Extended Energy Range Research Articles

Optical performance of materials for X-ray refractive optics in the energy range 8-100 keV.

A quantitative analysis of the crucial characteristics of currently used and promising materials for X-ray refractive optics is performed in the extended energy range 8-100 keV. According to the examined parameters, beryllium is the material of choice for X-ray compound refractive lenses (CRLs) in the energy range 8-25 keV. At higher energies the use of CRLs made of diamond and the cubic phase of boron nitride (c-BN) is beneficial. It was demonstrated that the presence of the elements of the fourth (or higher) period has a fatal effect on the functional X-ray properties even if low-Z elements dominate in the compound, like in YB66. Macroscopic properties are discussed: much higher melting points and thermal conductivities of C and c-BN enable them to be used at the new generation of synchrotron radiation sources and X-ray free-electron lasers. The role of crystal and internal structure is discussed: materials with high density are preferable for refractive applications while less dense phases are suitable for X-ray windows. Single-crystal or amorphous glass-like materials based on Li, Be, B or C that are free of diffuse scattering from grain boundaries, voids and inclusions are the best candidates for applications of highly coherent X-ray beams.

Primary spectrum and composition with IceCube/IceTop

IceCube, with its surface array IceTop, detects three different components of extensive air showers: the total signal at the surface, GeV muons in the periphery of the showers and TeV muons in the deep array of IceCube. The spectrum is measured with high resolution from the knee to the ankle with IceTop. Composition and spectrum are extracted from events seen in coincidence by the surface array and the deep array of IceCube. The muon lateral distribution at the surface is obtained from the data and used to provide a measurement of the muon density at 600 meters from the shower core up to 30 PeV. Results are compared to measurements from other experiments to obtain an overview of the spectrum and composition over an extended range of energy. Consistency of the surface muon measurements with hadronic interaction models and with measurements at higher energy is discussed.

Poster ‐ 25: Neutron Spectral Measurements around a Scanning Proton Beam

We describe the measurements of neutron spectra that we undertook around a scanning proton beam at the Skandion proton therapy clinic in Uppsala, Sweden. Measurements were undertaken using an extended energy range Nested Neutron Spectrometer (NNS, Detec Inc., Gatineau, QC) operated in pulsed and current mode. Spectra were measured as a function of location in the treatment room and for various Bragg peak depths. Our preliminary unfolded data clearly show the direct, evaporation and thermal neutron peaks and we can show the effect on the neutron spectrum of a water phantom in the primary proton beam.

Accurate X-ray Absorption Spectra of Dilute Systems: Absolute Measurements and Structural Analysis of Ferrocene and Decamethylferrocene

X-ray absorption fine structure (XAFS) of ferrocene (Fc) and Decamethylferrocene (DmFc) have been determined on an absolute scale using transmission measurements of multiple solutions of differing concentrations (15 mM, 3 mM, pure solvent) at operating temperatures of 10–20 K. Mass attenuation coefficients and photoelectric absorption cross sections are measured and tabulated for both molecules for an extended energy range in excess of 1.5 keV from the Fe K-shell absorption edge. At these temperatures, the minimization of of dynamic disorder has enabled a critical determination of the oscillatory absorption structures created by multiple-scattering paths of the excited photoelectron. These oscillatory structures are highly sensitive to the local conformation environment of the iron absorber in organometallic structures. Crystallographic and scattering studies have reported both structures characterized by staggered cyclopentadienyl rings, in contrast with low temperature crystallography and recent density functional theoretical predictions. Phase changes in the crystallographic space groups are reported for Fc at different temperatures, raising the possibility of alternative conformation states. Robust experimental techniques are described which have allowed the measurement of XAFS spectra of dilute systems by transmission at accuracies ranging from 0.2% to 2%, and observe statistically significant fine structure at photoelectron wavenumbers extending to >12 Å–1. The subtle signatures of the conformations are then investigated via extensive analysis of the XAFS spectra using the full multiple scattering theory as implemented by the FEFF package. Results indicate a near-eclipsed D5h geometry for low-temperature Fc, in contrast with a staggered D5d geometry observed for DmFc. The ability of this experimental approach and data analysis methodology combined with advanced theory to investigate and observe such subtle conformational differences using XAFS is a powerful tool for future challenges and widens the capacity of advanced XAFS to solve a broad range of challenging systems.

FDMX: extended X-ray absorption fine structure calculations using the finite difference method.

A new theoretical approach and computational package, FDMX, for general calculations of X-ray absorption fine structure (XAFS) over an extended energy range within a full-potential model is presented. The final-state photoelectron wavefunction is calculated over an energy-dependent spatial mesh, allowing for a complete representation of all scattering paths. The electronic potentials and corresponding wavefunctions are subject to constraints based on physicality and self-consistency, allowing for accurate absorption cross sections in the near-edge region, while higher-energy results are enabled by the implementation of effective Debye-Waller damping and new implementations of second-order lifetime broadening. These include inelastic photoelectron scattering and, for the first time, plasmon excitation coupling. This is the first full-potential package available that can calculate accurate XAFS spectra across a complete energy range within a single framework and without fitted parameters. Example spectra are provided for elemental Sn, rutile TiO2 and the FeO6 octahedron.

A technique for detection of PeV neutrinos using a phased radio array

The detection of high energy neutrinos (1015–1020 eV) is an important step toward understanding the most energetic cosmic accelerators and would enable tests of fundamental physics at energy scales that cannot easily be achieved on Earth. In this energy range, there are two expected populations of neutrinos: the astrophysical flux observed with IceCube at lower energies (∼1 PeV) and the predicted cosmogenic flux at higher energies (∼1018 eV) . Radio detector arrays such as RICE, ANITA, ARA, and ARIANNA exploit the Askaryan effect and the radio transparency of glacial ice, which together enable enormous volumes of ice to be monitored with sparse instrumentation. We describe here the design for a phased radio array that would lower the energy threshold of radio techniques to the PeV scale, allowing measurement of the astrophysical flux observed with IceCube over an extended energy range. Meaningful energy overlap with optical Cherenkov telescopes could be used for energy calibration. The phased radio array design would also provide more efficient coverage of the large effective volume required to discover cosmogenic neutrinos.

Fission Fragment Angular Distribution measurements of235U and238U at CERN n_TOF facility

Neutron-induced fission cross sections of 238U and 235U are used as standards in the fast neutron region up to 200 MeV. A high accuracy of the standards is relevant to experimentally determine other neutron reaction cross sections. Therefore, the detection effciency should be corrected by using the angular distribution of the fission fragments (FFAD), which are barely known above 20 MeV. In addition, the angular distribution of the fragments produced in the fission of highly excited and deformed nuclei is an important observable to investigate the nuclear fission process.In order to measure the FFAD of neutron-induced reactions, a fission detection setup based on parallel-plate avalanche counters (PPACs) has been developed and successfully used at the CERN-n_TOF facility. In this work, we present the preliminary results on the analysis of new 235 U(n,f) and 238 U(n,f) data in the extended energy range up to 200 MeV compared to the existing experimental data.

Electron-scattering studies of carbonyl fluoride

The present article reports calculations of total, momentum transfer, differential, excitation, and ionization cross sections for electron scattering from the carbonyl fluoride (${\mathrm{F}}_{2}\mathrm{CO}$) molecule. Total cross sections (TCSs) are presented over an extensive energy range from 0.5 to 5000 eV. The ab initio R-matrix and spherical complex optical potential methods were used to perform low-energy computations and intermediate- to high-energy calculations, respectively. The TCSs computed through these two formalisms are in good agreement in the 24--26 eV energy range. The consistency of the data in this overlapping region has allowed us to predict total cross sections over an extensive energy range. Electronic excitation, momentum transfer, and differential cross sections were also calculated using the $R$-matrix method at low incident energies. In the present study, a low-energy resonance at 3.67 eV was detected with a $^{2}B_{1}$ symmetry, indicating the probability of anion formation by the dissociative electron attachment process and further decay to neutral and negative ion fragments. The total ionization cross section for ${\mathrm{F}}_{2}\mathrm{CO}$ was also evaluated using the complex scattering potential--ionization contribution method and the binary encounter Bethe method up to 5 keV.

Electronic excitation of furfural as probed by high-resolution vacuum ultraviolet spectroscopy, electron energy loss spectroscopy, and ab initio calculations.

The electronic spectroscopy of isolated furfural (2-furaldehyde) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 3.5-10.8 eV energy-range, with absolute cross section measurements derived. Electron energy loss spectra are also measured over a range of kinematical conditions. Those energy loss spectra are used to derive differential cross sections and in turn generalised oscillator strengths. These experiments are supported by ab initio calculations in order to assign the excited states of the neutral molecule. The good agreement between the theoretical results and the measurements allows us to provide the first quantitative assignment of the electronic state spectroscopy of furfural over an extended energy range.

Interatomic scattering in energy dependent photoelectron spectra of Ar clusters.

Soft X-ray photoelectron spectra of Ar 2p levels of atomic argon and argon clusters are recorded over an extended range of photon energies. The Ar 2p intensity ratios between atomic argon and clusters' surface and bulk components reveal oscillations similar to photoelectron extended X-ray absorption fine structure signal (PEXAFS). We demonstrate here that this technique allows us to analyze separately the PEXAFS signals from surface and bulk sites of free-standing, neutral clusters, revealing a bond contraction at the surface.

Positron and electron-impact multiple-ionization

We present positron-impact multiple (single to quintuple) and total ionization cross sections of Ne, Ar, Kr, and Xe, covering an extended energy range from 50 eV to 7 keV. We improve on previous calculations of the ionization thresholds by adding the mean kinetic energy transferred to the target electrons. In this way the thresholds compare rather well with the experimental appearance energies for the different k-fold ionization cross sections. Present results include not only the novel energy threshold at low energies but also the post-collisional contribution at high energies. We performed a quite complete particle–antiparticle comparison by including our positron-impact results, new calculations for electron-impact ionization including the threshold correction, and a detailed compilation of experimental data. Present positron-impact multiple ionization cross sections are the first ones in such an extended energy region.

Positron and electron impact multiple-ionization of rare gases

SynopsisWe present a theoretical treatment of the multiple-ionization by light projectiles, which is valid in an extended energy range (from near threshold to the keV region). It covers the direct ionization and the post- collisional electron emission, and takes into account charge and mass effects: projectile trajectory, finite momentum transferred, energy threshold. Our results for positron and electron-impact on Ne, Ar, Kr and Xe, are compared with a detailed compilation of experimental data of multiple and of total ionization cross sections. These values and previous ones for antiproton and proton-impact let us to present an extended picture of the particle-antiparticle multiple-ionization.

Optimizing the design of a neutron dosemeter with an extended energy range for high energy accelerators

Different versions of the design of a neutron dosemeter for high energy accelerators based on a fast scintillation lithium glass detector of thermal neutrons are considered. The detector is placed at the center of a polyethylene moderator shaped as a sphere, a cylinder, or a truncated cylinder with a lead insert used to increase the dosemeter sensitivity to neutrons with energies above 20 MeV. Calculations of the design parameters have been performed to optimize the angular and energy dependences of the response at energies ranging from the thermal energy to 1 GeV. The best results have been obtained for dosemeter versions comprising a boron filter along with the lead insert. In this case, the instrument has the lowest mass. The dosemeter has been developed for use in the radiation monitoring systems of the IHEP U-70 accelerator complex and other accelerators. It can also be used outside shields of reactors and other low-energy facilities.

Rotational Excitations in CO-CO Collisions at Low Temperature: Time-Independent and Multiconfigurational Time-Dependent Hartree Calculations.

The rotational excitation in collisions between two carbon monoxide molecules was studied while combining the use of both time-independent and time-dependent formalisms. All of the calculations made use of a recently published four dimensional PES for CO dimer. Time-independent scattering calculations were performed in the lower part of the collision energy range, thus limiting the number of open channels and computational cost. The PES features a low-energy path for geared motion that appears to affect the excitation propensities in low-energy collisions. For reactants colliding without initial rotational excitation, symmetric excitations (both monomers excited equally) are strongly favored. This behavior deviates significantly from an exponential gap model based on endo- or exoergicity. Comparable time-dependent calculations were performed in an extended energy range made feasible by the lower cost of those calculations. The wave packet propagation in the time-dependent approach was performed with the multiconfiguration time-dependent hartree (MCTDH) method and analyses via the flux method, and the Tannor and Weeks approach was used to calculate the transition probabilities in the energy range up to 1000 cm(-1). We deduce from the cross sections the corresponding reaction rates for temperatures between 10 and 250 K. MCTDH was found to yield well-converged results, where the methods overlap, validating the use of MCTDH as an efficient tool to study collision processes.

Structure and Morphology of Silver Nanoparticles on the (111) Surface of Cerium Oxide

The structure of Ag nanoparticles of different size, supported on the cerium oxide (111) surface, was investigated by X-ray absorption fine structure at the Ag K-edge. The results of the data analysis in the near and extended energy range are interpreted with the help of the results obtained by X-ray photoelectron spectroscopy and scanning tunneling microscopy measurements and allow to obtain a detailed atomic scale description of the model system investigated. The Ag nanoparticles have an average size of a few tens of angstroms, which increases with increasing deposited Ag amount. The nanoparticles show a slight tendency to nucleate at the step edges between different cerium oxide layers and they have a face centered cubic structure with an Ag–Ag interatomic distance contracted by 3–4% with respect to the bulk value. The interatomic distance contraction is mainly ascribed to dimensionality induced effects, while epitaxial effects have a minor role. The presence of Ag–O bonds at the interface between the ...

IN1-LAGRANGE – the new ILL instrument to explore vibration dynamics of complex materials

We report on the first experimental results obtained with the recently commissioned IN1-Lagrange spectrometer, which has replaced the old IN1 Be-filter setup used for studies of lattice dynamics and molecular vibrations in an extended energy range, typically used for materials containing light chemical elements, in particular hydrogen. Unlike its predecessor, IN1-Lagrange uses, in addition to a cooled Be-filter, a large area crystal analyzer to collect the scattered neutrons and to define their final energy of 4.5 meV. Using the available set of double-focussing monochromators the incident neutron energy on IN1 can be scanned over the entire range of 4 – 600 meV provided by the ILL hot neutron source. Thanks to its large solid angle of 2.5 steradian and flexibly tuned energy resolution in the range of 1 – 5%, the IN1-Lagrange setup offers an unprecedented sensitivity permitting very rapid data acquisition and revealing fine spectral features in 'standard' samples as well as efficient measurements of hydrogen vibrations in samples containing equivalent masses of H2 as low as 100 μg.

Shielding behaviors of some polymer and plastic materials for gamma-rays

Gamma-rays interaction parameters with six polymer and plastic materials have been computed and investigated for their shielding behaviours in the experimental energy range 10–1400keV. Low mass-density and ability to transform into thin-sheets of H-containing plastic and polymer materials generate the curiosity for present study. Gamma Ray Interaction Coefficients (GRIC)-toolkit: a computer program designed in MS-Excel, 2007 for the investigation. The toolkit has the capability to compute different parameters linked to shielding properties of the sample-material such that; mass attenuation coefficients (μ/ρ), mass energy absorption coefficients (μen/ρ), equivalent atomic number (Zeq), KERMA (kinetic energy released per unit mass). Polyvinyl Chloride (PVC) seems to be the best shield for gamma radiations in energy range 10–110keV. The interaction parameters for selected samples have been computed and provided in the extended energy range 0.015–15MeV.

S-SAD phasing on SOLEIL Beamline PROXIMA 1

"PROXIMA 1, a beamline for macro-molecular crystallography at the 3rd generation synchrotron source SOLEIL, is equipped with a multi-circle goniometer (alpha 50 degrees) as well as a PILATUS 6M detector. These features, along with the extended energy range of the beam line towards the low energies (down to 5.5 keV) and the possibility to adapt the source size to the sample in order to optimize signal to noise ratio, have made the beam line very attractive for S-SAD phasing with more than seven examples of successful de novo phasing achieved over the last two years. The use of low energies has also proved a significant aid in assisting with MODEL building. The technical capabilities of the beam line for low energy data collections will be presented, along with a number of examples of the successful use of low wavelengths on the beam line. The importance of combining data from multiple sample orientations in order to achieve ""true multiplicity"" will be highlighted, as well as the importance of combining data from multiple crystals in order to achieve high multiplicity."

Electron-impact scattering by arsine

We present elastic cross sections for electron interactions with arsine (${\mathrm{AsH}}_{3}$) in gas phase over an extensive energy range from 0.5 to 5000 eV by combining two computational methods. The ab initio R-matrix method is employed for low-energy computations up to 15 eV and the intermediate to high-energy calculations were performed using the spherical complex optical potential (SCOP) method. The elastic cross section computed through the $R$ matrix and SCOP formalism shows consistency at crossover energy (11--12 eV) and gives reasonable accord with the available data. Besides elastic cross sections, the differential cross section at low and intermediate incident electron energies is reported. The electronic excitation cross section is also reported at low energies. Shape resonance is observed at around 2.4 eV due to the formation of a transient negative ion state.

Tachyonic quantum densities of relativistic electron plasmas: Cherenkov spectra of γ-ray pulsars

Abstract Tachyonic Cherenkov radiation in second quantization can explain the subexponential spectral tails of GeV γ-ray pulsars (Crab pulsar, PSR J1836+5925, PSR J0007+7303, PSR J2021+4026) recently observed with the Fermi-LAT, VERITAS and MAGIC telescopes. The radiation is emitted by a thermal ultra-relativistic electron plasma. The Cherenkov effect is derived from a Maxwell–Proca field with negative mass-square in a dispersive spacetime. The frequency variation of the tachyon mass results in exp ( − β ˆ ω 1 − ρ ) attenuation of the asymptotic Cherenkov energy flux, where β ˆ is a decay constant related to the electron temperature and ρ is the frequency scaling exponent of the tachyon mass. An exponent in the range 0 ρ 1 can reproduce the observed subexponential decay of the energy flux. For the Crab pulsar, we find ρ = 0.81 ± 0.02 , inferred from the substantially weaker-than-exponential decay of its spectral tail measured by MAGIC over an extended energy range. The scaling exponent ρ determines whether the group velocity of the tachyonic γ-rays is sub- or superluminal.