Yuhua Su

Inverse pole figure mapping of bulk crystalline grains in a polycrystalline steel plate by pulsed neutron Bragg-dip transmission imaging

A new mapping procedure for polycrystals using neutron Bragg-dip transmission is presented. This is expected to be useful as a new materials characterization tool which can simultaneously map the crystallographic direction of grains parallel to the incident beam. The method potentially has a higher spatial resolution than neutron diffraction imaging. As a demonstration, a Bragg-dip neutron transmission experiment was conducted at J-PARC on beamline MLF BL10 NOBORU. A large-grained Si–steel plate was used. Since this specimen included multiple grains along the neutron beam transmission path, it was a challenging task for existing methods to analyse the direction of the crystal lattice of each grain. A new data-analysis method for Bragg-dip transmission measurements was developed based on database matching. As a result, the number of grains and their crystallographic direction along the neutron transmission path have been determined.

Counting-type neutron imaging detectors of the energy-resolved neutron imaging system RADEN at the J-PARC/MLF

The recently commissioned Energy-Resolved Neutron Imaging System, RADEN, located at the J-PARC Materials and Life Science Experimental Facility (MLF), is the worlds first dedicated high-intensity, pulsed neutron imaging instrument. In addition to conventional radiography and tomography, the wide bandwidth and accurate measurement of neutron energy by time-of-flight is utilized to perform energy-resolved neutron imaging. Such techniques allow direct imaging of the macroscopic distribution of microscopic properties of materials in situ, including crystallographic structure and internal strain, nuclide-specific density and temperature distributions, and internal/external magnetic fields. To carry out such measurements in the high-rate, high-background environment at RADEN, we use cutting-edge detector systems, recently developed in Japan, employing micro-pattern detectors or fast Li-glass scintillators with high-speed, Field Programmable Gate Array-based data acquisition. These counting-type detectors offer sub-μs time resolution, high neutron count rates, and event-by-event gamma rejection. The available detectors offer a range of spatial resolutions from 0.3 to 3 mm and counting rates from 0.6 to 8 Mcps. In the present paper, we show the performance of these detectors as measured at RADEN. We also consider planned improvements to the detector systems that will allow us to achieve finer spatial resolutions by several factors and order-of-magnitude higher count rates.

Development of the next-generation micro pixel chamber-based neutron imaging detector (μNID) for energy-resolved neutron imaging at the J-PARC/MLF

The Energy-Resolved Neutron Imaging System RADEN, located at the J-PARC Materials and Life Science Experimental Facility in Japan, is the worlds first dedicated high-intensity, short-pulsed neutron imaging beam line. To carry out energy-resolved neutron imging at RADEN, we use cutting-edge detector systems employing micropattern detectors and data acquisition systems based on Field Programmable Gate Arrays to provide the necessary sub-μs time resolution, high counting rates, and event-by-event background rejection. One such detector, the Micro Pixel Chamber-based Neutron Imaging Detector (μNID), provides a spatial resolution of 120 μm (s), time resolution of 0.6 μs, 18% detection efficiency for thermal neutrons, and effective gamma sensitivity of less than 10−12. We have recently increased the rate capacity of the μNID from 600 kcps to more than 8 Mcps via an upgrade of the readout electronics and the introduction of a new gas mixture optimized for higher count rate, better spatial resolution, and higher detection efficiency. We are also developing new detection elements with strip pitches of 280 μm and 215 μm, down from 400 μm, with a corresponding improvement in the spatial resolution expected. Here, we present the progress of the ongoing development of the μNID, including the results of recent on-beam tests performed at RADEN.

Microstructure and Residual Strain Distribution in Cast Duplex Stainless Steel Studied by Neutron Imaging

The neutron imaging and diffraction instruments at Materials and Life Science Experimental Facility (MLF) at J-PARC are expected to play an important role in the microstructure characteristic evaluation of steel materials further for industry application. Neutron transmission spectrum measured at a neutron imaging detector coupled with time-of-flight (TOF) method at a pulsed source, can quantitatively and non-destructively visualize the spatial distributions of the wider area by 2D mapping of textures and the microstructures information inside a relatively thicker material than the traditional electron, X-ray and neutron experiments. In this study, neutron imaging experiment was performed using NOBORU, BL10 of MLF at J-PARC. Four kinds of cast duplex stainless steel with ferrite and austenite microstructure were studied here, which were produced by different casting method at different temperature. Firstly, a two-dimensional scintillation detector using wavelength-shifting (WLS) fibers [1] with pixel size of 0.52mm × 0.52mm and illuminated area 55mm × 55mm was used for data collection. Then, measurement by Micro Pixel Chamber (μPIC)-based neutron imaging detector [2] having higher spatial resolution about 0.2mm was conducted. Data analysis code RITS (Rietveld Imaging of Transmission Spectra) [3] will be used for microstructure including crystalline phase, lattice strain, crystallite size, texture evaluation. This work was supported by Photon and Quantum Basic Research Coordinated Development Program from the Ministry of Education, Culture, Sports, Science and Technology, Japan.

In Situ Observations of Microstructural Evolution During Annealing or Deformation in an Electro-Deposited Fine-Grained Iron

Fine grained electro-deposited pure iron shows ultra-high Lankford value larger than 7. Tensile deformation behavior at room temperature was studied using in situ neutron diffraction and semi in situ scanning electron microscopy with electron back scatter diffraction (SEM/EBSD) observation. The characteristic deformation mechanism to bring high R value accompanying grain coalescence is made clear. The sheet was annealed to observe hydrogen behavior and grain growth using thermal desorption spectroscopy, small angle neutron scattering, in situ neutron diffraction and SEM/EBSD. The shape of grain was changed from needle-like shape to polygonal with annealing, leading to a decrease of R value.