beam line, showing the good potential of this new technique. (C) 2013 Elsevier B.V. All rights reserved. (Less)

Roadmap of ultrafast x-ray atomic and molecular physics

Abstract: X-ray free-electron lasers (XFELs) and table-top sources of x-rays based upon high harmonic generation (HHG) have revolutionized the field of ultrafast x-ray atomic and molecular physics, largely due to an explosive growth in capabilities in the past decade. XFELs now provide unprecedented intensity (1020 W cm-2) of x-rays at wavelengths down to ∼1 Angstrom, and HHG provides unprecedented time resolution (∼50 attoseconds) and a correspondingly large coherent bandwidth at longer wavelengths. For context, timescales can be referenced to the Bohr orbital period in hydrogen atom of 150 attoseconds and the hydrogen-molecule vibrational period of 8 femtoseconds; wavelength scales can be referenced to the chemically significant carbon K-edge at a photon energy of ∼280 eV (44 Angstroms) and the bond length in methane of ∼1 Angstrom. With these modern x-ray sources one now has the ability to focus on individual atoms, even when embedded in a complex molecule, and view electronic and nuclear motion on their intrinsic scales (attoseconds and Angstroms). These sources have enabled coherent diffractive imaging, where one can image non-crystalline objects in three dimensions on ultrafast timescales, potentially with atomic resolution. The unprecedented intensity available with XFELs has opened new fields of multiphoton and nonlinear x-ray physics where behavior of matter under extreme conditions can be explored. The unprecedented time resolution and pulse synchronization provided by HHG sources has kindled fundamental investigations of time delays in photoionization, charge migration in molecules, and dynamics near conical intersections that are foundational to AMO physics and chemistry. This roadmap coincides with the year when three new XFEL facilities, operating at Angstrom wavelengths, opened for users (European XFEL, Swiss-FEL and PAL-FEL in Korea) almost doubling the present worldwide number of XFELs, and documents the remarkable progress in HHG capabilities since its discovery roughly 30 years ago, showcasing experiments in AMO physics and other applications. Here we capture the perspectives of 17 leading groups and organize the contributions into four categories: ultrafast molecular dynamics, multidimensional x-ray spectroscopies; high-intensity x-ray phenomena; attosecond x-ray science.

Recent advances in Wigner function approaches

Abstract: The Wigner function was formulated in 1932 by Eugene Paul Wigner, at a time when quantum mechanics was in its infancy. In doing so, he brought phase space representations into quantum mechanics. However, its unique nature also made it very interesting for classical approaches and for identifying the deviations from classical behavior and the entanglement that can occur in quantum systems. What stands out, though, is the feature to experimentally reconstruct the Wigner function, which provides far more information on the system than can be obtained by any other quantum approach. This feature is particularly important for the field of quantum information processing and quantum physics. However, the Wigner function finds wide-ranging use cases in other dominant and highly active fields as well, such as in quantum electronics—to model the electron transport, in quantum chemistry—to calculate the static and dynamical properties of many-body quantum systems, and in signal processing—to investigate waves passing through certain media. What is peculiar in recent years is a strong increase in applying it: Although originally formulated 86 years ago, only today the full potential of the Wigner function—both in ability and diversity—begins to surface. This review, as well as a growing, dedicated Wigner community, is a testament to this development and gives a broad and concise overview of recent advancements in different fields.

Megahertz serial crystallography

Abstract: The new European X-ray Free-Electron Laser is the first X-ray free-electron laser capable of delivering X-ray pulses with a megahertz inter-pulse spacing, more than four orders of magnitude higher than previously possible. However, to date, it has been unclear whether it would indeed be possible to measure high-quality diffraction data at megahertz pulse repetition rates. Here, we show that high-quality structures can indeed be obtained using currently available operating conditions at the European XFEL. We present two complete data sets, one from the well-known model system lysozyme and the other from a so far unknown complex of a β-lactamase from K. pneumoniae involved in antibiotic resistance. This result opens up megahertz serial femtosecond crystallography (SFX) as a tool for reliable structure determination, substrate screening and the efficient measurement of the evolution and dynamics of molecular structures using megahertz repetition rate pulses available at this new class of X-ray laser source.

The First Five Years

Abstract: Five years ago I founded Integrated Computer-Aided Engineering. We published two issues in 1993 and four issues per year during 1994-1997. The six 1993 and 1994 issues were published as Volume One. In my Editorial in the inaugural issue of the journal published in 1993 I wrote "The focus of ICAE is the integration of leading edge and emerging computer technologies for innovative solution of engineering problems. The journal fosters interdisciplinary research and presents a unique forum for innovative computer-aided engineering". During 1993-1997 every issue of the journal was published on schedule in a timely manner. This is an exceptional record among the new scholarly journals. During this period we published a good number of special issues reflecting the interdisciplinary nature of the journal such as: Object-Oriented Manufacturing Systems, Artificial Intelligence in Manufacturing and Robotics, Intelligent Information Systems, Real-Time Intelligent Control Systems, Integrated Product and Process Data Management, Faults in Automated Manufacturing, Massively Parallel Computing, Intelligent Manufacturing Systems