Sadao Aoki

X-ray detection characteristics of gold photocathodes and microchannel plates using synchrotron radiation (10 eV–82.5 keV)

Abstract X-ray detection characteristics of gold photocathodes, and microchannel plates (MCP) have been investigated using synchrotron radiation in the energy range from 12 eV to 82.5 keV. The quantum efficiency of gold is compared with the published data which were reported at some discrete energies, and we add several new data points in the 12–35.9 eV. The detection response of MCP has been represented for photons from the VUV regime of 12 eV to the hard X-ray region of 82.5 keV along with its incident angle dependence. This MCP response has demonstrated the following remarkable sensitivity in this wide energy range: The energy response of MCP remains within about one order of magnitude through this broad range. This comes from the contribution of the combination of various ingredients of MCP; namely, C, O, Si, Ba and Pb. For the energy response, these ingredients, in turn, make some jumps and humps at their edge energies. Another useful feature of the MCP response we obtained is a rapid decrease in the MCP response for the energies less than about ten eV; this is desirable for avoiding the effect of visible light on the X-ray data. Also, the MCP response is compared with the detection efficiency of a silicon surface barrier detector for the application to plasma X-ray diagnostics.

X-Ray Phase Imaging with Single Phase Grating

X-ray phase imaging with a single phase grating based on the fractional Talbot effect is described. A phase grating with an 8 µm pitch was placed behind a weakly absorbing object and illuminated with partially coherent 17.7 keV X-rays. Intensity patterns downstream of the grating were recorded with a high-resolution image detector. By the fringe scanning method, an X-ray wavefront inclination by the object was obtained. Phase tomography was performed and the three-dimensional structure of a piece of a polymer blend was revealed with an 8 µm spatial resolution and a 9 mg/cm3 detection limit of density deviation.

Fluorescence x‐ray absorption fine structure measurements using a synchrotron radiation x‐ray microprobe

X‐ray absorption fine structure (XAFS) measurements in regions less than 20 μm in diameter were realized using an x‐ray microprobe employing the fluorescence detection method. To realize an energy tunable intense small x‐ray beam, an ellipsoidal mirror was used as the synchrotron radiation focusing element combined with a double‐crystal monochromator. Distortion of a XAFS spectrum due to the self‐absorption effect is discussed in detail. The degree of the distortion was experimentally evaluated from the measurement of the x‐ray fluorescence intensity as a function of takeoff angle, and the distortion was significantly reduced with the small takeoff angle detection geometry. Utilizing this technique, reliable XAFS spectra were obtained from a rock sample containing several minerals.

X-ray microanalysis with energy tunable synchrotron X-rays

Abstract Focused intense monochromatic synchrotron radiation was realized with a combination of a Pt coated ellipsoidal mirror, a double crystal monochromator and a pinhole. Energy tunable X-ray microanalysis using a focused X-ray beam was compared to particle induced X-ray emission analysis. A section of Japanese cedar showed severe damage after proton irradiation, while another section of the tree showed no damage after the measurement of its trace element distribution by synchrotron radiation. Less damage, high sensitivity and energy tunability were demonstrated by utilizing synchrotron radiation.

Development of a scanning x‐ray microprobe with synchrotron radiation

An x‐ray focusing system with two Wolter type one mirrors was developed and used in a synchrotron radiation x‐ray micro analyzer (SRXMA). The SRXMA system and the characteristics of each Wolter mirror are described. The minimum beam size obtained was 1.6 μm in the sagittal plane but the beam size in the meridional plane was 34 μm because of the scattered x rays caused by the surface irregularities of the focusing mirror.

X‐ray detection characteristics of microchannel plates using synchrotron radiation in the energy range from 0.06 to 0.6 keV

The characteristics of microchannel plates (MCPs) for x‐ray detection have been investigated with continuous x‐ray energy variation using synchrotron radiation in the XUV and soft x‐ray region (from 60 to 600 eV). The current response data have shown x‐ray absorption fine structure (EXAFS or XANES) near the oxygen K absorption edge as well as a jump structure near the silicon L edge; these structures are explained by the surface composition of channel walls (SiO2). The data show that the surface layer of a microchannel is essential for x‐ray detection by MCPs in this energy range. The precise current response curve has been completed for the wide x‐ray energy range from 0.06 to 82 keV combined with the previously reported data [Kondoh et al., Rev. Sci. Instrum. 59, 252 (1988); Cho et al., ibid. 59, 2453 (1988); Yamaguchi et al., ibid. 60, 368, 2307 (1989)].

Sub-100 nm-Resolution Grazing Incidence Soft X-Ray Microscope with a Laser-Produced Plasma Source

A high-resolution soft X-ray microscope was constructed using grazing incidence mirrors and a laser-produced plasma source. An Nd-YAG pulse laser (1.064 µm) was focused onto an aluminum target to produce soft X-rays above 4 nm in wavelength. The beam energy of the laser was 1.4 J, with a pulse width of 8 ns. The Wolter type-I mirror was used as an objective mirror and the toroidal mirror as a condenser. The magnification of the objective was 20. A holographic plate was used as a detector. Resolution of about 40 nm was achieved with a single shot.

Current response characteristics of microchannel plates x‐ray detector using synchrotron radiation (0.6–2 keV and 5–20 keV)

The characteristics of microchannel plates (MCPs) for detection of x rays have been investigated using synchrotron radiation in the energy ranges from 0.6 to 2.0 keV and from 5 to 20 keV. Microchannel plates are operated under the condition of an unsaturated pulse‐height distribution mode. The current response curve of MCPs is measured continuously with x‐ray energy variation for the first time. The experimental result of some discontinuous jumps in the response is obtained at the energies corresponding to the absorption edge of the MCP materials. In the low‐energy range (hν 5 keV), a weak dependence on θ is observed, and is attributed mainly to the penetration of x rays through multiple channels.

A Scanning X-Ray Fluorescence Microprobe with Synchrotron Radiation

A scanning X-ray fluorescence (XRF) microprobe using Wolter type 1 optics was developed, and two-dimensional XRF measurements were carried out using synchrotron radiation up to 10 keV as an excitation source. The system of this microprobe and the results of two-dimensional measurements of a resolution check pattern and rock samples are described. The estimated spatial resolution was better than 10 µm.

Soft x-ray imaging with toroidal mirrors

The fabrication of small toroidal mirrors in tandem for x-ray imaging is discussed. First, a male mandrel is made by grinding and polishing a molybdenum rod. Then. a glass replica is cast and lightly polished. The method of polishing the male mandrel is described. A photograph of a copper mesh taken with a 8.3-A x ray is shown.