Chiaki Sakai

Characterization of a Hard X-ray Telescope at Synchrotron Facility SPring-8

Space-borne astronomical instruments require extensive characterization on the ground before launch. In the hard X-ray region however, it is difficult for a laboratory-based beamline using a conventional X-ray source to provide a capability sufficient for pre-flight high-precision calibration. In this paper, we describe an experiment to characterize a hard X-ray telescope at a synchrotron facility, mainly on the basis of experimental setup and examples of measured results. We have developed hard X-ray telescopes consisting of Wolter-I grazing incidence optics and platinum-carbon multilayer supermirror coatings. The telescopes have been characterized at the synchrotron facility SPring-8 beamline BL20B2. The measurements at BL20B2 have great advantages such as extremely high flux, large-sized and less-divergent beam, and monochromatic beam covering the entire hard X-ray region from 8 to over 100 keV. The telescope was illuminated by monochromatic hard X-rays, and the focused image was measured by high resolution hard X-ray imagers. The entire telescope aperture was mapped by a small beam, and the effective area and the point spread function were obtained as well as local optical properties for further diagnostics of the characteristics of the telescope.

Characteristics of buried humic horizons at the Shiiji archeological pits: I. Chemical properties and humus composition of buried horizons

To investigate changes in the nature of soil organic matter with lapse of time after burial, buried humic horizons derived from volcanic ash with an age from the present to 27,200 YBP were studied and the properties of the soil organic matter in each horizon were assessed. The results for the chemical properties and humus composition of the soil samples were as follows. 1) Based on stratigraphical studies (1), the Ashitaka Loam Formation is divided into two groups of alternate layers, Kuroboku soil in the surface part, and the Upper loam below the Kuroboku soil. The total carbon and nitrogen contents were high in the horizons of the Kuroboku soil and low in the Upper loam. The relationship between the total carbon and nitrogen contents had a positive correlation. 2) The humus compositions of the two groups were as follows. (1) Kuroboku soil: This was characterized by large amounts of humic acid extracted with NaOH and small amounts of both humic acid and fulvic acid extracted with Na6P2O7 Compare...

Characterization of a hard x-ray telescope at a synchrotron facility

This paper presents characterization of hard X-ray telescope using synchrotron facility, mainly on experimental setup, benefits of such experiment, and measurement results only available by means of bright synchrotron light. We have developed hard X-ray telescope consisting of Wolter-I grazing incidence optics with platinum-carbon multilayer supermirror surfaces. Telescopes have been fabricated for InFOCuS balloon experiment, and we achieved first scientific flight in 2004. The hard X-ray telescope on board InFOCuS has been characterized at synchrotron facility SPring-8/BL20B2, Japan. Measurement at BL20B2 has great advantages such as extremely high flux, large sized and less divergent beam, and monochromatic beam covering entire hard X-ray region from 8 to over 100keV. A 16m-long experiment hutch is another feature suitable for measurements of hard X-ray telescopes. The telescope was illuminated by monochromatic hard X-rays, and focused image was measured by high resolution hard X-ray imager. Whole telescope aperture was mapped by small beam, and effective area and point spread function are obtained as well as local optical properties for further diagnostics of telescope characteristics.

Upgraded hard x-ray telescope with multilayer supermirror for the InFOCμS balloon experiment

Hard X-ray focusing observation is important to reveal non-thermal emission mechanism and origin in active galaxies and clusters of galaxies. We have carried out the hard X-ray observation throughout the ¥infocus program, which is an international balloon-borne experiment in collaboration with NASA/GSFC and Nagoya University. The telescope is conical approximation of Wolter-I optics with 8 m focal length and 40 cm diameter. It consists of 255 nested thin (0.17 mm thickness) reflectors with incidence angles of 0.10° to 0.36°. Reflectors are coated with depth-graded platinum-carbon (Pt/C) multilayers, so-called supermirrors, with periodic length of 2.6 to 13 nm and bi-layer number of 28 to 79, depending on incidence angles. We are now continuously fabricating advanced next hard X-ray telescope for the second ¥infocus flight in 2004. Compared with the first telescope, the following improvements have been made on the second one. Supermirror reflectors have wider sensitivity in energy band of 20-60 keV adopting optimum supermirror design for balloon observation, and smaller interfacial roughness owing to complete replication technique. For upgrading of the image quality, we then adopted stiffer reflector substrate, selected replication mandrel with better shape, and the modified telescope housing with higher alignment accuracy for reflectors. The performance of the new hard X-ray telescope was measured in X-ray beamline facility in ISAS/JAXA and synchrotron radiation facility SPring-8. The effective area and image quality are obtained to be 45 cm2 at 30 keV and 23 cm2 at 40 keV, and 2.5 arcmin in half power diameter, respectively. In this paper we report our development of the upgraded hard X-ray telescope for the second balloon flight experiment.

Application of composite-layer mirror to soft x-ray telescopes

Recent development of cryogenic detectors enabled high resolution diagnostics of emission line and absorption line/edge structures. These studies are quite important to investigate physics of interstellar/intergalactic plasma and dynamics of matters around black holes, for example. Soft X-ray telescopes for such purpose, sensitive up to 10 keV, are usually designed using Au, Pt, or Ir for their large electron density and large critical angle. However in fact, these materials are not very suitable in a few to 8 keV region, because they have wide and deep M-shell absorption edge structures in 2--4 keV region. Considering absorption edges and also thin-film characteristics, C or Ni can be alternatives. However, these materials alone cannot be a good mirror, again from absorption edges in the energy region of interest (0.1-10 keV). We designed composite structure consisting of C, Ni and Pt with thickness of 30 to 300 A, to get smooth and high reflectivity all across the energy region. Test fabrication showed interfacial roughness is as low as expected, indicating match of materials is also good. We applied this result to the baseline design of NeXT/Soft X-ray Telescope, by substituting current material (Au) with C-Ni-Pt composite, and obtained 20% larger effective area in 2-8 keV region.

Development of hard x-ray telescope for the InFOCμS balloon experiment

The development of hard X-ray focusing optics for astrophysical observation is widely recognized as one of key technologies for future X-ray satellite missions. Utilizing InFOCμS balloon-borne experiment, we have developed thin-foil-nested hard X-ray telescope employing depth-graded Pt/C multilayer. Pre-flight calibration of the hard X-ray telescope for the 2004 flight was performed at X-ray beamline facilities in ISAS/JAXA and SPring-8. The effective area and image quality were estimated to be 51 cm2 and 2.4 arcmin (half power diameter) at 30 keV, respectively. Limiting factors of its performance also investigated. And we revealed that the main factor was image degradation of an individual reflector. Based on such an investigation we are now continuously developing advanced hard X-ray telescope for future balloon experiments. From evaluation of upgraded test telescope, we get a response toward high resolution telescope in future years.