Time-resolved neutron imaging at ANTARES cold neutron beamline

Abstract

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 timeresolved 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 1-2% when no filters are installed in the beam.

The new neutron grating interferometer at the ANTARES beamline: design, principles and applications

“…It provides a mixed spectrum of cold and thermal neutrons, peaked at λ = 1.6Å (Tremsin et al, 2015). The pinhole diameter can be varied between 2 and 36 mm to adjust the geometrical resolution (L/D-ratio) of the instrument.…”

Neutron Dark-Field Imaging of the Domain Distribution in the Intermediate State of Lead

“…Furthermore, although the exposure time was in the range of 18 min in the presented study, nGI should be considered for time-resolved investigations of domain structures as a faster data acquisition for samples revealing more pronounced scattering would be possible. In addition, an investigation of the domain propagation induced by periodic disturbances seems possible on a millisecond time scale via a stroboscopic imaging approach [34,35].…”

Evaluation of Wavelength-Dependent Detection Efficiency of Neutron-Sensitive Microchannel Plate Detector

“…By increasing the applied high voltage to the MCP or adjusting the threshold level, the absolute detection efficiency would be improved to the detection efficiency values exceeding 50%, as demonstrated previously. (4,8,10) In order to validate the simple evaluation procedures of the wavelength-dependent detection efficiency, we compared the efficiency curve with the absolute detection efficiency measured at the IMAT beamline, where the neutron flux was evaluated with the GS1 reference detector. Figure 4 shows the absolute detection efficiency of the MCP/Timepix detector evaluated at the IMAT beamline.…”

“…At present, a promising candidate is the borated-microchannel plate (MCP) detector combined with an array of Timepix chips, which are high-performance applicationspecific integrated circuit (ASIC) readout chips. (4,5) The borated-MCP, which is fabricated by Nova Scientific Inc., can work as a highly efficient neutron-to-electron converter with high spatial resolution. A stack of two or three MCPs can be used to perform sufficient amplification of the electron signal produced by the neutron-sensitive MCP.…”

“…(6,7) Some basic performances of the MCP/Timepix detector, such as the detection efficiency, and spatial and time resolutions, have already been investigated. (8,9) However, no detailed study on the energy-dependent or wavelength-dependent detection efficiency has been carried out for the present generation of devices, except for the theoretical predictions (4,10) and experimental data are sparse. (8) This information is useful for planning experiments of new energy-selective imaging applications, such as neutron resonance transmission imaging and stress mapping via Bragg-edge analysis.…”