Abstract
The investigation of microstructure of crystalline materials is one of the possible and frequently used applications of energy-resolved neutron imaging. The position of Bragg edges is defined by sharp changes in neutron transmission and can thus be determined by the measurement of the transmission spectra as a function of neutron wavelength. The accuracy of this measurement depends on both the data analysis technique and the quality of the measured spectra. While the optimization of reconstruction methods was addressed in several previous studies, here we introduce an important prerequisite when aiming for high resolution Bragg edge strain imaging — a well calibrated flight path across the entire field of view (FOV). Compared to e.g. powder diffraction, imaging often uses slightly different geometries and hence requires a calibration for each particular setup. We herein show the importance of this calibration across the entire FOV in order to determine the instrumental error correction for pulsed neutron beamlines. In addition, we also consider the precision of Bragg edge reconstruction as a function of integration time and the minimal sample area. We demonstrate that, with a proper calibration procedure, the Bragg edge wavelength distribution across the entire sample can be reconstructed with an accuracy of Δλ∕λ=±∼0.01%. Our experiments indicate that the strain maps of Inconel 625 samples printed by a direct metal laser melting additive manufacturing technique can be reconstructed with the precision of ±∼100με. The full FOV calibration technique becomes even more important with the development of advanced neutron energy-resolved imaging beamlines and detectors with large FOVs.
Original language | English |
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Article number | 165493 |
Journal | Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment |
Volume | 1009 |
DOIs | |
State | Published - Sep 1 2021 |
Externally published | Yes |
Funding
The authors acknowledge the access to unique neutron imaging user facilities at the Spallation Neutron Source (ORNL, USA) and Materials and Life Sciences Facility (JPARC, Japan, granted through proposal Proposals 2017B0111 and 2019A0104) and all the great help of our colleagues at these facilities. Authors would like to acknowledge the generous donation of the FPGA hardware (Kintex development boards) and design tools by Xilinx Inc. of San Jose, California, through their Xilinx University Program. The work on the development of energy resolved imaging at the University of California was partially funded through the research grants by the United States Department of Energy (DOE) under contract No. DE-AC02-05CH11231. A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-1008 00OR22725.
Keywords
- Bragg edges
- Energy-resolved neutron imaging
- Microstructure
- Strain