RESUMEN
Imaging using scintillators is a widespread and cost-effective approach in radiography. While different types of scintillator and sensor configurations exist, it can be stated that the detection efficiency and resolution of a scintillator-based system strongly depend on the scintillator material and its thickness. Recently developed event-driven detectors are capable of registering spots of light emitted by the scintillator after a particle interaction, allowing to reconstruct the Center-of-Mass of the interaction within the scintillator. This results in a more precise location of the event and therefore provides a pathway to overcome the scintillator thickness limitation and increase the effective spatial resolution of the system. Utilizing this principle, we present a detector capable of Time-of-Flight imaging with an adjustable field-of-view, ad-hoc binning and re-binning of data based on the requirements of the experiment including the possibility of particle discrimination via the analysis of the event shape in space and time. It is considered that this novel concept might replace regular cameras in neutron imaging detectors as it provides superior detection capabilities with the most recent results providing an increase by a factor 3 in image resolution and an increase by up to a factor of 7.5 in signal-to-noise for thermal neutron imaging.
RESUMEN
Time-resolved resonant inelastic X-ray scattering (RIXS) is one of the developing techniques enabled by the advent of X-ray free electron laser (FEL). It is important to evaluate how the FEL jitter, which is inherent in the self-amplified spontaneous emission process, influences the RIXS measurement. Here, we use a microchannel plate (MCP) based Timepix soft X-ray detector to conduct a time-resolved RIXS measurement at the Ti L3-edge on a charge-density-wave material TiSe2. The fast parallel Timepix readout and single photon sensitivity enable pulse-by-pulse data acquisition and analysis. Due to the FEL jitter, low detection efficiency of spectrometer, and low quantum yield of RIXS process, we find that less than 2% of the X-ray FEL pulses produce signals, preventing acquiring sufficient data statistics while maintaining temporal and energy resolution in this measurement. These limitations can be mitigated by using future X-ray FELs with high repetition rates, approaching MHz such as the European XFEL in Germany and LCLS-II in the USA, as well as by utilizing advanced detectors, such as the prototype used in this study.
RESUMEN
Energy-resolved neutron imaging experiments conducted on the Small Angle Neutron Scattering (SANS) instrument, Bilby, demonstrate how the capabilities of this instrument can be enhanced by a relatively simple addition of a compact neutron counting detector. Together with possible SANS sample surveying and location of the region of interest, this instrument is attractive for many imaging applications. In particular, the combination of the cold spectrum of the neutron beam and its pulsed nature enables unique non-destructive studies of the internal structure for samples that are opaque to other more traditional techniques. In addition to conventional white beam neutron radiography, we conducted energy-resolved imaging experiments capable of resolving features related to microstructure in crystalline materials with a spatial resolution down to â¼0.1 mm. The optimized settings for the beamline configuration were determined for the imaging modality, where the compromise between the beam intensity and the achievable spatial resolution is of key concern.
RESUMEN
This paper reports the design, making and characterisation of a series of Fe-based bulk metallic glass alloys with the aim of achieving the combined properties of high neutron absorption capability and sufficient glass forming ability. Synchrotron X-ray diffraction and pair distribution function methods were used to characterise the crystalline or amorphous states of the samples. Neutron transmission and macroscopic attenuation coefficients of the designed alloys were measured using energy resolved neutron imaging method and the very recently developed microchannel plate detector. The study found that the newly designed alloy (Fe48Cr15Mo14C15B6Gd2 with a glass forming ability of Ø5.8 mm) has the highest neutron absorption capability among all Fe-based bulk metallic glasses so far reported. It is a promising material for neutron shielding applications.
RESUMEN
The spatial resolution of position-sensitive detectors that use stacks of microchannel plates (MCP's) with high-resolution anodes can be better than 20-microm FWHM [Proc. SPIE 3114, 283-294 (1997)]. At this level of accuracy, channel misalignments of the MCP's in the stack can cause observable moiré interference patterns. We show that the flat-field detector response can have moiré beat pattern modulations of as great as approximately 27% with periods from as small as a few channel diameters to as great as the size of a MCP multifiber. These modulations, however, may be essentially eliminated by rotation of the MCP's or by a mismatch of the channel sizes. We also discuss how the modulation phenomena can be a useful tool for mapping the metric nonlinearities of MCP detector readout systems. Employing the optical moiré effect, we demonstrate a simple, but effective, technique for evaluation of geometrical deformations simultaneously over a large MCP area. For a typical MCP, with a 60-channel-wide multifiber, we can obtain accuracies of 1.2 mrad for multifiber rotations and twists and 35/(L/p) mrad for channel-long axis distortions (where L/p is MCP thickness to interchannel distance ratio). This technique may be used for the development of MCP x-ray optics, which impose tight limitations on geometrical distortions, which in turn are not otherwise easily measurable with high accuracy.