Time-resolved Neutron Radiography Research Articles

Investigation of image distortion due to MCP electronic readout misalignment and correction via customized GUI application

The MCP-based neutron counting detector is a novel device that allows high spatial resolution and time-resolved neutron radiography and tomography with epithermal, thermal and cold neutrons. Time resolution is possible by the high readout speeds of ∼ 1200 frames/sec, allowing high resolution event counting with relatively high rates without spatial resolution degradation due to event overlaps. The electronic readout is based on a Timepix sensor, a CMOS pixel readout chip developed at CERN. Currently, a geometry of a quad Timepix detector is used with an active format of 28 × 28 mm2 limited by the size of the Timepix quad (2 × 2 chips) readout. Measurements of a set of high-precision micrometers test samples have been performed at the Imaging and Materials Science & Engineering (IMAT) beamline operating at the ISIS spallation neutron source (U.K.). The aim of these experiments was the full characterization of the chip misalignment and of the gaps between each pad in the quad Timepix sensor. Such misalignment causes distortions of the recorded shape of the sample analyzed. We present in this work a post-processing image procedure that considers and corrects these effects. Results of the correction will be discussed and the efficacy of this method evaluated.

Time-resolved neutron imaging at ANTARES cold neutron beamline

In non-destructive evaluation with X-rays light elements embedded in dense, heavy (or high-Z) matrices show little contrast and their structural details can hardly be revealed. Neutron radiography, on the other hand, provides a solution for those cases, in particular for hydrogenous materials, owing to the large neutron scattering cross section of hydrogen and uncorrelated dependency of neutron cross section on the atomic number. The majority of neutron imaging experiments at the present time is conducted with static objects mainly due to the limited flux intensity of neutron beamline facilities and sometimes due to the limitations of the detectors. However, some applications require the studies of dynamic phenomena and can now be conducted at several high intensity beamlines such as the recently rebuilt ANTARES beam line at the FRM-II reactor. In this paper we demonstrate the capabilities of time resolved imaging for repetitive processes, where different phases of the process can be imaged simultaneously and integrated over multiple cycles. A fast MCP/Timepix neutron counting detector was used to image the water distribution within a model steam engine operating at 10 Hz frequency. Within <10 minutes integration the amount of water was measured as a function of cycle time with a sub-mm spatial resolution, thereby demonstrating the capabilities of time-resolved neutron radiography for the future applications. The neutron spectrum of the ANTARES beamline as well as transmission spectra of a Fe sample were also measured with the Time Of Flight (TOF) technique in combination with a high resolution beam chopper. The energy resolution of our setup was found to be ∼ 0.8% at 5 meV and ∼ 1.7% at 25 meV. The background level (most likely gammas and epithermal/fast neutrons) of the ANTARES beamline was also measured in our experiments and found to be on the scale of 3% when no filters are installed in the beam.Online supplementary data available from stacks.iop.org/jinst/10/P07008/mmedia. The videos are given as supplementary material linked to the main article.

Polymer foam evolution characterized by time-resolved neutron radiography

Abstract For the first time, the temporal evolution of different types of polypropylene (PP) foams has been studied using time-resolved neutron radiography. This technique is advantageous since it allows visualizing the internal structure of polymeric foams inside metallic moulds during its production with excellent contrast in comparison to X-ray imaging. The experiments have been carried out in heated aluminium moulds exposed to a neutron beam (exposure time of 5 s) during a long time (1–2 h typically) thus observing the foam expansion and ageing (foam evolution at high temperature). Foam stability has been analysed as a function of different variables (liquid fraction –density–, blowing agent content and polymer rheology) by using quantitative parameters obtained by image analysis. These parameters are directly associated to cell size evolution and coalescence events. The results obtained allow determining the influence of rheological properties and process variables on the foaming behaviour of the polymer blends under study when the foaming process is carried out inside a metallic mould.

Properties and Possible Applications of Kyoto University Accelerator Based Neutron Source (KUANS)

The results of preliminary experiments of Kyoto University Accelerator based Neutron Source (KUANS) is reported. The Time of Flight spectrum showing clear peak of thermal neutron is presented and neutron flux of 4000 n/cm2s at the 1.24 m from the moderator surface is evaluated. Preliminary results of time-resolved neutron radiography are also presented, which shows 10 minutes-exposure is enough to make clear images. Finally, some applications suitable for KUANS, such as reflectometer are suggested.

Morphology of physical soil crusts and infiltration patterns in an artificial catchment

Hydraulic properties of the soil surface control the partitioning of rainfall between infiltration and runoff. For agricultural soils in humid climate regions, physical soil crusts have mostly been reported to reduce water infiltration. For initial soils developing in such climate on unstructured sediments without organic carbon, effects of soil crusting and slaking on infiltration was largely unknown. The objective was to compare initial soil and porous system formation with infiltration from three locations in a constructed hydrological catchment that has been left to undirected ecological succession for three years. We expected to find characteristic, mainly textural, effects of physical soil crusts during this initial stage of soil development. The three-dimensional (3D) micro-morphology was described using the X-ray computed tomography (CT); two-dimensional (2D) infiltration patterns were obtained from drip infiltration experiments using time-resolved neutron radiography (NT). Selected samples from three locations represent major sediment types of the catchment. The CT data indicated structural crusts on soil consisting of sandy to loamy sediments and depositional crusts on more sandy sediments. A combination of these two types developed at locations with silt to fine sand sediments; probably as a result of aeolian deposition on a structural crust. Moreover, isolated vesicle-shaped pores mostly reported from soils in arid environments were observed in most samples. The 2D infiltration patterns reflected the structural alteration by crusts only in samples containing silt and fine sand. Infiltrating water tended to pond within the aeolian deposits above the underlying structural crust. For all other samples, 2D infiltration pattern were relatively uniform; only negligibly small effect of structural crusts and vesicular pores on infiltration and redistribution could be observed in NR experiments although field measured infiltration rates were different. The relatively small differences in moisture patterns observed using NT suggest that the texture-related differences in physical soil crusts indicated by pore structure images using CT had only little effects on infiltration. The study improved understanding soil structure and water distribution relations in a hydrological catchment during initial ecosystem development.

Observations of Transient Flooding in a Proton Exchange Membrane Fuel Cell Using Time-Resolved Neutron Radiography

The generation and transport of water in both liquid and gas phases during device operation are important areas to understand both steady state and transient performance of proton exchange membrane fuel cells. Localized concentrations of liquid water within the cell can cause flooding, which leads to decreases in cell performance, fuel starvation, degradation, or, in extreme cases, collapse of cell output. A variety of experimental and simulation techniques have been used to elucidate flooding events; yet, a comprehensive understanding of what leads to flooding and the specific details of how flooding affects fuel cell performance, especially during transient operation, have not been completely developed. The work reported here couples direct observations of liquid water flooding, primarily in the gas flow channel, with measurements of cell performance, outlet temperature, and outlet dew point during a step change in current density. Liquid water buildup and water slug dynamics were monitored with the temperature and electrical performance of the cell in real time. The size of the water slugs was connected to the cell performance to illustrate how the liquid water influences cell operation and how the conditions of the cathode gas flow control the liquid water content of the cell.

Visualization and Measurements of Two-Phase Flows in Metallic Ducts Using Neutrons as Microscopic Probes. 1st Report, Time-Resolved Neutron Radiography and Its Limited Time-Resolution.

Experiments on visualization of high-speed fluid phenomena in metallic ducts were conducted by three kinds of time-resolved neutron radiography techniques. In the direct film method with a pulsed neutron beam, frozen neutron radiographs of air-water flows in a rectangular duct were obtained successfully. The high-frame-rate neutron radiography with pulsed and steady neutron beams allowed visualization of boiling water two-phase flow in a tube at the recording speed of 500 frames/s and air-water flows in a rectangular duct at up to 1000 frames/s, respectively. The quality of the images obtained from the time-resolved neutron radiography was sufficient for observation of the fluid behavior. The limit of the time-resolution was clarified based on the sensitivity and light-decay constant of the converter and the measurement error of neutrons calculated by statistical analysis.

Time-Resolved Neutron Radiography Using a Fast Pulse Reactor

The feasibility of using a fast pulse reactor as a neutron source in the production of time-resolved neutron radiographs has been demonstrated at the U.S. Army Pulse Radiation Facility. The radiogr...