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Abstract:Fast neutron imaging has a great potential as a nondestructive technique for testing large objects. The main factor limiting applications of this technique is detection technology, offering relatively poor spatial resolution of images and low detection efficiency, which results in very long exposure times. Therefore, research on development of scintillators for fast neutron imaging is of high importance. A comparison of the light output, gamma radiation sensitivity and spatial resolution of commercially available scintillator screens composed of PP/ZnS:Cu and PP/ZnS:Ag of different thicknesses are presented. The scintillators were provided by RC Tritec AG company and the test performed at the NECTAR facility located at the FRM II nuclear research reactor. It was shown that light output increases and the spatial resolution decreases with the scintillator thickness. Both compositions of the scintillating material provide similar light output, while the gamma sensitivity of PP/ZnS:Cu is significantly higher as compared to PP/ZnS:Ag-based scintillators. Moreover, we report which factors should be considered when choosing a scintillator and what are the limitations of the investigated types of scintillators.

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Neutron Imaging is ideally suited for applications in cultural heritage even at small reactors with moderate image resolution. However, recently, high resolution imaging is being increasingly used for advanced studies, especially in paleontology. The special contrast for hydrogen and between neighboring elements in the periodic system allows for new applications that are not accessible for X-rays, like organic material in enclosed containers made of ceramics or metals, fossilized bones in chalk rock or in ferrous "red" beds, and even for animal and hominid teeth. Fission neutrons permit the examination of large samples that otherwise show large attenuation for thermal neutrons.

Powder bed density, flowability, and laser light absorption of the powder strongly influence the quality and performance of aluminum oxide parts processed by selective laser sintering and melting. By means of spray drying, highly dense granules with a good flowability are manufactured. An ultrasonic atomizer and a co-current droplet air mixing are used to spray aqueous slurries consisting of either bimodal or trimodal distributions of aluminum oxide. Nano-iron oxide improves the interaction with the green pulsed laser. The improved absorption of the green laser light is verified by means of an Ulbricht sphere. The appropriate amount of dispersant for consecutive water-based spray granulation is determined by Zeta Potential measurements. Dibasic ammonium citrate is found to be the most suitable dispersant. A final uniform distribution of the iron oxide within the spray dried granules is confirmed by X-ray μ-beam fluorescence tomography. The powder quality is characterized by apparent density, tapped density, Hausner ratio, moisture content, and particle size distribution. Powders with a tapped density of almost 50% of the theoretical density and an absorbance of 69% (green laser light) lead to maximum densities of the laser processed parts of around 96%.

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This article reports on in situ macroscopic scale imaging of NiO–YSZ (YSZ is yttria-stabilized zirconia) reduction under applied stress – a phase transition taking place in solid oxide electrochemical cells in a reducing atmosphere of a hydrogen/nitrogen mixture and at operation temperatures of up to 1073 K. This process is critical for the performance and lifetime of the cells. Energy-resolved neutron imaging was applied to observe the phase transition directly with time and spatial resolution. Two different approaches are presented for using this imaging technique for the investigation of chemical and physical processes requiring controlled atmosphere and elevated temperature. The first type of measurement is based on alternating stages of short-term partial chemical reaction and longer neutron image acquisition, and the second type is a real in situ neutron imaging experiment. Results of applying energy-resolved neutron imaging with both approaches to the NiO–YSZ reduction investigation indicate enhancement of the reduction rate due to applied stress, which is consistent with the results of the authors' previous research.