Medium Energy Resolution Research Articles

Asymmetric electrostatic dodecapole: compact bandpass filter with low aberrations for momentum microscopy.

Imaging energy filters in photoelectron microscopes and momentum microscopes use spherical fields with deflection angles of 90°, 180° and even 2 × 180°. These instruments are optimized for high energy resolution, and exhibit image aberrations when operated in high transmission mode at medium energy resolution. Here, a new approach is presented for bandpass-filtered imaging in real or reciprocal space using an electrostatic dodecapole with an asymmetric electrode array. In addition to energy-dispersive beam deflection, this multipole allows aberration correction up to the third order. Here, its use is described as a bandpass prefilter in a time-of-flight momentum microscope at the hard X-ray beamline P22 of PETRA III. The entire instrument is housed in a straight vacuum tube because the deflection angle is only 4° and the beam displacement in the filter is only ∼8 mm. The multipole is framed by transfer lenses in the entrance and exit branches. Two sets of 16 different-sized entrance and exit apertures on piezomotor-driven mounts allow selection of the desired bandpass. For pass energies between 100 and 1400 eV and slit widths between 0.5 and 4 mm, the transmitted kinetic energy intervals are between 10 eV and a few hundred electronvolts (full width at half-maximum). The filter eliminates all higher or lower energy signals outside the selected bandpass, significantly improving the signal-to-background ratio in the time-of-flight analyzer.

Application of peak based-Bayesian statistical method for isotope identification and categorization of depleted, natural and low enriched uranium measured by LaBr3:Ce scintillation detector

Todays, medium energy resolution detectors are preferably used in radioisotope identification devices(RID) in nuclear and radioactive material categorization. However, there is still a need to develop or enhance « automated identifiers » for the useful RID algorithms. To decide whether any material is SNM or NORM, a key parameter is the better energy resolution of the detector. Although masking, shielding and gain shift/stabilization and other affecting parameters on site are also important for successful operations, the suitability of the RID algorithm is also a critical point to enhance the identification reliability while extracting the features from the spectral analysis. In this study, a RID algorithm based on Bayesian statistical method has been modified for medium energy resolution detectors and applied to the uranium gamma-ray spectra taken by a LaBr3:Ce detector. The present Bayesian RID algorithm covers up to 2000 keV energy range. It uses the peak centroids, the peak areas from the measured gamma-ray spectra. The extraction features are derived from the peak-based Bayesian classifiers to estimate a posterior probability for each isotope in the ANSI library. The program operations were tested under a MATLAB platform.The present peak based Bayesian RID algorithm was validated by using single isotopes(241Am, 57Co, 137Cs, 54Mn, 60Co), and then applied to five standard nuclear materials(0.32–4.51% at.235U), as well as natural U- and Th-ores. The ID performance of the RID algorithm was quantified in terms of F-score for each isotope. The posterior probability is calculated to be 54.5–74.4% for 238U and 4.7–10.5% for 235U in EC-NRM171 uranium materials. For the case of the more complex gamma-ray spectra from CRMs, the total scoring (ST) method was preferred for its ID performance evaluation. It was shown that the present peak based Bayesian RID algorithm can be applied to identify 235U and 238U isotopes in LEU or natural U–Th samples if a medium energy resolution detector is was in the measurements.

Possibilities of the use of CeBr3 scintillation detectors for the measurement of the content of radionuclides in samples for environmental monitoring

The investigation of radioactivity in samples is an application of gamma-ray spectrometry dealing with low and very low level gamma-ray activities of different isotopes. Gamma-ray spectrometry performed in the framework of radiological environmental monitoring may be done after selective sampling processes or after a chemical purification of a sample. Both cases imply that only some specific radionuclides should contribute to the obtained spectrum. Gamma-ray spectrometry performed with medium energy resolution detectors may allow the possible distinction of their photopeaks. Therefore, a cerium bromide (CeBr3) detector can be particularly attractive for routine tasks in radiological environmental monitoring as it has a high efficiency, medium energy resolution and it can work at room temperature. This study describes the conditions under which a CeBr3 detector can serve for some routine analysis in radiological analysis of samples collected in the environment or collected by air-samplers in environmental radiological monitoring programmes.

Montel mirror based collimating analyzer system for high-pressure resonant inelastic X-ray scattering experiments.

Resonant inelastic X-ray scattering (RIXS) is increasingly playing a significant role in studying highly correlated systems, especially since it was proven capable of measuring low-energy magnetic excitations. However, despite high expectations for experimental evidence of novel magnetic phases at high pressure, unequivocal low-energy spectral signatures remain obscured by extrinsic scattering from material surrounding the sample in a diamond anvil cell (DAC): pressure media, Be gasket and the diamond anvils themselves. A scattered X-ray collimation based medium-energy resolution (∼100 meV) analyzer system for a RIXS spectrometer at the Ir L3-absorption edge has been designed and built to remediate these difficulties. Due to the confocal nature of the analyzer system, the majority of extrinsic scattering is rejected, yielding a clean low-energy excitation spectrum of an iridate Sr2IrO4 sample in a DAC cell. Furthermore, the energy resolution of different configurations of the collimating and analyzing optics are discussed.

A soft x-ray-ultraviolet (SUV) beamline and diffractometer for resonant elastic scattering and ultraviolet-vacuum ultraviolet reflectance at the Singapore synchrotron light source.

A new beamline and a six-circle UHV diffractometer have been constructed at the Singapore Synchrotron Light Source with a broad energy coverage from 3.5 to 1500 eV. The beamline is optimized for ultraviolet-vacuum-ultraviolet optical reflectivity and resonant soft X-ray scattering with medium energy resolution over a broad energy range, achieved by using a self-focusing monochromator consisting of a plane mirror and three variable line spacing gratings. The unique character of the diffractometer comprises 4-circles in the vertical plane and 2-circles in the horizontal plane. Thirteen motions are available inside the UHV chamber with a base pressure of 1 × 10-9 mbar. Two sample holders working independently over a temperature range of 37 K-400 K are controlled by a closed-cycle cryostat, while the bottom holder inside a high field compact pulsed magnet is available for measurements requiring a magnetic field.

X-ray spectroscopy with variable line spacing based on reflection zone plate optics.

X-ray spectroscopy is a method, ideally suited for investigating the electronic structure of matter, which has been enabled by the rapid developments in light sources and instruments. The x-ray fluorescence lines of life-relevant elements such as carbon, nitrogen, and oxygen are located in the soft x-ray regime and call for suitable spectrometer devices. In this Letter, we present a high-resolution spectrum of liquid water, recorded with a soft x-ray spectrometer based on a reflection zone plate (RZP) design. The RZP-based spectrometer with meridional variation of line space density from 2953 to 3757l/mm offers extremely high detection efficiency and, at the same time, medium energy resolution. We can reproduce the well-known splitting of liquid water in the lone pair regime with 10s acquisition time.

Pulse shape discrimination of Cs[formula omitted]LiYCl[formula omitted]:Ce[formula omitted] detectors at high count rate based on triangular and trapezoidal filters

Cs2LiYCl6:Ce3+ (CLYC) detectors have demonstrated the capability to simultaneously detect γ-rays and thermal and fast neutrons with medium energy resolution, reasonable detection efficiency, and substantially high pulse shape discrimination performance. A disadvantage of CLYC detectors is the long scintillation decay times, which causes pulse pile-up at moderate input count rate. Pulse processing algorithms were developed based on triangular and trapezoidal filters to discriminate between neutrons and γ-rays at high count rate. The algorithms were first tested using low-rate data. They exhibit a pulse-shape discrimination performance comparable to that of the charge comparison method, at low rate. Then, they were evaluated at high count rate. Neutrons and γ-rays were adequately identified with high throughput at rates of up to 375 kcps. The algorithm developed using the triangular filter exhibits discrimination capability marginally higher than that of the trapezoidal filter based algorithm irrespective of low or high rate. The algorithms exhibit low computational complexity and are executable on an FPGA in real-time. They are also suitable for application to other radiation detectors whose pulses are piled-up at high rate owing to long scintillation decay times.

Characteristics of an Energy-Resolving System Using Dynamic Time Over Threshold Method

The time over threshold (ToT) method can greatly simplify the data acquisition (DAQ) and control unit of a multichannel energy-resolving system. However, the system suffers from poor linearity. The linearity can be significantly improved by superimposing a delayed exponential rising voltage waveform over the constant preset threshold after the leading-edge triggering. This is called the dynamic time over threshold (DToT) method. In this paper, a theoretical model is proposed and verified by experimental results to characterize the noise transfer, integral nonlinearity (INL), and stability of a DToT-based system. The results show that the DToT system is able to achieve an INL of 2% or better over a wide dynamic range without outstanding increments of noise contributions to the energy resolution. Both the energy resolution and stability are significantly enhanced compared with those of a normal ToT system. We suggest that the DToT method can be applied to simplify the DAQ unit of a multichannel solid state detector system requiring medium energy resolution and linearity.

Strong anisotropic dynamics of ultra-confined water.

Dynamics of water confined in ∼5 Å diameter channels of beryl and cordierite single crystals were studied by using inelastic (INS) and quasielastic (QENS) neutron scattering. The INS spectra for both samples were similar and showed that there are no hydrogen bonds acting on water molecule, which experiences strong anisotropic potential, steep along the channels and very soft perpendicular to it. The high-resolution (3.4 μeV) QENS data revealed gradual freezing out of the water molecule dynamics for both minerals at temperatures below about 80 K when the scattering momentum transfer was parallel to the channels, but not when it was perpendicular to the channels. The QENS study with medium energy resolution (0.25 meV) of the beryl with the scattering momentum transfer along the channels showed gradual freezing out of water molecule dynamics at temperatures below about 200 K, whereas at higher temperatures the data could be described as 2-fold rotational jumps about the axis coinciding with the direction of the dipole moment (that is, perpendicular to the channels), with a residence time of 5.5 ps at 225 K. The energy resolution dependence of the apparent dynamics freezing temperature suggests gradual slowing down of the rotational jumps as the temperature is decreased, until the associated QENS broadening can no longer be detected, rather than actual freezing.

A DECADE-BASELINE STUDY OF THE PLASMA STATES OF EJECTA KNOTS IN CASSIOPEIA A

We present the analysis of 21 bright X-ray knots in the Cassiopeia A supernova remnant from observations spanning 10 yr. We performed a comprehensive set of measurements to reveal the kinematic and thermal state of the plasma in each knot, using a combined analysis of two high energy resolution High Energy Transmission Grating (HETG) and four medium energy resolution Advanced CCD Imaging Spectrometer (ACIS) sets of spectra. The ACIS electron temperature estimates agree with the HETG-derived values for approximately half of the knots studied, yielding one of the first comparisons between high resolution temperature estimates and ACIS-derived temperatures. We did not observe the expected spectral evolutionpredicted from the ionization age and density estimates for each knotin all but three of the knots studied. The incompatibility of these measurements with our assumptions has led us to propose a dissociated ejecta model, with the metals unmixed inside the knots, which could place strong constraints on supernova mixing models.

MERIX—Next generation medium energy resolution inelastic X-ray scattering instrument at the APS

MERIX (Medium Energy Resolution Inelastic X-ray Scattering) is an instrument for Resonant Inelastic X-ray Scattering (RIXS) studies, in the hard X-ray regime, designed to work with photons in the 5–12keV range, spanning atomic resonances near the K-edges of 3d elements, and the L-edges of 4f and 5d elements. The energy analysis of inelastically scattered photons is performed with segmented spherical crystal analyzers in close to Bragg backscattering geometry. For each resonance (edge) a specially designed analyzer is used, fabricated from Ge, Si, or LiNbO3 crystals. MERIX uses a position sensitive (micro-strip) detector to take snapshots of IXS spectra which are dispersed in space and over an energy range of a few eV with ≃20–40meV energy resolution. The spectral resolution of the MERIX spectrometer depends on the analyzer and varies from ≃45meV to ≃170meV, while the momentum transfer resolution is ≃1–4nm−1. Samples are illuminated by micro-focused beams of size ≃10μm×45μm, allowing for studies at high-pressure and other extreme conditions. Polarization selectivity is ensured by vertical or horizontal momentum transfer scans. MERIX features ≃100 times higher count-rates compared to previously built RIXS instruments.

Complex fragmentation pathways of rhodanine and rhodanine-3-acetic acid upon resonant capture of low-energy electrons

A detailed gas-phase study of dissociative electron attachment (DEA) to rhodanine ( Rd) and its 3-acetic acid derivative ( Rdaa) in the 0–14 eV energy range has been carried out with a magnetic mass spectrometer under conditions of medium energy resolution (0.4 eV) of the incident electron beam, and high sensitivity. The DEA spectra reveal the occurrence of numerous and complex dissociative decay channels of the molecular anions formed by resonances, involving multiple bond cleavage and structural rearrangements. Along with a variety of anion fragments normally formed in the collision cell at incident electron energies <1 eV, dissociation of a series of metastable anion species (occurring in the time scale of microseconds) is also detected. The observation of these slow processes is consistent with the complexity of many dissociative channels, and allows to propose schemes for the fragmentation pathways. The DEA spectra of both Rd and Rdaa also display small yields of molecular anions at zero energy. Their lifetimes with respect to electron detachment are experimentally evaluated to be about 30 μs and 200 μs, respectively. These (vibrationally excited) ground anion states formed by capture of thermal electrons mainly into the ring π* (C S) LUMO survive long enough to redistribute their excess energy before undergoing different dissociation channels.

Low-Energy Electron Attachment to the Dichlorodifluoromethane (CCl2F2) Molecule

Results from a joint experimental study of electron attachment to dichlorodifluoromethane (CCl(2)F(2)) molecules in the gas phase are reported. In a high resolution electron beam experiment involving two versions of the laser photoelectron attachment method, the relative cross section for formation of the dominant anion Cl(-) was measured over the energy range 0.001-1.8 eV at the gas temperature T(G) = 300 K. It exhibits cusp structure at thresholds for vibrational excitation of the nu(3)(a(1)) mode due to interaction with the attachment channels. With reference to the thermal attachment rate coefficient k(T = 300 K) = 2.2(8) x 10(-9) cm(3) s(-1) (fitted average from several data), a new highly resolved absolute attachment cross section for T(G) = 300 K was determined. Partial cross sections for formation of the anions Cl(-), Cl(2)(-), F(-), ClF(-), and CCl(2)F(-) were measured over the range 0-12 eV, using three different electron beam experiments of medium energy resolution. The dependence of the attachment rate coefficient k(T(e);T(G) = 300 K) on electron temperature T(e) was calculated over the range 50-15 000 K, based on a newly constructed total cross section for anion formation at T(G) = 300 K. R-matrix calculations for Cl(-) production have been carried out for comparison with the experimental data. The R-matrix results are in line with the main experimental observations and predict the dependence of the DEA cross section on the initial vibrational level nu(3)() and on the vibrational temperature. Furthermore, the cross section for vibrational excitation of the nu(3) mode has been computed.

X-ray beamlines for structural studies at the NSRRC superconducting wavelength shifter

Using a superconducting-wavelength-shifter X-ray source with a photon flux density of 10(11)-10(13) photons s(-1) mrad(-1) (0.1% bandwidth)(-1) (200 mA)(-1) in the energy range 5-35 keV, three hard X-ray beamlines, BL01A, BL01B and BL01C, have been designed and constructed at the 1.5 GeV storage ring of the National Synchrotron Radiation Research Center (NSRRC). These have been designed for structure-related research using X-ray imaging, absorption, scattering and diffraction. The branch beamline BL01A, which has an unmonochromatized beam, is suitable for phase-contrast X-ray imaging with a spatial resolution of 1 microm and an imaging efficiency of one frame per 10 ms. The main beamline BL01B has 1:1 beam focusing and a medium energy resolution of approximately 10(-3). It has been designed for small-angle X-ray scattering and transmission X-ray microscopy, used, respectively, in anomalous scattering and nanophase-contrast imaging with 30 nm spatial resolution. Finally, the branch beamline BL01C, which features collimating and focusing mirrors and a double-crystal monochromator for a high energy resolution of approximately 10(-4), has been designed for X-ray absorption spectroscopy and high-resolution powder X-ray diffraction. These instruments, providing complementary tools for studying multiphase structures, have opened up a new research trend of integrated structural study at the NSRRC, especially in biology and materials. Examples illustrating the performances of the beamlines and the instruments installed are presented.

Resonant double photoionization of lithium studied with medium energy resolution

We have measured the relative photoionization cross section for the formation of ${\mathrm{Li}}^{2+}$ ions between 148 and $161\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ photon energy with higher photon-energy resolution than in previous ${\mathrm{Li}}^{2+}$ studies. This energy region is characterized by double and triple excitations that lead to strong enhancements in the ${\mathrm{Li}}^{2+}$ cross section. As a result, the double-to-single photoionization ratio shows a dramatic resonance structure not seen before. We have determined the resonance positions and widths using Fano-profile fits to the ${\mathrm{Li}}^{2+}$ data and compare them to previously published values and a calculated ${\mathrm{Li}}^{2+}$ cross-section curve.

MERLIN, a new high count rate spectrometer at ISIS

MERLIN is designed to be a high intensity, medium energy resolution spectrometer. As such, it will complement the high-resolution MAPS spectrometer at ISIS. MERLIN will utilise all the latest advances in technology with a supermirror guide to enhance flux as well as 3 m long position-sensitive detectors in a vacuum making it ideal for single-crystal users. The detector bank will cover a massive π steradians of solid angle with an angular range from −45° to +135° degrees in the horizontal plane and ±30° degrees in the vertical plane. This will allow large swathes of Q, ω space to be accessed in a single run. The instrument will be ready for commissioning in February 2006. This paper presents details of design and performance of this new instrument.

International Standards on Calibration of XPS and AES Spectrometer

International standards of XPS and AES spectrometers have been established. Binding energy scale calibration for XPS spectrometers was standardized as ISO 15472. The calibration of kinetic energy scale for AES spectrometers was standardized as ISO 17973 and 17974. The calibrations for the intensity scale are now discussing. The calibrations for the XPS and AES spectrometers were reviewed. The standard for XPS spectrometers specifies the calibration methods to estimate uncertainty with 95% reliability using repeatability and the linearity of binding energy scale and to correct the binding energy scales. This standard also specifies the method to establish the calibration schedule. Moreover, the standards on AES spectrometers specify the calibrations with high energy resolution for the chemical state analysis and the calibration with the medium energy resolution for elemental analysis.

Merlin project begins

On June 11, 2002, a meeting was held at Milton Hill near the Rutherford Appleton Laboratory to discuss the MERLIN project with the user community. The project started in February 2002 with an official announcement that EPSRC was to fund the construction of the MERLIN chopper spectrometer at ISIS through grants to Keith McEwen (UCL), Stephen Hayden (Bristol), and Martin Dove (Cambridge). MERLIN is designed to be a high intensity, medium energy resolution spectrometer, using supermirror guides to provide a high neutron flux onto the sample. Position sensitive gas detectors, like those used on MAPS, will be used to provide more than JC steradians of solid angle coverage with an angular range from −45° to 135° in the horizontal plane and ±30° in the vertical plane. This will allow large swathes of q,ω space to be accessed simultaneously.

Performance characteristics of a chemical imaging time-of-flight mass spectrometer.

A chemical imaging time-of-flight secondary ion mass spectrometer is described. It consists of a liquid metal ion gun, medium energy resolution reflectron mass analyzer, liquid nitrogen cooled sample stage, preparation chamber and dual stage entry port. Unique features include compatibility with laser postionization experiments, large field of view, cryogenic sample handling capability and high incident ion beam current. Instrument performance is illustrated by the characterization of scanning electron microscopy grids, silver and functionalized polystyrene beads and the postionization of an organic overlayer on a gold substrate.

The imaging gamma-ray telescope COMPTEL aboard GRO

The imaging Compton telescope COMPTEL is one of the four instruments onboard NASA's Gamma Ray Observatory GRO which is to be launched in 1991 by the Space Shuttle Atlantis. COMPTEL will explore the 1 to 30 MeV energy range with an angular resolution of a few degrees within a large field-of-view of about 1 steradian. Its medium energy resolution (8.8 % FWHM at 1.27 MeV) in addition makes it to a powerful gamma-ray line spectrometer. Within a 2-weeks observation period COMPTEL will be able to detect sources which are about 20-times weaker than the Crab. With these properties COMPTEL is well suited to perform the first complete sky survey at MeV-energies. Targets of special interest are galactic gamma ray sources (like radio pulsars, X-ray binaries, the Galactic Center, the unidentified COS-B sources, supernova remnants and molecular clouds), external galaxies (especially the nuclei of active galaxies), gamma-ray line sources (e.g. the distribution of the 1.8 MeV line emissivity throughout the Galaxy), the diffuse gamma-ray emission from interstellar space, the cosmic gamma ray background, cosmic gamma-ray bursts, and gamma-ray and neutron emission during solar flares.