There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

J. Appl. Cryst.の発刊に際して

Additive manufacturing of metallic components – Process, structure and properties

Additive manufacturing of metals

Additive manufacturing (AM), widely known as 3D printing, is a method of manufacturing that forms parts from powder, wire or sheets in a process that proceeds layer by layer. Many techniques (using many different names) have been developed to accomplish this via melting or solid-state joining. In this review, these techniques for producing metal parts are explored, with a focus on the science of metal AM: processing defects, heat transfer, solidification, solid-state precipitation, mechanical properties and post-processing metallurgy. The various metal AM techniques are compared, with analysis of the strengths and limitations of each. Only a few alloys have been developed for commercial production, but recent efforts are presented as a path for the ongoing development of new materials for AM processes.

The metallurgy and processing science of metal additive manufacturing

Microchannel plate detectors with cross strip anodes have demonstrated excellent performance characteristics, their
resolution has reached the 6-10 μm scale (the typical size of pores in a microchannel plate) and the imaging nonlinearities
are small. Working at much lower gain (~5 x 10 5 ) than many other devices, the cross strip readout has many
other advantages, low complexity, robustness, compactness and the ability to fit many formats. We have now
implemented cross strip detectors in several formats including, 40mm open face (UV/particle) and 18mm sealed tube
(optical). These have been combined with a new signal processing technique which allows for high counting rates
exceeding 5 MHz with high spatial resolution (<20 μm FWHM). The imaging performance is dependent on optimization
of firmware algorithms that are used to calculate event position centroids. With new FPGA designs and implementation
considerable flexibility is gained, allowing the fidelity of the imaging readout to be progressively tuned for maximal
performance.

Development of cross strip MCP detectors for UV and optical instruments

Neutron imaging is a non-invasive method for material research on the macroscopic level It is carried out at laboratories equipped with powerful neutron sources, suitable neutron beam lines and neutron detection systems Decades ago neutron radiography began capturing images with film techniques These techniques yielded excellent spatial resolution even over large fields of view In the recent years, improvements in the detection techniques and their digitization have been the main forces driving successes in neutron imaging Several detector options have been developed, implemented and used in practical applications in order to achieve digital information from the neutron transmission process which is needed for a quantitative evaluation of image data by sophisticated methods like neutron tomography, phase contrast imaging, neutron interferometry and time dependent studies The most common approach in digital neutron imaging is a conversion of the neutron field information into visible light by a scintillation process, where a neutron converter is needed because neutrons do not excite directly due to their neutral charge Low level light signals can be observed either with sensitive camera systems or by using amorphous silicon based semiconductor plate devices However, these now established detection techniques are still limited in respect to spatial and time resolution The best possible spatial resolution which can be achieved today is available by a system built at PSI with about 10 μm pixel size Recently, it was upgraded with a tilted option for an increased resolution by a factor of 4 in one direction Scintillator based techniques are limited by the dissipation of the secondary particles This limitation has motivated the search for new detector options One approach is a pixilated system where the readout per incoming neutron can be used to calculate precisely the position of its impact Such devices are realized as the TIMEPIX system already The system was tested successfully at PSI and other neutron imaging facilities Other options might be to use MEDIPIX devices with neutron absorbing/converting materials A similar pixel detector, EIGER, has been developed recently at PSI and its performance in the field of neutron imaging is under investigation For future applications at the upcoming pulsed spallation sources the time = energy resolving aspect becomes even more important This will push the future use of pixilated systems This article intends to describe the present state-of-the-art even if most of the presented results are obtained at PSI's leading facilities, sometimes in collaboration with our partners

https://iopscience.iop.org/article/10.1088/1748-0221/6/01/C01050/pdf

Neutron imaging — Detector options in progress

Mapping residual strain induced by cold working and by laser shock peening using neutron transmission spectroscopy

The sensitivity of many detection devices is established by the use photocathodes for the conversion of incoming photons into photoelectrons. The choice of photocathode material is determined by the spectral range where the sensitivity of the device is most important. Alkali halides are very efficient photocathodes in the ultraviolet and soft X-ray wavelength ranges and are widely used in many scientific applications. Although they are relatively stable under short exposure to atmosphere, which substantially simplifies production and handling of detection devices, it was found that their sensitivity can be substantially reduced by intense UV or X-ray irradiation (photocathode's ageing). A detailed study of alkali halide photocathodes efficiency and their ageing under intense UV and X-ray irradiation as well as some methods of increasing the stability are presented. The quantum efficiency of amorphous diamond films were shown to be slightly lower than the efficiency of some alkali halide films, but the chemical and mechanical stability and yet to be confirmed radiation hardness of diamond photocathodes make them very attractive for many UV and soft X-ray applications. Multialkalis and new materials such as GaN, AlGaN, GaAs could be used to extend the sensitivity to longer wavelengths, but require in situ processing in very high vacuum.

The quantum efficiency and stability of UV and soft x-ray photocathodes

A detailed study of the stability of CsI and KBr photocathodes under UV irradiation is presented. UV quantum efficiency degradation was found to be more pronounced at lower illumination intensity for the same accumulated dose and illumination wavelength. For an equal number of extracted photoelectrons in-band UV exposure led to a larger sensitivity decay as compared to out-of-band illumination. The angle of radiation incidence was not important for the UV sensitivity degradation, while changes of visible light rejection (i.e. degradation of solar blindness) did depend on the incidence angle: the photocathodes illuminated at normal incidence were activated much faster than the films irradiated at grazing angle. We found that the increase of visible sensitivity can be characterized by the total accumulated dose and is independent of irradiation flux during UV activation. We also observed that heat annealing substantially improves the visible light rejection of CsI photocathodes.

/pdf/uv-radiation-resistance-and-solar-blindness-of-csi-and-kbr-30cadhn096.pdf

Anton S. Tremsin

Papers

Development of cross strip MCP detectors for UV and optical instruments

Neutron imaging — Detector options in progress

Mapping residual strain induced by cold working and by laser shock peening using neutron transmission spectroscopy

The quantum efficiency and stability of UV and soft x-ray photocathodes

UV radiation resistance and solar blindness of CsI and KBr photocathodes