On-axis Detector Research Articles

Multi-exposure diffraction pattern fusion applied to enable wider-angle transmission Kikuchi diffraction with direct electron detectors

Diffraction pattern analysis can be used to reveal the crystalline structure of materials, and this information is used to nano- and micro-structure of advanced engineering materials that enable modern life. For nano-structured materials typically diffraction pattern analysis is performed in the transmission electron microscope (TEM) and TEM diffraction patterns typically have a limited angular range (less than a few degrees) due to the long camera length, and this requires analysis of multiple patterns to probe a unit cell. As a different approach, wide angle Kikuchi patterns can be captured using an on-axis detector in the scanning electron microscope (SEM) with a shorter camera length. These ‘transmission Kikuchi diffraction’ (TKD) patterns present a direct projection of the unit cell and can be routinely analysed using EBSD-based methods and dynamical diffraction theory. In the present work, we enhance this analysis significantly and present a multi-exposure diffraction pattern fusion method that increases the dynamic range of the detected patterns captured with a Timepix3-based direct electron detector (DED). This method uses an easy-to-apply exposure fusion routine to collect data and extend the dynamic range, as well as normalise the intensity distribution within these very wide (>95°) angle patterns. The potential of this method is demonstrated with full diffraction sphere reprojection and highlight potential of the approach to rapidly probe the structure of nano-structured materials in the scanning electron microscope.

Energy and flavor discrimination using precision time structure in on-axis neutrino beams

We propose to use a higher-frequency RF bunch structure for the primary proton beam on target and precision timing to select different energy and flavor spectra from a wide-band neutrino beam, based on the relative arrival times of the neutrinos with respect to the RF bunch structure. This `stroboscopic' approach is complementary to techniques that select different neutrino energy spectra based on the angle with respect to the beam axis. A timing-based approach allows for the selection of varying energy spectra from the same on-axis detector, and applies equally to both the near and far detectors in an oscillation experiment. Energy and flavor discrimination of neutrinos produced by hadrons in-flight will require proton bunch lengths on the order of 100 ps and commensurate time resolution in the detector. Correlating neutrino events with the parent proton interaction is currently limited by the nanosecond-scale width of the proton bunches impinging on the target. We show that these limitations can be addressed by using a superconducting RF cavity to rebunch the present 53.1 MHz RF bunch structure with a factor of 10 higher RF frequency, thus attaining the required shorter bunch length.

Atomic Resolution Vibrational Spectroscopy with On-Axis Detector Geometry

Journal Article Atomic Resolution Vibrational Spectroscopy with On-Axis Detector Geometry Get access Kartik Venkatraman, Kartik Venkatraman School for the Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona, USA Corresponding author: kvenka16@asu.edu Search for other works by this author on: Oxford Academic Google Scholar Barnaby DA Levin, Barnaby DA Levin School for the Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona, USA Search for other works by this author on: Oxford Academic Google Scholar Katia March, Katia March Eyring Materials Center, Arizona State University, Tempe, Arizona, USA Search for other works by this author on: Oxford Academic Google Scholar Peter Rez, Peter Rez Department of Physics, Arizona State University, Tempe, Arizona, USA Search for other works by this author on: Oxford Academic Google Scholar Peter A Crozier Peter A Crozier School for the Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 25, Issue S2, 1 August 2019, Pages 596–597, https://doi.org/10.1017/S1431927619003714 Published: 01 August 2019

Improving the imaging capability of an on-axis transmission Kikuchi detector

Transmission Kikuchi Diffraction (TKD) in the scanning electron microscope has been developing at a fast pace since its introduction less than a decade ago. The recently presented on-axis detector configuration, with its optimized geometry, has significantly increased the signal yield and facilitated the acquisition of STEM images in bright field (BF) and dark field (DF) mode, in addition to the automated orientation mapping of nanocrystalline electron transparent samples. However, the physical position of the integrated imaging system, located outside the detector screen, requires its movement in order to combine high resolution STEM images with high resolution orientation measurements. The difference between the two positions makes it impossible to acquire optimal signals simultaneously, leading to challenges when investigating site-specific nanocrystalline microstructures. To eliminate this drawback, a new imaging capability was added at the centre of the on-axis TKD detector, thus enabling acquisition of optimal quality BF images and orientation maps without detector movement. The advantages brought about by this new configuration are presented and the associated limitations are discussed.

On-axis TKD for orientation mapping of nanocrystalline materials in SEM

A new configuration for Transmission Kikuchi Diffraction (TKD) in SEM was recently developed, with a scintillator perpendicular to the electron beam. This configuration, “on-axis” TKD, makes grains and twins below 10nm well visible in orientation maps and with high indexation rate, as demonstrated with an electrodeposited nanocrystalline Ni. This high lateral spatial resolution is achieved by combining high accelerating voltage and low sample thickness to reduce the interaction volume. Among the advantages of the on-axis TKD, orientation mapping of particularly thin samples can be realized thanks to the advantageous axial position of the detector. Indeed, the reduction of the solid angle of the transmitted intensity around the beam axis with decreasing sample thickness is much less of a problem with an axial detector than with an off-axis detector. With an on-axis detector, the only condition for production of an orientation map is that the sample must be thick enough to produce Kikuchi diffraction in addition to spots.

Analysis of muon and electron neutrino charged current interactions in the T2K near detectors

We present the updated measurement of the muon neutrino interaction rates and spectrum at the T2K near detector complex, ND280, located at the JPARC accelerator facility in Tokai, Japan, 280 meters downstream from the target. The measurements are obtained using all the data collected until 2014. The momentum-angle spectrum of muons from νμ charged current (CC) interactions measured at ND280 off-axis detector constrains the flux and cross-section uncertainties in the T2K oscillation analysis. This spectrum was also used to measure a differential cross-section measurement of muon neutrinos on carbon. Similarly the νe contamination of the T2K beam was measured to verify this intrinsic background for the electron neutrino appearance and provide the first electron neutrino cross-section result since the Gargamelle experiment. The νμ CC inclusive events selected in the on-axis detector (INGRID) at 280 m and originally used for monitoring the T2K beam stability were also used to measure the CC interaction cross sections on carbon and iron. The selections and results for both ND280 and INGRID will be presented in this paper as well as future prospects for both detectors.

Orientation mapping by transmission-SEM with an on-axis detector

Conventional orientation mapping in a scanning electron microscope (SEM) is a valuable technique for characterizing crystalline materials, but its application to ultrafine or nano-grain materials is limited by its spatial resolution. The resolution can be increased by collecting transmission diffraction patterns in SEM. In previous works, such patterns were collected using off-axis detectors in nearly vertical position. To avoid some drawbacks of such arrangement, a new configuration was devised in which the scintillator is located underneath the thin foil on the optical axis of the microscope, and the light is reflected towards the camera by a mirror. This simple configuration gives intense patterns even at very low probe currents, and can be potentially used for collecting maps of relatively high spatial resolution. Example maps reveal details with dimensions of about 5nm. Because of its resolution and geometric simplicity, the proposed configuration will open new opportunities in SEM-based characterization of nanocrystalline materials.

T2K on-axis detector results: cross section measurements

The T2K experiment brings the world leading constraints on the atmospheric parameters, sin2 θ 23 = 0.514 ± 0.082 and |Δm 32 2 | = (2.44−0.15 +0.17 ) × 10−3 eV2 .c−4 , along with first observation of the electron neutrino appearance in the muon neutrino beam. In the upcoming years, a higher precision measurement of the PMNS matrix parameters with possible evidence of a non zero CP violation phase requires a reduction in the main systematics which come from the cross section model. The INGRID detector is the onaxis detector of the long-baseline T2K experiment. Though its main goal is to monitor the neutrino flux intensity and off-axis angle, this proceeding presents the νμ cross section measurements that have been performed to reduce the uncertainty on the neutrino cross section models.

T2K on-axis detector results: cross section measurements

The T2K experiment brings the world leading constraints on the atmospheric parameters, sin2θ23 = 0.514 ± 0.082 and |Δm322| = (2.44−0.15+0.17) × 10−3eV2.c−4, along with first observation of the electron neutrino appearance in the muon neutrino beam. In the upcoming years, a higher precision measurement of the PMNS matrix parameters with possible evidence of a non zero CP violation phase requires a reduction in the main systematics which come from the cross section model. The INGRID detector is the onaxis detector of the long-baseline T2K experiment. Though its main goal is to monitor the neutrino flux intensity and off-axis angle, this proceeding presents the νμ cross section measurements that have been performed to reduce the uncertainty on the neutrino cross section models.

Scintillation of Airy beam arrays in atmospheric turbulence

We investigate the scintillation properties of Airy beam arrays in atmospheric turbulence. By utilizing the "self-bending" propagation property of Airy beams, the constituent beamlets propagate through relatively independent regions of turbulence but still largely overlap at the on-axis detector. Through numeric simulations, it is shown that the scintillation of an Airy beam array is significantly reduced and close to the theoretical minimum.

Hadron production uncertainties at NuMI

An improved approach for the extrapolation of the neutrino spectrum from the near to the far site is described. The method exploits the strong correlation between neutrino spectra at two arbitrary detector locations, provided that they come from the same parent hadron beam. Accuracy of the method was extensively studied on the particular example of hadron production uncertainties. Neutrino flux at the far on-axis site can be predicted more accurately than in the Far/Near ratio method. In an off-axis experiment, the integrated neutrino flux can be known to be 1–2%, even using only the on-axis near detector information. The off-axis intrinsic νe flux can be estimated to be 5% by correlating it to the νμ and ν̄μ flux measured in an on-axis detector.

Emissivities of diffuse cavities III Isothermal and nonisothermal double cones

Local hemispherical effective emissivities and integrated cavity emissivities are computed for isothermal and nonisothermal diffuse double cones (a conical section joined to a conical frustum) with and without lids, and are compared with corresponding values for cylindrocones. The local emissivities increase and become more uniform with increasing taper of the frustum. They are also considerably higher when there is a lid. For cavities with the same conical section, length, and aperture, a lidded double cone is blacker than a lidded cylindrocone when the front half of the frustum is invisible, but less black otherwise. For double cones of the same length, diameter, and aperture, the best choice of cone and frustum angles depends upon the particular viewing conditions. The integrated cavity emissivities vary only slightly with the angles of cone and frustum when the frustum is relatively long, and the normal emissivity (for a small on-axis detector a large distance away) is higher than the hemispherical emissivity (for a detector that fills the cavity aperture). When the frustum is relatively short, all of these vary substantially with angle, and the hemispherical emissivity can be higher than the normal emissivity. There is a marked variation of both local and integrated emissivities with wavelength in nonisothermal double cones; e.g., for the particular cases illustrated, the normal spectral emissivities change by from 4% to 6% and the hemispherical spectral emissivities by from 17% to 20% between 0.3 and 1 μm for a 1% temperature variation at 1300 K. The amount of the change in these spectral emissivities also depends upon the geometry of the cavity.